Spring rate vs Ride comfort vs Performance database (FD3S)
07-01-15, 02:42 PM
#26
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I can see how an 11K spring rate would be great on a smooth track and probably race compound as the G forces are higher. The problem I run into isn't the smooth corners per se, its the straight that aren't exactly smooth and when you rail on it the car likes to "dance" around. When I ran softer rates with higher damping the car wouldn't dance around, and the cornering forces seemed to be higher (more grip), the car wasn't as "darty" feeling but felt more solid. The springs/shocks would absorb more of the bumps and less was transmitted to the body of the car. It also felt softer, it feels like the spring stiffness has super short rapid strokes. perhaps its a droop in the susension not being sufficient, I don't know. I feel like the higher rates aren't at the same grip level. I remember some corners being amazed by just how much grip I had with softer rate springs. It was solid as well. I tried some high speed corners doing some "tighter inputs" to see how the car would react (little steering tighter turn to see how the car would respond) and the car just did a little slide a little bit. I also notice under higher acceleration in a straight line over bumps that the 11K springs jump over them, the softer 6KG springs followed the bump and hooked.
I honestly didn't feel the 8/6 spring set up felt slow or mushy. I thought it was still pretty damn tight feeling. I didn't feel much roll, I felt the largest difference in the weight being shifter to the rear when turning and accelerating, but the damn car would STICK. It planted and moved like no other. with the almost twice as stiff rear the car wants to jump more and hop cause of the spring rate and bumps, (this is low speed high acceleration). The car has a better flat ride with equal rates, and I don't mind the support back there in high speed corners, but its not nearly as forgiving as the softer rates. I also think it has a lot less "grip". It also suffers a lot in straight line stability over uneven roads with higher rates.
I will swap out the springs to 8/6 and do some runs. see if the car bottoms the shock and how stable it is. Obviously I will go slow and go faster and faster for testing, I don't want to damage anything.
I will report back my findings this weekend.
I honestly didn't feel the 8/6 spring set up felt slow or mushy. I thought it was still pretty damn tight feeling. I didn't feel much roll, I felt the largest difference in the weight being shifter to the rear when turning and accelerating, but the damn car would STICK. It planted and moved like no other. with the almost twice as stiff rear the car wants to jump more and hop cause of the spring rate and bumps, (this is low speed high acceleration). The car has a better flat ride with equal rates, and I don't mind the support back there in high speed corners, but its not nearly as forgiving as the softer rates. I also think it has a lot less "grip". It also suffers a lot in straight line stability over uneven roads with higher rates.
I will swap out the springs to 8/6 and do some runs. see if the car bottoms the shock and how stable it is. Obviously I will go slow and go faster and faster for testing, I don't want to damage anything.
I will report back my findings this weekend.
07-01-15, 02:53 PM
#27
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i think a little backwards. i also read the 'david and goliath' book, the bell curve notion really struck a chord.
the spring rate, actually wheel rate; bar and spring together is some proportion of lateral grip. the more grip you have = the more lateral force you can generate = the more spring rate you need to keep the movement of the cars body the same, or less.
the grip is more of a function of the tires, and the alignment of the tires at full lateral G. there is some crossover, as alignment of the tires has to do with body roll, and suspension geometry during said roll.
the shock then dampens the spring, but in three ways. 1. is the low speed, which = handling feel, second is the high speed, which is the ride, and then 3rd is the ability to soak up bumps at full lateral G and not upset the car.
so empirically; there is a range of spring rates that once you're in it, lap times will be nearly unaffected. the f/r balance becomes the important part. so once you are in this range, it is basically whatever the driver is most comfortable with, in theory they will drive best that way, although sometimes they check email and do their nails* and stuff.
for example, if say you looked through your collection of Japanese Rx7 magazines to see what spring rates the blingy coil overs use, you would actually find everything from 8/8 (HKS Hypermax II) to 14/14 (HKS hypermax pro), to the Apexi and Tein 16/16. Ohlins seems to prefer a slightly softer rate, 11/11 and the external reservoir ones are 14/14
*i had to go in my bag and get the nail clippers this year, it was an emergency too.
the spring rate, actually wheel rate; bar and spring together is some proportion of lateral grip. the more grip you have = the more lateral force you can generate = the more spring rate you need to keep the movement of the cars body the same, or less.
the grip is more of a function of the tires, and the alignment of the tires at full lateral G. there is some crossover, as alignment of the tires has to do with body roll, and suspension geometry during said roll.
the shock then dampens the spring, but in three ways. 1. is the low speed, which = handling feel, second is the high speed, which is the ride, and then 3rd is the ability to soak up bumps at full lateral G and not upset the car.
so empirically; there is a range of spring rates that once you're in it, lap times will be nearly unaffected. the f/r balance becomes the important part. so once you are in this range, it is basically whatever the driver is most comfortable with, in theory they will drive best that way, although sometimes they check email and do their nails* and stuff.
for example, if say you looked through your collection of Japanese Rx7 magazines to see what spring rates the blingy coil overs use, you would actually find everything from 8/8 (HKS Hypermax II) to 14/14 (HKS hypermax pro), to the Apexi and Tein 16/16. Ohlins seems to prefer a slightly softer rate, 11/11 and the external reservoir ones are 14/14
*i had to go in my bag and get the nail clippers this year, it was an emergency too.
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rotary#10 (09-03-23)
07-01-15, 03:15 PM
#28
LargeOrangeFont
On the street or canyons you need something a little more predictable
To nitpick, you always always always want a predictable chassis, I think you were meaning "forgiving".
------
Long rant
A car that always oversteers with the slightest input or change in condition is predictable- but could be said to not be forgiving.
However, a car that doesn't oversteer the *** end into on coming motorcycle when you make a mistake and let off the gas too fast by (wrong?) reflex when you see a baby stroller in front of you as you round a blind highway Right hand curve is forgiving, but also could easily be unpredictable if for instance at other times understeers on turn in when you hit a bump on braking from getting onto the bumpstops.
You want to fix that spring/damper/bumpstop issue and make car car predictable on turn in as well as forgiving- and you probably plowed right through that baby stroller.
Now, if you have well programmed reflexes from driving the always oversteering predictable car all the time you might lift throttle, then bury it with countersteer before your *** end swings into the motorcycle so you can change your trajectory to the inside of the curve and slam into the bank while avoiding the motorcycle and the baby stroller.
It still wasn't a forgiving chassis even if you avoided killing people with correct reflexes and a predictable chassis.
Hot tip- if you are driving a little slower you just steer (with throttle or wheel depending on oversteering predictable car or forgiving car) around the baby stroller on the inside of the turn.
Neither the forgiving car nor the predictable car will be safer than just driving a bit further under the chassis limits.
On the street or canyons you need something a little more predictable
To nitpick, you always always always want a predictable chassis, I think you were meaning "forgiving".
------
Long rant
A car that always oversteers with the slightest input or change in condition is predictable- but could be said to not be forgiving.
However, a car that doesn't oversteer the *** end into on coming motorcycle when you make a mistake and let off the gas too fast by (wrong?) reflex when you see a baby stroller in front of you as you round a blind highway Right hand curve is forgiving, but also could easily be unpredictable if for instance at other times understeers on turn in when you hit a bump on braking from getting onto the bumpstops.
You want to fix that spring/damper/bumpstop issue and make car car predictable on turn in as well as forgiving- and you probably plowed right through that baby stroller.
Now, if you have well programmed reflexes from driving the always oversteering predictable car all the time you might lift throttle, then bury it with countersteer before your *** end swings into the motorcycle so you can change your trajectory to the inside of the curve and slam into the bank while avoiding the motorcycle and the baby stroller.
It still wasn't a forgiving chassis even if you avoided killing people with correct reflexes and a predictable chassis.
Hot tip- if you are driving a little slower you just steer (with throttle or wheel depending on oversteering predictable car or forgiving car) around the baby stroller on the inside of the turn.
Neither the forgiving car nor the predictable car will be safer than just driving a bit further under the chassis limits.
07-01-15, 03:39 PM
#29
lOOkatme
I can see how an 11K spring rate would be great on a smooth track and probably race compound as the G forces are higher. The problem I run into isn't the smooth corners per se, its the straight that aren't exactly smooth and when you rail on it the car likes to "dance" around. When I ran softer rates with higher damping the car wouldn't dance around, and the cornering forces seemed to be higher (more grip), the car wasn't as "darty" feeling but felt more solid.
I am not doubting your findings at all, but I had exactly the opposite scenario as you did coming from Gab Super Rs on stock springs to the Ohlins DFV.
The damping on the Gabs was too high for the stock springs in general and especially the highspeed damping so it would skip over bumps as the spring could not push the tire back down onto the pavement fast enough and also they would jack down on braking/bumps/turn in (any consecutive input to the suspension) and soon I would be on the bumpstops with unpredictable handling.
Now that is an extreme (in spring softness- ~3k) and as j9fd3s says both your previous and current rates are more along lines of what should be working.
--------------
I never tried the Ohlins on a softer setting than the recommended.
It could be you are "bouncing" the tire after a bump (like with a blown shock) and not "floating". It also leaves the tire up in the air instead of on the ground.
Did you first start at the recommended baseline setting of all the way clockwise (full stiff) and then turning back 10 clicks (toward soft)?
Logic says you would start there and then add damping to offset the shock trying to control your heavier than stock wheel/tire.
You should be ~6 clicks from full clockwise range in my experience to keep my 49lb wheel/tire in check with the 11k springs on the Ohlins.
I can see how an 11K spring rate would be great on a smooth track and probably race compound as the G forces are higher. The problem I run into isn't the smooth corners per se, its the straight that aren't exactly smooth and when you rail on it the car likes to "dance" around. When I ran softer rates with higher damping the car wouldn't dance around, and the cornering forces seemed to be higher (more grip), the car wasn't as "darty" feeling but felt more solid.
I am not doubting your findings at all, but I had exactly the opposite scenario as you did coming from Gab Super Rs on stock springs to the Ohlins DFV.
The damping on the Gabs was too high for the stock springs in general and especially the highspeed damping so it would skip over bumps as the spring could not push the tire back down onto the pavement fast enough and also they would jack down on braking/bumps/turn in (any consecutive input to the suspension) and soon I would be on the bumpstops with unpredictable handling.
Now that is an extreme (in spring softness- ~3k) and as j9fd3s says both your previous and current rates are more along lines of what should be working.
--------------
I never tried the Ohlins on a softer setting than the recommended.
It could be you are "bouncing" the tire after a bump (like with a blown shock) and not "floating". It also leaves the tire up in the air instead of on the ground.
Did you first start at the recommended baseline setting of all the way clockwise (full stiff) and then turning back 10 clicks (toward soft)?
Logic says you would start there and then add damping to offset the shock trying to control your heavier than stock wheel/tire.
You should be ~6 clicks from full clockwise range in my experience to keep my 49lb wheel/tire in check with the 11k springs on the Ohlins.
07-01-15, 04:37 PM
#30
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you might be bottoming out, that dartiness is the first symptom
that is the upper limit, the Honda has 18k springs in the back, and its soft on the track, but its not streetable, bumps launch the car in the air
I also notice under higher acceleration in a straight line over bumps that the 11K springs jump over them, the softer 6KG springs followed the bump and hooked.
07-01-15, 05:36 PM
#31
LargeOrangeFont
On the street or canyons you need something a little more predictable
To nitpick, you always always always want a predictable chassis, I think you were meaning "forgiving".
------
Long rant
A car that always oversteers with the slightest input or change in condition is predictable- but could be said to not be forgiving.
However, a car that doesn't oversteer the *** end into on coming motorcycle when you make a mistake and let off the gas too fast by (wrong?) reflex when you see a baby stroller in front of you as you round a blind highway Right hand curve is forgiving, but also could easily be unpredictable if for instance at other times understeers on turn in when you hit a bump on braking from getting onto the bumpstops.
You want to fix that spring/damper/bumpstop issue and make car car predictable on turn in as well as forgiving- and you probably plowed right through that baby stroller.
Now, if you have well programmed reflexes from driving the always oversteering predictable car all the time you might lift throttle, then bury it with countersteer before your *** end swings into the motorcycle so you can change your trajectory to the inside of the curve and slam into the bank while avoiding the motorcycle and the baby stroller.
It still wasn't a forgiving chassis even if you avoided killing people with correct reflexes and a predictable chassis.
Hot tip- if you are driving a little slower you just steer (with throttle or wheel depending on oversteering predictable car or forgiving car) around the baby stroller on the inside of the turn.
Neither the forgiving car nor the predictable car will be safer than just driving a bit further under the chassis limits.
On the street or canyons you need something a little more predictable
To nitpick, you always always always want a predictable chassis, I think you were meaning "forgiving".
------
Long rant
A car that always oversteers with the slightest input or change in condition is predictable- but could be said to not be forgiving.
However, a car that doesn't oversteer the *** end into on coming motorcycle when you make a mistake and let off the gas too fast by (wrong?) reflex when you see a baby stroller in front of you as you round a blind highway Right hand curve is forgiving, but also could easily be unpredictable if for instance at other times understeers on turn in when you hit a bump on braking from getting onto the bumpstops.
You want to fix that spring/damper/bumpstop issue and make car car predictable on turn in as well as forgiving- and you probably plowed right through that baby stroller.
Now, if you have well programmed reflexes from driving the always oversteering predictable car all the time you might lift throttle, then bury it with countersteer before your *** end swings into the motorcycle so you can change your trajectory to the inside of the curve and slam into the bank while avoiding the motorcycle and the baby stroller.
It still wasn't a forgiving chassis even if you avoided killing people with correct reflexes and a predictable chassis.
Hot tip- if you are driving a little slower you just steer (with throttle or wheel depending on oversteering predictable car or forgiving car) around the baby stroller on the inside of the turn.
Neither the forgiving car nor the predictable car will be safer than just driving a bit further under the chassis limits.
Last edited by LargeOrangeFont; 07-01-15 at 05:39 PM.
07-01-15, 07:23 PM
#32
As far as traction over rough pavement my Mazda3 just gave me a lesson recently.
I had swapped to FD 16x8 and 205/50-16 Direzza Star Specs on my base model Mazda3 after wearing out the stock balloon tires on skinny steelies. My immediate impression was I really liked the steering response of the Dunlops.
Meanwhile I put the Ohlins on the FD and after that driving the Mazda3 I was constantly thinking how shitty the Mazda3 stock suspension was because it would loose traction so easily on rough pavement even at low speeds. It really felt like a damping issue.
Well... recently switched to the exact same size Federal RS-Rs on the Mazda3 and magically the stock suspension isn't **** over the rough pavement.
So, to come around to the point of the post... tire carcass/sidewall is an important part of suspension tuning and some tire designs may be incompatible with some suspension tuning.
lOOkatme, were you running the same tires on both suspension set-ups?
And by the way, I don't mean to sound like I am attacking you for preferring the ARK w/ 8K/6K springs over the Ohlins on rough pavement. I want to keep hearing your feedback and if you get the Ohlins sorted to where you feel they are as good over rough pavement.
I race on rough pavement so if the ARK 8K/6K stays ahead of the Ohlins in performance there I am INTERESTED in that!
I had swapped to FD 16x8 and 205/50-16 Direzza Star Specs on my base model Mazda3 after wearing out the stock balloon tires on skinny steelies. My immediate impression was I really liked the steering response of the Dunlops.
Meanwhile I put the Ohlins on the FD and after that driving the Mazda3 I was constantly thinking how shitty the Mazda3 stock suspension was because it would loose traction so easily on rough pavement even at low speeds. It really felt like a damping issue.
Well... recently switched to the exact same size Federal RS-Rs on the Mazda3 and magically the stock suspension isn't **** over the rough pavement.
So, to come around to the point of the post... tire carcass/sidewall is an important part of suspension tuning and some tire designs may be incompatible with some suspension tuning.
lOOkatme, were you running the same tires on both suspension set-ups?
And by the way, I don't mean to sound like I am attacking you for preferring the ARK w/ 8K/6K springs over the Ohlins on rough pavement. I want to keep hearing your feedback and if you get the Ohlins sorted to where you feel they are as good over rough pavement.
I race on rough pavement so if the ARK 8K/6K stays ahead of the Ohlins in performance there I am INTERESTED in that!
07-01-15, 07:52 PM
#33
Yes I agree you should never drive the car that hard on the street anyway. If anything unexpected happens it's going to be bad news. I meant forgiving and predictable I suppose. I would not necessarily call my track car predictable in a true street driving environment. It is however still somewhat forgiving in that I can gather it back up easily. There are not odd expansion joints, surface changes, harsh bumps, water, debris, dirt etc in a track environment. I don't drive it on the street much but when I do the car is affected a lot more by all of those other everyday factors than a softer suspended street setup.
Gotcha.
In the case of a wide FC I think its less the spring rate and more why you had to up the spring rate that makes the chassis less predictable.
Wrong offset wheels/wide tire really make the FC pull side to side over seams in pavement and differentials in traction side to side on the car.
Wide tires (especially on a light car) mean more chance for any leaves/needles/gravel/snow/ice on the road to get under a tire and skate the tire (though wide tire means less chance of dropping into holes in the road- yay).
Massive grip loads the "interesting" rear subframe mounting/bushings and suspension design in ways that really show its shortcomings.
You basically have to make your front springs solid to keep the Mac strut from doing Mac strut things so you go to a taller front tires/sidewall and have undamped sidewall as your front suspension.
If you *just* raised your spring rates on an FC to suit stock offset wheels and DOT-R tires it drives more predictably like a stock FC.
On an FD/RX-8 you just add wider wheels/tires and stiffer springs and it just works.
You are forced to using the stock offset to fit a wide wheel/tire and the suspension is pretty straight forward functional compared to the FC.
Gotcha.
In the case of a wide FC I think its less the spring rate and more why you had to up the spring rate that makes the chassis less predictable.
Wrong offset wheels/wide tire really make the FC pull side to side over seams in pavement and differentials in traction side to side on the car.
Wide tires (especially on a light car) mean more chance for any leaves/needles/gravel/snow/ice on the road to get under a tire and skate the tire (though wide tire means less chance of dropping into holes in the road- yay).
Massive grip loads the "interesting" rear subframe mounting/bushings and suspension design in ways that really show its shortcomings.
You basically have to make your front springs solid to keep the Mac strut from doing Mac strut things so you go to a taller front tires/sidewall and have undamped sidewall as your front suspension.
If you *just* raised your spring rates on an FC to suit stock offset wheels and DOT-R tires it drives more predictably like a stock FC.
On an FD/RX-8 you just add wider wheels/tires and stiffer springs and it just works.
You are forced to using the stock offset to fit a wide wheel/tire and the suspension is pretty straight forward functional compared to the FC.
07-01-15, 10:32 PM
#34
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I used 285/30/18 RE-11's with 18x11.5 wheels, used on both set ups. I also have seat time on the ARK STP with 12KG/12KG on 265/35/18 kumho XS tires.
The ohlins are definitely smoother with the higher rates than the ARK's are with high rates. ARK's were actually pretty good with 8/6 and the cornering grip was amazing. The spring rates of 8/6 are of a frequency around 1.5HZ which is supposed to be great for handling and grip, most sports cars are coming out around 1.3HZ. every article I have read says that lower frequency spring rates equal more mechanical grip at the expense of transitions. I rode in the 1.5HZ and I honestly couldn't feel much roll to me. I thought 8/6 was still too stiff IMO. I think a good mix would be 7/6 or 7/7 with flat ride. perhaps 6/6 might be awesome. Not sure.
I did some measurements tonight of both the ARK and Ohlins dampers.
Ohlins
front ~3.25" before bumpstop.
Rear ~2" before bumpstop
ARK
Front (no measurement)
Rear 2" before bumpstop
So there it is, I had GREAT handling and grip when I drove the ARK's, remember me saying that when I hit larger bumps at higher speeds I would literally jump off them, I was definitely hitting the bump stops. With the higher rate springs I wasn't hitting the bump stops but suffered worse handling and ride comfort.
So what to do........some math.
Given
Ohlins say preload the spring 2mm, 50lbs or so of spring rate. Estimate a 700lbs corner weight, 615lbs/in spring is used.
the rear is where the problem is in terms of stroke and staying off the bumpstops.
the car weight and passnger will compress the spring 650/615 = 1.057 inches.
if we have 2" of travel, we have .943" (= 2" - 1.057") of travel before the bumpstop or an impact of 580lbs per rear corner before bumpstop is engaged.
If I run 336lbs/in springs in the rear, 580/336 = 1.72" of travel to stay off the bumpstops per what Ohlins figured.
Ideally I would preload the car enough so when the car is sitting the car doesn't really compress the spring much at all. so 700lbs/336 = 2" of spring preload if I run this spring. 700/448 = 1.56" spring preload for an 8KG 8" spring.
So If I want to lower my spring rate I will need to run a longer spring, increase the preload to above or close to it, and I should be able to run softer spring rates while staying off the bumpstops. I need to ensure I have enough thread on the shock to do so. I might need to run a 8/8kg set up.
I am confident in saying that Ohlins didn't choose the ideal spring rate for the rx7, they chose it because I think they had a design package to fit into a space with so much suspension travel that they chose a spring rate that keeps them off the bumpstops. I have a feeling that most of the tuners are doing the same thing. as cars get faster and faster they are choosing higher rates to stay off the bump stops when they hit things going really fast. For a no downforce car, I don't see the reasoning to be running 2HZ area, when more grip and comfort can be had running closer to 1.3-1.5HZ frequencies. These frequencies do very well on bumpier roads.
quotes from articles
Lower frequencies produce a softer suspension with more mechanical grip, however the
response will be slower in transient (what drivers report as “lack of support”). Higher
frequencies create less suspension travel for a given track, allowing lower ride heights, and in
turn, lowering the center of gravity.
http://www.optimumg.com/docs/Springs...Tech_Tip_1.pdf
Race engineer
For a non aero car with a sensible suspension geometry you will maximise the grip from a tire if you can minimise the changes in vertical load it sees. Consequently the simplest way to set up spring rates for a given circuit is to make them as soft as you can without hitting the jounce and rebound springs or stops.
That may not be a practical approach for a weekend racer but at least it is a start. so figure out how to measure your suspension travel, drive a good lap, see if you are using most of your linear range spring travel up on each wheel.
A good quote.
"So, just as a thought experiment, in the world of engineering is it common to change a setting that works (spring rate) by a factor of 4 ? "
the stock rx7 spring rates are front 260ish, rear 190ish.
anyway, I have a feeling I am going to end up with 8/8kg on the ohlins dfv shocks.
another thing I can try is increase the pre-load with the ohlins 11/11 and see what happens as well (especially the rear) if I was hitting the bumpstops.
The ohlins are definitely smoother with the higher rates than the ARK's are with high rates. ARK's were actually pretty good with 8/6 and the cornering grip was amazing. The spring rates of 8/6 are of a frequency around 1.5HZ which is supposed to be great for handling and grip, most sports cars are coming out around 1.3HZ. every article I have read says that lower frequency spring rates equal more mechanical grip at the expense of transitions. I rode in the 1.5HZ and I honestly couldn't feel much roll to me. I thought 8/6 was still too stiff IMO. I think a good mix would be 7/6 or 7/7 with flat ride. perhaps 6/6 might be awesome. Not sure.
I did some measurements tonight of both the ARK and Ohlins dampers.
Ohlins
front ~3.25" before bumpstop.
Rear ~2" before bumpstop
ARK
Front (no measurement)
Rear 2" before bumpstop
So there it is, I had GREAT handling and grip when I drove the ARK's, remember me saying that when I hit larger bumps at higher speeds I would literally jump off them, I was definitely hitting the bump stops. With the higher rate springs I wasn't hitting the bump stops but suffered worse handling and ride comfort.
So what to do........some math.
Given
Ohlins say preload the spring 2mm, 50lbs or so of spring rate. Estimate a 700lbs corner weight, 615lbs/in spring is used.
the rear is where the problem is in terms of stroke and staying off the bumpstops.
the car weight and passnger will compress the spring 650/615 = 1.057 inches.
if we have 2" of travel, we have .943" (= 2" - 1.057") of travel before the bumpstop or an impact of 580lbs per rear corner before bumpstop is engaged.
If I run 336lbs/in springs in the rear, 580/336 = 1.72" of travel to stay off the bumpstops per what Ohlins figured.
Ideally I would preload the car enough so when the car is sitting the car doesn't really compress the spring much at all. so 700lbs/336 = 2" of spring preload if I run this spring. 700/448 = 1.56" spring preload for an 8KG 8" spring.
So If I want to lower my spring rate I will need to run a longer spring, increase the preload to above or close to it, and I should be able to run softer spring rates while staying off the bumpstops. I need to ensure I have enough thread on the shock to do so. I might need to run a 8/8kg set up.
I am confident in saying that Ohlins didn't choose the ideal spring rate for the rx7, they chose it because I think they had a design package to fit into a space with so much suspension travel that they chose a spring rate that keeps them off the bumpstops. I have a feeling that most of the tuners are doing the same thing. as cars get faster and faster they are choosing higher rates to stay off the bump stops when they hit things going really fast. For a no downforce car, I don't see the reasoning to be running 2HZ area, when more grip and comfort can be had running closer to 1.3-1.5HZ frequencies. These frequencies do very well on bumpier roads.
quotes from articles
Lower frequencies produce a softer suspension with more mechanical grip, however the
response will be slower in transient (what drivers report as “lack of support”). Higher
frequencies create less suspension travel for a given track, allowing lower ride heights, and in
turn, lowering the center of gravity.
http://www.optimumg.com/docs/Springs...Tech_Tip_1.pdf
Race engineer
For a non aero car with a sensible suspension geometry you will maximise the grip from a tire if you can minimise the changes in vertical load it sees. Consequently the simplest way to set up spring rates for a given circuit is to make them as soft as you can without hitting the jounce and rebound springs or stops.
That may not be a practical approach for a weekend racer but at least it is a start. so figure out how to measure your suspension travel, drive a good lap, see if you are using most of your linear range spring travel up on each wheel.
A good quote.
"So, just as a thought experiment, in the world of engineering is it common to change a setting that works (spring rate) by a factor of 4 ? "
the stock rx7 spring rates are front 260ish, rear 190ish.
anyway, I have a feeling I am going to end up with 8/8kg on the ohlins dfv shocks.
another thing I can try is increase the pre-load with the ohlins 11/11 and see what happens as well (especially the rear) if I was hitting the bumpstops.
Last edited by lOOkatme; 07-01-15 at 10:47 PM.
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Boost Lee (06-16-19)
07-02-15, 12:01 AM
#35
ARK
Front (no measurement)
What do you mean by "no measurement"?
another thing I can try is increase the pre-load with the ohlins 11/11 and see what happens as well (especially the rear) if I was hitting the bumpstops.
So your idea with pre-loading the spring is to sacrifice your droop travel so that at static ride height you have more damper compression stroke?
Well, try it- but my experience with cars that have limited droop is accelerating and braking traction sucks over dips in the pavement or after any gentle rise that didn't compress the spring. Not fun at all- I would rather run it overdamped to stop the bottoming.
If you have been running the Ohlins at super low damping you may have ruptured the seal on the monotubes nitrogen piston by bottoming the piston bumpstop against the nitrogen piston.
I did that trying to get the best ride quality out of some JIC FLT-TARs on my FC and was in denial for about a year of racing/street driving that they were blown out since they were a couple months old when I noticed the first symptom (car bunny hopping after dip in kart track at ~80mph). Finally a friend told me my rear wheels were bouncing like a basket ball while I was cornering. That explained 99% of the handling issues I was having
The tech that rebuilt them said don't run them so soft they bottom all the time.
Now when I feel a monotube bottom hard I raise the damping till it stops doing it.
Added durability, another bonus of remote reservoir monotubes! Someday...
Front (no measurement)
What do you mean by "no measurement"?
another thing I can try is increase the pre-load with the ohlins 11/11 and see what happens as well (especially the rear) if I was hitting the bumpstops.
So your idea with pre-loading the spring is to sacrifice your droop travel so that at static ride height you have more damper compression stroke?
Well, try it- but my experience with cars that have limited droop is accelerating and braking traction sucks over dips in the pavement or after any gentle rise that didn't compress the spring. Not fun at all- I would rather run it overdamped to stop the bottoming.
If you have been running the Ohlins at super low damping you may have ruptured the seal on the monotubes nitrogen piston by bottoming the piston bumpstop against the nitrogen piston.
I did that trying to get the best ride quality out of some JIC FLT-TARs on my FC and was in denial for about a year of racing/street driving that they were blown out since they were a couple months old when I noticed the first symptom (car bunny hopping after dip in kart track at ~80mph). Finally a friend told me my rear wheels were bouncing like a basket ball while I was cornering. That explained 99% of the handling issues I was having
The tech that rebuilt them said don't run them so soft they bottom all the time.Now when I feel a monotube bottom hard I raise the damping till it stops doing it.
Added durability, another bonus of remote reservoir monotubes! Someday...
Last edited by BLUE TII; 07-02-15 at 12:04 AM.
07-02-15, 02:31 AM
#36
I'm interested in this as I'm going through the same thing with my TEIN Street Flex, but I'm pretty new to suspension so please correct me if I said anything wrong 
Is that measured with the shaft fully extended? How tall are the bumpstop?
That is not a lot of room to go before bumpstop engage if that's fully extended, my Street Flex has 71mm from full droop to bumpstop. Also, did you add MR to the equation? 650lbs at the tire is 956lbs at the spring.
I don't think you'll have enough thread to put that much preload on the spring, especially with softer spring, even if you have the room you might risk running into coil bind. If you are hitting the bump stop now then you'll have a bigger chance to hit it with the softer spring, only way to avoid that is to put more preload on your current spring to gain bump travel. Ideally you would want 40/60 droop/bump travel, so you'll have to measure your shaft fully extended to see how much preload you need.
Here's the measurement I did with my Street Flex rear.
Rear MR = 0.68
Curb Weight = 2900lbs / 1300kg
Corner Weight = 1300kg / 4 = 325kg
Add MR = 325kg / 0.68 = 478kg
Rear Shaft Travel = 111mm
Rear bumpstop = 40mm
Full droop to bumpstop = 71mm
40/60 droop/bump = 44/67
478kg / 8kg/mm = 59.75mm
Preload needed = 15.75mm
478kg / 6kg/mm = 76.67mm
Preload needed = 32.67mm
With the original 8kg spring, preload 15.75mm put me right at the 40/60 mark, that is 27mm before touching the bumpstop, the rear bumpstop is 40mm, so I have about 65mm from static height till bottoming. I drove around with the original 10kg/8kg setup for a couple weeks and I think these are pretty good, ride pretty similar to my Tokico/Eibach setup on another car, only thing is the car feel very stiff on uneven road with a lot of small bumps, so I decided to try different spring rate to see if softer spring can solve this issue. I ordered some 6kg Swift spring with an extra inch to make up for the preload, with proper preload set my spring perch is about 4 full turn from the top, so there aren't much room to go if I need extra preload down the road, and my shock body is on the lowest setting with the car sitting about 25.75" fender to ground on the rear. If I want to lower the car more I'll have to remove some of the preload, but that will bring me closer to the bumpstop which I refused to do. And that's another thing about preload, it will raise the ride height, so you need to make sure the bottom portion has room to go back down to where you want it.
If the shock has limited shaft travel, they will pick higher spring rate to help stay off the bump stop.
So there it is, I had GREAT handling and grip when I drove the ARK's, remember me saying that when I hit larger bumps at higher speeds I would literally jump off them, I was definitely hitting the bump stops. With the higher rate springs I wasn't hitting the bump stops but suffered worse handling and ride comfort.
So what to do........some math.
Given
Ohlins say preload the spring 2mm, 50lbs or so of spring rate. Estimate a 700lbs corner weight, 615lbs/in spring is used.
the rear is where the problem is in terms of stroke and staying off the bumpstops.
the car weight and passnger will compress the spring 650/615 = 1.057 inches.
if we have 2" of travel, we have .943" (= 2" - 1.057") of travel before the bumpstop or an impact of 580lbs per rear corner before bumpstop is engaged.
So what to do........some math.
Given
Ohlins say preload the spring 2mm, 50lbs or so of spring rate. Estimate a 700lbs corner weight, 615lbs/in spring is used.
the rear is where the problem is in terms of stroke and staying off the bumpstops.
the car weight and passnger will compress the spring 650/615 = 1.057 inches.
if we have 2" of travel, we have .943" (= 2" - 1.057") of travel before the bumpstop or an impact of 580lbs per rear corner before bumpstop is engaged.
If I run 336lbs/in springs in the rear, 580/336 = 1.72" of travel to stay off the bumpstops per what Ohlins figured.
Ideally I would preload the car enough so when the car is sitting the car doesn't really compress the spring much at all. so 700lbs/336 = 2" of spring preload if I run this spring. 700/448 = 1.56" spring preload for an 8KG 8" spring.
So If I want to lower my spring rate I will need to run a longer spring, increase the preload to above or close to it, and I should be able to run softer spring rates while staying off the bumpstops. I need to ensure I have enough thread on the shock to do so. I might need to run a 8/8kg set up.
Ideally I would preload the car enough so when the car is sitting the car doesn't really compress the spring much at all. so 700lbs/336 = 2" of spring preload if I run this spring. 700/448 = 1.56" spring preload for an 8KG 8" spring.
So If I want to lower my spring rate I will need to run a longer spring, increase the preload to above or close to it, and I should be able to run softer spring rates while staying off the bumpstops. I need to ensure I have enough thread on the shock to do so. I might need to run a 8/8kg set up.
Here's the measurement I did with my Street Flex rear.
Rear MR = 0.68
Curb Weight = 2900lbs / 1300kg
Corner Weight = 1300kg / 4 = 325kg
Add MR = 325kg / 0.68 = 478kg
Rear Shaft Travel = 111mm
Rear bumpstop = 40mm
Full droop to bumpstop = 71mm
40/60 droop/bump = 44/67
478kg / 8kg/mm = 59.75mm
Preload needed = 15.75mm
478kg / 6kg/mm = 76.67mm
Preload needed = 32.67mm
With the original 8kg spring, preload 15.75mm put me right at the 40/60 mark, that is 27mm before touching the bumpstop, the rear bumpstop is 40mm, so I have about 65mm from static height till bottoming. I drove around with the original 10kg/8kg setup for a couple weeks and I think these are pretty good, ride pretty similar to my Tokico/Eibach setup on another car, only thing is the car feel very stiff on uneven road with a lot of small bumps, so I decided to try different spring rate to see if softer spring can solve this issue. I ordered some 6kg Swift spring with an extra inch to make up for the preload, with proper preload set my spring perch is about 4 full turn from the top, so there aren't much room to go if I need extra preload down the road, and my shock body is on the lowest setting with the car sitting about 25.75" fender to ground on the rear. If I want to lower the car more I'll have to remove some of the preload, but that will bring me closer to the bumpstop which I refused to do. And that's another thing about preload, it will raise the ride height, so you need to make sure the bottom portion has room to go back down to where you want it.
I am confident in saying that Ohlins didn't choose the ideal spring rate for the rx7, they chose it because I think they had a design package to fit into a space with so much suspension travel that they chose a spring rate that keeps them off the bumpstops. I have a feeling that most of the tuners are doing the same thing. as cars get faster and faster they are choosing higher rates to stay off the bump stops when they hit things going really fast. For a no downforce car, I don't see the reasoning to be running 2HZ area, when more grip and comfort can be had running closer to 1.3-1.5HZ frequencies. These frequencies do very well on bumpier roads.
07-02-15, 08:46 AM
#37
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ARK
Front (no measurement)
What do you mean by "no measurement"?
another thing I can try is increase the pre-load with the ohlins 11/11 and see what happens as well (especially the rear) if I was hitting the bumpstops.
So your idea with pre-loading the spring is to sacrifice your droop travel so that at static ride height you have more damper compression stroke?
Well, try it- but my experience with cars that have limited droop is accelerating and braking traction sucks over dips in the pavement or after any gentle rise that didn't compress the spring. Not fun at all- I would rather run it overdamped to stop the bottoming.
If you have been running the Ohlins at super low damping you may have ruptured the seal on the monotubes nitrogen piston by bottoming the piston bumpstop against the nitrogen piston.
I did that trying to get the best ride quality out of some JIC FLT-TARs on my FC and was in denial for about a year of racing/street driving that they were blown out since they were a couple months old when I noticed the first symptom (car bunny hopping after dip in kart track at ~80mph). Finally a friend told me my rear wheels were bouncing like a basket ball while I was cornering. That explained 99% of the handling issues I was having The tech that rebuilt them said don't run them so soft they bottom all the time.
Now when I feel a monotube bottom hard I raise the damping till it stops doing it.
Added durability, another bonus of remote reservoir monotubes! Someday...
Front (no measurement)
What do you mean by "no measurement"?
another thing I can try is increase the pre-load with the ohlins 11/11 and see what happens as well (especially the rear) if I was hitting the bumpstops.
So your idea with pre-loading the spring is to sacrifice your droop travel so that at static ride height you have more damper compression stroke?
Well, try it- but my experience with cars that have limited droop is accelerating and braking traction sucks over dips in the pavement or after any gentle rise that didn't compress the spring. Not fun at all- I would rather run it overdamped to stop the bottoming.
If you have been running the Ohlins at super low damping you may have ruptured the seal on the monotubes nitrogen piston by bottoming the piston bumpstop against the nitrogen piston.
I did that trying to get the best ride quality out of some JIC FLT-TARs on my FC and was in denial for about a year of racing/street driving that they were blown out since they were a couple months old when I noticed the first symptom (car bunny hopping after dip in kart track at ~80mph). Finally a friend told me my rear wheels were bouncing like a basket ball while I was cornering. That explained 99% of the handling issues I was having
The tech that rebuilt them said don't run them so soft they bottom all the time.Now when I feel a monotube bottom hard I raise the damping till it stops doing it.
Added durability, another bonus of remote reservoir monotubes! Someday...
I don't think I have bottomed the Ohlins yet. I know I bottomed my old ARK's every once in a while over the huge launching pad and I know why they felt like that. I don't think either Ohlins or ARK's shock is blown or damaged. I haven't bottomed anything THAT hard.
I can feel what little travel the ohlins have when going fast over bumpy roads (not like whoop section roads, but just uneven roads) that have high cycles. the car wants to hop due to the high frequency spring rate. I am so **** about handling that I notice every little thing. I could see how people might like a stiffer ride, it makes you feel like you are going faster as the limit is lower and its easier to slide the tires. The softer rates are nice but I am just hoping I can make it work with such little travel without hitting the bump stops at all. I already swapped the springs last night, I need to set the height of the car and go for a drive and test it all. I won't go gang busters on the rear pre-load but it will definitely be compressed atleast an inch or so. so 336lbs pre-load, if its 700lbs in the rear I will have roughly 1.08" of droop, same as the ohlins, but I will only have .92" of travel in the suspension before the bumpstop engages. that is only 310lbs force. I try it out and see how I like it and won't do anything crazy. Just try it out and see how smooth it is. I will probably have to buy an 8" long spring 8KG for the rear, preload it up, have about .7" droop, and 1.3" travel for 582lbs max hit before bumpstop, Ohlins has 580lbs on thier springs. I think this will work the best for being soft, damping rates being good, flat ride, and staying off the bump stops with adequate droop.
I hardly have any miles on the ohlins, perhaps 250-300 miles at a max.
07-02-15, 08:56 AM
#38
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I'm interested in this as I'm going through the same thing with my TEIN Street Flex, but I'm pretty new to suspension so please correct me if I said anything wrong
Is that measured with the shaft fully extended? How tall are the bumpstop?
this is fully extended with the spring off the shock. The bumpstop is about 1.5-1.75" in length or so.
That is not a lot of room to go before bumpstop engage if that's fully extended, my Street Flex has 71mm from full droop to bumpstop. Also, did you add MR to the equation? 650lbs at the tire is 956lbs at the spring.
I and not talking wheel rates, just spring rates.
I don't think you'll have enough thread to put that much preload on the spring, especially with softer spring, even if you have the room you might risk running into coil bind. If you are hitting the bump stop now then you'll have a bigger chance to hit it with the softer spring, only way to avoid that is to put more preload on your current spring to gain bump travel. Ideally you would want 40/60 droop/bump travel, so you'll have to measure your shaft fully extended to see how much preload you need.
Here's the measurement I did with my Street Flex rear.
Rear MR = 0.68
Curb Weight = 2900lbs / 1300kg
Corner Weight = 1300kg / 4 = 325kg
Add MR = 325kg / 0.68 = 478kg
Rear Shaft Travel = 111mm
Rear bumpstop = 40mm
Full droop to bumpstop = 71mm
40/60 droop/bump = 44/67
478kg / 8kg/mm = 59.75mm
Preload needed = 15.75mm
478kg / 6kg/mm = 76.67mm
Preload needed = 32.67mm
With the original 8kg spring, preload 15.75mm put me right at the 40/60 mark, that is 27mm before touching the bumpstop, the rear bumpstop is 40mm, so I have about 65mm from static height till bottoming. I drove around with the original 10kg/8kg setup for a couple weeks and I think these are pretty good, ride pretty similar to my Tokico/Eibach setup on another car, only thing is the car feel very stiff on uneven road with a lot of small bumps, so I decided to try different spring rate to see if softer spring can solve this issue. I ordered some 6kg Swift spring with an extra inch to make up for the preload, with proper preload set my spring perch is about 4 full turn from the top, so there aren't much room to go if I need extra preload down the road, and my shock body is on the lowest setting with the car sitting about 25.75" fender to ground on the rear. If I want to lower the car more I'll have to remove some of the preload, but that will bring me closer to the bumpstop which I refused to do. And that's another thing about preload, it will raise the ride height, so you need to make sure the bottom portion has room to go back down to where you want it.
Right now I have some preload on the spring and I dropped the car. its super low right now. I am going to add more preload and raise the bottom of the coilover back up. I am shooting for a 25.5" ride height in the rear and a 25" in the front. I am adding a hair more preload to the front as well as my measurements must have been slightly off (I am rounding everything to ball park it. I think the fronts are at 24.5 or 24.75ish right now. I am shooting for 25"+ a little.
If the shock has limited shaft travel, they will pick higher spring rate to help stay off the bump stop.
Is that measured with the shaft fully extended? How tall are the bumpstop?
this is fully extended with the spring off the shock. The bumpstop is about 1.5-1.75" in length or so.
That is not a lot of room to go before bumpstop engage if that's fully extended, my Street Flex has 71mm from full droop to bumpstop. Also, did you add MR to the equation? 650lbs at the tire is 956lbs at the spring.
I and not talking wheel rates, just spring rates.
I don't think you'll have enough thread to put that much preload on the spring, especially with softer spring, even if you have the room you might risk running into coil bind. If you are hitting the bump stop now then you'll have a bigger chance to hit it with the softer spring, only way to avoid that is to put more preload on your current spring to gain bump travel. Ideally you would want 40/60 droop/bump travel, so you'll have to measure your shaft fully extended to see how much preload you need.
Here's the measurement I did with my Street Flex rear.
Rear MR = 0.68
Curb Weight = 2900lbs / 1300kg
Corner Weight = 1300kg / 4 = 325kg
Add MR = 325kg / 0.68 = 478kg
Rear Shaft Travel = 111mm
Rear bumpstop = 40mm
Full droop to bumpstop = 71mm
40/60 droop/bump = 44/67
478kg / 8kg/mm = 59.75mm
Preload needed = 15.75mm
478kg / 6kg/mm = 76.67mm
Preload needed = 32.67mm
With the original 8kg spring, preload 15.75mm put me right at the 40/60 mark, that is 27mm before touching the bumpstop, the rear bumpstop is 40mm, so I have about 65mm from static height till bottoming. I drove around with the original 10kg/8kg setup for a couple weeks and I think these are pretty good, ride pretty similar to my Tokico/Eibach setup on another car, only thing is the car feel very stiff on uneven road with a lot of small bumps, so I decided to try different spring rate to see if softer spring can solve this issue. I ordered some 6kg Swift spring with an extra inch to make up for the preload, with proper preload set my spring perch is about 4 full turn from the top, so there aren't much room to go if I need extra preload down the road, and my shock body is on the lowest setting with the car sitting about 25.75" fender to ground on the rear. If I want to lower the car more I'll have to remove some of the preload, but that will bring me closer to the bumpstop which I refused to do. And that's another thing about preload, it will raise the ride height, so you need to make sure the bottom portion has room to go back down to where you want it.
Right now I have some preload on the spring and I dropped the car. its super low right now. I am going to add more preload and raise the bottom of the coilover back up. I am shooting for a 25.5" ride height in the rear and a 25" in the front. I am adding a hair more preload to the front as well as my measurements must have been slightly off (I am rounding everything to ball park it. I think the fronts are at 24.5 or 24.75ish right now. I am shooting for 25"+ a little.
If the shock has limited shaft travel, they will pick higher spring rate to help stay off the bump stop.
They chose higher rates because they don't have any shaft travel. I will preload the spring and get it to work with softer rates. I ran the 8/6 springs with the ARK coilovers on roughly the same shock travel and same bump stop height etc. I rarely hit the bumpstops, but I also didn't go crazy with the preload, I added perhaps 1/4" or 6-7mm of preload. This time around I am going to add more preload, keep good droop, and have a lot more travel than before.
07-02-15, 10:10 AM
#39
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Looks like the S2K guys have 2" rear travel and have an 8KG spring. I don't know their motion ratio but they are engaging the bumpstops in the rear of their cars with the 2mm preload.
OHLINS dfv question - S2KI Honda S2000 Forums
Looks like Ohlins is riding on the bumpstops with a progressive bumpstop and might be designed that way due to limited suspension travel.
OHLINS dfv question - S2KI Honda S2000 Forums
Looks like Ohlins is riding on the bumpstops with a progressive bumpstop and might be designed that way due to limited suspension travel.
07-02-15, 10:28 AM
#40
Senior Member
lOOkatme, I'm convinced something's wrong with your Ohlins setup. I am able to flat-foot it in 3rd gear (putting down well over 400rwhp) while cornering at 1+g, with the loaded right-side wheels going over ~2.5" high curbing at NHMS between turns 11 and 12 without upsetting the car at all, with 13kg front 11kg rear spring rates, with damping set 4-5 clicks out in front and 6 clicks out in back. It's like fricking magic, I couldn't anything like do that with my old 9kg/7kg Teins, the car was a total handful over any road/track bumps/potholes or other irregularities. Now it's perfectly stable, it's really unbelievable how smooth it is. The only times I've bottomed is when I've gone into giant potholes at unabated speed, which I'm tempted to do all the time because of how amazing a job the Ohlins dampers do soaking up bumps.
07-02-15, 10:35 AM
#41
this is fully extended with the spring off the shock. The bumpstop is about 1.5-1.75" in length or so.
Right now I have some preload on the spring and I dropped the car. its super low right now. I am going to add more preload and raise the bottom of the coilover back up. I am shooting for a 25.5" ride height in the rear and a 25" in the front. I am adding a hair more preload to the front as well as my measurements must have been slightly off (I am rounding everything to ball park it. I think the fronts are at 24.5 or 24.75ish right now. I am shooting for 25"+ a little.
They chose higher rates because they don't have any shaft travel. I will preload the spring and get it to work with softer rates. I ran the 8/6 springs with the ARK coilovers on roughly the same shock travel and same bump stop height etc. I rarely hit the bumpstops, but I also didn't go crazy with the preload, I added perhaps 1/4" or 6-7mm of preload. This time around I am going to add more preload, keep good droop, and have a lot more travel than before.
Right now I have some preload on the spring and I dropped the car. its super low right now. I am going to add more preload and raise the bottom of the coilover back up. I am shooting for a 25.5" ride height in the rear and a 25" in the front. I am adding a hair more preload to the front as well as my measurements must have been slightly off (I am rounding everything to ball park it. I think the fronts are at 24.5 or 24.75ish right now. I am shooting for 25"+ a little.
They chose higher rates because they don't have any shaft travel. I will preload the spring and get it to work with softer rates. I ran the 8/6 springs with the ARK coilovers on roughly the same shock travel and same bump stop height etc. I rarely hit the bumpstops, but I also didn't go crazy with the preload, I added perhaps 1/4" or 6-7mm of preload. This time around I am going to add more preload, keep good droop, and have a lot more travel than before.
Interestingly you didn't hit the bumpstops much on the ARK with just 1/4" of preload, my Street Flex with 6kg spring will basically sit on the bumpstop without preload, I follow my calculation and preload it 1.25", that brings it back to about 1" before bumpstop engage. Of course this is all base off of calculation, so it could be off, wish there's an easy way to measure it without a lift.
07-02-15, 10:46 AM
#42
My experiences are like ZDans with the Ohlins.
On the hillclimb there is a kinda- straight toward the end where the road snakes around a telephone pole with a frost heave and then a bumpy braking zone.
My FD was amazing there with the Ohlins allowing me to keep my foot flat deep in 4th past the pole and late brake over the bumps. My friend with radar gun said I had the highest mph past the pole in my little 250hp FD versus the Z06s and GT2.
The whole road is a mess of patches and crap pavement.
On the hillclimb there is a kinda- straight toward the end where the road snakes around a telephone pole with a frost heave and then a bumpy braking zone.
My FD was amazing there with the Ohlins allowing me to keep my foot flat deep in 4th past the pole and late brake over the bumps. My friend with radar gun said I had the highest mph past the pole in my little 250hp FD versus the Z06s and GT2.
The whole road is a mess of patches and crap pavement.
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Rocketeerbandit (05-27-21)
07-02-15, 11:04 AM
#43
If you turn the volume up you can hear (the broken power plant frame) the affect of the limited droop travel in the rear as lOOkatme notes.
The engine rpm momentarily picks up as the Torsen allows the unloaded wheel to spin a bit on the tight turns/crossing the crown.
If I had more power in the FD I would want a clutch type rear and/or more droop travel for sure for this hillclimb. This is the only place I have noticed this downside to the limited rear droop so far.
I have also heard this criticism of limited rear travel about the NC Ohlins application. I have pretty much that set up my RX-8 and I can say the rear is sprung too soft/too easy onto the bumpstops or not enough travel (haven't run into the limited droop problem yet on the 8).
The engine rpm momentarily picks up as the Torsen allows the unloaded wheel to spin a bit on the tight turns/crossing the crown.
If I had more power in the FD I would want a clutch type rear and/or more droop travel for sure for this hillclimb. This is the only place I have noticed this downside to the limited rear droop so far.
I have also heard this criticism of limited rear travel about the NC Ohlins application. I have pretty much that set up my RX-8 and I can say the rear is sprung too soft/too easy onto the bumpstops or not enough travel (haven't run into the limited droop problem yet on the 8).
07-02-15, 11:21 AM
#44
I can see where you need more rear droop there. I would say at your power level a clutch LSD may work better, but with more power a Torsen would be the hot ticket.. well for my driving style anyway, provided you can get the suspension to drop into those ruts.
That looks like fun.
That looks like fun.
07-02-15, 12:08 PM
#45
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lOOkatme, I'm convinced something's wrong with your Ohlins setup. I am able to flat-foot it in 3rd gear (putting down well over 400rwhp) while cornering at 1+g, with the loaded right-side wheels going over ~2.5" high curbing at NHMS between turns 11 and 12 without upsetting the car at all, with 13kg front 11kg rear spring rates, with damping set 4-5 clicks out in front and 6 clicks out in back. It's like fricking magic, I couldn't anything like do that with my old 9kg/7kg Teins, the car was a total handful over any road/track bumps/potholes or other irregularities. Now it's perfectly stable, it's really unbelievable how smooth it is. The only times I've bottomed is when I've gone into giant potholes at unabated speed, which I'm tempted to do all the time because of how amazing a job the Ohlins dampers do soaking up bumps.
I don't think anything is wrong with the shocks. I think it probably has more to do with the road and the stiffness of the springs. I am traveling at higher rates of speeds top of 4th gear on roads that aren't flat, the tires like to grab grooves or the crown or lane marks over the years. The softer springs were more forgiving, on the flat portion and newer roads the shocks handle very well, just seems like at a slightly lower grip limit. Perhaps my perception is off and I am really going that fast. it could be. I am going to try the ohlins with the softer spring rates, and if I don't like that or they are too soft I am going back to the 11's and running them with that or stepping up the rear to an 8KG spring.
Perhaps I had too soft a damping setting but I doubt it.
But you have to be reminded that I like soft spring rates. I think the damping is fine and I can tell its better than the ARK's. I am just overly picky as I want the car to be stable on unstable/uneven pavement with a large safety cushion. I am going to try softer rates and I will report back.
For some reason I find a good mix with soft spring rates and high critical damping ratio.
Another thing, these shocks are basically new, perhaps they need to break in or something?
I set them up 25" front 25.5" rear, 2mm preload, measured everything to the T like the manual said when I set them up origionally.
07-02-15, 12:12 PM
#46
LargeOrangeFont
I can see where you need more rear droop there. I would say at your power level a clutch LSD may work better, but with more power a Torsen would be the hot ticket.. well for my driving style anyway, provided you can get the suspension to drop into those ruts.
Yeah, but I would have to get a Ford 8.8 rear and pick a Torsen with higher bias ratio if I went that route.
I know from my FC that if I kept the stock Mazda Torsen and had real power it gets kinda iffy like trying to drive a high power car with an open diff.
I can see where you need more rear droop there. I would say at your power level a clutch LSD may work better, but with more power a Torsen would be the hot ticket.. well for my driving style anyway, provided you can get the suspension to drop into those ruts.
Yeah, but I would have to get a Ford 8.8 rear and pick a Torsen with higher bias ratio if I went that route.
I know from my FC that if I kept the stock Mazda Torsen and had real power it gets kinda iffy like trying to drive a high power car with an open diff.
07-02-15, 12:19 PM
#47
Perhaps my perception is off and I am really going that fast. it could be. I am going to try the ohlins with the softer spring rates, and if I don't like that or they are too soft I am going back to the 11's and running them with that or stepping up the rear to an 8KG spring.
I would trust my perception if I were you and keep setting up the car to where you the driver is most comfortable.
Another thing, these shocks are basically new, perhaps they need to break in or something?
Should be good to go.
In fact I have read that shocks perform at their peak when they are freshly rebuilt and slowly degrade/change damping as the oil breaks down. So if you have your set up really dialed in to where you want it you are always rebuilding to get back to that preferred set up.
I would trust my perception if I were you and keep setting up the car to where you the driver is most comfortable.
Another thing, these shocks are basically new, perhaps they need to break in or something?
Should be good to go.
In fact I have read that shocks perform at their peak when they are freshly rebuilt and slowly degrade/change damping as the oil breaks down. So if you have your set up really dialed in to where you want it you are always rebuilding to get back to that preferred set up.
07-02-15, 01:00 PM
#48
I am traveling at higher rates of speeds top of 4th gear on roads that aren't flat, the tires like to grab grooves or the crown or lane marks over the years.
You can hear I am on the 4th gear redline buzzer for over a second as I pass the telephone pole (2:05-2:07) into the treacherous bumpy braking zone (1 or 2 cars wreck a year it seems). But yes, the rest of the hill is slower.
Anyways, that confidence in the predictability is what you need with whatever set-up you end up with.
You can hear I am on the 4th gear redline buzzer for over a second as I pass the telephone pole (2:05-2:07) into the treacherous bumpy braking zone (1 or 2 cars wreck a year it seems). But yes, the rest of the hill is slower.
Anyways, that confidence in the predictability is what you need with whatever set-up you end up with.
07-02-15, 02:24 PM
#49
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more on being backwards....
we use the maths and the spreadsheets and stuff, but we collect data for a while, and tweak the model until the drivers *** and the model agree, only then can you make predictive changes. i guess you could say either we were lucky enough to have lots of racing before the maths were commonly available, or that we decided that the lap time was the important thing. racing is nice for that.
second we also spend a lot of time measuring stuff, and zero is never zero. nothing with an index ever lines up ever, we do start there, but it never ends there. or more bluntly, its not how much bump travel you have its how much you use. sometimes you need to know how much is in the glass!
actually the BIGGEST take away from racing, is that the hardest problem is to figure out what problem you actually have. usually once you figure out the problem the solution is a couple turns of something.
the next car we run, i wanna do #96 reverse cowgirl.
we use the maths and the spreadsheets and stuff, but we collect data for a while, and tweak the model until the drivers *** and the model agree, only then can you make predictive changes. i guess you could say either we were lucky enough to have lots of racing before the maths were commonly available, or that we decided that the lap time was the important thing. racing is nice for that.
second we also spend a lot of time measuring stuff, and zero is never zero. nothing with an index ever lines up ever, we do start there, but it never ends there. or more bluntly, its not how much bump travel you have its how much you use. sometimes you need to know how much is in the glass!
actually the BIGGEST take away from racing, is that the hardest problem is to figure out what problem you actually have. usually once you figure out the problem the solution is a couple turns of something.
the next car we run, i wanna do #96 reverse cowgirl.
Last edited by j9fd3s; 07-02-15 at 02:28 PM.
07-02-15, 04:38 PM
#50
LargeOrangeFont
I can see where you need more rear droop there. I would say at your power level a clutch LSD may work better, but with more power a Torsen would be the hot ticket.. well for my driving style anyway, provided you can get the suspension to drop into those ruts.
Yeah, but I would have to get a Ford 8.8 rear and pick a Torsen with higher bias ratio if I went that route.
I know from my FC that if I kept the stock Mazda Torsen and had real power it gets kinda iffy like trying to drive a high power car with an open diff.
I can see where you need more rear droop there. I would say at your power level a clutch LSD may work better, but with more power a Torsen would be the hot ticket.. well for my driving style anyway, provided you can get the suspension to drop into those ruts.
Yeah, but I would have to get a Ford 8.8 rear and pick a Torsen with higher bias ratio if I went that route.
I know from my FC that if I kept the stock Mazda Torsen and had real power it gets kinda iffy like trying to drive a high power car with an open diff.
