Another happy Ohlins DFV owner
11-13-15, 08:29 PM
#26
Eats, Sleeps, Dreams Rotary
it has to do with the motion ratio. a strut car, by definition has the spring at the end of the arm, so its motion ratio is 1:1. the FD has the spring in the middle of the arm, so the motion ratio is something like 0.7:1.
the motion ratio is computed with the spring rate to get what is called the wheel rate, the spring rate at the wheel. the wheel rate is comparable car to car.
so basically 11kg springs on the FD, with a motion ratio of .7 (not sure what it actually is, although the info has been posted, also easy to measure), gives you a wheel rate of 7.7kg, which is basically the same as the 8kg people run in the FC.
the motion ratio is computed with the spring rate to get what is called the wheel rate, the spring rate at the wheel. the wheel rate is comparable car to car.
so basically 11kg springs on the FD, with a motion ratio of .7 (not sure what it actually is, although the info has been posted, also easy to measure), gives you a wheel rate of 7.7kg, which is basically the same as the 8kg people run in the FC.
14 or 16 isn't that unusual for an FD track car, either.
11-13-15, 10:01 PM
#27
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We have deemed his car un-driveable...even he thinks its horrible. He is switching his entire set up soon. He and another member did a car swap and the guy who has ohlins 11/11 drove his 16/16 and was like....I barely took a turn and the car was sliding, not only that it was bumpy as all get out.
We drove/rode in his 11/11 set up and the car was much better but you could literally still feel every bump in the road.
We took out my 8/6 set up and all the little bumps weren't even felt. The ohlins 11/11 person in front of me was pushing his car decently hard with the rear end kicking out a little, and I was yawning behind him keeping up with out really trying.
I think people with stiffer rate springs, are going the wrong way. go as soft as possible without bottoming. wide as possible with slight stretch for tires.
11-13-15, 11:12 PM
#29
I think people with stiffer rate springs, are going the wrong way. go as soft as possible without bottoming
I totally agree with this.
But the counterpoint is that even with my FCs 16x8 with 225/50-16 R-S3 street tires my FD on 11k/11k Ohlins at recommended damping was healed over onto the bumpstops cornering at auto-x (I have pics).
I had to really crank the damping up on the FDs 18x11 295s Dot Rs to make up for not having enough spring.
I totally agree with this.
But the counterpoint is that even with my FCs 16x8 with 225/50-16 R-S3 street tires my FD on 11k/11k Ohlins at recommended damping was healed over onto the bumpstops cornering at auto-x (I have pics).
I had to really crank the damping up on the FDs 18x11 295s Dot Rs to make up for not having enough spring.
11-14-15, 08:23 AM
#30
Senior Member
Once again I'll pipe in and say that IMO the idea that softer spring rates gives "more grip" is at best an exaggeration, and that while softer spring rates are going to be a lot more enjoyable on the street, stiffer (up to a point, probably in the ~16 kg/mm range without downforce) is going to be better/faster at the track on serious tires (Hoosier R7/A7, BFG R1/R1S, etc).
Increasing spring rates/wheel rates doesn't reduce grip per se. I think a large part of this perception is because if you stiffen one end of a car you lose grip at that end, but that is due to changing roll stiffness distribution. Whether you go from 11/11 spring rates to 11/9 or 13/11, you are trading front grip for rear grip either way because you will be loading the outside front more and the inside rear less for a given level of cornering g's.
In dynamic conditions over bumps and road irregularities, softer suspension is going to keep the tire loads at contact patches more consistent and give more average grip, but *damping* is way more important than *spring rate* in this situation. Which is why I got more lateral and drive grip putting down power going over 2.5" high curbing with the outside tires at NHMS north chicane with Ohlins with 11/11 spring rates vs. the old Tein SS with 9/7 spring rates. The Ohlins better (reduced) high-speed damping allowed me to continuously put the power down going over the curbing while cornering hard, where I had to take it easy as the car was upset over the same piece of track on the Teins, which had quite harsh high-speed damping. I went nearly a second quicker at NHMS chicane/chicane with the Ohlins 11/11 vs. Tein SS 9/7 with no other changes.
Long/short:
1. good low- and high-speed damping is more important than spring rate for ride and grip over bumps/holes/road irregularities
2. 8/6 spring rates on an FD are going to be more enjoyable on the street, but stiffer rates are going to be better/faster at the track, assuming equally awesome damping for both.
Increasing spring rates/wheel rates doesn't reduce grip per se. I think a large part of this perception is because if you stiffen one end of a car you lose grip at that end, but that is due to changing roll stiffness distribution. Whether you go from 11/11 spring rates to 11/9 or 13/11, you are trading front grip for rear grip either way because you will be loading the outside front more and the inside rear less for a given level of cornering g's.
In dynamic conditions over bumps and road irregularities, softer suspension is going to keep the tire loads at contact patches more consistent and give more average grip, but *damping* is way more important than *spring rate* in this situation. Which is why I got more lateral and drive grip putting down power going over 2.5" high curbing with the outside tires at NHMS north chicane with Ohlins with 11/11 spring rates vs. the old Tein SS with 9/7 spring rates. The Ohlins better (reduced) high-speed damping allowed me to continuously put the power down going over the curbing while cornering hard, where I had to take it easy as the car was upset over the same piece of track on the Teins, which had quite harsh high-speed damping. I went nearly a second quicker at NHMS chicane/chicane with the Ohlins 11/11 vs. Tein SS 9/7 with no other changes.
Long/short:
1. good low- and high-speed damping is more important than spring rate for ride and grip over bumps/holes/road irregularities
2. 8/6 spring rates on an FD are going to be more enjoyable on the street, but stiffer rates are going to be better/faster at the track, assuming equally awesome damping for both.
Last edited by ZDan; 11-14-15 at 08:32 AM.
11-14-15, 09:48 AM
#31
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No uising 16/16 on the street here in colorado.
This isn't my opinion only, this is from 3 different people.
I could see how a little stiffer rate is needed for grippier tires, and I could also see a little more rate being needed for hard turns at slow speeds as I have noticed this on my car that the softer rate springs do roll more. I mainly use my car as a canyon carver and at high rates of speed which softer rates work VERY well at. The higher rates cannot handle the bumps. it unsettles the car.
If I tracked my car on race tires, I would probably first try a 9/7 or 10/8 set up if there were slow turns on race tires. I do prefer the 2KG split between front and rear, I also think a 1 KG split would work well. perhaps a 9/8 would be very nice if you want to go all out.
This isn't my opinion only, this is from 3 different people.
I could see how a little stiffer rate is needed for grippier tires, and I could also see a little more rate being needed for hard turns at slow speeds as I have noticed this on my car that the softer rate springs do roll more. I mainly use my car as a canyon carver and at high rates of speed which softer rates work VERY well at. The higher rates cannot handle the bumps. it unsettles the car.
If I tracked my car on race tires, I would probably first try a 9/7 or 10/8 set up if there were slow turns on race tires. I do prefer the 2KG split between front and rear, I also think a 1 KG split would work well. perhaps a 9/8 would be very nice if you want to go all out.
11-14-15, 10:54 AM
#32
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The multiplier is the *square* of the motion ratio.
11kg/mm springs with a motion ratio of 0.7 gives a wheel rate of 11kg/mm * (0.7)^2 = 5.39 kg/mm
I track my car and needed stiffer springs, so I swapped the 11kg/mm fronts for 13kg/mm.
I also do a fair amount of street miles on some poor roads, and this compromise works well for me overall.
For a street car, I would try the existing 11kg/mm up front with either 9 or 8 kg/mm rear springs like Sketch_hs is talking about.
IIRC, motion ratios are ~0.61 front and ~0.69 rear on the FD, so with 11kg/mm all around you end up with 4.09 kg/mm front wheel rate and 5.24 kg/mm rear. Stiffness is overly biased to the rear which results in somewhat more oversteery behavior and more front/less rear relative cornering grip. Don't know why the "stock" Ohlins DFV configuration for the FD is so rear-biased...
Loving the Ohlins on my car
11kg/mm springs with a motion ratio of 0.7 gives a wheel rate of 11kg/mm * (0.7)^2 = 5.39 kg/mm
I track my car and needed stiffer springs, so I swapped the 11kg/mm fronts for 13kg/mm.
I also do a fair amount of street miles on some poor roads, and this compromise works well for me overall.
For a street car, I would try the existing 11kg/mm up front with either 9 or 8 kg/mm rear springs like Sketch_hs is talking about.
IIRC, motion ratios are ~0.61 front and ~0.69 rear on the FD, so with 11kg/mm all around you end up with 4.09 kg/mm front wheel rate and 5.24 kg/mm rear. Stiffness is overly biased to the rear which results in somewhat more oversteery behavior and more front/less rear relative cornering grip. Don't know why the "stock" Ohlins DFV configuration for the FD is so rear-biased...
Loving the Ohlins on my car
11-14-15, 11:04 AM
#33
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14 or 16 isn't that unusual for an FD track car, either.
just as an FYI, l00katme is running on the street, and the rest of us are on a race track. we're all using the appropriate tool for the job, but its different, as the street isn't the track. so we're using stopwatches, and he's using the butt dyno.
11-14-15, 11:31 AM
#34
Senior Member
My FD understeers at Thompson Speedway, oversteers at NHMS! I connect the rear sway bar for Thompson and disconnect it for NHMS. Might start running less rear camber at Thompson...
11-14-15, 08:42 PM
#35
Eats, Sleeps, Dreams Rotary
I could have sworn I heard that somewhere, but in hindsight it does seem a little iffy.
I think the issue has to due different way the basic structure of the suspension works compared to struts.
Possibly, in the case of wishbones, you're sharing more of the energy between something like ten different contact points with the body (with only one being an upward component), while a strut only has four. So theoretically much more energy goes straight up into the strut towers (with upward thrusting being the biggest component of ride harshness).
And the way struts move isn't super favorable to allow the suspension move freely. And every bit of resistance that is added increases harshness.
I suspect at least 30% of what I just said is bullshit.
I think the issue has to due different way the basic structure of the suspension works compared to struts.
Possibly, in the case of wishbones, you're sharing more of the energy between something like ten different contact points with the body (with only one being an upward component), while a strut only has four. So theoretically much more energy goes straight up into the strut towers (with upward thrusting being the biggest component of ride harshness).
And the way struts move isn't super favorable to allow the suspension move freely. And every bit of resistance that is added increases harshness.
I suspect at least 30% of what I just said is bullshit.
11-14-15, 09:32 PM
#36
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I could have sworn I heard that somewhere, but in hindsight it does seem a little iffy.
I think the issue has to due different way the basic structure of the suspension works compared to struts.
Possibly, in the case of wishbones, you're sharing more of the energy between something like ten different contact points with the body (with only one being an upward component), while a strut only has four. So theoretically much more energy goes straight up into the strut towers (with upward thrusting being the biggest component of ride harshness).
And the way struts move isn't super favorable to allow the suspension move freely. And every bit of resistance that is added increases harshness.
I suspect at least 30% of what I just said is bullshit.
I think the issue has to due different way the basic structure of the suspension works compared to struts.
Possibly, in the case of wishbones, you're sharing more of the energy between something like ten different contact points with the body (with only one being an upward component), while a strut only has four. So theoretically much more energy goes straight up into the strut towers (with upward thrusting being the biggest component of ride harshness).
And the way struts move isn't super favorable to allow the suspension move freely. And every bit of resistance that is added increases harshness.
I suspect at least 30% of what I just said is bullshit.
i was going to say how the Mazda strut tops are usually beefier than the shock tops, but my brothers VW is a strut car, and they didn't even bolt the strut top to the car
11-15-15, 05:51 PM
#39
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11-15-15, 06:36 PM
#41
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we run 18kg on a car with no aero... its not that high of a spring rate, especially when you have a motion ratio that is in the .6's
Last edited by j9fd3s; 11-15-15 at 06:38 PM.
11-15-15, 06:48 PM
#42
Eats, Sleeps, Dreams Rotary
I know someone with an FC with fairly pedestrian aero (undersized GT wing for as much power as the car has, and an aggressive front bumper) who runs either 14 or a 16. It must be bone-jarring.
10-31-16, 09:54 AM
#44
Eats, Sleeps, Dreams Rotary
IIRC, damping force is measured in newtons for a given damper speed (in m/s), not kg/mm (that's the unit for spring rate).
So the answer to that would depend on whether you're talking about low-speed or high-speed damping.
The best thing would be to just look at a damper dyno graph.
So the answer to that would depend on whether you're talking about low-speed or high-speed damping.
The best thing would be to just look at a damper dyno graph.
10-31-16, 11:38 AM
#45
Quote:
Originally Posted by Valkyrie View Post
I know. But even then, double wishbones transmit somewhat less energy to the body.
Quote:
Originally Posted by j9fd3s View Post
how is that possible?
I could have sworn I heard that somewhere, but in hindsight it does seem a little iffy.
I think the issue has to due different way the basic structure of the suspension works compared to struts.
I think the double wishbone rides better than strut on monotube dampers because the dampers piston seal stiction drag also gets to go through the motion ratio on the double wishbone so has less effect on ride quality.
Originally Posted by Valkyrie View Post
I know. But even then, double wishbones transmit somewhat less energy to the body.
Quote:
Originally Posted by j9fd3s View Post
how is that possible?
I could have sworn I heard that somewhere, but in hindsight it does seem a little iffy.
I think the issue has to due different way the basic structure of the suspension works compared to struts.
I think the double wishbone rides better than strut on monotube dampers because the dampers piston seal stiction drag also gets to go through the motion ratio on the double wishbone so has less effect on ride quality.
10-31-16, 12:00 PM
#46
Quote:
Originally Posted by BLUE TII View Post
Don't know why the "stock" Ohlins DFV configuration for the FD is so rear-biased...
Probably has to do with how much understeer a stock FD has. I raced mine in stock class 1 year. FD was made "safe" before Vehicle Dynamic Stability was a thing.
-------------
How much front camber did you have? I think I may be able to get more negative camber with the Samberg V8-swap front subframe. I've been running just under -3 front, -2 rear.
My FD understeers at Thompson Speedway, oversteers at NHMS! I connect the rear sway bar for Thompson and disconnect it for NHMS. Might start running less rear camber at Thompson...
I had -2.6 front -1.4 rear camber and a stiffer Tripoint front sway bar, GAB Rs (stock springs/height).
I changed the front swaybar tube out for their softest which the Tripoint owner informed me was less stiff than stock.
The stock understeer of the FD chassis is purposeful and documented such as in the Yamaguchi RX-7 book.
11-02-16, 09:41 PM
#48
Contact us if you're interested in swapping spring rates or custom-valving the DFV's... we do it often and supply Swift springs for alternate spring rates (they're literally the best out there).
.....and one shameless plug, we've got a container of Ohlins on the way, which we've been able to swing some fantastic pricing on... 2/3 of our FD inventory is pre-sold but whatever is left is up for grabs, at a sale price of $2000 for any of the remaining kits
http://www.sakebombgarage.com/ohlins-road-track-dfv-coilovers-fd3s/
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Specialty aftermarket parts & service // Fremont, California
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11-03-16, 09:05 AM
#50
