howard coleman's FD Chassis/Setup
03-20-08, 09:04 AM
#151
Full Member
great post. thanks for sharing your experience. a lesson we should all keep in mind.
^^^^
Howard is correct, a street/track car leaves something on the table, no question about it. I put in alot of quality tracking with my car with Koni Yellow/GC's w/ 500/400 rates.
However, the car is a system. when I lost the A/C and some interior trim etc. to shave 100 lbs, ran 12 psi instead of 10, added a roll bar and Sparco seat, aggressive brake pads and 285 hoosiers, all of a sudden the weak link is shocks/springs. It doesn't feel as good under braking because that braking is occuring at 155 not 140 anymore, cornering speeds are way up, etc.
I'm not sure the car wasn't just as much fun on track, and more livable on the street before (try driving 5-6 hours back from the track in a Sparco EVO, in 95 degree heat with no A/C), but it is faster. Howard's right, if you want to retain ballance, you've gotta know when to say when.
Howard is correct, a street/track car leaves something on the table, no question about it. I put in alot of quality tracking with my car with Koni Yellow/GC's w/ 500/400 rates.
However, the car is a system. when I lost the A/C and some interior trim etc. to shave 100 lbs, ran 12 psi instead of 10, added a roll bar and Sparco seat, aggressive brake pads and 285 hoosiers, all of a sudden the weak link is shocks/springs. It doesn't feel as good under braking because that braking is occuring at 155 not 140 anymore, cornering speeds are way up, etc.
I'm not sure the car wasn't just as much fun on track, and more livable on the street before (try driving 5-6 hours back from the track in a Sparco EVO, in 95 degree heat with no A/C), but it is faster. Howard's right, if you want to retain ballance, you've gotta know when to say when.
03-20-08, 09:39 AM
#152
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Sometimes you can have it all in regard to coilovers. If you spend about 4 or 5k on some JRZs or equivalent coilovers even with 800 600 springs the dampers/shocks are so good they actually feel decent on the street and when you're ready for the track you can literally shave a second off your lap times.
Howard,
I'm really surprised you haven't gone this route with your FD. You have the funds and good coilovers make a tremendous difference in how the car handles. It's like cheating when you have a good set.
Howard,
I'm really surprised you haven't gone this route with your FD. You have the funds and good coilovers make a tremendous difference in how the car handles. It's like cheating when you have a good set.
03-20-08, 02:51 PM
#153
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wow after reading that is amazing to the array of aspects to the suspension elements that are assoicated with our cars. awesome writeup howard!!!! I am considering purchasing the adjustable tokico struts for my car but my concern is that all of the springs that i see for our cars say that they lower the car and that was the main reason for getting new struts in the first place my ls1 swapped fd would scrape the oil pan on the ground with the stock struts so i purchased a set of used jic's and the ride is horrible so I am trying to go another route. However costs are a huge restriction for me at the moment due to needing to allocate most of my funds to paying on my land and house. any and all suggestions are much appriciated. ps mostly i just run on the street. I havnt yet had the opportunity to enjoy my car on a track.
03-20-08, 04:06 PM
#154
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FDs have springs and shocks. Buicks have struts. struts, as in Macphereson struts, often don't add camber gain so essential for an ultra high performance suspension.
i mention this because i see that nasty 5 letter word too often on this site. please do not take it personally.
so you are scraping the ground w your ls1/fd...
what did you specifically purchase from the JIC line?
what springs do you have on your FD currently?
please measure the distance from the ground to the top of your wheel well (lip) in the front and rear.
fear not, we will straighten things out for you....
howard
i mention this because i see that nasty 5 letter word too often on this site. please do not take it personally.
so you are scraping the ground w your ls1/fd...
what did you specifically purchase from the JIC line?
what springs do you have on your FD currently?
please measure the distance from the ground to the top of your wheel well (lip) in the front and rear.
fear not, we will straighten things out for you....
howard
Last edited by Howard Coleman; 03-21-08 at 06:54 PM.
03-20-08, 04:30 PM
#155
Just like at the Porsche 996 and 997, which use MacPherson struts in the front:
http://www.flat-6.org/forum/showthread.php?t=22545
:-) neil
03-20-08, 05:15 PM
#156
... um, I'm not sure about that. Dynamic camber comes from upper and lower A arms operating at different arcs... McPherson strut asembys, by nature, move linearly with the compression of the strut. Unless you've got a gently arched strut, I don't see how that's possible.
03-20-08, 05:26 PM
#157
I think it can happen.
Follow the position of the lower balljoint at rest and full compression. Use these points to form a line. If the top of the strut is inboard of that line, there will be negative camber gain. If the top of the strut is outboard of that line, you get positive camber gain.
Now that said, the macpherson's I've seen don't pivot at the top of the strut, so the strut top is on that line. If my observations align with generality, then most Macpherson's have very little camber gain.
Dave
Follow the position of the lower balljoint at rest and full compression. Use these points to form a line. If the top of the strut is inboard of that line, there will be negative camber gain. If the top of the strut is outboard of that line, you get positive camber gain.
Now that said, the macpherson's I've seen don't pivot at the top of the strut, so the strut top is on that line. If my observations align with generality, then most Macpherson's have very little camber gain.
Dave
03-20-08, 06:50 PM
#158
Howard, shouldn't the rear ride height be slightly higher than the front to reduce lift/increase downforce at speed? I believe this is how the stock ride height is setup (but I may be wrong). One thing for sure, a ride height lower in the rear than the front would be bad.
03-21-08, 08:56 AM
#159
Well think about it:
If a McPherson strut were allowed to pivot at the top mount (ie: the shock tower mount), and then the lower arm were to follow an arch as suspension compressed, that would mean that the outer pivot of the lower arm would move inboard relative to the chassis, and since the upper strut mound can't move inboard, all you could ever get is a camber loss, not a camber gain.
That's how a double a-arm works. The upper arm is typically shorter and/or at a agreater andle to start with, so when suspension compresses, the arch the upper arm travels in is more acute, and moves it's outer pivot further inboard relative to the outer pivot of the lower arm, changing the camber angle that is formed by the hard connection between the two outer pivots (the spindle and hub)
If a McPherson strut were allowed to pivot at the top mount (ie: the shock tower mount), and then the lower arm were to follow an arch as suspension compressed, that would mean that the outer pivot of the lower arm would move inboard relative to the chassis, and since the upper strut mound can't move inboard, all you could ever get is a camber loss, not a camber gain.
That's how a double a-arm works. The upper arm is typically shorter and/or at a agreater andle to start with, so when suspension compresses, the arch the upper arm travels in is more acute, and moves it's outer pivot further inboard relative to the outer pivot of the lower arm, changing the camber angle that is formed by the hard connection between the two outer pivots (the spindle and hub)
I think it can happen.
Follow the position of the lower balljoint at rest and full compression. Use these points to form a line. If the top of the strut is inboard of that line, there will be negative camber gain. If the top of the strut is outboard of that line, you get positive camber gain.
Now that said, the macpherson's I've seen don't pivot at the top of the strut, so the strut top is on that line. If my observations align with generality, then most Macpherson's have very little camber gain.
Dave
Follow the position of the lower balljoint at rest and full compression. Use these points to form a line. If the top of the strut is inboard of that line, there will be negative camber gain. If the top of the strut is outboard of that line, you get positive camber gain.
Now that said, the macpherson's I've seen don't pivot at the top of the strut, so the strut top is on that line. If my observations align with generality, then most Macpherson's have very little camber gain.
Dave
03-21-08, 09:27 AM
#160
According to this article, the 997 GT2's front & rear suspension gains about 3-degrees of negative camber under full compression:
http://www.autoblog.com/2007/11/12/2...on-technology/
BTW: check out the hi-res images . . .
Also, note that the following regarding the rear suspension:
" The tightly-wound upper coils of the rear spring are there to provide just a bit of preload when the suspension is at full droop. Otherwise, the short, stiff spring that would be dictated by the engineers' desired spring rate would result in a coil that just rattles around as the suspension is unloaded. "
Here's an excerpt on the front suspension:
-- BEGIN QUOTE --
The front suspension [997 GT2] uses a relatively straightforward McPherson strut arrangement. Camber gain is similar to the rear suspension, while a slight amount of toe-out is added as the suspension compresses to further improve stability.
A closer look, however, shows that the front damper is mounted in the inverted position. Although this slightly increases the unsprung weight, the advantage is that the spindle can be clamped to the fat outer tube of the damper - thus increasing stiffness and decreasing camber change under lateral deflection. The spring perch is threaded to change the ride height; there is a second ring that establishes the clamping height of the damper in the upright, but this is not intended to be used as an additional adjustment.
The steering rack is mounted in front of the axle centerline, presumably to yield more room for the front seat footwells and pedals. Also visible here two of the hoses for a front-mounted cooler.
Both the front and rear subframes of the GT2 are attached with metallic bushings, where as the Turbo uses rubber. This creates a slight NVH penalty, but improves the responsiveness and road feel of the car.
The roll rate of the sway bars can be adjusted via a trio of endlink mounted locations. Both ends of the vehicle offer this option; we’d suggest altering the front-rear balance of the GT2 at your own risk.
-- END QUOTE --
http://www.autoblog.com/2007/11/12/2...on-technology/
BTW: check out the hi-res images . . .
Also, note that the following regarding the rear suspension:
" The tightly-wound upper coils of the rear spring are there to provide just a bit of preload when the suspension is at full droop. Otherwise, the short, stiff spring that would be dictated by the engineers' desired spring rate would result in a coil that just rattles around as the suspension is unloaded. "
Here's an excerpt on the front suspension:
-- BEGIN QUOTE --
The front suspension [997 GT2] uses a relatively straightforward McPherson strut arrangement. Camber gain is similar to the rear suspension, while a slight amount of toe-out is added as the suspension compresses to further improve stability.
A closer look, however, shows that the front damper is mounted in the inverted position. Although this slightly increases the unsprung weight, the advantage is that the spindle can be clamped to the fat outer tube of the damper - thus increasing stiffness and decreasing camber change under lateral deflection. The spring perch is threaded to change the ride height; there is a second ring that establishes the clamping height of the damper in the upright, but this is not intended to be used as an additional adjustment.
The steering rack is mounted in front of the axle centerline, presumably to yield more room for the front seat footwells and pedals. Also visible here two of the hoses for a front-mounted cooler.
Both the front and rear subframes of the GT2 are attached with metallic bushings, where as the Turbo uses rubber. This creates a slight NVH penalty, but improves the responsiveness and road feel of the car.
The roll rate of the sway bars can be adjusted via a trio of endlink mounted locations. Both ends of the vehicle offer this option; we’d suggest altering the front-rear balance of the GT2 at your own risk.
-- END QUOTE --
03-21-08, 10:03 AM
#161
The rear has upper links that roughly mimick the action of an upper A-arm... I wouldn't call that a true McPherson strut suspension. The "relatively straightforward" comment notwithanding about the front, I don't see where that's possible. Where does the gain come from??
03-21-08, 10:35 AM
#163
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Thread Starter
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a strut suspension can either gain or lose camber in bump.
if the lower lateral link is less than 90 degrees to the strut negative camber gain will occur as the lower link kicks out the bottom.
if the angle is 90 degrees or more positive camber gain will be generated.
lowered strut cars increase the angle thus screwing up camber in bump. it is possible to space down the outer ball joint to regain part of this.
there's lots of other issues w struts such as the inherent drag between the piston rod and the strut body and lots of other gremlins...
there is NO friction on a double A arm setup.
hc
if the lower lateral link is less than 90 degrees to the strut negative camber gain will occur as the lower link kicks out the bottom.
if the angle is 90 degrees or more positive camber gain will be generated.
lowered strut cars increase the angle thus screwing up camber in bump. it is possible to space down the outer ball joint to regain part of this.
there's lots of other issues w struts such as the inherent drag between the piston rod and the strut body and lots of other gremlins...
there is NO friction on a double A arm setup.
hc
03-21-08, 04:07 PM
#164
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03-22-08, 12:01 PM
#165
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UPS delivered 12 tires and Mother Nature delivered 12 inches......
o k, so there's only 8 tires but UPS delivered another 4 to TireRack for shaving so that makes 12.
my favorite subject: TIRES.
not just round and black. i spent more time w my tires when i was racing than with any other racing subsystem. tires tell you everything you need to know about your chassis. i ran Hoosiers and was fully sponsored to the point they would make tires for me for each race.... different compounds.
since i am finally going to get out on the track in 08, assuming the white stuff melts, i spent alot of time looking at FD tire options.
i started by determining what i considered the optimum size wheel. i elected 18 X 9.5 front and 18 X 10.5 rear. this led me to the right sized tire... 255/35 fr and 295/30 rear. i then examined my tire options. the Sumitomo HTR Z III, new this year, popped up front and center on my screen.
correct size, check.
nice tread pattern, check.
price, holy cow, they are giving them away. double check.
but the UTQG.... 300. maybe a dealbreaker. hmm. so if they are so "hard" how come they won dry adhesion in TireRack's test? i called John Rastetter. John is head of "consumer information" at TireRack and is an acquaintence from racing days gone by.
John suggested not to draw too tight a correlation between the UTQG number and "stick". 'sort of confirmed my suspicions...
don't forget there's alot of marketing going on w tires... the UTQG can be whatever the manufacturer wants to make it. my suspicions were confirmed yesterday when i checked the HTR Z IIIs w my durometer. 62!!!! 62 on a 45 degree ambient day is a good number. forget the 300 UTQG.
lot's of marketing in tread patterns too... all those cool "V"s. hey, they really "look" fast.
i was immediately drawn to the HTR Z III tread pattern.
i am very partial to circumferential gooves. you might note the tread pattern on the F1 cars. you'll see lots of circumfrential gooves. (though maybe the Vs look good at the Drive In.)
so We are going to be giving the Sumitomo's a spin this year. i say "We" as the (heavy footed-Skip Barber grad) wifey has a really nice FD (Eibachs etc) and she runs 17s. she will be running HTR Z IIIs... 235/45 and 275 40s. so we will have the evaluation covered. 17s and 18s.
in case you are wondering, i made the decision to run HTR Z IIIs based on the above factors and then approached the Co with cash in hand. i received a modest discount from an already very attractive price which i probably could have received from any other Mfr.
i picked HTR ZIIIs and i bought them.
my objective? ideally i have found the perfect DUAL PURPOSE FD tire. i will call it like i see it but they sure look good on paper and up close.
the fun is just starting on this thread. as soon as we get some high 40 degree temps it will be off to BlackHawk Farms w my pyrometer and all the good stuff to play w tires, suspension settings, swaybars, shock settings and my RacingBrakes.
do keep in mind we are building a Dual Purpose FD.... no R compound stuff here.
win win
stay tuned,
howard coleman
o k, so there's only 8 tires but UPS delivered another 4 to TireRack for shaving so that makes 12.
my favorite subject: TIRES.
not just round and black. i spent more time w my tires when i was racing than with any other racing subsystem. tires tell you everything you need to know about your chassis. i ran Hoosiers and was fully sponsored to the point they would make tires for me for each race.... different compounds.
since i am finally going to get out on the track in 08, assuming the white stuff melts, i spent alot of time looking at FD tire options.
i started by determining what i considered the optimum size wheel. i elected 18 X 9.5 front and 18 X 10.5 rear. this led me to the right sized tire... 255/35 fr and 295/30 rear. i then examined my tire options. the Sumitomo HTR Z III, new this year, popped up front and center on my screen.
correct size, check.
nice tread pattern, check.
price, holy cow, they are giving them away. double check.
but the UTQG.... 300. maybe a dealbreaker. hmm. so if they are so "hard" how come they won dry adhesion in TireRack's test? i called John Rastetter. John is head of "consumer information" at TireRack and is an acquaintence from racing days gone by.
John suggested not to draw too tight a correlation between the UTQG number and "stick". 'sort of confirmed my suspicions...
don't forget there's alot of marketing going on w tires... the UTQG can be whatever the manufacturer wants to make it. my suspicions were confirmed yesterday when i checked the HTR Z IIIs w my durometer. 62!!!! 62 on a 45 degree ambient day is a good number. forget the 300 UTQG.
lot's of marketing in tread patterns too... all those cool "V"s. hey, they really "look" fast.
i was immediately drawn to the HTR Z III tread pattern.
i am very partial to circumferential gooves. you might note the tread pattern on the F1 cars. you'll see lots of circumfrential gooves. (though maybe the Vs look good at the Drive In.)
so We are going to be giving the Sumitomo's a spin this year. i say "We" as the (heavy footed-Skip Barber grad) wifey has a really nice FD (Eibachs etc) and she runs 17s. she will be running HTR Z IIIs... 235/45 and 275 40s. so we will have the evaluation covered. 17s and 18s.
in case you are wondering, i made the decision to run HTR Z IIIs based on the above factors and then approached the Co with cash in hand. i received a modest discount from an already very attractive price which i probably could have received from any other Mfr.
i picked HTR ZIIIs and i bought them.
my objective? ideally i have found the perfect DUAL PURPOSE FD tire. i will call it like i see it but they sure look good on paper and up close.
the fun is just starting on this thread. as soon as we get some high 40 degree temps it will be off to BlackHawk Farms w my pyrometer and all the good stuff to play w tires, suspension settings, swaybars, shock settings and my RacingBrakes.
do keep in mind we are building a Dual Purpose FD.... no R compound stuff here.
win win
stay tuned,
howard coleman
Last edited by Howard Coleman; 04-16-08 at 01:49 PM.
03-22-08, 12:37 PM
#166
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hc
Thanks for the great thread..I have listend to all the advice and when I do my suspension upgrade I know exactly what im looking for now.
On the tyres question I dont have a clue! And the choices are limited in Ireland!!
However, my car came from Japan and still has the Jap rubber it came on which are Bridgestone Grid
215/45/ZR17 front
235/45/ZR17 rear
It looks like the tyres are stretched onto the wheels and I was about to replace with tyres of the same size. Is this a good idea or could you give me an idea of a better size tyr for street applications??
I noticed that I get massive aquaplaning in the wet and put this down to the tyres being stetched on there.
I a not sure what shocks I have on the car but the are probobly stock with aftermarket springs. The socks are black (look very new) and the springs are blue (also look very new).
The tyres on it are cracking so I need to replace asap. I was going to go with Toyo T1R's!! But advice on tyre size is really what im after as the RX7 is the first proper sports car I have owned and I dont want to wreck it due to poor tyre choice!!
Thanks again,
George.
Thanks for the great thread..I have listend to all the advice and when I do my suspension upgrade I know exactly what im looking for now.
On the tyres question I dont have a clue! And the choices are limited in Ireland!!
However, my car came from Japan and still has the Jap rubber it came on which are Bridgestone Grid
215/45/ZR17 front
235/45/ZR17 rear
It looks like the tyres are stretched onto the wheels and I was about to replace with tyres of the same size. Is this a good idea or could you give me an idea of a better size tyr for street applications??
I noticed that I get massive aquaplaning in the wet and put this down to the tyres being stetched on there.
I a not sure what shocks I have on the car but the are probobly stock with aftermarket springs. The socks are black (look very new) and the springs are blue (also look very new).
The tyres on it are cracking so I need to replace asap. I was going to go with Toyo T1R's!! But advice on tyre size is really what im after as the RX7 is the first proper sports car I have owned and I dont want to wreck it due to poor tyre choice!!
Thanks again,
George.
03-22-08, 02:28 PM
#167
Racing Rotary Since 1983
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generally as to tire sizing it is a good idea to stay in the neighborhood of having your tread width be approx similar to the wheel width...
stock FD are 16 X 8. that'd be all U S FDs... 93-95.
8 X 25.4 = 203 mm. tires are often referred to by max section width.
section width averages 107% of tread width.
1.07 X 203 = 218. the FD came w 225s. close enough. your current sizing straddles this and i like it as it gives a bit more stick in the rear. i would go up on the front to 225 and hold the rear at 235. if you go larger on the 8 inch wheel you will not really be accomplishing anything.
tire pressure is VERY important. run 30 front, 27 rear set cold. suspension settings are equally important so please refer to my first post.
do check your shocks closely. stock Fds are black. measure your ride height front and rear at the wheel wells and post it. check the springs carefully for a tag and let us know.
howard
stock FD are 16 X 8. that'd be all U S FDs... 93-95.
8 X 25.4 = 203 mm. tires are often referred to by max section width.
section width averages 107% of tread width.
1.07 X 203 = 218. the FD came w 225s. close enough. your current sizing straddles this and i like it as it gives a bit more stick in the rear. i would go up on the front to 225 and hold the rear at 235. if you go larger on the 8 inch wheel you will not really be accomplishing anything.
tire pressure is VERY important. run 30 front, 27 rear set cold. suspension settings are equally important so please refer to my first post.
do check your shocks closely. stock Fds are black. measure your ride height front and rear at the wheel wells and post it. check the springs carefully for a tag and let us know.
howard
Last edited by Howard Coleman; 03-25-08 at 06:37 AM.
03-22-08, 05:19 PM
#168
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Howard I have two questions.
1- I run nitrogen in my race tires which from what I read do not increase in psi as they heat up. What pressure would you recomend I run in this case? I.E. what would 30psi and 27psi translate to when hot?
2- Is running EIbach springs with base shocks OK? I read your post and you say the R1 shocks are too stiff even for Eibach springs so this leads me to thing that base shocks with Eibach springs would be a good match. True?
Thanks, Jason
03-22-08, 06:55 PM
#169
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tire pressure:
tire pressure is an extremely important tuning tool. the wrong tire pressure can make your car slide around w no bite. of course every tire has a slightly different optimal pressure. tires function like springs. adding air pressure is similar to running more spring rate. since we are always trying to add rear traction we run less tire pressure in the rear along w less springs and bar.
as you know tires build pressure w usage. you could start at 30 and end up after a few laps at 40.
the best way to determine optimal tire pressure is by using a pyrometer. as i have previously mentioned if you go anywhere near a track and you actually care about going fast you must have a pyrometer. they can be had for as little as
$150. temperature readings will tell you when you are over or underinflated.
as to nitrogen... it doesn't build hardly any pressure so you set your tires where they work hot when cold.
another way to deal w pressure buildup is to run bleeder valves. you set them for what you want hot, air up your tires to that pressure and they will bleed off any excess pressure. real neat. you will have to drill a hole in your wheel...
i prefer base shocks to R1s and have dynoed both. base shocks work very well w Eibach Pro Kit springs. they are probably the best single deal for the $ suspensionwise.
hc
tire pressure is an extremely important tuning tool. the wrong tire pressure can make your car slide around w no bite. of course every tire has a slightly different optimal pressure. tires function like springs. adding air pressure is similar to running more spring rate. since we are always trying to add rear traction we run less tire pressure in the rear along w less springs and bar.
as you know tires build pressure w usage. you could start at 30 and end up after a few laps at 40.
the best way to determine optimal tire pressure is by using a pyrometer. as i have previously mentioned if you go anywhere near a track and you actually care about going fast you must have a pyrometer. they can be had for as little as
$150. temperature readings will tell you when you are over or underinflated.
as to nitrogen... it doesn't build hardly any pressure so you set your tires where they work hot when cold.
another way to deal w pressure buildup is to run bleeder valves. you set them for what you want hot, air up your tires to that pressure and they will bleed off any excess pressure. real neat. you will have to drill a hole in your wheel...
i prefer base shocks to R1s and have dynoed both. base shocks work very well w Eibach Pro Kit springs. they are probably the best single deal for the $ suspensionwise.
hc
03-22-08, 07:55 PM
#170
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generally as to tire sizing it is a good idea to stay in the neighborhood of having your tread width be approx similar to the wheel width...
stock FD are 16 X 8. that'd be all U S FDs... 93-95.
8 X 25.4 = 203 cm. tires are often referred to by max section width.
section width averages 107% of tread width.
1.07 X 203 = 218. the FD came w 225s. close enough. your current sizing straddles this and i like it as it gives a bit more stick in the rear. i would go up on the front to 225 and hold the rear at 235. if you go larger on the 8 inch wheel you will not really be accomplishing anything.
tire pressure is VERY important. run 30 front, 27 rear set cold. suspension settings are equally important so please refer to my first post.
do check your shocks closely. stock Fds are black. measure your ride height front and rear at the wheel wells and post it. check the springs carefully for a tag and let us know.
howard
stock FD are 16 X 8. that'd be all U S FDs... 93-95.
8 X 25.4 = 203 cm. tires are often referred to by max section width.
section width averages 107% of tread width.
1.07 X 203 = 218. the FD came w 225s. close enough. your current sizing straddles this and i like it as it gives a bit more stick in the rear. i would go up on the front to 225 and hold the rear at 235. if you go larger on the 8 inch wheel you will not really be accomplishing anything.
tire pressure is VERY important. run 30 front, 27 rear set cold. suspension settings are equally important so please refer to my first post.
do check your shocks closely. stock Fds are black. measure your ride height front and rear at the wheel wells and post it. check the springs carefully for a tag and let us know.
howard
I will do as you say and go to 225 in the front....by the way I feel much better now that you have given my setup the thumbs up in terms of tyre size.
On the shock issue mine are indeed black and dont appear to be adjustable, the springs look after market to me (blue) I will try and get a closer look at them and take a pic or two.
By the way my 7 is the R2 model....im not sure if this has any bearing or not but I am pretty pleased with the ride as it is ie not too stiff not too soft and very responsive.
I will measure the ride height as advised tomorrow also.
Thanks again,
George.
03-22-08, 10:18 PM
#171
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as you know tires build pressure w usage. you could start at 30 and end up after a few laps at 40.
as to nitrogen... it doesn't build hardly any pressure so you set your tires where they work hot when cold.
i prefer base shocks to R1s and have dynoed both. base shocks work very well w Eibach Pro Kit springs. they are probably the best single deal for the $ suspensionwise.
hc
03-22-08, 10:23 PM
#172
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A side question. At what rate does the air pressure naturally decrease? I have to pretty much set the tire pressure every time i go to the track right? Even if i use nitrogen?
03-23-08, 12:54 AM
#174
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Hi eoph,
Your "natural" leak rate is going to be determined by a bunch of factors,
including condition and quality of the wheel (porosity, rim smoothness),
the age of the tire (older tires may have more internal delamination, aged
rubber is more prone to cracking and slight leaks), dryness of the gas
used to fill the tire (water in normal compressed air is one of the reasons
bottled nitrogen is used by race teams), and outside air and track
temperature.
Typically you'll be best off adjusting your air pressure each time you go
to the track, and many people do it before each run (at least check it).
Be very careful when and how you check tire pressures, as there's a lot
of variables that can change. Even having one side of the car exposed
to sunlight, and the other in shade will throw off tire pressures, and
(of course) whether you've been driving the car hard or not.
If you want to keep a good record of pressures, try to check under the
same conditions each time (e.g. car sitting in shade for a while to allow
tires to cool evenly), use a high quality dial type gauge, and make sure
to be consistent as to how you apply the gauge tip to the tire valve. Try
to minimize pressure loss from each reading, and be aware that if you
over-fill a tire, and then bleed an excessive amount of air out, the adiabatic
cooling of the air left in the tire can cause a false reading.
Howard et al can flesh this out, I'm just killing some time waiting for the
Malaysian GP to start...
David Breslau
Widefoot Racing Co