Opinions - 350#/30mm or 400#/31mm?
11-23-2007, 04:36 PM
#46
Former Vendor
Finally I have some extra time to comment this thread...
No problem, this can be useful.
It's no t a word from the God, but a good starting point.
Can't much argue with this, I wish I could have time to test few different things within reasonable time in reasonably similar circumstances.
Turbo cup cars are old technology, but this H&R's kit has been out just about 3-4 years. IMO there's at least one dividing thing when talking about spring stiffness, namely stiffness of the car's body. I seriously doubt that you can run 1000lb/in fr springs ( and matching rears ) and at the same time avoid the body being active part of suspension by flexing without a full cage. Similary tires and wheel alignmets are totally different. So we should talk street/trackday cars and race cars in different threads.
I saw this Karl's post too late ( two years, actually ) to take that into consideration. IF ( And why not, though Van questions it thin this quite informative thread : https://rennlist.com/forums/showthre...ht=van&page=11 ) it's correct, it does change my set-up significally. However it hardly affects 968's numbers...
No problem, this can be useful.
I tend to do silly things like look at trends of front running Stock and GT3 class 944 and when there is a definite trend of a given setup then it is worth taking notice. So if 8 out of 10 front runners run the way I describe, and 2 out of 10 follow your 968CS example, which would you follow? Personally I am going to follow the trends as well as listen to guys like Jason at Paragon, Eric Steinel, Chris Cervelli, etc. One key reason to look at the trends is it balances out personally driving styles, and guys who just drive what they were given. I have found that I tend to adapt my driving style to whatever setup I am driving. I have also found that I can be pretty quick with a crappy setup. I get used to it quickly and don't always realize how bad it was until I changed it to a better setup. I can't tell you many times I have talking to someone about their setup, and asked them why it is setup like that and get "that's what XYZ guy told me I should do" or "I based it on XYZ factory setup" and they have never tried anything else. Personally I like to tinker and have driven multiple setups. I started with 300# springs with 29 mm Torsion bars (wheel rate of 292), and thought it was great until I went to 400# springs - and wow it was a lot better and my lap times dropped. Car was better balanced and I could carry more entry speed and get on the gas harder, sooner. I also have tried 968 M030 sways, Tarret sway, almost every R-comp tire on the market, rubber bushing, sphericals, and the list goes on. Most of my changes were from talking to a lot of guys, looking at trends and then most importantly, testing it out for myself - lap times don't lie.
Personally, I don't put much stock in what Porsche setup for the cars 15-20 years ago - technology has evolved and guys with a lot more money and talent than us have been testing, testing, and testing and have found that there are faster options. If the Escort Cup or CS setup was the end all be all setup then guys would still be running their progressive fronts with tbars+helper springs and not have ditched them for more modern setups like the Leda setup you are running. Chris Cervelli was running 1000 # springs in arguably the most successful GT1R 951 ever - that is 3 times stiffer than the Escort Cup cars, why would he do that. Because after extensive testing he determined it was faster and a lot had to do with how much shock technology has advanced.
All that said I do have some corrections with your original post. The rear spring rate to wheel rate multiplier is 0.42 not 0.56 (per Porsche Motorsport), so the revised math would be
F: 160lb/in x 0.9 = 144 lb/in ( wheel rate )
R: 25,5 mm t-b = 175 lb/in ( wheel rate ) +
Rh: 100lb/in x 0,42 = 42 lb/in
Rtotal: 175+42 = 231 lb/in
Front to rear bias: 1:1,5
That said you are not following you're own advice with your setup:
F: 400 lb/in * .9 = 360 (wheel rate)
R: 850 lb/in * 0.42 = 357 (wheel rate)
Front to rear bias: 1:1
So you yourself are running almost a 1:1 ratio, which is not bad. I personally don't think it is optimal, but is certainly not "extremely dangerous and impossible to handle". I have no doubt your buddy is fast witth this setup, but I bet he could be faster if he increased his front spring rate to 600#. Now if you followed your example of Porsche 1:1.5 ratio you would need 1300# rear springs which would be impossible to handle. So I think you proved your own theory wrong.
F: 160lb/in x 0.9 = 144 lb/in ( wheel rate )
R: 25,5 mm t-b = 175 lb/in ( wheel rate ) +
Rh: 100lb/in x 0,42 = 42 lb/in
Rtotal: 175+42 = 231 lb/in
Front to rear bias: 1:1,5
That said you are not following you're own advice with your setup:
F: 400 lb/in * .9 = 360 (wheel rate)
R: 850 lb/in * 0.42 = 357 (wheel rate)
Front to rear bias: 1:1
So you yourself are running almost a 1:1 ratio, which is not bad. I personally don't think it is optimal, but is certainly not "extremely dangerous and impossible to handle". I have no doubt your buddy is fast witth this setup, but I bet he could be faster if he increased his front spring rate to 600#. Now if you followed your example of Porsche 1:1.5 ratio you would need 1300# rear springs which would be impossible to handle. So I think you proved your own theory wrong.
11-23-2007, 05:24 PM
#47
Former Vendor
One source is this classic one: http://dialspace.dial.pipex.com/town...suspension.htm , but I'm pretty sure that I read it also from different sourece. I scanned through my archives of Excellences, but I didn't find it...
SET: H&R RSS-37-827-1/1
............................. Front.................... Rear
MAIN...................... 180/70-60mm....... 120/150-60mm
Free length.............. 180..................... 120
Spring force............ 70....................... 150
Length compressed.. 69....................... 53
Spring travel........... 111..................... 67
Block load............... 7770................... 10040
TENDER.................. 130-60-10........... 80-60-20
Free length............. 130.................... 80
Spring force............ 10...................... 20
Length compressed.. 34...................... 33
Spring travel........... 96...................... 47
Block load............... 1070.................. 940
Total length max....... 310.................... 200
Total length minimum. 103.................... 86
Total travel............... 207.................... 114
Forces are N/mm, loads in Nm and lenghts in mm.
Yes, I previously had 225/255-17" 's, but then I got this '02 Carrera wheel/tyre package with a very good price...and 17" 's do not fit around my brakes anymore.
While looking through my magazines, I found this Excellence #134's ( Dec '04 ) article about Turbo Cup cars. It says that fronts were 200-370 lb/in progressives and rears 180-460 lb/in progressive PLUS 25.5 mm torsion bar...
400 fr/ 850 rr sounds like it would very much be a tail happy car, and very well suited to auto-x'ing; so that makes sense that your friend is successful at auto-x with that car, and prefers that type of setup.
I cant find it in the link, what spring rates do the H&R setups come with?
I cant find it in the link, what spring rates do the H&R setups come with?
............................. Front.................... Rear
MAIN...................... 180/70-60mm....... 120/150-60mm
Free length.............. 180..................... 120
Spring force............ 70....................... 150
Length compressed.. 69....................... 53
Spring travel........... 111..................... 67
Block load............... 7770................... 10040
TENDER.................. 130-60-10........... 80-60-20
Free length............. 130.................... 80
Spring force............ 10...................... 20
Length compressed.. 34...................... 33
Spring travel........... 96...................... 47
Block load............... 1070.................. 940
Total length max....... 310.................... 200
Total length minimum. 103.................... 86
Total travel............... 207.................... 114
Forces are N/mm, loads in Nm and lenghts in mm.
While looking through my magazines, I found this Excellence #134's ( Dec '04 ) article about Turbo Cup cars. It says that fronts were 200-370 lb/in progressives and rears 180-460 lb/in progressive PLUS 25.5 mm torsion bar...
05-23-2008, 10:10 PM
#48
Burning Brakes
Thread Starter
Well, I just thought I'd close off this thread by giving an update on what I ended up doing with my suspension.
I ended up replacing the 300# front springs, rebuild/revalved M030 Koni struts, 28mm t-bars, Koni yellow rear shocks with a good used Bilstein Escort Cup setup (600/190 front valving, 565/218 rear valving), with 400# front springs and 550# rear springs. The effective spring rates are about 360# front and 308# rear, for a front/rear ratio of 1.17:1. This compares to a f/r ratio of 1.06:1 with my old Koni setup. The ride is still fine on all but rough roads. I wouldn't want to go too much stiffer on the street though.
I have gone more aggressive with my alignment, and am now running -2.5 deg front camber, 10 minutes total toe, 3.2 degrees (max) caster, -1.85 deg rear camber, 5 minutes toe each side. I'm still running 225/50-16 front and 245/45-16 rear on the track, but I plan on switching to 245's all around once I've worn out my current sets of front tires.
The car still tends to understeer. It's an overall great set-up, and is very safe and manageable on the track. I can easily induce neutral or oversteer with the throttle. The car was an absolute blast at Infineon and Laguna Seca last month. I do have pretty bad turn-in understeer in autocross though. I've set my Weltmeisters to full soft front and full stiff rear.
I'll see how it handles when I move to 245's all around, and I may end up going to -3.0 degrees of front camber before too long. If those changes still result in some understeer, I may move to 600# rear springs (1.07 f/r ratio) or 650# (0.99 f/r ratio).
I ended up replacing the 300# front springs, rebuild/revalved M030 Koni struts, 28mm t-bars, Koni yellow rear shocks with a good used Bilstein Escort Cup setup (600/190 front valving, 565/218 rear valving), with 400# front springs and 550# rear springs. The effective spring rates are about 360# front and 308# rear, for a front/rear ratio of 1.17:1. This compares to a f/r ratio of 1.06:1 with my old Koni setup. The ride is still fine on all but rough roads. I wouldn't want to go too much stiffer on the street though.
I have gone more aggressive with my alignment, and am now running -2.5 deg front camber, 10 minutes total toe, 3.2 degrees (max) caster, -1.85 deg rear camber, 5 minutes toe each side. I'm still running 225/50-16 front and 245/45-16 rear on the track, but I plan on switching to 245's all around once I've worn out my current sets of front tires.
The car still tends to understeer. It's an overall great set-up, and is very safe and manageable on the track. I can easily induce neutral or oversteer with the throttle. The car was an absolute blast at Infineon and Laguna Seca last month. I do have pretty bad turn-in understeer in autocross though. I've set my Weltmeisters to full soft front and full stiff rear.
I'll see how it handles when I move to 245's all around, and I may end up going to -3.0 degrees of front camber before too long. If those changes still result in some understeer, I may move to 600# rear springs (1.07 f/r ratio) or 650# (0.99 f/r ratio).
