Beantown Kman

Does anyone know what the oem spring rates are? I have 700/800 on my 987 track car. Some guys even run 800/1,000 on those.

Now that more GT4 owners are getting their cars to the track it's interesting to see how widespread the understeer and tire wear issues are becoming. While most folks are attempting to address this through alignment modifications I think more people will eventually follow Trojan's lead and they'll come around to understanding that stiffer springs and roll bars will be much more effective at resolving these issues. Race shops have already begun to do this to some customers' cars but they're not posting details here. These problems are not endemic to the 981 platform per se. Once it's set up properly the 981 platform is fantastic. This is just a matter of fine tuning some of the components. And it won't be terribly pricey to do this.

IProkopiw

Site search revealed 257/457 Front/Rear stock. GT4 Clubsport running 800/800. At what spring rate do you run risk of being out of the damper range? Would adding a DSC sport controller let you program for a stiffer spring?

mooty

450/550 u are closr to limit of dampers
8@0/800 on CS is totally different.

usctrojanGT3

Yeah, that sounds about right. My suspension guy said be almost doubled the front spring stiffness in the front and bumped the rear by 20-25%. He recommended I don't go any higher than 450/550 unless I revalued the OEM dampers or went to aftermarket ones like JRZs, KWs, or Ohlins.

TRAKCAR

Great thread, look forward to the data and consensus after this summer..
I lot of what I read about handeling and tire wear also applies to the RS mins the under steer problem.

zmon

your running a hell of alot of camber for rcomp/street tires... have you checked your tire temps with a pyrometer?

Beantown Kman

I agree that 3.2 is a lot for a street car. A pyrometer would only confirm what is already evident from the tire wear. The stock suspension is too soft, especially the front springs. With all the grip these tires are generating there is an excessive amount of body roll.

ShakeNBake

-3.5F/-3R didn't help much this weekend at TWS. Car was ludicrous fast, but it just grinds off the outer 2 inches of tire. Temp profile was pretty good on the front, but the rear was too steep, -3R is too much.

Springs next I guess.

Tire pressure wise, I kept it under 38 on track, which translated into 23 dead cold. Seemed to work OK.

nxfedlt1

What times are you running at TWS? Do you have video or data I can overlay? I saw somewhere I think you posted 1:54...and I can't get sub 1:57...help...

ShakeNBake

I posted this in another thread. 4 is super fast...times took me by surprise. But at this rate, I think the tires are maybe 2-days. The rear would last 3-4 days, but fronts are getting too much outside 1"-2" wear.

(Taken on different track days)
Purple (1:50ish) = Andy Lally in a .2RS new R6 tires (open track)
Blue (1:48) = GT4 with 2-cycle R7 tires (and proper alignment, but DE traffic)
Red (1:48) = .2RS with new Pirelli DH (open track)

myBailey07

Forgot to ask this weekend. Why did you go with the 295/30's in the back vs the 295/35's? Unless I am missing something the 295/35's in the back should work well...

ShakeNBake

1) I wanted the F/R diameter ratios to be close to stock, 2) gearing, 3) ride height, and 4) more space in the fender.

zedcat

TWSCCW sub 1:50 is very impressive and a little surprising vs the 7.2 RS, but the data doesn't lie. Maybe a little cooler conditions for the GT4 lap? In any case that is hauling the mail. Thanks for posting.

doba_s

265 seems like a way too much tire which will induce understeer and premature tire wear. Too much side wall flex. The contact patch of 235 will be same or close to 265 and no side wall flexing.

I would go to 235 on a 9 wheel. Run it hot at ~ 38psi

if my gt4 gets here before your event we can compare

GT3 Nut

You did mean oversteer and not understeer, right?