RKD in OKC

Was a little disappointed with the new Iris Blue GTS at my first autocross. 3 seconds behind fastest cars on street tires. Got to checking, Pilot Sports had lots of tread but were 4 years old. Put on the ultra cool looking Carerra III wheels with new 225F and 285R Pilot Sports. Then just to make sure had the car aligned and ride height set to aggressive side of factory specs.

Results:
FTD for street tires and only 2.5 seconds behind Competition Tire FTD, Viper no Hoosiers.

Our autocrosses are almost track events no turns below 2nd gear, and 2 straights I got well into 3rd and 1 straight I redlined 3rd as hitting the chicane brake zone.

Handling impressions:
With the 285s on back zero wheel spin. The PSD light comes on while accelerating, but no spin. I do get a chirp on 2nd to 3rd gear changes.

With the 225/285 stagger in the steady state 180 turns it pushes out just a bit instead of a nice 4 wheel drift. Controllable, but could be faster with just a little more rubber in the front. Then could throttle steer the drift without abrupt throttle changes and apply corner exit throttle sooner to drift into the straight instead of push out.

In transitions ie., slaloms applying throttle lifts the front and it pushes for just a second, I think I can firm up the front rebound on the Konis to balance between lifting the front to push and not lifting at all and spinning the rears.

Going into the chicanes off the high speed straights this car could go incredibly deep. I just tap the brakes hard once on entry, then trail brake just enough to keep the rear light, rotate, than smash full throttle mid chicane and power on through without slowing too much at all. To me this means the rear rebound is good.

Overall everyone was impressed with "such a heavy car" doing so well. One 911 guy even teased saying the 928 was made for the autobahn. I told him, "Well then, I will just have to go real fast."

Who says 928s don't autocross well!

AO

Sounds like you're having lots of fun! Good for you!

RKD in OKC

Yes, I am enjoying the heck out of the new to me GTS!!

Bertrand Daoust

What are your ride heights now?

pcar928fan

Excellent. To help the understeer you can stiffen the rear sway bar via the adjustable drop links. Bigger tires will be a HUGE help though too. Both are pretty easy to do...

RKD in OKC

Bertrand, sorry I don't know what the heights are at. Alignment and adjustment was done at my local Porsche dealer. A got 2 sheets of alignment specs and settings, but nothing on ride height other than he set it for what works best. Looks a little high compared to other 928s.

marlinspike

Sway bar is really only going to help for slow corners, and from the sounds of it these turns are fast. What would be ideal would be to find someone who will make spring rubbers for the car and put some medium spring rubbers in the back. If you find such a place, let me know, because the people I find who make them won't make them for anything short of a stock car. Depending on how your tire temps are right now, you might want to try closing the gap in front-rear pressure some.

Alan

You can go to 235/45R17 on the front easily on the stock wheels - are you still at 17"

I'm running PS2's and it helps at the front (with 275's on back)

Alan

RKD in OKC

Okay, I am running 8x18 Front and 10x18 Reat Carerra III wheels with 225/18 front and 285/18 rear, forgot the sidewall ratios but and standard 18in tires. I am running them at 28psi front and rear as GTS does not have any tire pressure stagger. Yes I should be able to fit 235 without any problems on the 8x18 et 56 fronts, maybe even 245s.

The car is a GTS with Koni adjustables and Procoil springs, Devek HD front swaybar and a bigger rear bar. The setup was done by DEVEK.

marlinspike

Ah, well there's a quick possible fix. If your understeer is only on corner entry and exit (and I don't know that it is, I'm just saying if it is), simply firm up the rear shocks.

Alan

So I assume your RDK is disabled and the new wheels don't have sensors?

BTW 28psi sounds awfully low for those tires... I run my PS2's at ~40PSI The stock RDK sensors are calibrated to 36 PSI (2.5bar) which implies that was the minumum stock pressure.

I actually use a Smartire system to monitor mine now - if you don't have the RDK active I recommend it. It has individual real time actual pressure & temperateure monitoring per wheel with programmable warning set points for both pressure & temperature.

Alan

ew928

+1 on what Alan said.
I normally shoot for 32-35psi. But mine are only 17". 245 front and 275 rears.

Try a 35 front and 32 rear stagger and go up from there.

wds928

RDK was not offered for 1994 and 1995 GTS's. I'm running 235/40x17 fronts and 275/40x17 rears, Michelin PS2's, with about 38 psi cold to start. Won the P17 class (928's) at the June Porsche Parade at Lowe's Motorspeedway with this setup. The autocross course was setup on the infield road course.....not the banked turns or straights used for NASCAR, so was a 2nd gear run for me, other than a quick 1st gear start.

Congrats on the FTD on street tires.

Alan

Bill - well it depends... the first 17 '94 VIN cars still had it - mine included - but yes after that correct...

BTW my 40psi is at ~100F so compensating down somewhat for typical usage elesewhere at ~1 psi per 10 degrees - equates to only about 36 psi at 60F.

Alan

Jim bailey - 928 International

Bill for some that would be considered a "National Championship " !!!! The national Porsche get together and an autocross win !!