Stang2Goat

Invariably I run into certain walls where I need some hardcore help from folks who truly race and push the limits of their cars. Can't find much of this on ls1gto.com...

I have a heavily modified GTO with a lot of power and a healthy dose of weight reduction, but I am limited on tire sizes due to the small space on the front of the car.

I have full poly on the suspension and I recently added BC coilovers which add several mm of clearance up front. Car weighs 3490 on stock 17x8s with half a tank of fuel and no driver. Looking to pull trigger on lightweight 18s and sticky rubber. 255s are widest I can fit up front without rubbing issues.

Texas car, street driven 1-2x a week in dry weather and tracked 1-2x month in San Antonio for auto-x events. Want to run DEs soon as my skill level progresses as I learn to drive on the new setup.


Cliff's Notes of my dilemma:

Will I be better running a 245-255 square setup on NT01s (or comparable r-compounds) for neutral handling and reduced understeer, or will the high whp level of my car (554whp NA, brutal but awesome) necessitate a staggered setup with widest possible meats out back? Corvette and even F-body guys please chime in.


I have the clearance in rear to run a 315 Toyo R888 or NT01 on 18x11 wheels, but I don't want to waste coin of it's only going to worsen or exaggerate the car's tendency to plow and understeer.

Speak your minds! In a perfect world I'd run 275s all around and STFU, but I cant fit them up front without destroying the fenders and running insane negative camber...not worth the effort for this car.

Thanks in advance!

-Michael

mountainbiker2

Put on the widest front tire as possible. If it hits in some spots, see what you can do to eliminate it. How much cutting are you willing to do? That would be your answer. Put on the widest in the back as you can. If the car understeers to much, you have many choices. For example. Raise the car in the back, bigger rear sway bar, stiffer rear springs, etc. This will help transfer more weight to the front. Giving the front more traction. Make sure you have done everything you can to maximize the front end first. Neg. camber, toe out, Lower the front, etc. Change your driving style to suit whatever you end up with. Trail braking, late apex etc.

Steve A.

dbs1

I am running similar power and I use a 315/18 on the rear and would go a tad wider if possible, but certainly not narrower even if it meant a staggered setup.

ls1 1990 VN

I run a 245-18 fr & 295r it's in your suspension setup as to how your car under or over-steers

trans_am7935

iTrader: (15)

i am currently running 275's an all 4 corners, i have been wanting to run that wheel and tire combo for street use that you mentioned, will a 245 40 18 give me more understeer on the track vs the 275 40 17 up front?

jcsperson

This gets hashed around on Corvette Forum quite a bit with no resolution in sight. There seems to be a little agreement that chassis set-up is more important than tire width. Having the right springs, shocks, swaybars, cornerweighting and alignment mean more than a few centimeters worth of tread. Of course, that's Corvette guys talking and they consider anything less than 275 up front to be skinny.

I spent a lot of time chasing down four C5Z rear wheels to run a square set-up on my C5 coupe. I ended up buying a stock staggered set of C5Zs with mounted slicks from a guy who held the TTA lap record at VIR. He ran a staggered set-up and said he didn't really think it was necessary to run 18x10.5s up front unless I was going to go with a BBK. On my budget that's a long way off. One nice byproduct is that I don't have any clearance issues and that I pay about $70-80 less per tire for 275/40/17s up front than I would for 295/35/18s.

I'm making about 525 rwhp and I don't really notice a push at all. If anything I have a problem over-rotating the car out of low-speed turns like 1 and Oak Tree at VIR.

ls1 1990 VN

It's possible it could if your suspension isn't as it should be for the given track you are on.
Mine can get a little understeer on a long sweeping corner while under power.
Mine is my weekend car that I sometimes roadrace

Hardrvin

iTrader: (1)

Although I agree that suspension is a bigger purveyor of understeer/oversteer, 245 to 315 is a significant difference.

With that said, I've run other vehicles (ie, not a GTO) on severly staggered setups, 245F vs. 285R, and it still handled pretty neutral to subtle oversteer in off throttle conditions. On power, it would understeer to full throttle oversteer.

End point, I think you can get the characteristics you want with a staggered setup, and to put down the power you're making, you'll need it to make the most of the engine.

Now, can you save a bunch of money going for square setup (because 315's are going to be vastly more expensive), and being able to rotate tires, or flexibility if one gets a flat really nice. Oh yea. And your right foot can always modulate the power and realistically you'll learn just as much if not more on the track with a square setup. But it depends on your definitely of fun and what you'll find enjoyable on the track.