kromberg

How bad would the under/over steer be with the 255/40/17s up front with 345/30/18s in the rear? Also a 255/40/17 should fit on 17x8.5 rim right? TIA.

Keith

VetteDrmr

1. HUGE understeer
2. Yes, 255s will fit on stock front wheels.

The C5s understeer with a 245/275 f/r split. Adding 70mm to the rears without going to at least a 275 up front (which will also work nicely on 8.5 rims) will make the situation much worse.

I'm changing over to a 275/315 split for autocross, but haven't had a chance to try it yet. I'm expecting a small amount of understeer, but hopefully will cure my oversteering problem (currently running 275s all around).

HTH, and have a good one,
Mike

vette.se

I'm running 285/30*18 (18*10 wheel) front and 345/30*18(18*12 wheel) rear and have understeer, will go for 295/30*18(18*11 wheel) front next season.

kromberg

I guess another thing is that I do not road race or autocross the car. The main convern with this combo would be 'normal' city street and highway driving.

Keith

JeffC5

I always get understeer and oversteer mixed up. Can someone tell me what each is?
Thanks,
Jeff

Dan_the_C5_Man

Understeer= front end "pushes" at the limit.

Oversteer= rear end "comes around" at the limit.

VetteDrmr

Well, if you're getting into any significant understeer on the streets, you're probably going WAY TOO FAST!. Ditto oversteer in the middle of a corner.

Now, with 345s out back, you probably won't have much problem with power oversteer, except in a tight corner (like an intersection).

Curious, why are you running such huge tires on the rears?

kromberg

Just about to fire the new combo up: 402 Stroker with a F-1R Procharger. I also have 3.90:1 gears and 3800 stall converter. I am hoping the 345 DR will give some type of traction

Keith

JakeL

Just IMO, but I'd look elsewhere to solve your understeering problem. I, and many others are running a non-staggered tire size arrangement (same size front as rear - 315/35-17, in my case) without issue - in fact, the car is astoundingly good this way (big smiles!)

Perhaps you need to adjust your rear toe (1/8" in works well), rear camber (more is better up to around 1.5 or 1.6*), too much rake (try lowering the back of the car a bit), too much rear rebound in the shocks (try softening the rear rebound), or, perish the thought , an overly ambitious right foot? Is it corner entry oversteer, corner exit, mid-corner, or transitions/slaloms?

Keith - just puttering around on the street, I'm sure understeer won't be a problem - it's tough (not to mention irresponsbile) to push a C5 hard enough on the street that you approach its limits.

Advice worth the electrons used to make it,

-Jake

Umrswimr

I think your traction problems far outweigh any oversteer/understeer concerns you will have. You're gonna be makign huge power and need the big rear tires. I would look into running 275's on the front if you can.

Additionally, you can adjust the balance of the car with suspension changes. Go to a stiffer rear bar, for example.

kromberg

LOL I love that little gold nugget of wisdom.

Keith

VetteDrmr

Good grief! With that kind of torque, power, and traction on the street, you'll start getting bills from the city for road repair!

Have a good one,
Mike

VetteDrmr

Driver problems? NEVER!!! Gotta be an equipment problem! The problem is usually corner exit, sometimes mid-corner. I just have to feather that throttle more than I want.

I might have a bit too much rake, and it wouldn't hurt to get an alignment. Shocks are stock Z51, about a year old.

Any other ideas?

Sorry for the thread hijack, but hopefully it'll help others.

Have a good one,
Mike