Legacy Z06

I'm looking at picking up some wheels 17x10 / 17x11 and running a square 315/35/17 setup. This will be for an HDPE based car but I do drive it on the street often enough that I'd like to know if I'm going to cause issues. Will this setup mess with the traction control/active handling on a C5Z ?

And if I decide to run a 275/40/17 & 315/35/17 will this throw off the traction control (or anything else) as the rears will be slightly smaller in diameter than the fronts ?

I'm planning on running NT05's or NT01's.

Hi Volts Z06

You should be fine. Staggered setups are typically selected foe equal diameter wheels.

0Anthony @ LGMotorsports

Only issues I have seen with doing something like that is making sure the front tires don't hit at lock. Of course you shouldn't ever be lock to lock on track but some tight parking spots my cause a track wheel/tire setup to hit when you are on the street.

The only other concern would be alignment and tire wear but that doesn't really matter as to the width of the tire so much, track alignments are going to wear tires faster no matter what setup is on it.

hklvette

There are anecdotes on here about smaller rear tires than the fronts really giving AH, TC, and ABS fits. Some have good luck with a square setup (same diameter all around) and some don't. I make sure to keep a staggered diameter setup to avoid such headaches. One thing to keep in mind with wide front rubber depending on wheel offset is the tendency to "grab" bumps or ridges in the road. I know with a square setup on my car it can be very "darty".

Last C5

I run an 01Z with a square set up - 315/30/18 all around without any problems. Obviously TC has to be turned of, but Competitive mode is unaffected, and the car turns in very well, remains neutral in the curves, and only rubs the smallest amount in the pits. I would try the 315/35/17 all square set up first.

froggy47

mrr23

both the 275 and the 315 are the same diameter of 25.7" tall. So yes AH AND TC are affected.

Having the 315 on a 10" wheel will pull down on the tread area of the tire actually reduced amount of contact. So the 275 is a better choice.

Apocolipse

Also need to dial in some rake since you loose it going square.

chetly

Going to a true square setup would mean same size rims and tires. Why don't you run a 10.5 inch wheel front and rear with 315's? You'll be able to take advantage of another bonus of running a square setup, rotating the tires...

Legacy Z06

All good input, reason for the wheel size is I'm looking at a used set of wheels.... you get what you find.. So it seems that at best its a crap shoot with AH/TC on a square setup. I'm just wondering if I should keep it simple and stay with the OEM wheels 275 front & 295 rears which so far has worked well .

Can someone explain why square or smaller diameter rear affects AH/TC ? That cause the diameters are outside what GM coded into the CPU so it thinks something's wrong ?

Supercharged111

It never affected AH for me or many of the other satisfied customers now running a square setup. I hear more good than bad and typically the bad is just someone who thinks it'll affect it and hasn't actually tried themselves.

descartesfool

I just had some 315/30/18 Nitto NT-01's mounted onto four C5Z06 18x0.5" rear Speedline wheels for my C7 Z51. Before I had the tires mounted, I put the car on a lift and just put the wheels on by themselves to check for fit. One issue I found is that the wheel on the front rubs the upper A-arm when at full lock and full droop. I fit different thickness washers between the wheels and the hub to see if fitting spacers would prevent the wheel touching the A-arm, but I could not fit enough washers using the OEM length wheel studs, So that might be an issue on the street. Not likely ever going to be at full lock and full droop on track, but I will have to watch out for that when I drive to the track on those wheels. Full droop is not too likely to happen, but you have to be mindful of it. I think I am going to put some tape around the A-arm where there is a potential for rubbing and check that it does not get worn.

mrr23

the front tires are 1" smaller in diameter when compared to the rear. 25.7 versus 26.7. so with the rears being shorter, the pcm sees the rear spinning faster than the fronts, or rather the fronts spinning slower than the far. so the pcm thinks the front tires are sliding and wants to activate the traction control. i've read active handling tries to compensate as well.

froggy47

Anyone who says these systems operate the SAME when you go about messing with tire diameters should refrain from giving advice on the forum.

Will the light come on? Maybe/maybe not.

But that's the least of it when it comes to how the systems will work under "compromised" traction conditions.

I have run a setup with slightly SMALLER diameter rears and got no light.

So what?

The tc/ah are right on the edge of triggering when you run those kinds of setups.

So to answer the OP.

Will this setup mess with the traction control/active handling on a C5Z ?



Yes, of course it will.

Will "you" be able to "drive around" the changes? Maybe, I don't know, I do it all the time. Street & track.

But let's not just tell OP, everything will be hunky/dory as long as the lights off.

wtb-z

A slightly smaller rear than front seemed to cause my C5Z to have pretty jumpy TC - a hard shift often would set it off. Same size rear and front tire caused nothing to report..

No error messages in either case, though. AH/TC always off on the track so no performance related problems.

Apocolipse

Do you guys put the rake back in once you go square? Or do you run without rake?

sean.b

my 2nd pair of 18x10.5's are in the garage now, and i plan on dialing the rake back in and seeing what it looks like. you're compromising some downforce if you dont. unless you have a wing/aero setup, then i'd like to hear people's opinions in that case.

Apocolipse

Not only downforce but it also changes the roll axis angle.

sean.b

does that matter as much after all we've done to the road course cars in terms of weight reduction, coilovers, etc? not disagreeing, just provoking discussion on it.

Apocolipse

Yes, it still matters. Roll axis angle controls the front and rear weight transfer. Raising the rear gives more oversteer, lowering the rear (going square without adjusting rake) increases understeer.

Now, typically when one goes square the front gets larger tires to match the rear. This will reduce understeer push that's stock in a vette (base c5). That causes more oversteer, but then the reduction in axis angle by going square reduces the oversteer, and we are left with a more neutral car.

Now depending on your sway bars and spring rates...if you understeer too much, raise the rear and vice versa.

Yes, it is aero as well since a rake gives you some rear downforce, but you have to be going some good speeds to have that happen...not your typical auto x speeds.