jcarothers

So, I'm in the process of buying a C5z to use for autox. I plan on using it for AS while I collect parts for a possible, but low effort, move to CAM in the next season or so. My question here is what size tire is everyone else running on the C5z? My original intent was to move up to 18s in front to sort of open up tire options, but it seems pairing with a suitable rear tire muddies up the water a bit with regards to tire height.

I'm coming from an STR S2000 on square 255s, and using that same size tire for the front of a heavier car with a wider rear tire doesn't seem like a great option and ideally I'd like to get a 275 or so up front. So my question is what is everyone else running AS using on the C5z? I tried searching, but most threads are prior to the ability to change rim diameter. I'm not in a terrible hurry to buy tires right now, but I've been staring at my options and I'm just stuck with trying to figure out advantages and disadvantages to each brand of tire and size.

Thanks for any help or suggestions.

cpt11gs

One of the local guys with a C5z runs with me, and he is using BFG Rival S in a 275/315 Combo, and that seems to work well for him. I also use BFB Rival S on my C6 GS, but in a 275/335 combo.

Chris

69autoXr

275 front on 18x9.5's, 315 rear on 18x10.5's.

jcarothers

Are the front the 275/35/18? And if so, are there any issues from running a slightly smaller rear tire than the front? Or is that sort of negated from the rear being slightly more pinched onto the wheel?

Thank you both for your responses.

nickb45502

Same here. Falken 615k+

nickb45502

275/35/18 same diameter as 265/40/17. 315/30/18 rear is a full 1/2 in shorter than 295 stock. No pinch on the rears with 10.5 wide wheel.

cpt11gs

Yes, 275/35-18's on the front. Seems to work great.

Acid666

I've been wondering about a square setup for AS, I'm currently running in CAM-S with my Forgestar 18/19s with 275/305 and was going to move to 4X 315s but I don't think you can for AS since even tho the 18 is a stock rim it's not the same width as a 17" front stocker.
Can anyone clarify if they're running 315s in AS on a square 18 setup?
If I can, I might change my setup to that and get to AS.

mattastick

If your current wheels are factory width and meet the offset rule (+/- 7mm, IIRC), then you can run in AS without buying anything. The hot Bridgestone setup seems to be an 18/19 wheel and 275/305 tire sizes. The BFG setup is either 275/315 or 315/335 on 18s. Both have won national events on C5Z's.

Acid666

So if the stock C5Z Z06 18" rim is within ±7mm offset of the front 17" then I can run stock Z06 18"s all around and put as wide of a tire as I want on the front? That's my issue, I've read that I can put as wide of a tire on the factory width rim, but the grey area is that the 18" is wider and factory, but it's not the rim that's on the front of the car stock.
From what I found it's only 4mm difference.

Currently I'm running RE-71Rs on my 18/19 Forgestars but I want to have a dedicated set of 315s for autocross so I was going to get a set of Rival-S on the 18s. Sorry if it looks like I hijacked your thread OP. I think it's relative though so we can both get some questions answered.

mattastick

The rule is factory width for that position on that model year/package car. So a base car can't run Z06 wheels without doing a full Z06 conversion. You can change diameter by 1", up or down, but offset must be within +/-7mm. For a C5Z, your wheel options are as follows:

Front:
16x9.5, 17x9.5, 18x9.5
Offset: +47 - +61

Rear
17x10.5, 18x10.5, 19x10.5
Offset: +51 - +65

You can mix/match any of those combos you want (you could go 16s front and 19s rear).

Acid666

OK that answers it. So you can't run the wider rear 18" on the front for AS. So I'll be sticking to CAM for my square 18" setup.
Appreciate the clarification!

jcarothers

I'm just curious in terms of the active handling system giving any grief for the setup. There is a 0.1" difference in height in favor of the front according to BFGs specs. It's a small difference, but I don't know how finicky the AH is on the C5.

Yea, no square setup allowed. Otherwise I never would have asked this question and just ran square 315s. haha.

Acid666

From what I've read it's not too bad. If it starts to act up you just turn off the traction control. But if you're in the general range of the same height difference between front and rear as stock it's ok. I don't know what that number is, I think it's 1" total difference... I'd look it up before I made any assumptions.

jcarothers

That's the thing, they're closer in height than stock and the front is supposedly taller than the rear. Not that I'm worried about having to turn the AH off, but it'd be great if turning it off prior to driving wasn't a necessity.
If it doesn't trigger the system, it's a slam dunk for which tire to run.
I've read that up to, and including, same diameter front and rear is fine. I'm just curious if this includes a slight bit of supposed increased height at the front.

mattastick

Why are you running with AH on anyway? Unless it's raining, turn that off...

nickb45502

AH goes crazy on an autocross. I run with it off anyway. to/from the track and it is fine. To clarify AH on street no problem. At autocross AH OFF.

jcarothers

it'd be off on course. I was only particularly worried about street driving for AH. As having a light on the dash to stare at on the way to an event doesn't appeal to me.
thank you for your answer, now I just have some tires to buy.

ryanman95

You can't put the 18s on the front in AS :no:

mattastick

Yes you can. Street allows +/-1" diameter wheels, but they must still be factory width and offset. So a C5Z can run 18x9.5" front wheels in AS with no issue. You can also run a 19x10.5" rear, if you wanted to. That's what most people running Bridgestones at the top level are doing.