I have a 99 coupe. I track the car a few times a year (road course). I’ve been reading a lot of posts on the Forum but haven’t found what I am looking for (Given the volume of info in here thinking Its my bad). I am positive there is someone out there that has done exactly what I am looking to do and I am hoping they can help me out.
I installed flared fenders and am looking for a set of wheels to use when I track the car. Other than the flared fenders I’ve done no other body mods (I.e. I haven’t tubbed the car), just suspension, brake, hp mods.
I am looking for guidance on wheel size - but more specifically I am looking for offset size for a 12” rear wheel. I suspect to fill the rear with tire I am looking at a 26 to 32mm offset but I am hoping someone can provide an exact - already working for me on the track answer.
The set of wheels I have on there now are for show and frankly when I built them (3 piece wheels) I screwed up the offset a bit (too low - so I get some fender rub). So hoping I can avoid that by going to y’all.
I would REALLY appreciate any info you have.

 

If you're rebuilding or spacing your current set of wheels, why not just measure for exactly what you want/need? It'll take 5 minutes assuming the wheels are still on the car

Someone will chime in with 12" wide offsets I'm sure, but guys with 13s usually end up somewhere between mid 30s to mid 40s if that helps. Another member here just posted his new 12" wide rears with 23mm offset and they stick out past his flared fenders by about 1/2", so that might help as well.

Some of it will also depend on which fenders you got. Another member just mounted the new TPE style fenders and it looks like they're more towards a 1.5" flare vs 2".

With all of these variations, I would 100% recommend measuring yourself for what's on YOUR car and the way you like it. If you're getting new custom wheels, that's a lot of dough to be spending based on other peoples' measurements that may have a slightly different setup.

 

Paging @Zeek

 

Sorry, bud, I cant help. I purchased my 20x12 F4's from Vibemotorsports, a vendor here. They gave me great advise as to what backspacing and offset to use. I bought my wheels on their recommendation and they fit and look great! Unfortunately, once purchased, I had no need to worry about the specs and it was a while ago, so I don't remember what they are.

Im sure fyrarms and his sidekick usazr1 will be along shortly, as one is the resident expert on all things C5 and the other is his butt kisser....

 

Well hey, it was worth a try. I don't love the whole wheel spacing thing myself. I'd rather have a root canal than have to figure them out.

 

So i have tpe fenders, they are f14's 19x12 with 24mm offsets on the rears. michellin cup 2 tire's 345/30/19 the tire sticks out just alittle..not sure if this helps?

 

Just because you're not smart enough to figure anything out, doesn't mean others aren't. It's obvious you're still butt-hurt about your lack of wheel knowledge.
I suggest you STFU and let it go.

 

What rear fenders do you have on your car now, Dave?

 

I have the 2 inch CC rear fenders and am running a 19x12 LG World Challenge rear wheel in the C6Z offset of +59mm. Currently I have 325 Super Sports with a 20mm hub centric spacer in the rear to have them sit flush, but over the summer I had a 345 Nt05 without a spacer and it filled up the fender just fine. If you go with a spacer, motorsport tech has some nice hub centric units for the C5.

 

I ran F14’s 18x12 in the back with 53mm offset 315/40/18 Nt05r 18x9 front 256/35/18 555

 

Thanks for all the information everyone. Let me try to answer a few questions. I bought the fender flares years ago from (I believe their name is/was) Lewis 5. That was a story - but one for another time.
Over the past couple weeks I've been doing some work. +Someone suggested that it would be best to start measuring with a known measurement. So I grabbed a C7 Z06 19" wheel with a 335 Pilot Cup 2 tire on it - and put it on my car. It's +59mm offset and too deep to fit. I put a 1" spacer on it. That should have reduced the offset to +33.6mm. No rub on the inside . . . but still sticking out too far with that 335 on there.
04zjimc - I don't know how you got that Michelin 345 tire with a +24mm offset on your car with it just sticking out a little! At +33.6mm mine was sticking out about a quarter inch. That's why I am thinking a +39mm offset would be close for a 335 tire (and I can use a small spacer if I'm running a 325).
So here is where I am - I've been working with someone on calculations and this is what he came up with. Rear wheel is a 19" x 12" (+39mm offset) with a Goodyear Eagle F1 Supercar 3R 325/30-19 tire. On the front a 19" x 10" (+50mm offset) with a Goodyear Eagle F1 Supercar 3R 305/30-19. Any opinions on the front wheel/tire/offset (I'm hoping there is no rub)? Anyone running that set up on the track? Anyone running those tires? I plan on going with Forgestar F14's (like 04zjimc).
Thank you everyone.

 

the tire does stick out very little not enough that it looks stupid.. hardly noticeable. I was afraid it would stick out more. I went for it and it worked out!

 

"Sticks out very little" is subjective and is often down played by the owner haha. No offense meant to 04zjimc, just being realistic. Some people think 1/2" of poke (~12-13mm) is nothing and some people think it looks ridiculous. I'd feel better with pics and/or an actual measurement before buying custom wheels based on that.

I may be wrong, but didn't Lewis make rear fender flares in different sizes at one time? I swear I remember seeing that they offered 1,1.5, and 2" options. Unfortunately a Google search doesn't yield much other than recent beware posts haha. If so, that's another reason to measure for your car specifically if you don't know which ones you have.

 

Well, I can tell you mine stick out far enough that I’m stripping rubber off the edge of the tire. Fine for non aggressive driving - but looking to correct that plus my understeer for the track. For those interested - here is what I ended up with as my track setup:
- 19 x 12 F14 rim @ 39mm offset and a 325/30-19 Goodyear Eagle Supercar 3 Extreme Performance tire for rear
- 19 x 10 F14 rim @ 44mm offset and a 295/30-19 Goodyear Eagle Supercar 3 Extreme Performance tire for front.
Its going to be about a month but once they come I’ll repost and let you know how they fit.
I’d welcome opinions on the setup - and thanks to all those that responded.

 

Here is a pic I took.. in person you would never notice only if you were looking for it. Actually that little bit makes it look more aggressive.

 

For anyone interested let me complete this post. You recall I have 2” rear fender flares and was looking for an HPDE set up. Ended up ended up working with Sam Strano. Went with Forgestar F-14 wheels (which between COVID and screwups took forever - but that’s a story for another time).
As mentioned I went with 12” rear, 10” front. 39 mm offset rear with a 325/30/19 Eagles F1Supercar 3R tire. This tire is tucked nicely into that flared fender. In front a 10” wheel with a 44mm offset and a 295/30/19 similar tire. This tire does stick out a bit and doesn’t tuck into the front fender well.
Got an aggressive track suspension set up from Phoenix Performance (Phoenixville, PA - expensive but good). They actually raised the car a bit - no tire rubbing issues at all. On the track it ran well at NJMP - both tracks. All in all I am happy with the look and performance.

 

That's a pretty conservative offset in the rear for a 2" flare, you could easily mount some 345s on those and have plenty of space still. I have a similar situation where my rears could come out another 5mm but my fronts stick out almost an inch and it drives me crazy. Made me order front fenders to match the rears. Always something with these damn cars!

 

A 19x10 front wheel on a C5 usually needs a +56 or +57 offset so that's why you're seeing that much poke. I'm planning to buy a set of Forgelines maybe next year and if I go with 19x12 rears, my calculations keep coming up with a +38 offset.

 

If I recall, your TPE style fenders are a little shy of 2" right? That width/offset would be pretty conservative on a 2" fender like the non-TPE styles, but I know you've definitely measured for your own fenders haha. A lot of guys run offsets in the mid-high 30's with a 13 inch wheel on a 2" fender. Mine are 19x13 with an effective offset of 43 and there's room to knock that down at least another 5mm with a 345/30 mounted.

 

On a 13" width wheel, an offset of +44 would equate to a max 8.75" backspacing and would almost certainly require removing the rear brake ducts. A rear wheel, with those specs, would be a really snug fit, on my car.

13" width wheels are cool but the "law of diminishing returns" starts to come into play. Tire selection becomes much more limited with that width, as opposed to a 12" width. With a 13" width, you're pretty much limited to a 335 (only one of those available in 19") or a 345. With a 12" width, you can fit anything from a 305 to a 345. If some tire sizes are ever discontinued, things could get dicey. I remember when 335/35/17's were plentiful. Now, hardly anyone offers them. 335/35/18's are almost, as bad.