I am looking to get some new wheels for my 1985 corvette sometime. I found some from esr that I really like. I want them in 18x10.5” because I want to put 315/30r18 tires on but I wondered what offset would work. They come in 22mm offset and I didn’t know if that was too far out or not. I figured since the c5 z06 wheels fit with a 1 inch spacer and they are 56mm offset then these should work. 1 inch is just over 25 mm so they should only be a few mm out further right? Here’s a link to them.
https://esrwheels.com/collections/rf...31792676929654

 

The factory 9.5” x 16” wheels have a 38mm offset. If you have 8.5” x 16” on the fronts they have a 32mm offset.
So taking into account the change in offset (16mm) and the wider wheel (12.5mm each side), the wheel will be 28mm closer to he fender assuming 9.5” original wheels all round.
Personally I think they will stick out too far but the best way is for you to drop a string line down and measure. They might fit on the rear but I don’t think they will on the front

 

A string and measuring device will 'seldom' let you down. (operator error maybe but not the 'string & device')

OP - What is the 'up-charge' for 'custom' bolt-circle? Merely an observation but they seem to offer a 9.5 @35 with bolt-circle options!

 

I keep on making the mistake that people know the correct bolt circle. Assuming that is the first thing checked, 35mm offset would be better.

 

I saw that they have the 9.5” wide wheel at 35 offset but I was wanting to put 315 tires all around and I’ve heard many not recommend that wide of a tire on a 9.5” wheel. If I would have to then I could get the 10.5” in the rear with 315 and then put the 9.5” in the front with 295 if you think that would work good. That wouldn’t cause any issues with not as wide of a tire in the front would it? I have sent them an email to see what they say about if the offset would work, maybe they could make them in a lower offset too. I really like the style of this wheel, I saw a picture of a c4 with hre p101’s and I thought it was one of the best looking wheels and these look exactly like those to me. The hre wheels cost over $2,000 each.

 

i think there are some reasonably priced 11” rims with 50mm offset that would work on the rear and are a better size for 315s. I really think you might struggle with the front but like has been said earlier you will need to measure for yourself.

 

For any year C4 I generally compare any desired combination to what is 'thought to be' maximum rim width/offset. It's generally thought that an 11" @36 is max for an early C4. A direct comparison of that to the 10.5 @22 says it's a 'stretch'! Is it? String & measure! That's actually just a 'wheel comparison' with no considerations of rubber being mounted!.

I honestly don't quite understand the desire for extreme tire section width/foot print for a road car!

Greg @50 won't work for his rears!

 

Yeah, I saw someone said to do that to see what offset would work but mine had custom wheels on it when I bought it and I don’t know what offset they are.

 

Pull one or more and check!!! Nearly always width & offset is cast into the back-side!! The 'string & measuring device' works!!! Always!

 

Why do you say that. So bare with me here (it’s 1:30 in the morning where I am) standard wheels are 38mm offset and fitted with 255mm tyres. If you fit 315mm on the 11” with 50mm offset you are adding 30mm to each side of the tyre but moving the wheel in by 12mm. So by my maths they are 18mm closer to the fender but 42mm closer to the inside wheel well. Are you saying they will rub on the inboard side? I have a set here (without tyres) but I haven’t had time to pull a wheel and have a look. They will definitely fit on the outside and fill the guards quite nicely but I don’t know about inside.

 

ok, I’ll check them when I get a chance to try to find the offset. I know it tells the width and diameter in inside the hub center cap but I don’t remember seeing the offset.

 

I'd be somewhat surprised if it's not presented on the back-side BUT if not measure the back-spacing , post back mentioning width and that back-spacing and it's pretty straight forward operation to determine the offset!

@GregMartin - when you've the opportunity since you've a wheel I'd suggest you just try your 11' @ 50.

 

Yeah I’ve been meaning to do it for a couple of weeks now but bits of life keep getting in the way. Genuine ZR-1 rears apparently fit I think they had a 36mm offset. But I have seen people fit them on YouTube and they look like they stick out to far to me. I haven’t dropped a plumb bob off my guards but it looks like there is around 3/4” space in the rears so the 50mm offset could work if it doesn’t fowl on the inboard side of the wheel. But like we’ve both said the ruler will tell all. I’ll post when I know more for sure.

 

An 11 wheel with 315 tire and 50mm offset isn't going to work on a 1985 C4. They require around 18mm less offset than 88-96 C4s. 50mm offset does work on the later cars front and rear. People have used 36mm-offset ZR1 rear wheels on early C4s, and you could try that. If it rubs something on the inside, you may need a 1/8" or 1/4" spacers. If you buy a wheel with a little too much offset spacers will effectively subtract from the offset to make it fit. However, a wheel with too little offset is just going to stick out - there's no way to adapt that to fit, short of making fender flares.

To the OP's original question, a 10.5"/315 with 22mm offset is probably going to poke out. I think you'll find that 32mm is what you want with this wheel size, too. All of what I wrote above still applies.

 

I actually believe @GregMartin 'gets it' and doesn't need your advice! He's also located where I believe spacers/adapters aren't legal!!

 

I was really speaking to the OP vis-a-vis Greg's posts. But if Greg can't use spacers or adapters and has a 84-87 C4, then the 50mm offset is going to be a problem.

 

I haven’t had a change to physically measure them yet but looking at my 84 the rears (9.5”@38) sit about 20mm inside the guard. I haven put a ruler on it so I don’t know if it’s 17mm or 21mm but it’s there somewhere. The 11” wheels with 315mm tyres @50 will stick out 18mm further which will be pretty close to perfect. They will also protrude 42mm further towards the center of the car so that might be where there is an issue but again the tape measure will reveal all. I have another thread going about these exact wheels because I was offered a set at a price to good to refuse. I knew at the time the offset was wrong but looking at it I think the rears can probably work. I don’t think the fronts will but that’s another story. The Rules are pretty clear cut here the wheels can’t stick out past the guards and you can’t use wheel spacers or adapters.

 

Ok, well I’m hoping I can at least use one in the rear and then the 9.5” on the front because I want a 315 in the rear no matter what when I buy new wheels. It looks so much better and would give you more grip whenever you launch fast. I’m going to call the place and see what they think and if they can make them in less of an offset. The only thing I was thinking of that seems like they would fit is that people use c5 z06 wheels with a 1.25 inch spacer on those and they are 10.5” with a 56mm offset. So subtracting the 1.25” from the 56mm seems like it should be almost the same exact as the wheels I want in the 22mm offset.

 

Right, the inside clearance is where you'll encounter the interference. IME, any more backspacing than 8" on an 88-96 car will cause interference inside in the rear, and for a 84-87 car that backspacing limit should be about 7.25". An 11" wheel with 50mm offset will have 7.96" backspacing, so that's likely to be the issue for you. IME, with the car off the ground you may not see any interference. But when you drop it on the ground and start driving on it, you'll probably get the inside corner of the tire touching the trailing arm bracket. You might get the sidewall touching the trailing arms themselves, but I'm not sure. Up front, the interference will of course be when you approach full steering lock. On my car, I actually seemed to get away with more backspacing up front than in the rear, though.

RE your laws, it's going to depend on how they measure "stick out past the guards." Also, you wrote "wheels," which would give some wiggle room to work with; but if the law is that sidewalls can't be outside the fenders then 11/315 is going to be really hard to make work. IME, with properly fitted 11/315s, the edge of the tread is about even with the top of the fender edge, but the middle of the sidewall where it bulges out on most tires will protrude past the fender edge. If you can't run 50mm offset due to inside interference, then the Grand Sport flares would be one obvious solution: GM tacked them on specifically to make the Grand Sport street legal in the US for the same reason.

PS - I know you can figure this stuff out on your own! I'm just trying to give you a head start on what to check for when you try those wheels and tires.

 

Unfortunately, unless this place specializes in Corvettes there's very little chance they will know what offset you need.

The C5z rear wheels are 10.5" wide with 58mm offset. Earlier you were saying people use them on early C4s with 1" spacers/adapters, and that would give a net offset of 33mm which is probably just right. Using 1.25" spacers/adapters with those would give a net offset of 26.25mm (they will sit 1/4" further outside). You can bolt those on the car and they won't hit anything on the inside. They may stick out of the fenders a bit: with a 10.5" wheel there's a touch more wiggle room on sidewall and wheel rim poke, but the 315 tire is ultimately going to have the same tread width no matter whether the wheel is 10.5" or 11". Whether this looks bad is a matter of opinion. My concern would be for rubbing on the upper fender edge at full suspension compression (maybe it will, maybe it won't), and for the outside tire edge rubbing on the fender liner at full steering lock (again, maybe it will and maybe it won't). Also, you should check your state's inspection regs to see if such protrusion is allowed: manufacturers can't sell new cars with protrusion like that, but it may not fail your safety inspections.