mlm0

1989. Automatic stock

i have been looking at buying new wheels lately. Every time I look at wheel specs, it states they will fit my car and list the off set. The confusion for me is that numerous wheels list their off sets at different numbers , but all state they will fit my car. Is there a maximum and minimum off set to fit my car?

Mike

vader86

A lot will fit the 5 lug hub, not all of it will fit flush with the body.

56mm offset is what youre looking for on a 9.5" wide wheel. If its within a few mm of that, youre fine. 50mm on an 11" rear, which was used on the 96 GS, will stick out just a bit but its fine really.

Backspacing is another measure for the same thing, but that number I forget off the top of my head.

WVZR-1

Easier I'd think to just ask if you spot something that interests you. Depending upon width sometimes an offset as low as 40 could be interesting. The online wheel comparison charts aren't always to be believed. They need to be confirmed.

The one in the 'TOOLS' section of the 'CF header' once you get familiar works quite well. I learned the 'math' years ago and still use manual calculations.

For an '89 use 9 1/2 @ 56 for comparisons.

kael

Good reference for the various stock size on all years:
http://mirrockcorvette.com/c4-parts-guide/wheels/

hcbph

I know this is going to sound like a Grinch, but it bothers me a lot and is an honest opinion. You don't mention the year of car or offset of your existing wheels, only you want to know the spacers to put on. Why don't you look for rims with the correct offset to begin with instead of trying to modify something to fit using spacers or adapters? Early C4's either had a backspacing of 32 or 38mm depending on rim width while later ones had 56. I ended up getting new rims for my 86 that are 18", up from the 16" that came on it originally so I could easily find some tires. By selecting the right size rims and tires I have a setup that fits just like the originals did but have a much larger selection than if I'd stayed with the 16's that came on the car in the first place and there's no spacers or adapters used to make them fit.

Here's a website I used while researching mine: https://www.wheel-size.com/calc/?whe...cl=50mm&sr=0mm
It proved very useful in determining what would fit and what wouldn't.

MatthewMiller

This is all pretty much correct. The thing about offset is that if your wheel and tire are narrower than the fender well can accomodate, then you have "fudge factor" in your offset. For example, in the front or rear of a 88-96 C4, an 11" wheel with 315 tire is about the most that can fit within the fender edges and also not rub on the inside anywhere, so offset is quite critical. As vader said, that offset needs to be 50mm. The backspacing there is 7.96", which also tells us that the "frontspacing" (the width that sits outside of the wheel mounting surface of the hub) is 4.04". You don't want to exceed those backspacing and frontspacing numbers with any wheel.

But what you realize from the above is that with a 9.5" wheel and 275 tire, you have 1.5" of wiggle room to play with. A stock 9.5" wheel on a later C4 has 56mm offset, and 7.45" backspacing with 3.05" frontspacing. Now, if you've seen that setup, you know you won't want them to sit further inside than they already do - it looks goofy. So you don't want more offset. But since we know you can push them outward a whole inch and still be right at the edge of the fenders, you know you can take 25mm off the stock offset and still be around the edge of the fender. Let's say only 20mm to be safe. So with a 9.5" wheel on a later C4, you're in good shape with anywhere from 36-56mm offset. The less offset, the more toward the outside they will sit. That tends to look more aggressive, but it also exposes more of the undercut lower fenders to everything the tires throw off as you roll. So that's the tradeoff.

Basically, the rule on a later C4 is to keep your frontspacing at or under 4", and keep your backspacing under 8". The formula for backspacing is: (nominal width +1)/2 + offset/25.4. For frontspacing, just subtract backspacing from nominal width and add 1.

WVZR-1

This is a 'damned mess' - back-spacing calculation is correct but you don't/can't even seem to apply your own math. Back-spacing is based on 'actual rim width'. You mention 'nominal' and I know what you mean BUT apply that to all numbers you mention (IT DON'T WORK)

9 1/2" advertised width using your formula converts to 'actual' of 10 1/2 so any back-spacing and front spacing numbers need to match that 'actual dimension'! 7.45 + 2.05 ain't 10.5 and neither is 7.96 + 3.04 the 12" 'actual rim width' of an 11" advertised wheel. Someone 15 or so years ago made a very similar statement regarding 'front spacing'. Best advice - don't attempt to even reference it!

I 'STILL' stand by my mentioning to the OP - if you find wheels of interest bring that wheel to the forum for a conversation. The CF 'Width Offset Calculator" in the TOOLS @ CF HEADER works very well for very basic calculations, Just disregard all of the tire dimensions displayed.

I assumed the OP was looking for very 'simple' shopping references and I tried to keep it like that. He mentioned no interest in 'width stagger'. OP deleted a post from earlier that made sense to me!

OP had everything required in the 1st line of his original post.

MatthewMiller

I had the backspacing formula correct (note the "+1" in the formula). I just forgot to add the one on the "frontspacing" formula. So the correct "frontspacing" on the stock 9.5" wheel is 3.05", and on the 11" wheel it is 4.04". It's not the end of the world or a "damned mess" - just a single error that is now corrected in my post above. I'm glad you caught it, though.

WVZR-1

I overlooked 'nothing' - I understand the MATH!! But it doesn't actually help the OP!! It's his thread! I'd say 'damned mess' if your intention was to help the OP. - I understood full well what you 'missed'. Many struggle enough with 'back-spacing' and you want to add to the confusion with front-spacing. The OP's effort is more easily answered with just off-set and leave the rest of the nonsense aside!

MatthewMiller

I didn't say you overlooked anything. I said I'm glad you caught my mistake. Wow, I hope whatever crawled up your *** to put you in such a bad mood crawls back out soon!

We're going to have a difference of opinion here. The OP didn't say what width of wheels he's looking for, so we can't give him a set answer for the offset range he needs. Frontspacing is important because we're assuming that nobody wants to tuck his wheels in more than stock. So the critical limit for figuring the offset is where the tire starts to poke outside the fender edge. The point was to give the range between stock wheel placement and the outer-edge limit, which is what is useful to the OP.

My logic in providing the formula for backspacing and frontspacing was to give him the tools to run the numbers himself for whatever wheels he's looking at, whereas you're advising him to come to the forum to ask about every wheel he looks at. Either way will work - I just thought it would be more efficient for him to run his own numbers on any wheels he looks at. Better to teach him to fish rather than just giving him a fish. But it doesn't matter to me which way he goes about it. I suppose another way to go about this would be to create a chart for early and late C4s showing usable range of offsets for various width wheels. That wouldn't be hard to do, using the stock 8.5 or 9.5 frontspacing as an inner (max-offset) limit, and the fender edge as the outer limit.