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I'm curious if anyone has put 12in wide rims on a C4. They have a -63 offset I believe (not confirmed) any thoughts? Just going for a cool look factor.
There was a ZR1 for sale here running 12s or 13s on the rear…
What year C4 and are you talking ZR1?
The late non-ZR1 C4s I know can take 11s all the way around with the right offsets and some camber. I am going to run 10.5s starting in the spring on my 93. AFAIK, No way a 12 inch is fitting though especially without using fender flares and perhaps some wheel well trimming.
Search the threads there are tons of them on biggest rims etc…. Especially look for ones with @MatthewMiller . Lots of discussions on wheel width, offsets, years etc…
There was a ZR1 for sale here running 12s or 13s on the rear…
What year C4 and are you talking ZR1?
The late non-ZR1 C4s I know can take 11s all the way around with the right offsets and some camber. I am going to run 10.5s starting in the spring on my 93. AFAIK, No way a 12 inch is fitting though especially without using fender flares and perhaps some wheel well trimming.
Search the threads there are tons of them on biggest rims etc…. Especially look for ones with @MatthewMiller . Lots of discussions on wheel width, offsets, years etc…
It's a 84 base model, I don't mind the wheels hanging out a bit either
I have a heavily modded c4 1990 I bought on this site last year. 396 tpis forged engine etc.. coilovers,,auto to zf 6 speed conversion.. along with 12 inch weld rts wheels in the back. fits very nicely. previous owner took painstaking accuracy to order these custom wheels with custom offsets from weld. looks very nasty. they look huge but stays within the body maybe .5 of an inch on the side since it has nitto nt01 drag radiials on all fours. fronts tires 275.. rear 315. definitely makes a statement.
I have a heavily modded c4 1990 I bought on this site last year. 396 tpis forged engine etc.. coilovers,,auto to zf 6 speed conversion.. along with 12 inch weld rts wheels in the back. fits very nicely. previous owner took painstaking accuracy to order these custom wheels with custom offsets from weld. looks very nasty. they look huge but stays within the body maybe .5 of an inch on the side since it has nitto nt01 drag radiials on all fours. fronts tires 275.. rear 315. definitely makes a statement.
12s don't fit within the fenders of a stock C4 front or rear, except for the rear of a ZR1. And 84 car like yours can handle no more than 7.4" of backspacing. A 12" wheel with 63mm offset has 9" backspacing. Not gonna work unless you use at least 1.6" spacers/adapters. When you do that, they will poke outside of the top fender edges by nearly 1". Whether you like that look or not, you are at serious risk of cracking the fenders if you go over a bump and compress the rear suspension too much.
I'm assuming you didn't actually mean negative 63mm offset like you wrote. If you do, then that means only 4" of backspacing, but they're gonna poke out of the fenders by 4"!
How about filling us in on what wheels these actually are, and what their specs are?
Last edited by MatthewMiller; Oct 10, 2022 at 11:50 PM.
12s don't fit within the fenders of a stock C4 front or rear, except for the rear of a ZR1. And 84 car like yours can handle no more than 7.4" of backspacing. A 12" wheel with 63mm offset has 9" backspacing. Not gonna work unless you use at least 1.6" spacers/adapters. When you do that, they will poke outside of the top fender edges by nearly 1". Whether you like that look or not, you are at serious risk of cracking the fenders if you go over a bump and compress the rear suspension too much.
I'm assuming you didn't actually mean negative 63mm offset like you wrote. If you do, then that means only 4" of backspacing, but they're gonna poke out of the fenders by 4"!
How filling us in on what wheels these actually are, and what their specs are?
You nailed it. I went and looked at these wheels cause the guy wasn't sure if the numbers were right. Once I confirmed his numbers yeah it was no good. I figured I ask the group prior to looking and kind of have an idea whether 12s would work at all.
Thanks all
I will look at my receipts (a box full) and I know the builder wrote the specs down. They do fit. barely. I have had a modded zr1 so I know what a 12 inch wheel is. the back tire is the exact same size as the tires I had on my zr-1. I will respond later. It takes me a while and I had a very long day.
This was Mick Stevens car. It is set up for road racing. I almost bought a few years ago a Dick Guldstrand Grand Sport 80 car. When I figured out what was in this car and the set up it is very much like a Grand Sport 80 except more powerful. I made it a tribute car. It doesn't disappoint.
I have a set of widened real ZR1 AMolds that are 12” wide and fit perfect on a 1986 (85-87 perhaps), with standard rear 11” AMold on the front ET36… for the rear I had to remove the rear sway bar, and trim the bumpstop, install rod end dogbones spaced inboard another 1/2” or so. Installed 275 RT660s in the front and 315 Nittos in the rear. Still have the wheels tires if anyone near Arizona is interested, as I changed to 18’s
Last edited by AZSP33D; Oct 11, 2022 at 01:34 AM.
Reason: Better pictures added for 12 inch rear wheels
here is my 1991 zr-1 with 2007 z06 wheels, tires and 6 piston brakes. the wheels are 19 x 12 x 59offset with a 12 mm spacer and the wheels/tires fit right in the middle of the wheel house. the fronts are 18 x 9.5 x 40offset and they poke about 3/4" outside of the fender. i just ordered a set of bc forged wheels with offsets to bring the fronts in and the rears exactly where they are at with no spacers.
I think everyone providing examples of their cars is overlooking the fact that the OP's car is an 84 and requires 14-20mm less offset than 88+ models.
Posted 1986 which should be the same for offset, no?
12 inch rears and 11” fronts. CB Ramey runs 12 wheels and 335 tires on all 4 corners, on a 1987, but he needs some more serious mods to do it. Rear works out to be about 61mm offset (ET36 and 1” spacer welded in) so I would say 58-61 fits if my math is correct. Front is 17X11 ET36 (same as the rear without the widening).
Posted 1986 which should be the same for offset, no?
12 inch rears and 11” fronts. CB Ramey runs 12 wheels and 335 tires on all 4 corners, on a 1987, but he needs some more serious mods to do it.
You're right, I somehow missed that yours is an 86. Sorry! I went to college with Ramey (a loooong time ago), and we're still friends. As you note, his car is pretty modified these days so his fitment probably can't just be bolted on to an otherwise stock C4 (e.g., I don't think he has inner fender liners anymore).
Rear works out to be about 61mm offset (ET36 and 1” spacer welded in) so I would say 58-61 fits if my math is correct. Front is 17X11 ET36 (same as the rear without the widening).
I think you worked the math backwards: positive offset is to the inside, just like positive backspacing. If you add width to the outside of the wheel, it subtracts offset. A common wheel spacer does the same thing. So if you start with a 36mm offset wheel and add 1" (25mm) of rim width to the outside of the mounting surface (I'm ***-uming that's where the extra width was mounted?), or if you add a 1" spacer between the wheel and hub, you end up with a net offset of 11mm.
It is widened on the inboard side (you can kind of see it in the picture from the underside pf the car) so offset from center goes from 36 to 61mm… 11mm would stick way out. Modifications were made as stated, but I just remembered clearancing the toe knuckle forging also, but thats probably not hardly needed for 18’s… forgot to mention that.
From the side it looks just like a regular ZR1 wheel, got the widened set here on the Corvette Forum, and they fit the ZR1 almost the same way, lots more room can be made on the inside without fender flares, but much wider tires would not work for a Non-Z
It is widened on the inboard side (you can kind of see it in the picture from the underside pf the car) so offset from center goes from 36 to 61mm… 11mm would stick way out. Modifications were made as stated, but I just remembered clearancing the toe knuckle forging also, but thats probably not hardly needed for 18’s… forgot to mention that.
From the side it looks just like a regular ZR1 wheel, got the widened set here on the Corvette Forum, and they fit the ZR1 almost the same way, lots more room can be made on the inside without fender flares, but much wider tires would not work for a Non-Z
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
I'd also like to point out 12" wheels aren't needed to have 12" TIRES on the rear. ZR1 rears (for a C4) are 315/35-17 which have a section width of 12.4". That's pretty FAT. It's what I have on mine (and have had since 2010). They stick out a bit (like Mick's old car). I've never had them rub but mine isn't lowered either. Can't due to the sidepipes.
Anyway...stock ZR1 wheels (or wheels with the same config) SHOULD sit about the same as GS wheels on a late model base C4. They have 18mm less offset (38mm vs 56mm). So, ZR1 wheels would fit pretty well (on an early base C4) and you'd been running 12.4" wide tires. I suspect that's what the OP is looking for.
Note: I think AZSP33D's wheels are what I'm talking about. I don't think they are 12" wheels (as he stated). Unless widened, I suspect they are 10.5" ZR1 "A-mold" wheels with 12"+ tires on them. I'm not even sure you could mount 315/35-17's on a 12" wheel. The wheel is probably too wide. 335's....yeah. (FWIW: This is w/o looking online for mounting specs).
