If you hang around a lot of autocrosses—and we do—you may notice a lot of fifth-generation Corvette Z06s running in the SCCA’s A Street class with mismatched wheels. There’s a simple reason for this peculiar condition, and it comes down to a rules allowance and tire availability among the top choices of rubber.
A stock C5 Z06 comes with 17 …
Guys keep in mind that the true factory takeoff C5 corvette base 18x9.5" rear rims, both the 5-spoke thin or the 5-spoke magnesium designs have a 65mm offset. So you would need 10mm or 12mm hubcentirc wheel spacers to run those on the front of a C5 plus most definitely some of those longer ARP wheel studs.
Also the OE Wheel site lists the offset for the reproduction 18x9.5" rims, like the ones you are using #CV05-D18095-5475-54BM as having a 54mm offset - not 57mm as you noted. Maybe somethings have changes thought the years?
https://www.oewheelsllc.com/CV05-D18095-deep-dish-black-rims-fit-Corvette-C5-style
deaconblue said:Guys keep in mind that the true factory takeoff C5 corvette base 18x9.5" rear rims, both the 5-spoke thin or the 5-spoke magnesium designs have a 65mm offset. So you would need 10mm or 12mm hubcentirc wheel spacers to run those on the front of a C5 plus most definitely some of those longer ARP wheel studs.
Also the OE Wheel site lists the offset for the reproduction 18x9.5" rims, like the ones you are using #CV05-D18095-5475-54BM as having a 54mm offset - not 57mm as you noted. Maybe somethings have changes thought the years?
https://www.oewheelsllc.com/CV05-D18095-deep-dish-black-rims-fit-Corvette-C5-style
That's not the first time I've heard of the 65mm offset for the base rears, but I've never been able to find any independent confirmation of it. This is the chart we've been using, and it seems to match up with what we've observed in the wild: https://www.corvettecentral.com/wheel-offset
As for the OE Wheels repros offset being off, well that just an oversight on my part. I guess I assumed that they were repros of rears, so they carried the standard rear offset, but they actually have proper offset from the getgo. Even with the 3mm spacers we're stil legal, though (SCCA rules allow up to 7mm of offset variation from stock). Good catch on that one. Dumb mistake on my part.
Hmm. I'm planning to run similar sizing on my M3, 18x9.5 front and 18x11 rear. Apparently the Azenis RT615K in the same 275/315 sizing is a little narrower so it will be more likely to fit in back. Hope so - that 315 Rival looks pretty pinched on the 18x10.5. Not many options for really wide 18s in a sticky street tire!
The magnesium wheels had more offset and stuck in more, approx 1/4" per side as I recall.
The magnesium wheels were used on the export version, blah blah track width narrow roads blah blah.
I had 11" wide rear wheels on my C5 and they fit nice with 305 Nittos.
JG Pasterjak said:deaconblue said:Guys keep in mind that the true factory takeoff C5 corvette base 18x9.5" rear rims, both the 5-spoke thin or the 5-spoke magnesium designs have a 65mm offset. So you would need 10mm or 12mm hubcentirc wheel spacers to run those on the front of a C5 plus most definitely some of those longer ARP wheel studs.
Also the OE Wheel site lists the offset for the reproduction 18x9.5" rims, like the ones you are using #CV05-D18095-5475-54BM as having a 54mm offset - not 57mm as you noted. Maybe somethings have changes thought the years?
https://www.oewheelsllc.com/CV05-D18095-deep-dish-black-rims-fit-Corvette-C5-style
That's not the first time I've heard of the 65mm offset for the base rears, but I've never been able to find any independent confirmation of it. This is the chart we've been using, and it seems to match up with what we've observed in the wild: https://www.corvettecentral.com/wheel-offset
As for the OE Wheels repros offset being off, well that just an oversight on my part. I guess I assumed that they were repros of rears, so they carried the standard rear offset, but they actually have proper offset from the getgo. Even with the 3mm spacers we're stil legal, though (SCCA rules allow up to 7mm of offset variation from stock). Good catch on that one. Dumb mistake on my part.
Best way to confirm is to look at the photos on the eBay posting that have the wheels for sale. Some folks have higher resolution photos of the back of the wheels that can be enlarger and you can clearly see the OE Speedline name, the GM p/n and the size and offset specs cast into or etched into the back side of the spokes.
turtl631 said:Hmm. I'm planning to run similar sizing on my M3, 18x9.5 front and 18x11 rear. Apparently the Azenis RT615K in the same 275/315 sizing is a little narrower so it will be more likely to fit in back. Hope so - that 315 Rival looks pretty pinched on the 18x10.5. Not many options for really wide 18s in a sticky street tire!
The RT615K is the spec tire for the new Spec Corvette class. The Rival S tends to be one of the "tires of choice" for the top autocross finishers.
I'm pretty sure OEwheels offsets are off too. I don't have any numbers handy but I have run several sets of their wheels and have always been happy with the look and performance of them, I think there is a little more offset than they rate them at for certain ones. Also like it was said, the 18x9.5 rear wagon wheels are dirt cheap. I picked up one set for 100 bucks and another set for a little more than that, then needed a replacement that I got for around 50. I wish they were the 10.5 z06 wheels but for the price and tire availability, can't beat em! Painting them is a must though, they are ugly!
New to Autocross and the Forum. Thanks for all the info and videos. I bought my wife a 2004 C5 Z06 CE for autocross and ordered the BFG Rival S in 275/35/18 fronts and 315/30/18 rears. Is this the same as you were running in AS? If so were there any issues with the front diameter larger than rear? Any first hand insight would be greatly appreciated.
HomeyDClown said:New to Autocross and the Forum. Thanks for all the info and videos. I bought my wife a 2004 C5 Z06 CE for autocross and ordered the BFG Rival S in 275/35/18 fronts and 315/30/18 rears. Is this the same as you were running in AS? If so were there any issues with the front diameter larger than rear? Any first hand insight would be greatly appreciated.
That's the preferred setup for AS with BFGs and what we ran in AS. No weirdness to report with the diameter change with regards to ABS or anything like that.
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