C3 Wheels
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Instructor
Joined: Oct 2004
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From: Hattiesburg MS
C3 Wheels
Because my Vette sat in a fiels so long before I got it........the trim rings and everything else are toast. I really don't like the look of the rally wheels look or even the stock Corvette alum. wheels anyway. Can't find any aftermarket wheel company that offers the correct backspacing as the stock wheels in the needed bolt pattern. How critical is the backspacing and does anyone know who makes wheels that will fit correctly?
Safety Car
Joined: Jun 2004
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From: Lakeland Florida
Hello,
You will need to be careful when looking for aftermarket wheels when determining the offset and the backspacing. The Offset is the distance from the centerline of the wheel to the part that actually bolts to the hub. Backspacing is the distance between the edge of the inner rim to the part that bolts to the hub.
If your wheel offset is incorrect, you may have a tire that extends beyond the fenderwheel, or is too far inboard and will rub on the inside. The backspacing is the area between the part that bolts to the hub and the inner wheel edge. I think that this part may be constant, but the offset is what will move the tire in or out of position.
I found a website to help explain some of this.
http://www.usacomp.com/Offset.htm
Good Luck,
kdf
You will need to be careful when looking for aftermarket wheels when determining the offset and the backspacing. The Offset is the distance from the centerline of the wheel to the part that actually bolts to the hub. Backspacing is the distance between the edge of the inner rim to the part that bolts to the hub.
If your wheel offset is incorrect, you may have a tire that extends beyond the fenderwheel, or is too far inboard and will rub on the inside. The backspacing is the area between the part that bolts to the hub and the inner wheel edge. I think that this part may be constant, but the offset is what will move the tire in or out of position.
I found a website to help explain some of this.
http://www.usacomp.com/Offset.htm
Good Luck,
kdf
Race Director
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actually, for backspacing they don't count the rim lip, so about 1/4th of an inch is not included (could be more or less depending on wheel) Offset and backspacing are of course related, as offset goes to negative (rim heart to otuside of wheel) the backspacing increases and vice versa.
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From: FL
Stock is 15x8 with 4" backspacing. Basically, the surface where the wheel bolts to the hub is exactly on the centerline of an 8" wheel. Mine have a 3.75" backspacing, therefore the outer edge is 1/4" further out than stock.
The biggest issue with aftermarket rims for the C3's is clearance for our disc brake calipers. Very few aftermarket rims will clear our calipers without spacers. Obviously, a spacer will move the hub further out so you have to increase the backspacing to keep the wheel at the same position in the wheel well.
For example, the popular Cragar SS rims need a 1/4" spacer to avoid hitting the brake calipers. The danger here is making sure that you have enough thread engagement on the lug nuts and that they stay torqued. The American Racing Torque Thrust II (usually refered to as TTII) clear the calipers in both a 15x8 or 17x8 size with 4" backspacing. The 17x8 will allow you to run more modern low profile tires.
FYI. My tim are American Racing AR-136 15x8 with 3.75 backspacing and BFG Radial T/A 255/60R15 on all four corners. This rim was listed in the catalog as a generic rear wheel drive rim for pickups.
The biggest issue with aftermarket rims for the C3's is clearance for our disc brake calipers. Very few aftermarket rims will clear our calipers without spacers. Obviously, a spacer will move the hub further out so you have to increase the backspacing to keep the wheel at the same position in the wheel well.
For example, the popular Cragar SS rims need a 1/4" spacer to avoid hitting the brake calipers. The danger here is making sure that you have enough thread engagement on the lug nuts and that they stay torqued. The American Racing Torque Thrust II (usually refered to as TTII) clear the calipers in both a 15x8 or 17x8 size with 4" backspacing. The 17x8 will allow you to run more modern low profile tires.
FYI. My tim are American Racing AR-136 15x8 with 3.75 backspacing and BFG Radial T/A 255/60R15 on all four corners. This rim was listed in the catalog as a generic rear wheel drive rim for pickups.
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Instructor
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From: Hattiesburg MS
Originally Posted by Mr Fanuc
Never thought about backspacing.......good point. Very helpful site. Thanks!
From reading the previous post I gather that many wheels will work as long as backspacing, offset, and thread engagement are calculated to keep the wheels off the calipers and prevent turning the fenders into fiberglass fotter.
Any ideas on what amount of thread engagement would be considered min. required for safety? Also, I have access to a full blown machine shop and could modify the lugs if necessary. Would this be a bad idea?
Race Director
Joined: Jun 2000
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From: FL
Originally Posted by Mr Fanuc
Messed this all up......meant to type offset instead of backspacing. Not trying to be a smart a_ _, just a mistake.
From reading the previous post I gather that many wheels will work as long as backspacing, offset, and thread engagement are calculated to keep the wheels off the calipers and prevent turning the fenders into fiberglass fotter.
Any ideas on what amount of thread engagement would be considered min. required for safety? Also, I have access to a full blown machine shop and could modify the lugs if necessary. Would this be a bad idea?
From reading the previous post I gather that many wheels will work as long as backspacing, offset, and thread engagement are calculated to keep the wheels off the calipers and prevent turning the fenders into fiberglass fotter.
Any ideas on what amount of thread engagement would be considered min. required for safety? Also, I have access to a full blown machine shop and could modify the lugs if necessary. Would this be a bad idea?
The bigger issue with the thin spacers is ensuring that they are parallel and concentric. If the two sides are not parallel then you wheel will be crooked in relation to the hub.
There is a C3 wheel guide at www.corvettefaq.com .
These guys make some nice stuff. www.coloradocustom.com
Steve
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From: Hattiesburg MS
This is the American Racing site, look under wheels, vew all, then its page 2 of 5. You will see them but in 16x8, the 15x8 has 3 3/4 backspacing. http://www.americanracing.com/
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