Wheel adapters? Help needed...
Thread Starter
Instructor
Joined: Aug 2004
Posts: 150
Likes: 0
From: Pittsburgh Pa.
Wheel adapters? Help needed...
About 10 years ago I bought a set of BBS wheels, size 17 x 9.5. I mounted them straight up on my '86, not knowing at the time I was supposed to be using an adapter of a certain width if my car was a pre-88 model. I've never had any problems with this set-up, but it's always nagged me that my car might not be set up properly. Now for my questions: Have I been risking anything for the past decade by not using adapters? What size adapter should I be looking for to make this 'right'? After looking at my car, I can see the wheels sit inboard of the wheel wells an inch or so, but that's the only thing I can see that's actually affected. If you absolutely know the answers to my questions, I'd greatly appreciate your response.
Thread Starter
Instructor
Joined: Aug 2004
Posts: 150
Likes: 0
From: Pittsburgh Pa.
Okay, after a little research I came up with this: I found the adapters I believe would work the best, now another question...The adapters I found are for a Corvette, or any Chevrolet with a 5 on 4.75 bolt pattern and 12mm x 1.5 inch studs. Is this correct? I'm thinking of a 1.5" adapter for the rear and a 1.25" for the front. Sound right?
Drifting
Joined: Feb 2003
Posts: 1,614
Likes: 163
From: Davis CA
The reason that you need adapters is to use younger Corvette wheels on older Corvettes (88 or more recent on 87 and older). Your BBS wheels are not factory Corvette and could have been made to your 87 and older specs. I have aftermarket wheels on my 86 that were made using the offset of 86 so no adapters are needed. There are lots of sites that show you how to measure offset. You need to do that before using adapters. You might not need them.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
There was a signifigant change in the offset of the factory wheels in 1988. 84 to 87 wheels used a 38mm offset and the later 17" wheels used a 56mm offset. This is about 3/4" between the two. In order to install the later wheels on the early cars, adapters are needed to get the newer wheels to sit properly in the wheel well. The later wheels would be 3/4" further in without adapters. They bolt on but just look funny.
One thing about Corvette (and similar 5-lugf hubs) lug patterns is that they are metric; the lugs measurements will be shown as 5x120.5mm. The 4.75 inch measurement is close but not the same as the metric measurement.
You should measure the BBS wheel backspace and offset to make sure it will work especially with the adpaters you purchased. Offset is the distance from the wheel mounting flance to the center of the wheel rim. Backspace is the distance from the wheel mounting flange to the inside edge of the wheel rim where the tire bead contacts the lip.
For a 88 and later wheel, the factory backspace is about 7.4" and the 84-87 wheel (the 9.5" wide version) has a backspace of about 6.8".
One thing about Corvette (and similar 5-lugf hubs) lug patterns is that they are metric; the lugs measurements will be shown as 5x120.5mm. The 4.75 inch measurement is close but not the same as the metric measurement.
You should measure the BBS wheel backspace and offset to make sure it will work especially with the adpaters you purchased. Offset is the distance from the wheel mounting flance to the center of the wheel rim. Backspace is the distance from the wheel mounting flange to the inside edge of the wheel rim where the tire bead contacts the lip.
For a 88 and later wheel, the factory backspace is about 7.4" and the 84-87 wheel (the 9.5" wide version) has a backspace of about 6.8".
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