#1 |
I want to put 275/40/17’s with 9†wheels on the rear & 255/40/17’s with 8†wheels on the front of my 85.5 Turbocoupe. I don’t want the outside edge of the wheel to move much further out than it is with the stock 7†10 Holes, and the Quad shocks are removed.
Here’s the problem: I’ve read every applicable post on NATO that I can find, and a lot of numbers don’t seem to jive. Using my stock wheel as an example, tell me where I’m wrong. 7†wheel w/0.88†(22.35mm) offset. If the centerline is 7†divided by 2, I get 3.5 + the 0.88 positive offset equals 4.38 (I read numerous times that the backspacing is 5â€, but my math doesn’t tell me this). This should be my backspacing. Correct? If this is correct and I subtract 4.38†from the total wheel width of 7â€, I have a remainder of 2.62â€, which is the distance from the wheel mount to the outside edge of the wheel.
Lets say I want to put 275/40/17’s on the rear using a 9†wheel, w/ 2.7†from the wheel mount to the outside edge of the wheel. Subtracting 2.7†from 9†leaves 6.3†for back-spacing. Wheel centerline would be 4.5â€, subtracted from 6.3†gives me an offset of 1.8†or 45.7mm +offset. Yet I keep seeing numbers like 15mm offsets to 20mm, even though the stock offset was 22.35mm on a narrower wheel.
What am I missing here? Are most people moving the outside edge of the wheel a lot further outboard than I am? Do I have to move more outboard to find any wheels that will have an offset that works? Do my numbers make any sense?
Here’s the problem: I’ve read every applicable post on NATO that I can find, and a lot of numbers don’t seem to jive. Using my stock wheel as an example, tell me where I’m wrong. 7†wheel w/0.88†(22.35mm) offset. If the centerline is 7†divided by 2, I get 3.5 + the 0.88 positive offset equals 4.38 (I read numerous times that the backspacing is 5â€, but my math doesn’t tell me this). This should be my backspacing. Correct? If this is correct and I subtract 4.38†from the total wheel width of 7â€, I have a remainder of 2.62â€, which is the distance from the wheel mount to the outside edge of the wheel.
Lets say I want to put 275/40/17’s on the rear using a 9†wheel, w/ 2.7†from the wheel mount to the outside edge of the wheel. Subtracting 2.7†from 9†leaves 6.3†for back-spacing. Wheel centerline would be 4.5â€, subtracted from 6.3†gives me an offset of 1.8†or 45.7mm +offset. Yet I keep seeing numbers like 15mm offsets to 20mm, even though the stock offset was 22.35mm on a narrower wheel.
What am I missing here? Are most people moving the outside edge of the wheel a lot further outboard than I am? Do I have to move more outboard to find any wheels that will have an offset that works? Do my numbers make any sense?
R. Libby
85.5 Med. Regatta Blue TC
85.5 Med. Regatta Blue TC