# backspacing question



## Ky Bob (Sep 3, 2017)

If this is covered elsewhere could someone point me to the thread? I have 66 GTO with a 72 Chevelle 12 Bolt rearend and a disc brake conversion kit. I know the rearend is 1/2 inch wider on either side, and I believe the disc brake conversion also adds similar. I am looking at 15 inch Weld racing Pro Stars with 5.5 backspace with +12 offset, on a 9 inch wheel. I plan on running BF T/As 275/60/15. Will that much backspace work without hitting shock mounts or calipers? Hoping with the 9 inch wheel it also tucks the tire in with ample wheel well clearance.
I would like to run biggest tire possible, and thought this would work with the extra width of the rearend and disc brakes. I plan on running same wheel on front in 8 inch with 4.5 backspace with maybe a 245/60/15. Any thoughts would be much appreciated thanks


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## Pinion head (Jan 3, 2015)

Bob, unless your '66 was built extremely early and originally had a a late '65 production version of the"narrow" '64-65-extreme early '66 width Pontiac 8.2 width rear , the original '66 Pontiac 8.2 rear would be exact same width as the '68-72 Chevelle 12 bolt rear.

Adding 4 3/4" bolt pattern rear disc brakes only spaces the wheel mounting flange out a hair over 1/8" on each side. Have built or gone through every style of early GM A-body rear, 275-60R15 tire/wheel fit is possible with correct back spacing 15x8 or 15x8.5 wheels. The tightest fit I've ever managed to get a pair of 275/60R15's to fit with the later width rear was with a built up HD 8.5 A-body rear that went in a customer's '64 Malibu. Was very tight fit, so tight had to mount the tire/wheels on the fresh built rear & roll it under the car, then hook up the upper and lower controll arms, brake line, and bleed the brakes while the car was up on 4 HD jack stands. The '64 Malibu has quarter panels that extend well down into the area that would normally be open on other '64 GM A-body's. '66 & 67's had even larger rear wheel houses, just have to measure and make sure the section width is not out into the inner edge of the stainless rear wheel openings. Best to you.


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## Ky Bob (Sep 3, 2017)

Thanks Pinon Head
I have changed my plans and am now going with a different wheel. I now plan on doing 8 inch wide, 15 inch wheels with 4 1/2 backspace all around, and hope I can run 275/60s. I am wondering if that 4 1/2 inch backspace will work on front? I have tube control arms and a disc brake conversion kit. I have found a great deal on 4 American Racing wheels and hate to pass on them. What are your thoughts about that backspacing on the front with maybe a 245/60/15 tire?


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