porsche cup wheels. Help please!?

[oasis]

Your front wheels are 7" wide. That calculates to roughly 177.8 mm. With an offset of 55 mm, those wheels have a backspacing of 143.9 mm (approx. 5 11/16"). Backspacing is the amount of the width of the wheel that "extends" inward to the center of the car near the struts. The remaining 33.9 mm (1 3/8") extends to the street.

Your rear wheels are 8" wide. That calculates to roughly 203.2 mm. With an offset of 70 mm, those wheels have a backspacing of 171.6 mm (approx. 6 3/4"). The remaining 31.6 mm (1 1/4") extends to the street.

The measuring is now up to you. Keep in mind that if you need a spacer to move the wheels away from the suspension and brakes, that will also extend the wheels more to the street. And don't forget the tires. A 9 1/2" tire extends 3/4" more to the inside and 3/4" more to the outside than the 8" rear wheels.

This also does not address the height of the tires with respect to how much your Super is lowered. I can tell you from personal experience all of the careful planning in the world may not prevent you from needing to tweak away to get to the final results you desire.

In my case, I had to get a slightly narrower tire for the front with a slightly lower aspect ratio. I wasn't too keen to have to buy two more tires when the ones I had possessed perfectly good tread. In the end, it was small price to pay and the results were dynamite.

[fast Ed]

Originally Posted by oasis

A 9 1/2" tire extends 3/4" more to the inside and 3/4" more to the outside than the 8" rear wheels.

That's not quite right. An 8" wheel will actually have an overall width from edge to edge of close to 9". So a tire with a section width of 9-1/2" will only hang over roughly 1/4" on each side of the wheel.


cheers
Ed N.

[oasis]

Originally Posted by fast Ed

That's not quite right. An 8" wheel will actually have an overall width from edge to edge of close to 9". So a tire with a section width of 9-1/2" will only hang over roughly 1/4" on each side of the wheel.

Thanks. I learned something new, and it will be better for the application at hand.