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-   -   porsche cup wheels. Help please!? (https://www.germanlook.net/forums/showthread.php?t=9885)

hurley209 December 4th 2008 14:55

porsche cup wheels. Help please!?
 
hey guys can i fit 16" 55offset wheels in the front of my super, and 16" 70offset in the back?

i have aftermarket struts.

petevw December 4th 2008 18:38

How wide are they?

16x?

hurley209 December 4th 2008 18:43

7 in front, 8 in back i believe...
would i have to customize some stuff.?
im guesing re do the bolt pattern on my rotors and drums, is that expensive?

also, the wheels come with 9.5" tires on the rear wheels.

oasis December 5th 2008 11:22

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 December 5th 2008 15:07

Quote:

Originally Posted by oasis (Post 68631)
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.

Steve C December 7th 2008 06:50

Hi

The front will be fine. The rears will go in a bit too far.

I know that 15x7 Cookies that have a 23 Et work fine on the rear, so plugging those numbers into wheel offset calculator http://www.1010tires.com/WheelOffsetCalculator.asp your wheels will be 60mm closer to spring plate and have 34mm more clearance from the fender lip.

Maybe someone else can tell you how much clearance a 7 inch Cookie has from the spring plate.

Steve

excello December 7th 2008 09:13

I had 16 inches (I believe they are called C4 or design 90) under my 1302. In the front 7 ET 55 and in the back 8 ET 52. (or front 52 and back 55) The front coils are thinner in diameter, all the fenders are wider and I had spacers between them of about 1 inch thick. Now I've got Cup 2's. In the front the same size but 17's and in the back 9 ET 55. With the spacers they are still very close to the bolts of the spring plate. So with 16 inch ET 70 without spacers you'll probably be hitting the bolts. And ripping up your tires. And with spacers you'll probably need wider fenders. Off course I am not a 100% sure because I haven't had 8 inch ET 70 under my car but if I were in your place I would look for rear wheels with a lower offset to make everything a little bit easier on yourself..... just my 2 cents. Oh and check my blog if you want to see what I was talking about.

Edit: Oh forgot to mention I've got a 944 adjustable rear, which off course changes things a bit. Doh. But still it's close to original sizes I guess.....

oasis December 8th 2008 08:22

Quote:

Originally Posted by fast Ed (Post 68634)
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.


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