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12in rear on C4s - offset

coullstar

Well-known member
Joined
15 Sep 2015
Messages
2,832
Folks,

Im looking at a set of wheels that were on a 997 with the following dims

8.5x18 et53
12x18 et51

I know my current wheels are 8x18 et50 and 11x18 et45 and have worked out the differences in terms of how much less space and how much more the new ones would stick out.

What I can see is that Id need 10mm on the front to get same clearance in the inside and almost 20mm on the rear. I fear the rears would stick out to far then. Ideally 5mm all round would work I think.

Whats the best offset for the 12in rear and would the front fit fine without any spacers?

Tyre will be 235 front and 315 rear.
 
I calculate that your new wheels would sit as follows:

Fronts: 9mm less inner clearance. Outer wheel extend 3mm

Rears: 19mm less clearance. Outer wheel extend 7mm
 
Other way around isn't it? The new wheels are wider and have a higher offset so sit further into the arches.

So I would have 9mm less clearance on front inside and 19mm less on the back with new wheels.

That's my concern. I know GT2 wheels work with same widths but with et40 up front and 45 rear but I'm sure I read somewhere GT2 wings are slightly different.

Basically would I get away with 5mm all round spacers?
 
coullstar said:
Other way around isn't it? The new wheels are wider and have a higher offset so sit further into the arches.

So I would have 9mm less clearance on front inside and 19mm less on the back with new wheels.

That's my concern. I know GT2 wheels work with same widths but with et40 up front and 45 rear but I'm sure I read somewhere GT2 wings are slightly different.

Basically would I get away with 5mm all round spacers?

Sorry fellow you are quite correct, I miss read your post above.
I would be concerned with having already 7mm extension on the rear combined with trying to combat the 19mm clearance you have lost. Best to get under the car now and measure the clearance you currently have just to be sure. You may have 50mm clearance on the rear so have nothing to fear. I have fitted 15mm spacers all round on my car with stock wheels which sit just right, so if you were to fit 8mm on the rear that may be perfect.
 
Thanks, had a look last night and rear does have loads more room for the strut but liner might come into play. As you say it would work with spacers etc but I would like to use without and 12in rear is going to limit tyre availability so Im going to leave them.
 

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