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Assuming there is no rubbing anywhere, how far can you deviate from the factory wheel offset before there will be some degradation in handling, or any other problem? I can't find any wheels that I like at a price I want to pay that match the Cayman offset, 57mm front, 43mm rear. Yes, replies on the other form have been helpful, just looking for some more thoughts.
 

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There is no universal answer. It depends on the width of the new rims vs old rims and your suspension setup. A lowered suspension will likely not handle wider tires/rims as well as stock or else will need a custom offset.

Say you want a 8.5 inch front rim vs an 8 inch stock rim. The .5 inch is about 12.7 mm, so half that, 6.3mm (rounded down to 6mm) needs to be subtracted to get the offset, or 51mm. Now this assumes you have the .25 inch clearance on both sides. Go too far out and you will hit the fender, too far inward, you hit the shocks/struts. Best bet is to load car with weights equivalent to driver and passenger and take a tape measure and see what the clearances are at multiple steering angles. Then you can decide how much clearance you want and that will give you the range of offsets your particular car can handle and from there select a tire with appropriate width and offset or else use spacers to make up the difference.

However, go too much wider and you will run into problems. For example, I have only heard of people able to run 911 11" rears on a Cayman if they used spacers and rolled the lip of their fender. So in general, 10" wide rears are the max without bodywork.
 
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