[rxter]

Seems like one key here is the 25" overall diameter limit and I think I have that sussed.



The offset and clearance piece has me puzzled though.



Here's the info.





Rim Width: Front: 8" / Rear: 9"

Number of Bolts: 5

Offset: Front: 57mm / Rear: 43mm

Manufacturer Part Number: Fr: 98736213601 / Rr: 98736213801

Rim Diameter: 18

Bolt Pattern: 5x130

Rim Material: AlloyRim

Structure: One PieceRim

Brand: Factory, OEM



Stamping:



8J x 18H2 – ET 57



887.862.136.01







And I think this is the right way to do the wheel calculator. I added a calc that shows the overall diameter in inches. Looks like the rear is over an inch closer to the fender in the rear. Is there a rule of thumb on the clearances? I've all but shredded my PS rears in 7000 miles so now might be the right time to upsize.

WHEEL CALCULATOR.Cayman 18.pdf Size: 64.57 KB  Downloads: 19

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[flash]

with the right tires, yes



i would run a 255-35-18 on the rear and a 225-40-18 on the front

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[rxter]

The wheels have the following tires on them. They appear to be in good shape so I'd like to keep them on if they'll fit, but they look too big.



Fronts: 235/40 18s

Rear: 265/40 18s

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[flash]

the front is a little big but isn't horrible - the rear is really big, and it will very likely throw the abs out, and will definitely mess with your gearing

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[Ryan]

Front hub could be a problem on th 68.

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[rxter]

I'm not even sure that the rear will fit. Various calculators put diameter at somewhere between 26 1/4 to 26 1/2 in. Seems like that might be a bit tight.



Could I leave the fronts and replace the rears with 255/35s? Would that fix the ABS/gearing issue?



I've seen the warnings about the ABS and gearing in other posts, but don't really get it. Anyone care to add a simple tech explanation?

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[wiseman]

I've run 2354018 on the front.........but it depends largely on the tire, they are all different. I have 17'X 9" Et55 Boxter wheels all around for autocross. Fronts sit out perfect, but the rears are a bit inward. ET57's will be worse.

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[flash]

the issue with the abs is the differential between the front and rear diameters - go too far and the abs is disabled and might even throw a code putting you into limp mode



larger diameters will raise the gear ratio, which might help with fuel economy, but will throw off the speedo, and cost you acceleration out of the hole





definitely check the hub diameter to see that it will fit over our hub centers

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