wheel offset question...
 

Friends- Interested in using a winter wheel/tire setup for my 2017 C4S. Porsche calls for using 8.5 X 20 and 11 X 20 wheel widths with offsets 49 front and 56 rear. I have those wheels but the offsets are 51 front and 52 rear, so 2mm different for the fronts and 4mm different for the rears. Anyone see any potential issues with using these wheels? Clearance is not an issue.


Original wheel/tire: Front 8.5X20/49, 245/35/20 Rear 11.5X20/56, 305/30/20
Suggested winter: Front 8.5X20/49, 245/35/20 Rear 11X20/56, 295/30/20
What I have: Front 8.5X20/51, 245/35/20 Rear 11X20/52, 295/30/20

For the fronts:
Compared to your existing (not P recommended) wheel, this winter wheel will have an inner rim which is 2mm closer to the suspension strut. The outer rim will poke out 2mm less than before. No speedometer error and no ride height difference.

For the rears:
Compared to your existing (not P recommended) wheel, this winter wheel will have an inner rim which is 10.4mm further away from the suspension strut. The outer rim will poke out 2.3mm less than before. You will have a slight speedometer error .88%. Ride height will be 3mm lower.


Looks like both will fit. To be sure eyeball the current (existing Wheel) strut clearance in the front to be sure that it is at least 2mm away from the strut.

991Carreradriver- thanks for the reply. I'm assuming you used the tire rim calculator on the website, I saw that also. Not worried about clearances, more just looking for education. Tire guy at discount tires said to be careful changing offsets even a few mm, something about having an effect on 4 wheel drive systems. Initially was worried about the smaller overall circumference for the rear wheels but if Porsche is recommending a 295/30 for winter tires instead of the original fitment 305/30 then that part must be ok.
Any comments are appreciated. Thanks again.

this calculation tool tells you before and after in/out/rolling circum / speedo affects comparing two tire/wheel sets but no tool can show whether an alt wheel combo will hit a partic car's strut, calipers , fender lip or plastic wheel well liner - when turning / going straight ahead.... when static or when rolling

http://www.willtheyfit.com/#isPage=1