deverest

I know this is probably an elementary question, but I want to be certain I am not missing anything.

I have a 997.2 C2, she came with 18" rim/tire setup. I am putting on a 19" setup. Do I need to do anything other than register the new tires in my TPMS system? Thanks all.

Spiffyjiff

i would measure/calculate out so that the new wheel size + tire size circumference is the same and ensure the offsets will work with your model, but other than that...

deverest

How do I calculate this?

Thanks

chris.hanle

Rim plus side wall height must be close to equal. IE 305/30 (30 = 30% is sidewall) so 305 x .30 = 91.5 mm =3.63 inches. 19+3.63 equals 22.63 inches total height. Then compare the two tire sizes. I am doing this on the fly so my calculations may be a little off. At the tire rack there is a calculator in the up sizing wheel section, somewhere.

chris.hanle

I think a comparable size is 295/35 r 18( is just over 22 inches) to the 295/30 r 19.

malexgcab

Wouldn't it be on the safe side if the OP upgrades to 235/19 and 295/19, if he choose to do so since that is the setup for 19's? (I'm thinking of using OEM 19" rims).

chris.hanle

Yes the 295/30 19 are very close to the 295/35 18's and corresponding front tires as well. The 19 will have a slightly larger circumference but I think acceptable with out reprogramming.

chris.hanle

The only other consideration would be rim width. If 11.5 rears then you could go up to 305 (appearance of stretch of the tire around the rim would be less. But 11 inch width the 295's are perfect. Plus there are more options in the 295/30 19 size.

okbarnett

( you should to use 305 on 11.5, but you could use 11" with 305.)
you cant do anything about the height of the tires, you are staying with the factory sizes so its correct, you have to stay with the same 35 front, 30 rear. that will keep the diameter the same.
you can reset your computer tire size info in the menu

7500rpm

Does the C4S or Turbo owner's manual say anything about damage caused by tire diameter variance? Side wall deflection from different tire brands are different and tire pressures could change effective diameter significantly. The differentials are supposed to take care of these differentials, no?

7500rpm

Oops, please ignore me. I was on another subject ....

deverest

Thank you everyone for the great information.

WindyCityC2S

Not about your car, but if I draw a line thru the center of the rim, I have 2 sidewalls. 305/30/19 is a 26.2" tall tire, not 22.6".

deverest

I put 19x8.5 with 235 35ZR 19 on the front and 19x11 with 305 30ZR 19 on the rear.... Michelin Pilot Super Sports

chris.hanle

[Not about your car, but if I draw a line thru the center of the rim, I have 2 sidewalls. 305/30/19 is a 26.2" tall tire, not 22.6".]
Yes this is correct, I was doing the math on the fly and did forget to add the second sidewall height. So around 26.2 should be correct.