what happens if you put 285/30/18 instead of 295 on the rear?

[porsche996tt_tpe]

For 295/30/18, the choices are PS2, AD08, CSC2, and others. However, I realize if I go instead with 285/30/18, there's a Federal 595RS-R that is half the price of the usual 295/30/18 choices.

The shop tells me the only thing would be the rims would stick out a little. I'm not exactly sure that he means by that... Can't visualize it. Otherwise, using 285 is completely safe. Is this true?? Any potential issues with the downsizing??

I'm using stock alloy wheels.

Thanks!

D.

[porsche996tt_tpe]

BTW, the 285/30/18 would have smaller diameter than 295/30/18, this would affect the speedometer (showing higher speed than actual) somewhat, correct? Also, would a smaller tire at the rear affect the 4-wheel differential?

Thanks.

D.

[wross996TT]

the 996TT is AWD. If you have different running diameters front to back, you could destroy your diff. You didn't post what you are running in the front. I think the guidance is <3%, but I would keep it to <1%.

[turbo4 me]

With the different diameters, your PSM likely will be kicking in at inappropriate times (even if you don't destroy the diff).

Have you looked at Hankook Ventus V12's? I just put a set on mine at about half the price of the Michelins. Reviews on Rennlist and 6speedonline are mostly positive.

[cannon1000]

I run Continental DW Extreme 285/30/18's in the rear and 225/30/18 in the fronts since they don't make 295's.

The difference in diameter of these two tires is almost zero. Car handles great! Did several AutoX and DE's at Road Atlanta on them. They are great tires.

Don't worry about the difference between 295 and 285 - but as others said the diameter differences of your tires front to back.

[Lemikson]

I run Continental DW Extreme 285/30/18's in the rear and 225/30/18 in the fronts since they don't make 295's. The difference in diameter of these two tires is almost zero. Car handles great! Did several AutoX and DE's at Road Atlanta on them. They are great tires. Don't worry about the difference between 295 and 285 - but as others said the diameter differences of your tires front to back.

 

Hi cannon1000, may I ask you to reconfirm Conti DWs you have (had) on your 996tt? 

225/30/18 does not exist - was this a typo? 

[cannon1000]

I will try to find a close up photo since I no longer have the car. But yes, I believe it is a typo and should be 225/40/18 not 225/30/18