Different size tyres front and rear
 

My 2003 Boxster 2.7 came with 235/35/19 on the front and 275/35/19 on the rear when I bought it a year ago. I have just changed the rears and the garage said that I should really have 275/30/19s on the rears.

I did about 10,000 miles on the previous tyres which were on the car when I bought it. I have really struggled to unstick the rear in the dry and even in the wet it handles well. How might the lack of reduced aspect ratio(?) between the fronts and rears affect the handling?


My 997 has 35s on the front and 30s on the rear.

I believe your front and rear tires are close in diameter to each other. If you go shorter on the rear, you will prob need to go shorter on the front due to stability control expecting them to rotate at similar speeds.

Your speedo is effected by the height of tires. You could check what your speedo reads compared to GPS to determine.

I think you are just fine.

275/30/19 is the stock size for a 986. You could probably use either tire without noticing much difference. Handling would be about the same but the car is higher in the rear on 275/35/19. The higher aspect tire is 1" larger in diameter and rotates more slowly than a 30 aspect. Effective gear ratio is also higher so your speedo is probably right now but you are giving up some torque advantage with higher effective final ratio.

I use 235/35/19 for fronts and 265/30/19 for rear and it feels great if my input matters at all.