245/40/17 instead of 255/40/17 on the Rear of 2001 986 with "Boxster Design" Rims?

[boxst3r]

Hello All,

A friend gave me two lightly used Michelin Pilot Sport A/S Plus with the following size:
245/40/ZR17 91 Y.

currently my 986 rears are using the Toyo R1R 255/40/ZR17 94Y.

The wheels are standard 2001 "Boxster Design" rims - size 17 x 8.5"

Is there any potential issue of using 245 instead of 255?

Many thanks in advance for your advices!

[Topless]

The change in size will result in a slightly smaller diameter rear tire. You will get a slight increase in torque and decrease in top speed. It will also affect your speedo approx 1-2 mph.

Does it matter? The change in diameter probably doesn't but changes in tire compound probably do. If you are currently running Max summer tires on the front and put all season tires on the rear it will drastically affect handling and the rear will tend to step-out easily in corners. This is not ideal as backing into hard objects at speed may result.

[boxst3r]

Thank you Topless!

Excellent point about the different tire compounds. I will make sure not mix-and-match tires.

I am planning to use the donated all season tires for winter (light) and regular street driving...and keep the Toyo Summer tires for autocross/DE uses only.

Just need to find two lightly used Michelin Pilot Sport A/S 205/50/17 or 225/45/17 for the fronts now