ninjabones

After I installed the kumho Ecsta MXs (shaved to 6/32") 235/40/18 and 275/35/18, I had serious speedo error (about 8 mph above actual, as indicated on my GPS). Looking now for new tires (those MXs wore quickly... 10 track days and about 2,000 street miles). Wondering what the stock 993 tire diameter is. Definitely don't want a taller tire than stock, as the stock gearing is already too tall. Tires I'm looking at now will be 25.39 in. up front (818 revs/mile) and 25.55 in rear (813 revs/mile). Difference is less then 3% so shouldn't cause any ABS issues. Thanks for feedback.

Bill Verburg

There were 4 different stock rear tires used
245/45x16 24.6 844
255/40x17 25 834
265/35x18 25.3 821
285/30x18 24.8 836

I don't know that they changed the speedometer in any way for any of these so one should expect that most speedometers will be off to a certain extent

as you can see the 245/45x16 is shortest and 265/35 is tallest

if the 16 is used as a base then 275/35x18 will have ~4% lower speedo reading

Personally I like 225/40 & 265/35 x18 or 235/40 & 265/35 x18 but could see where some might like 245/35 & 285/30, they will be a tight fit though.


keep in mind that as the spread gets increasingly big, biased to the back, understeer becomes a bigger problem. Adjustable sways and different spring combos can help but only so much.