986 Forum - for Porsche Boxster & Cayman Owners

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-   -   Another tire question (http://986forum.com/forums/performance-technical-chat/53118-another-tire-question.html)

shadrach74 07-08-2014 12:13 PM

Another tire question
 
So I've been searching the forums and it seems plenty of folks are running wider than stock tires up front on factory 17s. I was wondering if any one had considered trying to correct the factory "built in" speedo error with slightly larger tires.

My calculations show that 225/55/17 and 265/45/17 (255/45/17 would be close as well) would give me a much more accurate speedo (its conservative by about 4 mph on the highway). Has anyone tried this? Will it have affect ABS function?

Topless 07-08-2014 03:47 PM

On a 986 it might work but the 8% loss of torque from effectively up-gearing would overshadow the benefit of a true speedo for me. Tire choices are also somewhat limited in those sizes. I'll pass.

ekam 07-08-2014 04:40 PM

Very few manufacturer make factory 17" tire sizes let alone the sizes that you listed which I'm fairly positive nobody makes 265/45/17. Part of the reason why I went 18"s.

stephen wilson 07-09-2014 03:04 AM

If you have PSM, making the front taller relative to the rear can cause issues with the traction control.

shadrach74 07-09-2014 03:45 AM

Quote:

Originally Posted by stephen wilson (Post 409226)
If you have PSM, making the front taller relative to the rear can cause issues with the traction control.

Good info to have! However, I specifically sought out a non-PSM car.

shadrach74 07-09-2014 03:52 AM

Quote:

Originally Posted by ekam (Post 409186)
Very few manufacturer make factory 17" tire sizes let alone the sizes that you listed which I'm fairly positive nobody makes 265/45/17. Part of the reason why I went 18"s.

True. I have found a few 265/40/17s that should work. This would only be 1.6% difference in diameter and would bring speedo accuracy to within about 2.5mph.


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