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Old 07-08-2014, 12:13 PM   #1
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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?

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Old 07-08-2014, 03:47 PM   #2
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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.
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Old 07-08-2014, 04:40 PM   #3
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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.
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Old 07-09-2014, 03:04 AM   #4
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If you have PSM, making the front taller relative to the rear can cause issues with the traction control.
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Old 07-09-2014, 03:45 AM   #5
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Quote:
Originally Posted by stephen wilson View Post
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.
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Old 07-09-2014, 03:52 AM   #6
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Originally Posted by ekam View Post
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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