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      11-15-2012, 12:40 AM   #1

Drives: 2011 M3
Join Date: Sep 2011
Location: Toronto

iTrader: (0)

Major Speedo Error


Today I thought that I was going a little slower than was indicated and decided to check with GPS. Mind you its only an iPhone app, but it can't be off that much. I checked and my jaw dropped. Going indicated 80km/h GPS showed 73km/h. Going 140km/h GPS showed 129km/h. Thats 9%!!!

I just switched to 235/40/18 winter tires on OEM winter package rims - they have at least 60% thread left. My summers are 245/35/19F and 264/30/19R.

The diameter for the tires are:
235/40/18 - 25.40"
245/35/19 - 25.75"
265/35/19 - 26.30"

What could be wrong? Can it be fixed at the dealership through programing?
Where do our cars pick up the speedometer reading front or rear tires?

Thanks in advance.

Last edited by Superfly_M3; 11-15-2012 at 02:05 AM.