09 Gmc 2500hd Speedometer

[Ridgerunner30]

I have an 09 GMC 2500HD 4x4 6.0 373 with factory wheels and 245 75 16 factory tires. The tires are Bridgestone V-steel highway tires. The speedometer, as compared to my Garmin GPS, reads about 1 to 2 mph fast at 60 mph. When my speedometer says I am going 60 mph the GPS says I am going 58 mph. The odometer reads fast as compared to the mile markers on the interstate. The odometer registers a mile before a mile is complete. When you look at a tire size comparison program it appears that 265 75 16 tires would result in my speedometer and odometer to be much closer to accurate. Have any of you noticed anything similiar?

[Ape0r]

IIRC, SAE spec is only +/-4%. Not very tight at all - means you could be up to 4000 miles off for every 100k, and still be within spec!

[Zembonez]

Odometers are not 100% accurate for sure, In fact, Honda is in a big suit over theirs being too far off... Mine in the truck reads about 2MPH off and the one in my Scion reads on the money using my Garmin as a reference. My Explorer is about 6 miles off at 70.