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For almost the entire time I've had my FJ (15+ years), I have had 305/65/17 ProComp Extreme AT tires. I've had 3 sets, with each getting at least 90,000 miles. Over the years on long trips I would check the odometer reading against the mile markers on the highway and GPS. Consistently, over probably 1,800 miles of testing, the odometer would read 3% low versus the mile markers and GPS (which consistently matched each other). A few months ago I got 285/70/17 Mickey Thompson Baja MTZ tires. I couple weeks ago I drove from Los Angeles to Washington, DC and going through eastern Colorado and Kansas I decided to check what the new tires were doing (because there is nothing else to do while driving through Kansas...). I tested for 100 miles in Colorado and 400 miles across Kansas. Consistently the new tires were making the odometer read 5% lower than the mile markers and GPS. What is interesting is the 3% difference mathematically matches the difference between the stock tires and the ProComps, but the new tires are only slightly bigger than the ProComps (an additional 1.01% in circumference), but in reality cause an additional 2% change in the odometer reading.

Over the course of 300,000+ miles with oversize tires on my FJ it means I have actually driven over 9,000 miles more than the odometer indicates.
 

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Not sure about the odometer but for the speed, stock tires at 60mph read a little less than 2mph high, 275's on the money, 285's about 2mph low. Checked with GPS.
 

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265/75/16 tires - 60 mph on speedometer, 59 mph GPS, 59 mph traffic exit sensor...

 
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