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The manufacturer of my tire has a "revolutions per mile" for my tire, so I used that and calculated a mile divided by the revolutions, to get circumference, then converted to millimeters, I think I ended up with 2625 mm... Anyway, it seemed to work, speedo seems accurate. My tire is Yokohama AT G015 in size 285/75/17
Are you using what a tire calculator converts that size to in inches, or what the actual diameter is as it sits on your truck? Go with the actual diameter as it is on your truck, at the tire pressure you’re gonna be running. The tire calculator can vary by as much as an inch between manufacturers.
I’d say don’t worry about what the tire says, or what the manufacturer claims. If you’re dialed in at 2689, that’s what matters. 2689mm/25.4=105.87 inches actually being covered in one revolution. If the speedometer is matching gps, you’re all set.
Convert those inches to millimeters and you are there!
2520 vs 2521, is less than you could accurately measure, it is 0.03%. your speedo has a lot less accuracy than that, so you have nothing to worry about.
Actually in my way home from work speedy was accurate with gps, before speedy was showing about 3 mph less than gps now all is good
