Given DTH numbers, am I overlooking something? I went to Bridgestone's website and it's showing much lower numbers for my tires (601 and 648). Or is this a different number? Images say OD (outer diameter)? Or is that a measurement from top to bottom (12 to 6) and I have to measure the outer diameter in a clock method, from 12:00 all the way around the entire tire back to 12:00; approx 77 inches, etc.Actual tire circumference. That's something measured on the tire, not provided by most manufacturers. 1967mm is 77 inches. You have to measure the outer circumference of the specific tires you're using to update the information in Woolich to account for that.
UPDATE: Just measured my tires outer diameter using a fiberglass (non-stretch) tape measure and measured 74 inches front, 80 inches rear. Converted, that equals 1879.6 (1880mm) Front and 2032mm Rear. I believe my buddy input "standard" sizing, which may or may not be close to the current diameters of my Bridgestone S22s. To be determined. And interesting enough, I will remeasure at the end of my tire lifespan to see how great the difference in diameter is when worn down.
Given different measurements, how does this effect the speedometer in mph? Say, if the inputted data in mm is off by 1/2 inch, 1 inch, 3 inches, etc? Is it a factor like, off by 1/2 mph per every 1 inch or something? Or off 1 mph per every inch the data is incorrect? Just curious if anyone knows this or has tested this theory.