What Rear Tire Size is needed to correct the speedo?

[pauly1]

In addition to ColemanJ table and Pete Aawan's explanation, tire wear can account for up to 2% change in speedo/odometer indications. Pete included in his description of the many variables: it's the rolling diameter that impacts accuracy. If you have a heavy load (big person, 2-up, lot's of cargo, etc.), the tire will squat to carry the load, dependent, of course, on tire pressure. (Both the F3 and RT use the same tire; the RT weighs >200#/91kg more than an F3-S.) That squat changes the rolling diameter of the tire. The rolling diameter affects both speedometer and odometer readings. A change of 3/8"/10mm in the height of the axle centerline to the ground causes the speedometer to read fast by 5%, or 4 mph @ 65 mph: nothing has changed but to load the vehicle and perhaps tire wear on an experienced tire.

 

[BajaRon]

Ron, mines an 2018 F3L

It's hard to believe that there would be that much difference bike to bike. We've found the Altimax to be very true to size, tire to tire. It's a quandary for sure.

 

[Cobranut]

Not sure about other years, but I was able to adjust my speedometer with BUDS Megatech on my 2014 RSS. It was off 2-3 mph with stock tires.

View attachment 212351 off 2-3 mph with stock tires.

Not sure I want to be selecting tire size based on speedo accuracy.
BUDS allows easy adjustment. Interestingly, changing the speedo correction setting from the factory value to zero, changed my speedo from 5% high to around 1% high, with the worn out original tire.
When I install my new tire I'll re-calibrate to read slightly low, so tire wear will bring it in over the life of the tire.

 

[T.P.]

Is a couple miles difference in speed between your speedo and your GPS really worth worrying about?
Chances are you're not going to ride the posted speed anyway, and if you do, you will probably get run over by everyone passing you!
T.P.