FWIW: Old to New Tire Roll out vs Speedo Error = 2.5%

[FinalImpact]

For kicks I measured the roll out distance of of NEW and USED tire to see how it impacts speedometer error during tire life. Specifically a Battlax BT023 rear tire inflated but worn into center wear bars and the new tire inflated to the same 37PSI but never ran on the bike.

Used mounted 37PSI:
Roll out: 75.5", wear passed tread bars
Tire OD: 24.03"

NEW mounted 37PSI:
Roll out: 77.375"
Tire OD: 24.63"
Tread bar depth near center: 0.22"

CALCULATED @6000RPM, 6th gear using Measured Tires:
OLD: Speed = 70.50mph, Distance = 1.175miles
NEW: Speed = 72.26mph, Distance = 1.204miles

Moral of the story: Old to new changes Speed by 2.5% or ~1.75MPH at 6000RPM. I thought it would have a greater impact based on the diameter being 0.60" different. Nope!

PS:
New unmounted BT023:
76.625" roll out
Tire OD: 24.39"

Also, 180/55/17 calculates to:
77.9" or an OD: 24.795"

TAG: JJD952 Speed Diameter

 

[FinalImpact]

With all the concern of the speedo being off by 5% and now we add in the tires condition as part of the equation.... Something to think about.

A link on the same topic --> RPM, Gear, Sprockets, Tire = Actual Speed!

 

[mxgolf]

SpeedoHealer would fix that correct? I have that because I changed the front sprocket. I am sure it would work for the tire change also. :thumbup: