Gear/Tire Changes vs Speed Calculations Made Simple
Posted by Craig Stumph on
True GPS speed decreases proportional to the % reduction in gearing. This applies to transmission and portal gear lift/reductions. GPS true speed also increases proportional to tire size increase. Speed decreases with tire size reductions.
In the example below we will not talk about reverse because it closely mirrors low range reduction.
Example:
Polaris Turbo with 30" tires moves up to 35" tires. (1- (30/25)) x 100 = 14.29% tire size increase.
Same Polaris Turbo lowers transmission gearing by 21% in low range and 32% in high range. High and low gear changes are additive to low range Polaris turbo transmissions. High range gear swaps apply to high range only and high is unaffected by low range gear changes.
Total Low Range Reduction = 21% + 32% = 53%
Top Speed Stock 30" tire (TSS) = 80 mph
Total Low Range Reduction (TLRR) = 53%
Low Range Reduction (LRG) = 21%
High Range Reduction (HRG) = 32%
Tire Size Increase (TSI) = 14.29%
New Top Speed (NTS)
(1- (HRG - TSI/100)) x TSS = NTS
(1 - (32%-14.29%/100)) x 80 mph = NTS = 65.83mph
Note: If you want your speedometer to read correctly see below.
https://www.proutvparts.com/products/polaris-speeddoctor-speedometer-correction-kit?_pos=1&_sid=912457ff3&_ss=r
https://www.proutvparts.com/products/super-atv-honda-speeddoctor-speedometer-correction-kit?_pos=2&_sid=912457ff3&_ss=r
https://www.proutvparts.com/products/super-atv-can-am-speeddoctor-speedometer-correction-kit?_pos=3&_sid=912457ff3&_ss=r
