Join Date: Apr 2012
Location: 9000 ft. ASL in Southwest Colorado, USA
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Perhaps a more accurate way to describe the different results from various final drive ratios, would be as a performance change, rather than a gain or loss of power.
Power output from a given engine throughout it's operating RPM range doesn't change unless that engine is modified in one way or another, or it's power output is affected by significant changes in elevation and/or ambient air temperature. While many owners have changed to a 15T front sprocket on their CBR250R's, I went in the opposite direction changing to a 13T front sprocket due to the fact that I live & ride at a relatively high altitude (9000 ft above sea level). Every 1000 ft increase elevation causes a loss of about 2.5% of an engine's rated sea level horsepower. And that net decrease in available HP is after the EFI system has adjusted the fuel/air ratio for elevation, or in the case of carbureted fuel systems, after jetting has been adjusted for the elevation change.
For me, changing to a lower final drive ratio with the 13T front sprocket helped to regain some of the bikes performance (acceleration) which was lost to higher elevation.
Former Factory Test Rider/Technician
Last edited by MotoMike; 05-31-2018 at 12:37 PM.