I have stock 17/42 gearing on my 08...at 70 MPH GPS verified im running 4,000 RPM. I just dropped a tooth in the front to 16/42 and it runs the exact RPM at 70 GPS verified. How is that possible? And yes i counted the teeth on both sprockets to make sure.

The Russians obviously hacked your gps to influence the outcome, either that or the 2% change in the ratio cannot be resolved by your Mark 1 eyeball sensor of the rpm change

Somebody is on drugs

gearing commander says there's a "239" rpm difference at 70mph

70mph - 17/42 = 3827
70mph - 16/42 = 4066

and....

16/42 4000rpm = 68.9mph
17/42 4000rpm = 73.20

Operator error.

Ive had the bike for 2 1/2 years...yes im old and wear glasses but i can still see well enough to know what my speedo and tach read...lol
I had a 15 tooth on the front and the tach read 4,500 at 70 which makes sense. This is the second time i have tried the 16/42 and got the same result i posted both times. I have a hard time believing it was my error twice.

Twice huh?

weird.

I was to lazy to look at gearing commander but Piken has the details. I'm guessing measurement error is the probable root cause. A bit off on the speed and the rpm data and the difference is in the noise

* Last updated by: cruderudy on 6/5/2018 @ 9:52 PM *

Tire wear could do that.

On the same day?

Sure if he also did a tire change on the same day...twice. I'm guessing not but that's my only explanation.

Or if that 17T was really worn, it might be as small in diameter as the new 16T. Twice. Doubt it but that's all I got.

* Last updated by: Rook on 6/6/2018 @ 10:25 PM *