Topic: How to determine RPM change with rear sprocket change?

[TimLoon]

One project for the off season is to lower my cruising rpms. Right now my stock '81 cb650c is doing 4500 rpm's at 55 mph. How do i calculate rpm change for 1 or 2 tooth change on rear sprocket.
Thanks, Tim

[Jerry Rxman Griffin aka MuthaF'er]

Increase the front 1 tooth. Better results for what you want plus it's easier. Probably save you ~ 500rpm??

[754]

 1 on the front, usually like 3 on the back..and really easy to change..

[Deltarider]

One project for the off season is to lower my cruising rpms.

Why? If your mirrors are vibrating and become blurry at your favourite cruising speed, I can understand it. When not, I would leave it like it is. You might end up with your mirrors vibrating and blurry at your favourite cruising speed...

[robvangulik]

www.gearingcommander.com lets you try all possibilities and does the math for you.

[Little_Phil]

If just changing the rear sprocket the new rpm = Original rpm (4500) x New no of teeth/Original no of teeth. Therefore if changing from 36 to 34 teeth new rpm at 55 will be 4250rpm.

[1976cb750f836]

Id also recommended the front, its cheaper,easier to go back if wrong, and no chain modification .

[BenelliSEI]

You can also do the math. For an easy example. Say you are running 12/42. The overall ratio is 42/12=3.5. If you go 13/42 the ratio becomes 3.23 so there is a 7.7% drop (3.5/0.27 X100). Instead of 4500RPM, you would be turning 4154RPM.

[TimLoon]

Thanks folks for all the good advice.