number of teeth on sprocket

[Anonymous]

I have a 1980 GS750E and I installed an aluminum swing arm off a 1980 GS1100, along with the rear wheel. The original wheel is an 18, with 41 teeth on the sprocket. The wheel from the 1100 is a 17, and has 42 teeth. (this is the wheel that is presently on the bike. I need to replace the chain and sprockets, and am looking for advice as to what sprocket with what wheel should I run for the best performance.

[Anonymous]

You will have to do some playing around, The gear ratio is found by dividing the front sprocket teeth into the rear sprocket teeth. For example 41 divided by 14 equals 2.92 for the final gear ratio. The rim size makes a difference due to the larger circumference of tire. As long as you stay close to the original gear ratio, it will be a good starting place. As far as best performance it depends on the application, 1/4 mile gearing is totally different that top speed cruzing. My GS 750 buzzes around 5000 rpm at highway cruzing speed, but runs redline in fifth gear at the end of the quarter mile. Front sprockets are cheap and the best way to finalize your final gearing.

Hope this helps,

Andre

[Anonymous]

Thanks, I quess what i'm wondering is will a smaller gear ratio give me more low end?

[Hoomgar]

It wont really matter. 41 will be slightly taller. 42 slightly shorter. You'll be hard pressed to tell the difference of one tooth on the rear. The front sprocket is a different story.

[Anonymous]

thanks, I think i'll go with the 42 tooth sprocket, as that is what I have been riding with all summer.

[Red_Phil]

The final gearing is
(rear sprocket size / front sprockets size ) x diameter at tire surface
Assuming the same tyre height you could approximate using rim size.

so you used to have (41 / 14) x 18 = 52.7
you'll be getting (42 / 14) x 17 = 51
or (41 / 14) x 17 = 49.8
or if you want closest match (43/14) x 17 = 52.2


SO with what you have you'll get closest to the original gearing with the 42 tooth rear.
The lower this figure is the better the acceleration and low speed on the bike will be, but you'll lose top end speed and have to change gears slightly more often.