Topic: Sprocket change suggestions

[adamb]

Hey fellas.

I've got a 1981 CB 650 Custom, and I'm wondering about changing the sprockets so that it runs the engine more slowly at highway speeds.  My commute is ~22 miles, ranging from 55 to 75 MPH; as soon as the engine spools up past the ~5800 RPM range, it starts to vibrate more than I care for (running it up in the RPMs is fine if I need the power, running like that for half an hour isn't very nice for my hands.)  I don't seem to want for power, although I wouldn't be surprised if my clutch is is a little weak and needs replacing. 

Not sure what my current sprockets are; I'm assuming they are stock.   What's the suggestion for sprockets?  Front sprockets are cheaper; ~ $20 for an aftermarket high-strength one (whatever) but I'm wondering how many teeth I should change? I haven't figured out the "math" for figuring out how my RPMs will change at a given speed for each tooth I add to the front.

Also, I'm getting ~45 MPG currently, think that'll go down?  Running in lower RPMs *should* help that out, but I'm not sure if it'll require more 'power' and therefore more gas. 

Suggestions?  I love the bike so far, only need a few cosmetic things for it to be running well enough for me, but I'd like a bit more top-speed.

[Hush]

I've been looking at this myself, my 650 (old 79 Z model) has very quick speed around town and pick-up but suffers from "where is my 6th gear" syndrome on the highway.
I know my bike's problem is that it is an ex Police bike, used for short chases around town so geard for that purpose.
I'm thinking of putting a bigger sprocket on the front and a smaller one on the rear, this will detract from my acceleration but will make highway running more enjoyable.
I think I put the formulea for this on the site somewhere, bigger back sprocket=quicker acceleration but more revs on highway (like a trail bike) smaller rear sprocket=lower revs on highway riding.

[Sam Green Racing]

Two more teeth on the geabox sprocket should do it.
Remove the cover before ordering and make sure the larger sprocket and chain run will fit.
Check clearence behind the chain as well as in front.

Sam.