TOPIC:

SO I got hold of some new wheels for my 1979 Z650. They are off a 1982 Z650SR I think. So a smaller 16" rear wheel...yipee. The rear sprocket has just about had it though, the rest of the bits, spindle etc polished up nicely. The sprocket has 38 teeth.

My question is do I replace like for like considering I'm now putting the wheel onto my 1979 Z650? Or will I need a bigger sprocket like the one thats on the spoked wheel thats on at the moment?

Does that quesion make sense? I know there are issues with different teeth numbers etc that have an effect on gear ratios or something. I'm not that technically minded so its a steep learning curve which is bringing great satisfaction with each thing I do.

Thanks for your help in advance.

Most pre-81 650s were born with a 16F/42R gearing - running a smaller rear sprocket (or larger front) will increase the top speed/lower rpms at the cost of acceleration, obviously depending on how small you go, it´s a compromise. Generally speaking one tooth up in the front equals three teeth down in the rear.

I changed from stock 42T to a 38T rear sprocket myself, dropped my 60mph rpms some 5-600 without much acceleration loss.

Here´s a link to some more info on sprockets and drive ratios and how to calculate them:

www.xs4all.nl/~ator0437/gc/

The only difference in gearing between the 650B and the SR is 42/16 vs. 41/16. The 38 T sprocket won't hurt anything as I'm running one on my SR. It dropped the revs at highway speed by about 400 or so.

- Nate >>

So if I put a 42 tooth sprocket on the rear instead of the 38 tooth there shouldnt be any great difference in performance then?

Is that right?

Cheers,

The only difference will be what OnkleB was talking about.
When riding at 60 mph with at 42 tooth sprocket you will be at about 5500 rpms.
And the 38 tooth will make 60 mph at about 4700(?)rpms.
That's my two cents, but I am not running a 16 inch rear wheel either, so I don't know if that will make any difference.