What size rear sprocket??

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16 Sep 2006 13:04 #77217 by Fourtoes
What size rear sprocket?? was created by Fourtoes
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.

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17 Sep 2006 04:45 #77359 by OnkelB
Replied by OnkelB on topic What size rear sprocket??
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/

77 KZ 650 B1, 82 GPz 1100 B2.

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17 Sep 2006 06:27 #77375 by N0NB
Replied by N0NB on topic What size rear sprocket??
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 >>

Nate

Nates vintage bike axiom: Riding is the reward for time spent wrenching.
Murphys corollary: Wrenching is the result of time spent riding.

1979 KZ650 (Complete!)
1979 KZ650 SR (Sold!)
1979 KL250 (For sale)
1994 Bayou 400 (four wheel peel :D )

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17 Sep 2006 15:45 #77470 by Fourtoes
Replied by Fourtoes on topic What size rear sprocket??
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,

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18 Sep 2006 06:46 #77621 by mariozappa
Replied by mariozappa on topic What size rear sprocket??
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.

1977 KZ650C1
and the KZ650/KZ750 Conversion ;)

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