Will a 30 tooth sprocket fit? KZ750 LTD

I decided to investigate the gear ratios of my new-to-me 1981 KZ750 LTD, as they seemed all wrong. Turns out someone has replaced the rear sprocket with a 38 tooth (up from the stock 32). This means I'm running about 5600rpm at 100kph - not good for crusing, and I spend 98% of my time in 5th gear.

The stock gearing has the rpm at 100kph at about 4300rpm, if I fit a 30 tooth rear end that will drop it pretty close to 4000rpm, which sounds like a good number to me. I want to replace the back instead of the front, since it's the wrong size and needs replacing anyway.

I have a 630 chain, and I don't know what the size of a 30 tooth sprocket would be. Would one fit on my rear hub? Or will I need to get a new front sprocket?

Edit: Having said all this, I'm not sure a 30 tooth sprocket of the correct size even exists. But I'm still interested to know.

I can't seem to find a 30T either. I didn't see it at Z1Enterprises or eebbaayy.
JT Sprockets doesn't list a 30T JTR501. I'm pretty sure that size was available fairly recently, in the last couple of years or so, or at least a compatible 30T.

JT Sprockets. catalogue. JTR501

Turns out someone has replaced the rear sprocket with a 38 tooth (up from the stock 32).

Wow. 38 teeth! and I thought I was bad when I found PO had put a 37 tooth sprocket on my rear. ! I bet you were fast off the line :woohoo: I have since gone to a 530 chain and have what would be the equivalent of a 34 tooth 630 sprocket on the rear now and think its a reasonable compromise.

Like Martin I couldn't find a 30 tooth 630 rear sprocket either.

JR wrote:

I bet you were fast off the line :woohoo:

I was - for about half a second before I needed to shift up. I'm in 5th at 50kph and even then I still have plenty of grunt.

My theory is that when the sprocket was replaced last, they looked up the number of teeth and accidentally got mixed up with the KZ750 twin, which I believe has 38 teeth from the factory (and more teeth on the front sprocket too).

I can get the front sprocket for about $20 so it's not the end of the world if I replace that. I'm thinking about going for a 14/32 ratio. I'm staying with the 630 chain for now I think, since the chain is a good RK o-ring chain with plenty of life left.

Sounds like a plan. Saves having to take the rear wheel off and 14/32 is close to the 13/30 you were thinking of.
Let us know how it works out for you.
I have been thinking about trying a smaller rear sprocket on mine also.

I thought I'd check the front sprocket for wear and to make sure it was indeed a 13 tooth before I ordered new sprockets. This is what I found.



The 'guard' has been broken and bent back a little. This doesn't really worry me so much as it is still doing its job. It is very close to the clutch push rod, but not rubbing or wearing on it.

However, there isn't much space here at all, probably not enough for another tooth. Since I've read on this forum a few times that replacing the front sprocket is quite common, is my setup here different to anybody else's? I'm wondering if the damage has changed the clearance in some way,