Changing gear ratios (rear sprocket) on KZ650

Has anyone ever used a smaller rear sprocket on a KZ650? Mine is running at nearly 4500 RPM at 70mph. I was thinking that I can change the rear sprocket to get the RPMs down. Anyone have any advice on this idea? I have a '78 KZ650 with a 42t rear sprocket.

The front sprocket is cheaper than the rear, and going up one tooth on front equals approximately 3 teeth on the rear. Buy a front sprocket one tooth larger than your current one and see if you like it better. There will probably be enough adjustment with your chain adjusters to take up the slack, assuming your chain and sprockets are good.

Post edited by: steell, at: 2006/02/06 14:20

It sounds like your gearing is low to start with, my bike runs 58mph at 4500 rpm. I have stock gearing too. What is your front sprocket now?
Stock is 16 front - 42 rear.

Post edited by: OKC_Kent, at: 2006/02/06 16:04

Steell is right. Better to change the cheaper front one and it is far simpler of a task than swapping out the rear sprocket. You will find that your acceleration off the line will suffer and you might have to bang it down a gear to 4th to pull out to pass on the highway if it is a bone-stock 650.
Cheers-Colin

Apart from everything being said so far being correct, a 38T rear sprocket for a 750 Twin is a direct bolt-on to the 650 sprocket hub - the center hole is slightly larger, but the bolt holes line up perfectly.

I´ve been running the 38T rear with a stock 16T front on my 650 for a couple of years and have been very happy with it. It will slow acceleration a bit, but I think the benefit on the highway is worth it. Actually think the rear is easier to change too, but maybe that´s just me.

Thats it? Hell! My 305 is up around 6000RPMs at 60mph!

Yea, I think the 4500rpm @70 is a mistake. Stock gearing is between 5000-5500rpm at 70mph depending on tire sizes and tach/speedo variations.

TLH101 wrote:

Has anyone ever used a smaller rear sprocket on a KZ650? Mine is running at nearly 4500 RPM at 70mph. I was thinking that I can change the rear sprocket to get the RPMs down. Anyone have any advice on this idea? I have a '78 KZ650 with a 42t rear sprocket.

Terry, are you sure you're doing 4500rpm@70? I would think that's pretty good. Look at what the other's have posted w/their bikes. "58mph at 4500 rpm", "6000RPMs at 60mph", I'm doing 5K@70, with my twin, and I thought that was good. I went up to the 17T on the front sprocket and I'm quite pleased as it doesn't seem to have taken anything off the lowend.
Ron

Post edited by: ronjones, at: 2007/06/20 16:20

I think 4500 is low too,,:laugh: :woohoo: . I went up 1 tooth on the front with mine and get 5K @ 70 too and once in a while take off in second from a stop at a stop light with no problem at all. I'm thinking about dropping to a 40 on the rear too but I'm not a performance minded individual either.. :laugh: :laugh:
Ride safe.

ronjones wrote:

TLH101 wrote:

Has anyone ever used a smaller rear sprocket on a KZ650? Mine is running at nearly 4500 RPM at 70mph. I was thinking that I can change the rear sprocket to get the RPMs down. Anyone have any advice on this idea? I have a '78 KZ650 with a 42t rear sprocket.

Terry, are you sure you're doing 4500rpm@70? I would think that's pretty good. Look at what the other's have posted w/their bikes. "58mph at 4500 rpm", "6000RPMs at 60mph", I'm doing 5K@70, with my twin, and I thought that was good. I went up to the 17T on the front sprocket and I'm quite pleased as it doesn't seem to have taken anything off the lowend.
Ron<br><br>Post edited by: ronjones, at: 2007/06/20 16:20

I agree with the above. My SR 650 turns 5300 rpm at 70 mph.
I posted my experience about changing my 16-41 to a 16-40 ratio last spring. I'd be pleased to get 4500 rpm at 70 mph!

Here's the link to my post:

kzrider.com/component/option,com_joomlab...w/catid,5/id,123898/

I'm running 16/42 combo and tac out at about 5,800rpm @ 70mph.

If you have Excel on the top of this picture you can copy the link, and input your gear, tire, and sprocket information, and have fun playing.

www.cunnington1.freeserve.co.uk/gearing_v12.xls

I've previewed it, and posted the link here. This computer I'm using doesn't have Excel, so I can't check to see if it works.