41/18 sprockets

Anyone running 41 rear 18 front sprockets on their KZ650's?
I'm currently running 51/18 and mileage is @28 mpg. 40 mph@ 4000, 50mph @5000, and 60 @6000. Since I got a sportster swingarm (Harley) w/Dyna wheel the KZ rear sprocket doesn't work but considering machining it to use on this set-up. @2.4gl Sportster tank @28mpg ain't too good!! Any idea what MPG I might get at 2.27 instead of 2.83?

Just went out to the shed and counted the old KZ sprocket and got 38 teeth which was 38/16 this was a '78 KZ650 SR was this the stock set-up. I think the book said 41/16 or 2.56 38/16 is like 2.375

I don;t know what model KZ650, tire size, etc. you're running, but you should be shooting for 4500 RPM @ 60 MPH (that's what stock setup runs). 6000 RPM @ 60 MPH is WAAAY high! Ed

For sure!!
Fun in town but SUCKS (literally) on the highway. I got the 18 tooth on the front but that's about it (no more room). finding a 38-42 or so rear with a 2 1/4" hole is the trick. KZ runs 80mm and Harley goes down to 49 w/2". I figure I will have to get one "custom-made" but just want to make sure I'm on the right track.

Try www.gearingcommander.com when doing ratio calculating.

Try Sprocket Specialists for sprocket availability. Keep in mind that fuel mileage suffers if you gear too tall also.

FYI....stock sprockets are 16 / 42 for KZ650C1 using 18" rear wheel. Ed

Are you getting 60mph at 4500 with these gears? I located a sprocket w/ 45 teeth bolt on, $50 chrome . This would get me a heck of alot closer.(2.5 final drive)running a 16x150x80 rear tire not sure if bigger is better on reartire or not. I started out at 16 tooth front X 51 rear, now at 18 tooth front X 51 rear or 3.18 to 2.83.
this was a huge improvment so i think 2.5 or 18 front X 45 rear would be real close to where I want to be.
I tried that gearing commander but didn't have much luck.

So I take it you no longer have any sort of cush drive
on your bike now?
Hows that working out?
I plan to run a Harley wheel also but really think I should
keep the cush drive somehow....?

gdubya wrote:

Are you getting 60mph at 4500 with these gears? I located a sprocket w/ 45 teeth bolt on, $50 chrome . This would get me a heck of alot closer.(2.5 final drive)running a 16x150x80 rear tire not sure if bigger is better on reartire or not. I started out at 16 tooth front X 51 rear, now at 18 tooth front X 51 rear or 3.18 to 2.83.
this was a huge improvment so i think 2.5 or 18 front X 45 rear would be real close to where I want to be.
I tried that gearing commander but didn't have much luck.

Yes; with the 16/42 sprockets mine KZ650 turns 4500=60mph; 6000=80mph; 9000=120mph (approx). If the outside diameter of the tire your running = the outside diameter of a 4.00 x 18 (stock '77 KZ650 size) or roughly that of a 120/90 18 tire you should get similar results. If the outside diameter of your tire is larger your rpm will be lower for a given speed, if your tire diameter is smaller the rpm will be greater for the same speed. I would compare your tire diameter to stock (if you plan to keep that size tire) before selecting sprocket sizes. Ed

Genius wrote:

So I take it you no longer have any sort of cush drive
on your bike now?
Hows that working out?
I plan to run a Harley wheel also but really think I should
keep the cush drive somehow....?

I set it up similar to my '92 sportster ...no cush on this bike (that i am aware of). I have 22,000 on the sporty w/ one sprocket and chain change. Torque is an issue I'm sure with the KZ engine and the one real slammin' test I did I got a little clutch slip 2nd to 3rd. 4th to 5th was tight.
My son in law passed me the other day a couple of times and really we haven't logged enough miles on the harly-saki to tell if it is self destructing or not. harley did start using a cush a couple of years ago but until he gets a few more miles on this bike I will pass for now.

650ed wrote:

gdubya wrote:

Are you getting 60mph at 4500 with these gears? I located a sprocket w/ 45 teeth bolt on, $50 chrome . This would get me a heck of alot closer.(2.5 final drive)running a 16x150x80 rear tire not sure if bigger is better on reartire or not. I started out at 16 tooth front X 51 rear, now at 18 tooth front X 51 rear or 3.18 to 2.83.
this was a huge improvment so i think 2.5 or 18 front X 45 rear would be real close to where I want to be.
I tried that gearing commander but didn't have much luck.

Yes; with the 16/42 sprockets mine KZ650 turns 4500=60mph; 6000=80mph; 9000=120mph (approx). If the outside diameter of the tire your running = the outside diameter of a 4.00 x 18 (stock '77 KZ650 size) or roughly that of a 120/90 18 tire you should get similar results. If the outside diameter of your tire is larger your rpm will be lower for a given speed, if your tire diameter is smaller the rpm will be greater for the same speed. I would compare your tire diameter to stock (if you plan to keep that size tire) before selecting sprocket sizes. Ed

Ok thanks a bunch Ed!
So I have to correct two wrongs in my "design". smaller tire plus bigger sprocket. i'm off tomorrow and will do a side by side. I had a 17X180 X90 for mock-up but when I went to put power to it i could'nt get enough clearance in the swingarm(to far forward and no room backwards) so used the 16"wheel with better results. man! i wonder what my final ratios were? I know before I put the 18 tooth front sprocket it was one fast little motorscooter. 80 at 6000 would be too cool!!! I might try that 17" wheel again.
Checked the tire size...This is a KZ650 1978 "D" and the rear tire is a MT90-16T gots to have a lot to do with the 16 front 38 rear sprockets man that 45 tooth rear sure sounds like it will help on top end...