Sprocket change, gear ratio

WABBMW wrote:

My Primary reduction ratio = 2.55 (27/23 x 63/29).
5th Gear ratio = .88 (21/24)
Sprocket reduction ratio = 2.36 (33/14)

Therefore the Overall Drive Ratio = 5.30 ( 2.55 x .88 x 2.36 )

With a 140/90-16" rear tire the engine is running about 4,600 at a true 60 MPH.

Yeoww.... I put a 16/32 on my 750 twin and it turned 3600 @ 60. Ran good, but the twin is a lower RPM engine with wider torque curve. I ran that ratio for 25 years.

In my build (piston kit, head/valve work, camshafts and degreeing and tire circumferences), I gave up top end speed for umphka (acceleration)...

As depicted in the gear calc program and in comparing to riding mph & rpm, pretty much dead on...

NOTE: Acewell tach +/-200rpm, mph +/-2mph... Fairly accurate in any system...

Note 2: I also went 2 up on the rear sprocket...
Gear ration went from 2.33 to 2.46

5th gear, difference of 20... 70mph = 5000rpm
4th gear, difference of 15... 70mph = 5500rpm

@ 106 miles on the nose I hit reserve...
1978 KZ1000-A1 tank.... 4.4 gallon but not 100% sure.
~ 31 miles per gallon if calculating 1 gallon reserve...

Just the way it works!

with the stock 15/39 setup and a 630 chain,stock rear wheel and tyre,I also run 3500 rpm at 60,but my mileage is a bit over 180 on a 4.1 gallon tank.82 KZ1000 CSR with mild mods.My tach is problematic,but bike has plenty of power at stop lites and while cruising.bj

its a motorcycle,if you want a bazillion mpg buy one of those 50cc mopeds with pedals! :laugh:

or ride a bicycle-or walk.healthier for u anyways.Lol.bj

otakar wrote:

on mine I am turning just over 2900@60 and about 4000@75 And 5000@94

What's your sprocket setup?

This is my gearing on my 1200. I short shift this bike at 2800RPM...get it right up into 5th gear and just roll on the throttle. No wait..not downshift....just pulls clean and crisp with old VM 33 mikunis leaned out with O-6 needle jets and needles 1 clip from full lean.

And my port runners are NOT small I sized them for the fuel injection I have for the bike. The Mics are just there for now so I can ride it and have some fun :woohoo:

18/40-530. I will say that stop and Go traffic is a real pain with this setup.

1.732/1.040/2.222 final ratio 4.002 Tire circumference 79.5"

larrycavan wrote:

otakar wrote:

on mine I am turning just over 2900@60 and about 4000@75 And 5000@94

What's your sprocket setup?

This is my gearing on my 1200. I short shift this bike at 2800RPM...get it right up into 5th gear and just roll on the throttle. No wait..not downshift....just pulls clean and crisp with old VM 33 mikunis leaned out with O-6 needle jets and needles 1 clip from full lean.

And my port runners are NOT small I sized them for the fuel injection I have for the bike. The Mics are just there for now so I can ride it and have some fun :woohoo:

The "J" engine has totally different gear ratios than the 73-79 motors.

1st=2.64
2nd=1.83
3rd=1.43
4th=1.17
5th=1.04

The primary is the same as yours
1.73

otakar wrote:

18/40-530. I will say that stop and Go traffic is a real pain with this setup.

1.732/1.040/2.222 final ratio 4.002 Tire circumference 79.5"

Here's the Gearcalc screenshot on that. I used 77" for rear tire circumferance...might be off a tad


I wish I did a J trans conversion in mine. It will pull that taller gearing no problem. It would love it actually

Here's one with the 79.5 tire...

I use a different program but the #s are the same. 4200=79MPH

Mine is sluggish below 2500 RPM but God help you once you get past 4500revs. When I am on the highway and am doing 60 in Fifth (about 3300) and I downshift to second (about 5700) and punch it, things really start to happen.