Sprocket change, gear ratio

I have a '79 KZ1000 LTD that I mostly ride on highway. Don't care about get up and go from lights,as fun as it is, but more about getting rpms down on highway. Right now I have 15/33 530 setup which gives me 2.2:1 ratio. I ws looking at changing to 16" front sprocket for 2.06:1 ratio or even 16/32 for 2:1 ratio. I find that rpms are quite high at cruising speeds.
I am assuming there is enough clearance at front for 16 tooth, is 2.06:1 or 2:1 an acceptable ratio? Are there any problems I may encounter?

What do you call high RPM?

I geared my KZ650 really high, with 13 & 26 for a ratio of 2.00 to 1. (630 chain) It was sweet at speeds up to about 65 MPH, but if you tried to run 80 or 85, the engine just did not have the torque to push through the air at that speed without laboring. The throttle would open quite wide, especially if there was a headwind. Gas mileage was fantastic at low speeds, but would really suffer as you went faster.

Now I experimented with numerous different ratios and finally settled on 14 and 33 for a ratio of 2.36. This is about all my 650 can handle without laboring & loosing gas mileage. I would estimate that your KZ1000 is at an optimium ratio right now with the 2.2. Yes, the engine is spinning pretty fast, but the bike is so much more responsive and the gas mileage is better than when it was geared so high. In other words, you can go too far with the gearing, trying to lower the RPMs.

Hope this helps.

I did the #s and you're really pushing it as is. I have almost the same ration on my bike and it is a BUILT 1150 pushing some serious HP. I have to slip the clutch quite a bit to get it rolling from a stop. You will start to destroy clutches and you will not have ANY passing power unless you shift down to 2nd. I would say that i am at the absolute limit on my 1150cc bike. Our "Primary" reduction ratios are identical at 1.73:1 our first gear however is worlds apart. I have a 2.64 1st gear while you have a 3.17. This will give you a little easier start from a dead stop than I have. But our 5th gears are also a mile apart. I have a 1.04 while you have a 1.22 5th gear. This gives you a bit more room to play with than me, but I am running a Final reduction ratio of 4.00:1 and I have to down-shift to second gear at 65MPH to have any real passing power. You also have to take into consideration your fuel consumption curves and HP/Torque curves. At 4000 RPM you consume as mush fuel per minute as you do at 8300. On your bike the lowest fuel consumption is at 6600RPM at 5000RPM it's 5% higher and at 4000RPM it's 7% higher. The best RPM for that motor on the highway is between 5800 and 7100. You also have the highest available torque at those RPM.


Edit: talking about the chain reduction ratio means little when you have to take into account all the other reduction ratios. My chain ratio is 2.222:1 which puts me into the final ratio of 4:1. If YOU got to 2.22:1 you will be at 4.68:1 in final ratio. this is what gives you a bit more wiggle room. But I also have about 30+ more HP than you do.

WABBMW wrote:

I geared my KZ650 really high, with 13 & 26 for a ratio of 2.00 to 1. (630 chain) It was sweet at speeds up to about 65 MPH, but if you tried to run 80 or 85, the engine just did not have the torque to push through the air at that speed without laboring. The throttle would open quite wide, especially if there was a headwind. Gas mileage was fantastic at low speeds, but would really suffer as you went faster.

Now I experimented with numerous different ratios and finally settled on 14 and 33 for a ratio of 2.36. This is about all my 650 can handle without laboring & loosing gas mileage. I would estimate that your KZ1000 is at an optimium ratio right now with the 2.2. Yes, the engine is spinning pretty fast, but the bike is so much more responsive and the gas mileage is better than when it was geared so high. In other words, you can go too far with the gearing, trying to lower the RPMs.

Hope this helps.

What is your final reduction ratio on your 650 with the sprockets you are running right now?

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.

WoW At that RPM you are at about the peak of your fuel consumption.

xxsierraxx wrote:

I have a '79 KZ1000 LTD that I mostly ride on highway. Don't care about get up and go from lights,as fun as it is, but more about getting rpms down on highway. Right now I have 15/33 530 setup which gives me 2.2:1 ratio. I ws looking at changing to 16" front sprocket for 2.06:1 ratio or even 16/32 for 2:1 ratio. I find that rpms are quite high at cruising speeds.
I am assuming there is enough clearance at front for 16 tooth, is 2.06:1 or 2:1 an acceptable ratio? Are there any problems I may encounter?

If your rear tire circumferance is 79", going to a 16T CS sprocket would put you at 3954RPM @60mph.

Gearcalc is downloadable and very handy program to have.

otakar wrote:

I did the #s and you're really pushing it as is. I have almost the same ration on my bike and it is a BUILT 1150 pushing some serious HP. I have to slip the clutch quite a bit to get it rolling from a stop. You will start to destroy clutches and you will not have ANY passing power unless you shift down to 2nd. I would say that i am at the absolute limit on my 1150cc bike. Our "Primary" reduction ratios are identical at 1.73:1 our first gear however is worlds apart. I have a 2.64 1st gear while you have a 3.17. This will give you a little easier start from a dead stop than I have. But our 5th gears are also a mile apart. I have a 1.04 while you have a 1.22 5th gear. This gives you a bit more room to play with than me, but I am running a Final reduction ratio of 4.00:1 and I have to down-shift to second gear at 65MPH to have any real passing power. You also have to take into consideration your fuel consumption curves and HP/Torque curves. At 4000 RPM you consume as mush fuel per minute as you do at 8300. On your bike the lowest fuel consumption is at 6600RPM at 5000RPM it's 5% higher and at 4000RPM it's 7% higher. The best RPM for that motor on the highway is between 5800 and 7100. You also have the highest available torque at those RPM.


Edit: talking about the chain reduction ratio means little when you have to take into account all the other reduction ratios. My chain ratio is 2.222:1 which puts me into the final ratio of 4:1. If YOU got to 2.22:1 you will be at 4.68:1 in final ratio. this is what gives you a bit more wiggle room. But I also have about 30+ more HP than you do.

No way does the motor consume as much fuel at 4000 as it does at 8300 RPM :ohmy:

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

otakar wrote:But I also have about 30+ more HP than you do.[/quote]

So you're saying you have about 95 at the rear wheel?

Looks like there's more to consider than just the ratio difference. I would have thought, and obviously I did, any percentage reduction or increase in gear ratio woould translate to same reduction in RPM. Guess not. At present I am approx 4000 RPM at 100K (60mph) with plenty of power to accelerate and pass. And I am not sure that my speedo is correct, feels more like 90k. I figured that if I went from 2.2 to 2.06:1 I would likely end up around 4k rpm at a true 100k and still hsve lots of room to accelerate and pass etc. But maybe there will be no real benefit with mileage etc, so perhaps leave as is.