Changing Sproket Ratios

[Lancelot]

Has anyone changed their sprocket ratios for higher cruising speeds? My little CZi does not like to cruise at speeds above 90-95 kms and I haveconsiderd changing out the sprocket(s) for a higher gear ratio.

I just counted both sprocket's teeth; the front has 14 and the rear has 35, so the ratio is 2.5. If I were to replace the original front sprocket with a larger one having 15 teeth, the ratio would be 2.333, yielding a 7.144% gain in top speed as well?

I used calculations from this site: http://www.motorcycleanchor.com/katana/Katana_sprockets.html

(( (NewRear/NewFront) / (OldRear/OldFront) ) - 1) * 100 = % change.

Example (using the same numbers as from the sprocket drive ratio examples):

(( (50 / 15) / (47 / 15) ) - 1) * 100 =

(( 3.3333 / 3.1333 ) - 1 ) * 100 =

(1.0638 - 1) * 100 =

(0.0638) * 100 = 6.38

Thus, changing from 47 to 50 tooth rear with a 15 tooth front is a 6.38% change

Also according to this site ratio changes greater than 8% will give "undesirable results."

Has any one changed their sprockets for higher speed and were you successful?

Thanks in advance for any replies

Lance

Edited September 22, 2009 by Lancelot

[PeaceBlondie]

Yes. More teeth on front or less teeth at rear.

[Lancelot]

Yes. More teeth on front or less teeth at rear.

PB, Do you recall the gain on top end speed? Did it significantly effect your low end torque?

Thanks

[thaicbr]

Lancelot its so cheap. couple hundred baht just do it and see if ya like it.

[Lancelot]

Lancelot its so cheap. couple hundred baht just do it and see if ya like it.

Yeah, I think your right CBR, no guts no glory. I think I might test out the theory with a new one tooth larger front sprocket. Should give me a 7% higher ratio and hopefully a bit more top end. I'd like to be able to cruise at 100 - 110 kmh.

[PeaceBlondie]

I've not tried yet. I cruise daily around 115 with bursts to 130. I plan on going the opposite direction.

[Bard]

Normally you don't get a higher top speed, you calm down the rpm thats all. Normally you don't gain any top speed and decrease acceleration by doing so.

The available HP for top speed on a bike is normally on high revs and by gearing it up you can even loose top speed. What people usually do is to do a stage 1, then you get same top speed, faster acceleration but you will always be on higher revs.

If the ride is buzzy gearing it the other way will calm it down, but there is nothing to really gain unless you use wind or downhill to help you get there...

[Lancelot]

Normally you don't get a higher top speed, you calm down the rpm thats all. Normally you don't gain any top speed and decrease acceleration by doing so.

The available HP for top speed on a bike is normally on high revs and by gearing it up you can even loose top speed. What people usually do is to do a stage 1, then you get same top speed, faster acceleration but you will always be on higher revs.

If the ride is buzzy gearing it the other way will calm it down, but there is nothing to really gain unless you use wind or downhill to help you get there...

Bard, thanks for the info. You must be one smart dude because I am reading online exactly what you've said - that higher gearing will not yield higher speed. Now that I think about it, it makes sense in that I had a couple of cars with overdrive and it basically just allowed the engine to cruise at lower RPMs.

Again, thanks

[blakegeee]

Just go one step at a time. Change out the front one first, cheap and dont need to change the chain anyways. If that gets you where you wanted, leave it at that. If you want that change again, than make the rear sprocket smaller but I bet the single front will do. You only have 110cc's, so you still need all the HP you can get.

I just did it on my XR 300 offroad bike. With an offroad sprocket set up, you will certainly gain top speed although I was just looking for lower rpm at cruising speed. All my gears where so close together. First I did the one tooth bigger front and that helped by about 10km/h difference. It was better but still not enough so I then got a new chain and 4 tooth smaller rear sprocket. The gears are spread out way more but I still have lots of torque and I can cruise over 100km/h effortlessly.

Originally I had a 14/46 setup, and now 15/42 but thats a totally different bike keep in mind.

If you happen to be in CM, let me know and I could recommend a Thai guy that is good at modifying small bikes. He'd know the best set up off the top of his head probably. I am sure he could do other performance upgrade so you don't lose your HP when you change your ratio. Unlike nearly all Thai shops, this guy does respectable work.

[Lancelot]

Just go one step at a time. Change out the front one first, cheap and dont need to change the chain anyways. If that gets you where you wanted, leave it at that. If you want that change again, than make the rear sprocket smaller but I bet the single front will do. You only have 110cc's, so you still need all the HP you can get.

I just did it on my XR 300 offroad bike. With an offroad sprocket set up, you will certainly gain top speed although I was just looking for lower rpm at cruising speed. All my gears where so close together. First I did the one tooth bigger front and that helped by about 10km/h difference. It was better but still not enough so I then got a new chain and 4 tooth smaller rear sprocket. The gears are spread out way more but I still have lots of torque and I can cruise over 100km/h effortlessly.

Originally I had a 14/46 setup, and now 15/42 but thats a totally different bike keep in mind.

If you happen to be in CM, let me know and I could recommend a Thai guy that is good at modifying small bikes. He'd know the best set up off the top of his head probably. I am sure he could do other performance upgrade so you don't lose your HP when you change your ratio. Unlike nearly all Thai shops, this guy does respectable work.

Thanks Blakedee!