Sprocket Size and Removal of Chain Tensioner

[bakaneko]

Hello! I am using the stock 44T sprocket that came with my 2-stroke kit. I cruise at around 20mph and can hit 27 at high revs. While this is great, I am a lighter rider, can do away with some of the torque, and would like more speed (~27 cruise and +30 top speed). I guess this means I need to get a smaller sprocket.

Additionally, I would also love to get rid of the chain tensioner as this seem to add friction. Any recommendations on the sprocket size that I should get (36, 32, 30T)? And, do you know at what sprocket size will there be no need of a chain tensioner? Also, can I use my old bolts and rubber J clamps for a smaller sprocket or do I have to buy a specific rubber J clamps for the smaller sprocket?

I read a lot of people happy at 36T and 40T. I saw one guy say that he was able to do away with the chain tensioner at 30T. But, I am wondering if that is also possible at 36T. :helmet:

Sorry for the horrendous English...

 

[Timbone]

I run a 41T, which yields a high rev cruise speed of 29 mph. 40T would be OK, too. 44T is a pretty small gear.

 

[The_Aleman]

With a 26" wheel and 44T sprocket, you're at 6K RPM @ 26MPH. Every tooth smaller gains you about 1MPH at same RPM. Hence why 36T is a common upgrade.
You can re-use your ragjoint for a 36T, but you might want to look at getting a hub-mount adapter or disc brake wheel for mounting the sprocket.

If you want to eliminate the chain idler, you'll have to make sure your chainline is just about perfectly straight with minimum sprocket wobble. A halflink may be necessary.
Axle adjusters are a plus!

 

[crassius]

regardless of sprocket size, chain tension can be adjusted by adding spacers to the rear motor mount when needed due to chain stretch

 

[bakaneko]

Thanks for the nice estimation technique. I am looking at the 36T sprocket, which should put me at 28 cruise. I think that is fine and I'll try to eliminate the chain tensioner while making this change...

But, I saw some folks on the forums with as low as 30T sprocket!

 

[The_Aleman]

A friend of mine used to run a 28T with 24" wheel on his reversed-jug chinagirl bike. MotorBicycleRacing and I saw him hit a GPS-verified 55MPH on it a couple times.

Despite his bike having a really tall gear (11.48:1) he was able to take off from a dead stop pretty quickly. I think being a light guy helped a lot there!

When I ran chinagirls I used a 34T. I had to pedal up some hills, but I tend to pedal more often than not, anyway. The cruise speed made it worth it! 20-25 was quiet!

 

[bikejock]

I ran a 44T sprocket on a 24 rim and it drove great on my 4G bike for a while. Was able to hit 30 mph easily on level ground with my 2.5 HP engine. Ran great up until the transmission broke on me thanks to the poor quality of Chinese parts.

 

[Timbone]

30 mph with 24" rim 44T combo would mean very high RPM. Not surprised you had problems.

 

[bikejock]

Yeah. Might have to go with a 26 rear wheel for my cruiser. It had a 26 in the front and a 24 in the back because it had a 24x3 rear tire and a 26x2 front tire to make the bike look like a retro hot rod/chopper.

I was thinking of going from a 4G kit to a 2 stroke so I can modify the engine better for racing. Plus 2 strokes are easier to work on and replace parts when things go wrong.

 

[bakaneko]

Thanks for the inputs. Looking at other threads and this post, it seems like going with a lower sprocket will definitely help with increasing speed, lower cruising revs and thus prolong engine life, and also make it easier to pedal. I went and ordered a 36T sprocket and hopefully I can eliminate the chain tensioner too. :helmet: