Sprocket Size and Removal of Chain Tensioner

Discussion in '2-Stroke Engines' started by bakaneko, Nov 20, 2015.

  1. bakaneko

    bakaneko Active Member

    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...
     

  2. Timbone

    Timbone Active Member

    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.
     
  3. The_Aleman

    The_Aleman Active Member

    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!
     
  4. crassius

    crassius Well-Known Member

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

    bakaneko Active Member

    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! :tt1:
     
  6. The_Aleman

    The_Aleman Active Member

    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!
     
  7. bikejock

    bikejock Member

    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.
     
  8. Timbone

    Timbone Active Member

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

    bikejock Member

    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.
     
  10. bakaneko

    bakaneko Active Member

    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:
     
  11. bikejock

    bikejock Member

    I've thought of going tensionerless on my next in-frame build but that would mean getting a different sprocket size to help get the proper chain slack level. My first 2 stroke bike I had a couple years ago had the kit tensioner & it slipped off destroying a few of the spokes in my rear wheel. Really wish they made these kits so they won't need a tensioner out of the box. To me, it's just another part that could cause problems down the road.
     
  12. crassius

    crassius Well-Known Member

    most of the bike frames are diff lengths - cut rear mount block smaller, then make flat plates to go under it for easy adjustments
     
  13. The_Aleman

    The_Aleman Active Member

    I spose I was lucky when I ran chinagirls, I never had a problem with the kit idlers. Perhaps because I never treated them as a chain tensioner.
     
  14. bakaneko

    bakaneko Active Member

    Guys, I got the new 36T sprocket on from the stock 44T sprocket and wanted to report the performance differences and my thoughts. I know a lot of this would be old news for many but hopefully it will help newer folks decide.

    Rider: light rider
    Terrain: 50% flat, 40% low to moderate hills, 10% difficult hills (suburbs Wisconsin)
    Bike: 26" standard mountain bike at a slightly below average build quality

    44T cruise: 18 to 20
    44T acceleration to cruise: 1-2 sec
    44T max speed: 24 (at much as I want to push the RPMs)
    44T low-moderate hill: 1 mph speed reduction
    44T difficult hill: 2-3 mph reduction

    36T cruise: 24 to 28
    36T acceleration to cruise: 2-3 sec
    36T max speed: 30+
    36T low-moderate hill: 2-3 mph reduction
    36T difficult hill: 5-7 mph reduction and I pedaled (but this is an insane hill)

    Overall, I think the 36T sprocket is definitely worth the sacrifice to hill performance. The acceleration to cruising speed is just a paltry ~1 second longer, and unless the hill is insane I am fine with the speed reduction or helping the motor along a little with pedaling. The other benefit is that the sprocket I ordered seem to be pure steel and did not bend in the rubber mounts unlike the stock sprocket which is slightly bend due to quality. There was some difficult adjusting my tensioner and engine setting to fit the 36T sprocket but its probably more my low mechanical skill than a difficulty per say. The sprocket cost me $15 off of eBay. Here is a picture of the size comparison; sorry for the blurriness. :helmet:

    photo.jpg
     
  15. bikejock

    bikejock Member

    Nice sprocket setup. If you have gears on your bike hills aren't too much of an issue I got gears on my friction drive mountain bike so when I encounter a steep enough incline I just ease off the throttle & pedal up it on a lower gear.
     
  16. aquielisunari

    aquielisunari Member

    I'm having trouble with this. I am fairly new to MBs so I need help understanding how a smaller sprocket size would mean no chain tensioner. I didn't like stock tensioner so I went with an engine mounted tensioner as you can see https://www.youtube.com/watch?v=UqDusg8VNgM . I'm a bigger rider so I went the other way with a 48 tooth sprocket.
     
  17. bakaneko

    bakaneko Active Member

    Sorry, let me clarify, originally I intended to remove the chain tensioner with the 36T sprocket but was unable to do so with the tools and materials available. I have the tensioner on there now. I read a guy do it in another thread who reduce the size of his sprocket. I think the idea is just the smaller sprocket will allow for chain clearance from the engine since the diameter of the smaller sprocket is less. I guess something like the below crude drawing. I just read it once so I guess it wasn't that reliable.

    Untitled.jpg

    Nice bike btw. I want to do a fat tire build in the spring with a big engine.
     
  18. aquielisunari

    aquielisunari Member

    Thank you. Nice graphic illustration. It does make sense. I'll take some more slack out of my chain after I get a master-link for my bicycle's drive chain.
     
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