Floating sprocket at the wheel?

[John in CR]

The motorcycle I hacked up for parts had a floating sprocket at the wheel. I assume that's to counter flex in the frame under high load. Is that something we need to consider, or is a perfect chain alignment via an adjustable motor mount sufficient? Does it make a difference if the motor is mounted on the swingarm?

 

[LI-ghtcycle]

I assume you mean the rubber insert that cushions the chain inputs to the wheel? I think it might be less needed with our stuff since our power is more linear than a gas engine, but I am really curious to hear the answer too! Would make sense to include it if it is easy enough to use it.

 

[John in CR]

I assume you mean the rubber insert that cushions the chain inputs to the wheel? I think it might be less needed with our stuff since our power is more linear than a gas engine, but I am really curious to hear the answer too! Would make sense to include it if it is easy enough to use it.

On the motorcycle wheel they weren't rubber, but more like a thin metal leaf springs that allowed the sprocket to "float", so it wasn't fixed rigidly to the plane of the wheel. I guess chain and wheel don't stay in a straight line, so this allows the sprocket to always follow the chain. I suspect our bikes could flex even more.

 

[LI-ghtcycle]

OIC, on my motorcycles I don't think I ever saw something that would allow the sprocket to move side to side, but I did remember there being a massive rubber "hub" section that would absorb shock from fore and aft movement of the chain onto the rear wheel's hub so that if you slammed it into gear and dropped the clutch hard, it would take some of the shock so that the chain & sprockets didn't as much.

 

[Thud]

Rubber mounted sprockets were very common. Apptlyl titled "cush sleeves". It softens the shock loading on the entire drive line.
All the suzuki's in the garage have the rubber in the rear hub.
All the more modern stuff has a heavy rubber cush built into the clutch. you can't even see it as it is rivited between the gear & clutch basket. Shocks a lot of guys when upgrading to an aftermarke clutch basket to find squishy rubber in their monsters.

We discussed this in length in the Sturmey archer 3-speed thread....I still think a proper cush on the sprocket could really ease the shock loading on the chain & internals of of the hub.

 

[Hillhater]

Floating sprockets ( as distinct from "Cush Drive" sprockets ) are common on Karts (219 chain) . They mount much like floating brake rotors with sleeves on the mounting bolts. Claimed to eliminate "binding" in the drive chain from chassis flex, and hence reduce power loss.

 

[John in CR]

I forgot about one floating sprocket on a bike, and that's the input sprocket on my Nexus3 geared hubs. It leads me to believe even more that we need them on our bikes. Something flexes and the drive and driven sprockets are no longer on the same plane.

 

[Hillhater]

Minor misalignment is not a big issue on a bike with the typical long chain runs between crank and wheel hub particularly with the relatively small sprocket sizes and type of chain used.
Remember, bike chain is intentionally misaligned when using derailleur gearing.
Compared to motor bike chain (#520) and the larger sprockets and higher power loadings, where alignment is more critical.
A Kart using 219 chain on large 80+T sprockets , and short link counts (110 typically), can completely destroy both sprockets and the chain in a few minutes, if the alignment is bad.