Duel rear sprockets?

[Umbre]

I've been thinking about getting a second rear wheel so I could swap ratios (and maybe thicker knobbies) relatively easy. But while looking for wheels I started thinking about the old cub 50s with their duel hodaka rear sprockets and started wondering how possible it might be to retrofit a modern 125 with one or something similar. I like the stock ratio for commuting and a decent chunk of trails but it would be nice to have an available low ratio for trips that are a bit more demanding (Its very steep here to put it lightly). Is this doable?

 

[oldskool]

Anything is possible given enough time money and drive. You will obviously need to also lengthen the chain for the larger sprocket. I suspect you might be better off just changing to a smaller front sprocket as well as a larger rear sprocket when you want to climb trees There are limits if the radius of the front sprocket gets too small the chain will be subject to stress early wear and be more prone to failure.

 

[m in sc]

you also need to get a dished larger rear sprocket and be able to center it over the smaller rear sprocket when its 'trail time'. My 67 kawasaki has that exact setup from the factory. its neat but honestly, a huge pain in the ass. It has 4 bolts that go thru the smaller sprocket with machined recesses on the back side, and 4 small springs that hold the larger sprocket 'out' when not in use. the process is to unto chain, tighten the 4 bolts to bring the larger sprocket over center, than add like the 10 links it came with and go ride trails. Heres the old girl sporting the dual rear sprocket setup.

IF you have machining capabilities probably anything is possible.

 

[AZ7000']

Part of the allure of the CT-90 to me is the simplicity. I have had mine for 25 months, hose it off occasionally, lives outside in the snow all winter and other then tires, an oil change, drilling the fender and a 13t front I have never pulled a plastic panel, seen the battery or the air filter...

As was stated above sure, it could be done but I'm not sure how your equation looks for effort vs reward. Let us know if you do do it, it would be interesting to see.

 

[m in sc]

IF you decide to do it, I would highly recommend getting a hold of Rebel Gears, they have made some custom stuff for me over the years, offsets in weird sizes, carriers, etc., and probably the only reasonable company to deal with that could custom make a sprocket like this I'd even consider talking to . http://www.rebelgears.com/

 

[SneakyDingo]

There are limits if the radius of the front sprocket gets too small the chain will be subject to stress early wear and be more prone to failure.

You hit the limits of the bolt heads on the fixing plate (P/N 23802-GN5-910) clearing the chain before you hit those limits. 12T may be possible for a sufficiently talented ambitious machinist, if only we had one of those on the forum... 13T is the smallest I can personally guarantee without special modifications.

Alternatively, increase both front and rear sprocket sizes to get the "on road ratio" you want, and then drop down the front as needed. We've seen 13T, 14T and 15T successfully run. 15/43 approximates OEM ratio. There might be other clearances to acknowledge and work around, and you'll never get that crawling gear the CT110 had, but it's a start. That would be the equivalent of going from 14/40 to 14/46T.

 

[dmonkey]

For the front sprocket Kitaco sell a chain guide plate for the JA55 (2020-2022) and one for the JA65 (2023) that will supposedly let you run up to 17T.

https://www.kitaco.co.jp/goods_detail_en/36679

https://www.kitaco.co.jp/goods_detail_en/36677

I followed the Motorcycle Cannonball Run earlier this year and at least two riders on single-speed motorcycles changed out their sprockets and chain lengths at each significant incline. Completely different setup than our bikes as they were changing the primary ratio instead of the final drive ratio and they didn't address chain tension at all other than choosing a somewhat appropriate length chain. One trick I noted was that instead of adding or removing links, they just carried a chain for each sprocket combinations they expected to use. That's a lot more chain to carry if you're doing it for the final drive on the CT125, but it was a major time saver for them in that they were able to stop, dump their tools and parts, swap a sprocket and chain, pack back up, and pedal-start off again in around 5 minutes, riding away with hands coated in chain grease.

 

[m in sc]

its always better to go up on the rear if you can. its just cheaper/easier to go down on the front. (on the trail especially) id never run a 12t.

 

[Umbre]

IF you decide to do it, I would highly recommend getting a hold of Rebel Gears, they have made some custom stuff for me over the years, offsets in weird sizes, carriers, etc., and probably the only reasonable company to deal with that could custom make a sprocket like this I'd even consider talking to . http://www.rebelgears.com/

I've seen good things about them. I'll send them a message