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Replacement parts question

 
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I recently purchased a TMX Tri-Aid tricycle for my wife to use in our campground. The trouble is the chainring is so small it has difficulty getting out of its own way let alone climbing any incline. My question is: Is anyone familiar with this brand and if so, can the chainring be replaced with a larger one (say 32T vs orig. 20T) safely to increase power to the wheels while pedaling?  What size chain should I buy to replace the original? Finally, how difficult is this project?  Thanks in advance. Tom W.
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master pollinator
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Unless I am misunderstanding your goal, you will need to make the back sprocket larger, not the front one.  If you make the front sprocket larger, you will get more speed, but less power, so less ability to climb hills.  If you make the back sprocket bigger, hills will be easier, but you will lose top end speed.
 
steward
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that looks like an old cottered crank and chainring as one piece. that crank also looks really short. really, really short. cottered cranks aren't hard to find, though I've never looked for anything that short. most cranks are in the 165 to 175 mm range. if I had to guess, that one looks closer to 100 mm.

if there's enough clearance, I would think about getting longer cranks and a bigger chainring. if you're happy with the cotters, there's no need to change that. if you're not certain about what size chainring you want, it might make sense to get cranks with a spider instead of an integrated chainring. that way you can try out a new size without buying a new crank. make sure you hammer or press the cotter in instead of just tightening it with the nut.

if you want to switch to a different sort of crank (square taper, for example), you'll have to change the bottom bracket and spindle, too, which isn't terribly difficult, but does involve either some specialized tools or the patience of Job.

since you don't have any deraillers to worry about, an 1/8-inch single-speed chain should be fine. they are cheaper and more durable than derailler chains. you'll probably want a chain tool for that job, though it does look like you've got an adjustable tensioner that might be able to take up any slack if you don't want to cut your chain.
 
tel jetson
steward
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spent a couple minutes poking around. looks like those short cranks aren't hard to find, either. here's one example with 34 teeth: 4" COTTERED Right CRANK ARM WALD 34 tooth
 
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