Chainwheel on Schwinn Meridian

[dancer]

I am 85 years old and do not have much strength in my thighs. I just bought a Schwinn Meridian 26 inch trike. Can the sprocket ( I guess it is called a chainwheel nowadays) on the crank be changed to one with a smaller diameter? That way, may be the trike will be easier for me to pedal. Like if it is now a 6 inch sprocket, could I get a 4 inch sprocket put on? Would this be an easy job for a bike mechanic? I suppose the present chain could be used then too if it were shortened?

[DaveM]

That is probably the best solution. It may also be possible to change the cogs in the back, but I suspect changing the crank in front is easier. (There's a few trike familiar people on this list so they may tell us different.) You'll want to count the teeth on the crank you have now and then try to guess how much lower you want it to be. (I.e. if you have a 40 tooth crank now and go to a 36, that would be a 10% reduction, etc.)

Just from pictures, it looks like the crank on this is one piece with the chainring, so you may have to swap the whole thing.

You may not be able to get the exact tooth count you want, so you may have to balance what you want with what is available. But any decent shop can help you find what will work.

[dancer]

(04-05-2014, 11:51 PM)DaveM Wrote:  That is probably the best solution. It may also be possible to change the cogs in the back, but I suspect changing the crank in front is easier. (There's a few trike familiar people on this list so they may tell us different.) You'll want to count the teeth on the crank you have now and then try to guess how much lower you want it to be. (I.e. if you have a 40 tooth crank now and go to a 36, that would be a 10% reduction, etc.)

Just from pictures, it looks like the crank on this is one piece with the chainring, so you may have to swap the whole thing.

You may not be able to get the exact tooth count you want, so you may have to balance what you want with what is available. But any decent shop can help you find what will work.

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thanks DaveM. Is there a tutorial on the Web where I can learn about changing sprockets? Not so much the mechanics of actually using tools to do it, but rather, the theory? I am in the dark in this. Like is there different spacing between the cogs on different sprockets so if you put the wrong sprocket on, the cogs would not even mesh with the spacing in the chain links?

I guess I am thinking of metal gearing, where if two different diameter gears needed to mesh with each other, the spacing of the gear teeth would have to calculated carefully in order for the two gears to mesh. Or is not the chain drive of bikes not this critical?

[dancer]

This is DANCER again with a concern about another trike we have. It is a Worksman “Port a Trike” with 20 inch wheels. It has a 7.5 inch crank arm. This means it is kind to my wife's knees. But the effort to propel the trike is so great that her knees are still hurting. The hurt is not coming from extreme bending of the knee, but from the power it takes to pedal the trike.

Has anyone changed the chainwheel on this this trike to a smaller chainwheel so that the pedaling will be easier for her?

[GeorgeET]

Congratulations for still riding a bike . I have not seen any pictures, but if it is a one piece crank getting a replacement and the job is a bit tricky for beginners. Examine the front chainwheel to see if it has bolts in it connecting it to crank. Photos of the rear sprocket would help. Although change would require removing of the rear axle.

Its not so much about the size of sprockets as their ratio to each other. Reducing the ratio makes pedaling easier.

AS per your wife's bike sounds like the seat may be adjusted too low. There should not be any extreme banding of the knees.

Where did you buy the trike? Perhaps they can help.

[dancer]

(04-06-2014, 12:39 PM)GeorgeET Wrote:  Congratulations for still riding a bike . I have not seen any pictures, but if it is a one piece crank getting a replacement and the job is a bit tricky for beginners. Examine the front chainwheel to see if it has bolts in it connecting it to crank. Photos of the rear sprocket would help. Although change would require removing of the rear axle.

Its not so much about the size of sprockets as their ratio to each other. Reducing the ratio makes pedaling easier.

AS per your wife's bike sounds like the seat may be adjusted too low. There should not be any extreme banding of the knees.

Where did you buy the trike? Perhaps they can help.

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GerogeET thanks for the help. Her bike seat is good and high, her leg is almost straight out at the low position of the pedal. We got the trike from walmart. I am not planning to do any of the mechanical work myself, I will take it to a bike shop. I just wanted to know if smaller diameter chainwheels (also known as the sprocket on the crank) were available, and if the change could even be made. Expense is not too much a factor. Thanks for the encouragement. Our minds still think we are only 20 years old.

[DaveM]

The tooth spacing on bike gearing is standard, so you don't have to worry about that. There are a couple different types of cranks that attach in different ways and sometime use different bearing assemblies in the frame. But if you're going to get a shop to help you with this, I don't think you need to worry about it much.

The key issues to worry about are teeth counts and crank length. Less teeth means a lower (easier) gear, but slower speed at the same pedaling RPMs. How much lower you want to go will be something of a guess. On some cranks you can replace just the chainring (the "gear wheel"), on some you have to replace the whole crank assembly.

Crank length can affect pedaling power also. Longer cranks give you more leverage and so can make the same gear ratio feel a bit easier. But you don't want to go too much longer as it forces your legs to make a larger circle, bending the knees more at the top stroke. I wouldn't worry about this too much, but just make sure you don't radically change the crank arm length in either direction.

I suspect you won't have that many choices anyway. Not every combination of crank arm and tooth count will be available in the style you need. Let them shop find out what is available and try to make your best guess as to what will give you what you need.

As always, this is the situation where a good shop where they're willing to spend more than 2 seconds "seeing what they have in the back" is needed.

[dancer]

(04-07-2014, 01:23 PM)DaveM Wrote:  The tooth spacing on bike gearing is standard, so you don't have to worry about that. There are a couple different types of cranks that attach in different ways and sometime use different bearing assemblies in the frame. But if you're going to get a shop to help you with this, I don't think you need to worry about it much.

The key issues to worry about are teeth counts and crank length. Less teeth means a lower (easier) gear, but slower speed at the same pedaling RPMs. How much lower you want to go will be something of a guess. On some cranks you can replace just the chainring (the "gear wheel"), on some you have to replace the whole crank assembly.

Crank length can affect pedaling power also. Longer cranks give you more leverage and so can make the same gear ratio feel a bit easier. But you don't want to go too much longer as it forces your legs to make a larger circle, bending the knees more at the top stroke. I wouldn't worry about this too much, but just make sure you don't radically change the crank arm length in either direction.

I suspect you won't have that many choices anyway. Not every combination of crank arm and tooth count will be available in the style you need. Let them shop find out what is available and try to make your best guess as to what will give you what you need.

As always, this is the situation where a good shop where they're willing to spend more than 2 seconds "seeing what they have in the back" is needed.

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(04-07-2014, 02:19 PM)dancer Wrote:  

(04-07-2014, 01:23 PM)DaveM Wrote:  The tooth spacing on bike gearing is standard, so you don't have to worry about that. There are a couple different types of cranks that attach in different ways and sometime use different bearing assemblies in the frame. But if you're going to get a shop to help you with this, I don't think you need to worry about it much.

The key issues to worry about are teeth counts and crank length. Less teeth means a lower (easier) gear, but slower speed at the same pedaling RPMs. How much lower you want to go will be something of a guess. On some cranks you can replace just the chainring (the "gear wheel"), on some you have to replace the whole crank assembly.

Crank length can affect pedaling power also. Longer cranks give you more leverage and so can make the same gear ratio feel a bit easier. But you don't want to go too much longer as it forces your legs to make a larger circle, bending the knees more at the top stroke. I wouldn't worry about this too much, but just make sure you don't radically change the crank arm length in either direction.

I suspect you won't have that many choices anyway. Not every combination of crank arm and tooth count will be available in the style you need. Let them shop find out what is available and try to make your best guess as to what will give you what you need.

As always, this is the situation where a good shop where they're willing to spend more than 2 seconds "seeing what they have in the back" is needed.

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Hi DaveM

Just what I needed to hear. thanks so much. Yes, and knee bending at the top of the pedaling stroke is a big worry for us too. Will take it from here.