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Replace 20" = Hard to Pedal - Remove Coaster Brake and Increase Crank Arm Length?

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Replace 20" = Hard to Pedal - Remove Coaster Brake and Increase Crank Arm Length?

Old 08-16-16, 08:45 PM
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treefrog1
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20" Bike = Hard to Pedal - Remove Coaster Brake and Increase Crank Arm Length?

Hi all,

My First Question:

To get ride of a rear coaster brake on a 20" bike, is it really as easy as buying a rim off Ebay and a freewheel sprocket and switching out the tire, or is it more complicated than that? I'm posting on this forum because I'm assuming someone can give me sound advice.

My Second Question:

I think the crank arms are too short and this is leading to the bike being hard to pedal. Can I swap out the current crankset with a new one that is has longer cranks? My goal is to make this bike smoother and easier to pedal for my son.

Story:

Frustrated Dad here. Got a 20" Dyno Blaze for my 7-year-old son (nothing special since it is from around the year 2000...not like the Dynos I grew up with!!!) off Craigslist for $20. He upgraded from a smaller bike to keep up with his older sister's on our bike rides. Anyway, the bike is very hard to pedal and my first thought was that is was due to the small length of the crank arms. While I still think this is true, I did notice there was some grumbling from the rear bearings. Being a tinkerer, I took apart the hub and then remembered it was the dreaded coaster brake...there is just too much friction in that hub for it to spin freely. Nevertheless, I took pictures as I disassembled it, cleaned all parts in paint thinner, repacked with grease and had a bunch of trouble getting it back together so it spun SOMEWHAT freely. Man, it was frustrating due to the amount of time and care taking it apart and putting it back together, only to be left in the same place: the bike is still hard to pedal and I think it is partly due to the friction of the rear coaster brake and the fact that the crank arms are too short.
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Old 08-16-16, 09:34 PM
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Knock your self out, you have permission to try.
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Old 08-16-16, 09:42 PM
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Originally Posted by treefrog1
Hi all,

My First Question:

To get ride of a rear coaster brake on a 20" bike, is it really as easy as buying a rim off Ebay and a freewheel sprocket and switching out the tire, or is it more complicated than that?
Get a rear wheel. Gotta check axle size, so that it fits rear dropouts of frame, as BMX bikes have a ton of choices in rear axle size.

If part of the "hard to pedal" situation is too high of a gear, then get more teeth on the freewheel than are currently on the coaster sprocket.
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Old 08-16-16, 11:59 PM
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Bill Kapaun
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If the bike has knobby tires, that makes things much harder to move.
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Old 08-17-16, 05:09 AM
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Keep in mind that it's seen as desirable to keep the crank arm length proportional to the leg length of the rider. While they might look short to you, they might actually be quite appropriate.
If it was me, I'd start with fitting a bigger rear sprocket (and a longer) chain.
It's such an easy and inexpensive fix that it really should be tried first.
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Old 08-17-16, 05:28 AM
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Originally Posted by treefrog1
Hi all,

My First Question:

To get ride of a rear coaster brake on a 20" bike, is it really as easy as buying a rim off Ebay and a freewheel sprocket and switching out the tire, or is it more complicated than that? I'm posting on this forum because I'm assuming someone can give me sound advice.
If you're gonna be your own mechanic I suggest you invest some effort in learning the language.
The rim is the metal hoop that the tire sits on. Nothing more.
A "freewheel sprocket" can be several different things.
There are screw-on freewheels with one sprocket size integrated.
Coaster brake hubs can have both screw-on sprockets as well as spline-fit sprockets held in place with a circlip.
"Cassette" MTB hubs have spline-fit sprockets with a threaded lockring.
And of course, you should have something to replace the removed coaster brake with.
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Old 08-17-16, 05:58 AM
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What kind of riding do you do as the parent?

As mentioned, long cranks might be good for a teenager riding a BMX bike, but not necessarily a 7 yr old.

If it was me, I'd probably leave the 20" bike alone, and then start looking for a 24" bike, road or MTB, depending on your type of riding for the kid for Christmas, or next Spring.

Oh...
The coaster hub should spin just fine. If not, they can be disassembled, greased, and have the cones set, just like any other hub.
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Old 08-17-16, 06:50 AM
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Originally Posted by CliffordK
What kind of riding do you do as the parent?

Oh...
The coaster hub should spin just fine. If not, they can be disassembled, greased, and have the cones set, just like any other hub.
What he said! If adjusted and greased properly they should perform fine for your child. They were used many decades and still manufactured today.

May have a bit more drag than a free wheel, but hardly noticeable for your application. Many on a balloon tire forum to which I belong take their coaster brake bikes on 20, 30, or 40 mile rides and live to tell about it!
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Old 08-17-16, 07:52 AM
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Another thing that can make pedaling difficult is having the chain too tight
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