Sprocket Change Gearing Question

[wheelhorseman]

I am playing around with the gearing on my old 20in. Freespirit banana bike. It had the factory 34 tooth crank with short arms and i think a 15 tooth rear sprocket. You were pedaling yourself to death to get any where. My goal is to achieve less and easier pedaling.

I installed a crank from an old 10 speed and plan to use the smaller 40t sprocket and change to a 20t rear. What will be the result if i do that combo? What if i use the BIG crank sprocket? Think its about 52t.

 

[hubgearfreak]

AASHTA

i'd start with aiming for 66" gear

http://sheldonbrown.com/gears/

 

[Walker]

My goal is to achieve less and easier pedaling.

....only ride downhill?

sorry couldn't resist! I have an old bicycle repair book from the 70's, there is a gearing/wheel chart in there, I'll take a look.

 

[FunkyStickman]

Most 26" cruiser bikes have a 42T or 44T front, and a 16T rear. You could use the 52T front with a 16T rear and it would be close.

 

[Wildcat]

My Dahon 20" Boardwalk used a 48 front with 16 rear and it was nearly the same as a normal 26" cruiser with 46 front/ 19 rear. You have short crank arms, so try the 40 front with the present 15 rear to see how that does.

 

[wheelhorseman]

What if i use the origonal 34t front with the larger 20t rear?

 

[FunkyStickman]

What if i use the origonal 34t front with the larger 20t rear?

You want to not have to pedal as fast? Then you want a taller gear ratio. You either make the front gear bigger, or the rear gear smaller to do this. Putting a bigger gear in back will have you pedaling like a circus monkey!

Do you know how to calculate gear-inches? You multiply the size of the rear tire by the front/rear gear ratio.

Let's say you have a 40T in front, and a 20T in back. That gives you a 2:1 ratio. The rear wheel will spin twice as fast as you pedal. It's like having a 52" wheel.(edit) Sorry, with a 20" tire that's like a 40" wheel... not very fast!Fast road bikes push around 100 gear inches.

For climbing hills, you want a lower gear ratio. For cruising and going fast, you want a higher ratio.

 

[wheelhorseman]

OK so i will leave the 16t in back.

With the longer crank arms which front sprocket is best to use the 40t or 52t?? I dont want the bike so high geared that i will have to push it up the slightest hill or have leg muscles like the Incredible Hulk.

 

[FunkyStickman]

Well, good thing about it is, it's a bike, you can try it and change it if you don't like it. Give it a shot!

 

[rusty1]

...depending which frame you're using, using longer crank arms can be a problem when turning,...they will hit the ground. I've used 24 " cranks before as some are midway between 20-26" cranks in arm length.

 

[wheelhorseman]

Crank clearence is fine i just want to know which of the 2 sprockets would be the best choice. I only want to do this once.