26" = 18.75:1..... 20" = ?????????????

[Bonefish]

If the standard gear ratio for a 26 inch wheel is 18.75 :1 to hit a good torque/speed ratio, then what would the ratio be for a 20 inch wheel? Like one that fits on a Dahon Folding bicycle?

Thanks,

 

[kerf]

Well, I would think that 20"/26" = .7692 X 18.75 = 14.42:1

I guess, what say others?

 

[motorpsycho]

in my experience, a 44 tooth sprocket on a 20" wheel will give you a lot of bottom end torque and a top speed @ 24-26 mph.
i think this would be similar to putting a 56 tooth sprocket on a 26" wheel.
i have dropped to a 42 tooth sprocket on my 20" wheel, and i am still only getting about 25-28 mph top end, with good low end torque.
I think if you want a good crusing speed without having the engine screaming, a 36-38 tooth sprocket would a good choice for a 20" wheel.
smaller tire/rim diameter, will give you more bottom end torque when using the standard 41-44 tooth sprocket. i might try going with a 36 tooth sprocket on one of my 20" wheels, just to see what happens, i think that the wheel/tire size is small enough to allow it to still have enough bottom end torque to take off without peddling.
the only way to find out tho, is to get a 36 tooth sprocket and try it.