Gear ratio?

[ghost681]

ok so how fast would i have to pedal the bike before the engine would start to do anything? and no one answered how many teeth id need on sprockets for a jack shaft. If I wanted to make one what two sprockets would I put on either end? Thanks for all the help btw.

 

[zippinaround]

just use the ratio calculator to work it out!

 

[5-7HEAVEN]

ok so how fast would i have to pedal the bike before the engine would start to do anything? and no one answered how many teeth id need on sprockets for a jack shaft. If I wanted to make one what two sprockets would I put on either end? Thanks for all the help btw.

I would say 30mph downhill.
In other words, no matter how fast you pedal, the engine will not help you.

Using Murphy's Law, the smallest engine sprocket you'll find is a T8F 11-tooth one.
Match that to a 54t on the jackshaft to get 4.91. Use another 11t on the other jackshaft end and a 72t chainring.
The inside chainring is 24t, which chains to the 8-speed cassette. First gear is 34t, with a 45.52:1 gear ratio.
This allows you to climb very steep hills and ramps. Second gear is 28t with a ratio of 37.49'
which you can easily drive away from a stop. Seventh gear is 17.4:1 and highway 8th gear is 14.73:1.

With these gears, your engine will scream up to 40mph.