Gear ratio help

S

sleepy hollow

New Member
ok so let me start off by saying my bike is a daily commuter, 80cc ht with 44t sprocket, its all bone stock, my usual speed is 28-35mph, my bike is a cranbrook (i know bad choice) due to consistent problems with the rear hub literally falling apart, i have decided to buy a 3,or 5 speed internal geared hub(haven't decided with one yet). I'm a fabricator/machinist, i plan on making my own jackshaft to use the hub, eliminating the pedal crank. I'm also using the factory coaster gears for my jackshaft, how many teeth do i need to run on the hub, the goal for is direct drive in 2nd gear(3 spd hub), or direct drive in 3rd gear(5speed hub)
 
I cant open it i have mac, but i know with my 44t sprocket, im at 16:1 gear ratio, im going to use the sa 3 speed fixed hub, id like to keep the ratio as close to 16:1 in 2nd gear as possible, i just need to know what tooth counts i need on my jack shaft and rear hub
 
sleepy hollow said:
I cant open it i have mac, but i know with my 44t sprocket, im at 16:1 gear ratio, im going to use the sa 3 speed fixed hub, id like to keep the ratio as close to 16:1 in 2nd gear as possible, i just need to know what tooth counts i need on my jack shaft and rear hub
Click to expand...

Actually, the gear ratio you currently have is ~18:1, not 16:1.

There are wayyyy too many variables in gearing for one of us to figure out your jackshaft gear ratio for you. You not being able to play with gear ratios yourself isn't helping matters any, either. If I were you, being on a blasted Mac, I'd install Boot Camp and Windows XP so the gear calculator is useable.

Anyway, if you use the standard SBP shift kit ratios (4.1:1 initial 10T output, >17>10>44>36 and figure an 18T rear sprocket, you get 15.33:1 overall in 2nd gear with a 3-speed Sturmey. All you've given us is the engine. There's 5 more sprockets to figure out! Tooo many dang variables.
 
understandable, I'm just new to the whole gear ratio calculations, but in search of a rear hub i acquired one for free, bassicly. if you give me the formula i can figure it out, is 15.33:1 higher/lower engine rpm than 18:1. so if i have 10t on my engine out put and 18t in the rear i just need the formula to figure out jackshaft gears, example. A=(engine output gear) B=(jackshaft input gear) C=(jackshaft output gear) D=(hub input gear) and I'm using the shimano nexus 3 speed coaster hub (modified to fixie)
 
You must log in or register to reply here.
Back
Top