# Jackshaft Hopeless gearing?

Discussion in 'Transmission / Drivetrain' started by Charles Laypool, Feb 5, 2016.

1. ### Charles LaypoolMember

Im just trying to figure out what gearing is best for me with a jackshaft kit

If my motors Max rpm is 5500 and its internal gear reduction is 4.1 so my output sprockets rpm is 1341.4634146
So 10t to 17t is 1.7:1
(789.09612623 rpm)
17t to 10t is 1.7
(469.17419194 rpm)
10t to 44t is 4.4444444444
(105.49413453 rpm(at the pedals)
44t to 36t is 1.2222222222 (86.313382798 rpm(to rear tire)
Now if i calculate

Axle teeth / Pedal teeth = gear ratio.

Sprocket RPM / Gear Ratio = Wheel RPM (wRPM)

Tire circumfrence in feet * wRPM = feet per minute.

Feet per minute * 60 = feet per hour.

Feet per hour / 5280 = miles per hour.

1st----9mph
2nd-10mph
3rd-12mph
4th-16mph
5th-18mph
6th-21mph
7th-24mph
8th-27mph

Now i really hope im doing something wrong i ordered my shift kit im jus waiting to get it but i want to get best gearing and these results are crap someone enlighten me

2. ### bakanekoActive Member

What is going on here? You are going from 10T to 17T at 1:1.7 for 1341 to 789 RPM. And, then you are going from 17T back to 10T for 789 to 469 RPM. Wouldn't it be back to 1341 RPM? Also, there is a 10% power reduction when using a jackshaft apparently. Cheers

3. ### Charles LaypoolMember

Ooooo snap see i knew i was missing something. Thank u for the info

4. ### bakanekoActive Member

No problem, m8. We all make mistakes. I suspect the new speed numbers would be much higher now. Have fun and stay safe!