Jackshaft gearing on 72T rear sprocket help

[R67]

Anyone have any recommendation on the jackshaft gearing for an average speed and torque. I am running a 12T clutch and 72T rear sprocket. I am running a 6" Astro wheel with standard tires. I am not looking for speed but an overall ride.

 

[Motra]

http://www.oldminibikes.com/forum/general-minibike-talk/75438-gearing-calculations.html

 

[Oldsalt]

6 inch rim = about 12 inch dia. tire. 12 and 72 = 6 to 1 final ratio. MPH at 3600rpm is about 21.5. Kinda normal for a bike that is not to be extensively used on grass with a heavy rider with frequent stop-n-goes.....the clutch will have a hard time coping. You could use a 60 tooth at the rear [5 to 1 ratio] but only for blacktop. That would give about 25.7 mph. The formula for mph is: [RPM X tire dia.] divided by [final ratio X 336].

For me? I like something around 7 to 1 or lower. 7 to 1 equals about 18 or so mph. I don't wish to fall off at even 15 mph. A bike without suspension on anything but blacktop is a handful at 15 MPH in the rough.

 

[TANKSAREUS]

@R67,

I am running a 12 clutch - 15T on shaft to 12T to a 70, but the wheels I have are large 19 - 7.00 - 8. Still its a nice ratio good power and nice top end

 

[R67]

Thanks for the help. I ordered a 14t and 16t from OldMiniBikes. I already have the standard 12T and 11T. I aiming for a good balance of power at take off and top speed.