torque converter and big sprocket... doable?

[beltbuckle]

So already thinking about my next build. Would like to use the predator and a torque converter.

The torque converter with 7" driven has a 3.13 (low) to 1.12 (high) primary ratio, with a 10t sprocket on the jackshaft. If I am doing my math right, assuming a 26" wheel, an 80t rear sprocket would work well yielding a 8:1 secondary ratio. Final drive ratio would be 8.96:1 to 25.04:1.


This would make a theoretical top speed of 43mph @ 5000 RPM, and theoretical low speed of 6.8 MPH @ 2200 RPM.

Does this sound about right to you guys? Want to make sure I don't screw this up and order an expensive sprocket that is the wrong size.

 

[culvercityclassic]

80 tooth is way too big. I have two bikes with the converters on them and one runs a 44 tooth and the other is a race bike with a 58 tooth and both are fine. A good all around size for your application would be 50 tooth.

 

[Ibedayank]

depends on what pred the 99cc or 212
id use a 72 tooth on the 99 top speed in the low 40s with the 72 tooth @3600 rpm

 

[beltbuckle]

it'll be the 99cc. there will be no intermediate jackshaft, just straight from the jackshaft of the torque converter to the rear sprocket.

 

[Ibedayank]

using a jackshaft allows you to put the motor on the centerline of the bike and still not have chain alignment issues. it also allows you to use a freewheel so you do not have to spin the cvt in order to pedal the bike with the motor off. Just a couple things to think about

 

[beltbuckle]

thanks. I'll probably get the motor and torque converter first and see how things line up first... just would like to avoid a jackshaft if possible but we'll see.

culvercityclassic - you are going right from the torque converter to the rear sprocket? that seems like a pretty tall ratio. does it have good low end acceleration?

 

[culvercityclassic]

thanks. I'll probably get the motor and torque converter first and see how things line up first... just would like to avoid a jackshaft if possible but we'll see.

culvercityclassic - you are going right from the torque converter to the rear sprocket? that seems like a pretty tall ratio. does it have good low end acceleration?

Yes it does, some of the local guys know how these bikes run and can vouch for me. Check out my boardtrack bike build and you will see the setup. Clean and simple.