First friction drive bike, few questions.

Discussion in 'Friction Drive' started by Jake.B, May 14, 2012.

  1. Jake.B

    Jake.B New Member

    Hey guys im new to the forum, i was pointed in this direction from a member of DIY Go-kart. I have been surfing some threads and found alot of helpful info.

    I have a 20 inch dimondback that i plan on mounting a chainsaw to. Its a homlite C-72, its 80cc, direct drive, Meaning it has no centrifical clutch.

    I plan on welding a frame up that i can mount to my seat post area with U-bolts so i can remove the setup if id like. I will use turnbuckles to adjust the force of the spindle, i plan on using a large spring with the turnbuckle so i can pull a lever and lift the roller from the tire like a clutch system. I know how to hook up all mentioned above and throttle, killswitch, ect.

    My main question is my spindle size im new to this area of "gearing" i beleive the main factors are RPM and spindle. Ive read a few post on how tire size dosent really factor into the gearing. It an average 20inch steel bike frame, im around 130 pounds and the mount/frame and chainsaw probably will weigh 20-40 pounds. (not real sure). Its all flat land and if there are any hills they will be pedled up. Also, it will be a pedal start so the gearing dosent need much as much tourqe. I want to be pretty fast probably 35-45 mph, im not sure if this is acheiveable? What should my spindle size and gear ratio be?

  2. darwin

    darwin Well-Known Member

    80cc wow, people use from 7/8ths all the way up to 1 3/4ths roller. With that powerful a motor I'd go with an 1 3/8ths. That should give you the best of both worlds speed/torque. Those extensions that bmxers use on the axles might make a good spindle choice if you can adapt it some how.
  3. Jake.B

    Jake.B New Member

    I figured wratchet sockets come in many sizes, i could mesure a few of those to get a good size. Ive seen alot of friction guys using steel spindles to their tires. Dosent rubber to rubber make alot better grip and wear is minimal? I wanted to find a rubber boot of some sort, and epoxy it to my spindle. Depending on the thickness of the boot i would have to make sure the size is 1 3/8. Therefore getting a slightly smaller spindle and thick boot.