Ideas to make Friction Drive Bikes more Stable at High Speeds?

Discussion in 'Friction Drive' started by cpuaid, Jun 13, 2011.

  1. cpuaid

    cpuaid Member

    I have a mid 90's Univega Cro-Mo MTB frame with ultra light components and quick release axles fitted with a brand new Staton friction mount kit with 1.50" drive roller and my old Mitsubishi TLE43. Recently mounted with new Kevlar 26 x 1.75 tires with comfort treads on Araya rims. Most of the components have been replaced with light weight material and with the engine mounted it's around 55 lbs. I also use it as a regular peddle bike thus the reason why I wanted light weight components. It's one of the lightest and fastest motorized bikes around. I've lost some weight and currently weigh about 140 lbs. thus my top speed can easily exceed 40+ MPH. My question is high speed stability. I keep my spokes tight and wheels true but with constant downward pressure I can feel the bike's rear end feel like it wants to drift or wander around 40 MPH. At my age it's a little bit disconcerting when you know what can happen if the bike shakes apart at that rate of speed. The bike is capable of going faster but I don't want to push my luck or the bike's capabilities. The wheels don't really shake or vibrate very much. I'm thinking the wheel is slightly out of round as the rims have taken quite a beating through the years. Maybe it's a combination of my light weight, the downward force of the drive roller, and out of round wheels. It may even be the new Kevlar tires causing the problems. I'm thinking about buying a newer and beefier wheel set just in case but really hate to give up on my lightweight Araya's. Old tires were non-Kevlar Kenda's street slicks. Current tires are Kevlar Innova's comfort treads. Any thoughts or ideas to make this beast more stable at high speeds?
    Last edited: Jun 13, 2011

  2. ratdoggg

    ratdoggg Member

    I have had my recumbent up to 65 mph going down hill
    under pedal power and Thoughts of a tire blow out made
    me slow her down.. Stock bicycles just are not meant to go
    that fast.. I for one remember how much it hurts to crash at
    that speed and I am a little wiser in my old age..
  3. 5-7HEAVEN

    5-7HEAVEN Guest

    I think a front suspension fork would help stabilize your bike. Correct tire pressure helps.

    I ran friction drive for years, also used 1.5" roller and TLE43 engine.

    I always ride faster(40 mph+) on the flats than I do going downhill (25-35 mph).
  4. cpuaid

    cpuaid Member

    Re-trued my rear wheel and it was still acting up. Did a closer inspection on the new tires and found they were defective. For some reason there was a slight bead in the center of the tire on the tread side during the manufacturing process. You sometimes see this as excess rubber that is very thin and wears off. On my new tires where the beads joined, one side was raised much higher than the other, as if they were mis-joined. The bead's height varied and was uneven thus making the tire slightly out of round. Swapped tires with my other bike which was identical to the new set but had no center bead and the drifting went away. Funny how even small things can affect a friction drive's performance.
  5. 5-7HEAVEN

    5-7HEAVEN Guest

    Excellent troubleshooting!:detective:

    Good job!:grin5:
  6. Excellent detective work. I think many of us push the roller down onto the tire a bit harder than nessesary. With the power you are getting, that might be nessesary, but with the SR 33.5 cc engines I use I backed off some and lost a vibration I could never chase down.
  7. greguk

    greguk Member

    You can always leave that rear lock open and reshape tire a bit by few miles.
  8. rawly old

    rawly old Member

    I think tire pressure is very important. The firmer your tire, the more down pressure
    you can apply with the roller without adding extra drag. I was amazed how much
    my performance improved when added 15 pds. to my under-inflated tire. This also
    seemed to give a more stable ride albeit at the expense of my bottom.
  9. u2seek42

    u2seek42 Banned

    Yow! 40 plus on a bike, not me, fast motor and slow breaks
    leads to brokes.

    I am having grinding bearing ... sounds coming from my front wheel a 25.

    I have to say the one friction kit like really like was one I can't remember the name of.
    Was a mid frame engine mount with the roller contacting wheel right behind the engine. looked balanced and sharp,1145166

    see the attachment on the site for pix.
    I like it!
  10. happycheapskate

    happycheapskate Active Member

    You should check the front wheel bearing before riding it any more! I found a BMX bike one time that was abandoned because it had been run dry (grease gone) and the cones turned on the axle and locked the front wheel up. I salvaged the wheel by readjusting and greasing the hub, but the cones had some wear, and the wheel rim is bent a little. I trued it best I can but wouldn't ride it more than for pedaling around a camp site or checking the mail with it. BB's can be replaced easily, cones less easily, and hubs less easy than that, but a whole wheel can be replaced with a phone call. (my favorite bike parts shop)
    Last edited: Oct 20, 2011
  11. happycheapskate

    happycheapskate Active Member
    Here is something like it, also from a "retired" small company "zipp cycle" roller drive with weeder motor in frame.