Quick release rear axle ok?

Discussion in 'Friction Drive' started by ThunderDuck, Oct 21, 2009.

  1. ThunderDuck

    ThunderDuck New Member

    Hi guys ... got a Staton kit on the way , do I need to swap
    out the rear axle for the non qr version?


  2. loquin

    loquin Active Member

    Not for a friction drive.
  3. Esteban

    Esteban Active Member

    Weak !!!!!!
  4. ThunderDuck

    ThunderDuck New Member

    I assume by the number of exclamation marks used that you don't agree with loqin's advice ...
  5. loquin

    loquin Active Member

    I've been running a quick release rear axle on my Trek (with a friction drive) for more than a year now, and have had zero problems with it. (And, I'm over 300 pounds!)

    Think about it... (and refer to the attached force diagram sketch, which uses red arrows to represent the normal forces, and blue arrows to represent the additional force caused by the friction drive.)

    The axle is normally under stress when you ride, by an upwards force F2 at the hub (via the spokes, through the hub and hub bearings, to the axle) balanced by a downward force F1 at the axle (transmitted via the chain stays and seat stays to the rear dropout) These forces tend to deflect, or bend, the axle slightly under load, represented by the light-gray 'center line' through the axle. The reason the axle bends is that the forces, while opposite but equal, are applied at different locations (F2 @ hub bearings versus F1 @ the dropout.)

    If you have a friction drive pressing down (F3, it will reduce the overall stress on the hub by the amount of force used to press down, and add that same force F4 (upwards) to the axle at the stays. So, you reduce the axle forces by the amount of down pressure of the friction drive at the hub, but, that is balanced by the upwards force at the stays. However, the forces on the axle use the stays as the fulcrum, so, the moment arm of the forces at the hub is much greater than at the stays (which is, effectively, zero) and the overall axle stress is reduced with a friction drive.

    Note - the forces in the diagram are opposite but equal. F1 and F2 are opposite in direction, but equal in magnitude. F3 and F4 are also opposite in direction, but equal in magnitude (and are less than F1/F2, unless you placed your entire weight on the friction drive when locking it into place...)

    Now, the strain reduction in the axle doesn't come for free - they are transferred to the seatstays and the drop rods.

    Direct link to the bikeparts image: http://lh5.ggpht.com/_SDd59HFkDQI/SSjctXBLhdI/AAAAAAAAALw/jDJgESEoLa4/s800/bicycle_parts_labeled.jpg

    There's one final point to consider. A motorized bike will normally be ridden faster, on average, than the same bike, non-motorized. This means that the dynamic forces to the axles (potholes, bumps, etc) will be greater on a motorized bike. The friction drive helps reduce the effect of these forces, but, if you hit a pothole fast enough, the axle could break, whether the bike is motorized or not. At the same time you install the friction drive (or, for that matter, ANY motor drive system,) I strongly recommend that you also add a suspension seatpost, if the bike doesn't already have one (or rear suspension.) Not only will your back (and backside) thank you, it dampens (spreads out over time) the dynamic forces and resulting stress on the bike as well.

    Attached Files:

    Last edited: Nov 2, 2009
  6. cpuaid

    cpuaid Member

    i have to agree with loquin, i have no problems running a friction drive kit on my quick release MTB. i use it to test out new kits on a rotational basis and have tried (4) different rack mount kits with a total of almost 1000 MOTORIZED miles on my original 1990 something Univega MTB with quick release skewers. it all depends on how smooth the roads are that you'll be riding. friction drives aren't very good for potholes, jumping curbs, or dirt roads so if you stay away from those things then you shouldn't have any problems. just check it every now and then to make sure there has been no slippage. if you have a quick release with nylon or some plastic components then i would recommend you not using them.
  7. Happy Valley

    Happy Valley Active Member

    Ever see or ride downhill and freeride mountain bikes?
    QR axles are no problem.
  8. moondog

    moondog Member

    I see more bent solid axles than qr ones. I am thinking most of the qr axles are made of stronger steel than some of the cheaper solid axles.
    Last edited: Oct 27, 2009
  9. moondog

    moondog Member

    This post put me way into thought for about 3 days ! :idea:

    This is not your first post to do that to me ! :thinking:
    Last edited: Oct 30, 2009
  10. ThunderDuck

    ThunderDuck New Member

    Thankyou Loqin for your comprehensive reply. It has dispelled any doubt regarding use of qr axles. As a rider in the "heavyweight" class, I find your comments regarding use of a suspension seatpost interesting ... and I have indeed suffered frame damage in the seatclamp area of a Dahon folder I used to travel with. I trust that my sprung Brooks saddle will help reduce stress in a similar fashion.
    Last edited: Oct 30, 2009
  11. Mountainman

    Mountainman Active Member

    qr been working fine for a long time on mine

    we sure do like to ride those things !!!
  12. loquin

    loquin Active Member

    Well, most seats are sprung in some manner or another. If the spring is bottomed out, though, it won't help! :whistling: :ack2:

    A suspension seatpost has a spring, and a shock absorber built-in, so that the stresses are averaged out. If it's just a spring, it may help the backside, but, it may not help the frame as much as the seatpost would. (in a car with bad shocks, you can bounce up & down more...)
  13. loquin

    loquin Active Member

    LOL. I was that way thinking about how torsion bars work! :confused:
  14. Esteban

    Esteban Active Member

    When I said, " weak," I was referring to quick-release . I agree with Loquin's advice.