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I have a fixie and I'm finding the rear wheel slips forward when riding (horizontal dropouts), causing the chain to loosen and thus a sub-optimal riding experience. It's not enough to be critical, just annoying.

I have the bolts extremely tight on the frame with the chain taut, but it still slips a little when riding. I'm wondering if there are any tricks out there to solve this problem, or if I'm doing something wrong?

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5 Answers 5

Some things to try:

  1. Make sure there isn't any grease on dropouts, axle, or bolts.
  2. Make sure the nuts for the rear axle have some bite to them.
  3. Make sure the rear hub has some bite to it where it touches the rear dropouts.
  4. More spinning the pedals, less hammering on them.
  5. Increase the size of the rear cog, and if you need to, the front chain ring. If you don't see how this can help, do a free body diagram, Hint, it's a lever problem.*
  6. Get chain tugs**

*: Imagine your going up a really steep hill and your allmost at a stop. Regarless of anything else, the force appled to the bottom of your wheel must be constant to keep you from going in reverse. Now do a free body diagram on the wheel. In statics, we can sum the moments about any point, so choose the point which the chain connects with the rear cog. If A is the force applied to the wheel by the axel, G is the force applied to the wheel by the ground, r is the rear cog radius, D is the rear wheel diameter, Then summing the moments we have that A*r-G*(r+D) = 0, solving for A, we have that A = G + G*D/r, so as r is increased, the force at the axel is decreased. These results won't deviate much if a fully dynamics system were to be concidered.

**: Make sure the chain tugs that you get are beafy, small spindaly chain tugs are only designed to take the forces needed to properly position the tire in the drop outs and will bend or break if they need to take pedeling loads due to slipage of the rear axel.

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1  
Good answer, except for "If you don't know what a free body diagram is, take physics." Perhaps you can link to an explanation? Being derisive of those who don't know this doesn't explain the concept. –  Neil Fein Feb 23 '11 at 21:38
    
Increasing the size of the front ring will result in less pull/tension on the chain: it's like being in a higher gear. But I don't see how increasing the size of the rear cog will help: it will decrease the torque on the axle, but not decrease the straight-forward pull. –  ChrisW Feb 23 '11 at 21:43
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So the larger front ring causes decreased tension in the chain, and the correspondingly larger back ring ensure the same effective gearing even with the reduced chain tension. The net effect is the same gearing with reduced chain tension. The reduced chain tension means less pull on the axle. –  ChrisW Feb 23 '11 at 22:10
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@moz "I think you're over-thinking this." - Yes, perhaps. It has become second-nature to you; I'm still working it out for the first time. –  ChrisW Feb 23 '11 at 22:15
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@ChrisW: only if the front ring remains the same size (with the same force on the pedals). If the gearing remains constant or you still keep mashing the pedals just as hard then the chain tension will be the same. This answer would be perfect if point 5 was removed. –  darkcanuck Feb 25 '11 at 0:48

You could look into getting some chain tugs which basically create a link between the axle and frame. Here is an example:

Surly Tuggnut

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First make sure there's no grease lubricating the nut/dropout area. Also make sure you're using washers, not just bare nuts (or nuts with washers built in). If slippage is still a problem you have three choices:

  1. change your gearing so you're spinning rather than grinding (get a lower gear)
  2. tighten the nuts so you're denting the dropouts and things stay where they are (may not work, will damage the bike)
  3. buy a chain tug The are devices that slip over the axle and brace against the end of the dropouts. They're more common on BMX's. I use those on my QR hub gear bicycles because you can't crank a QR up tight enough to hold. BMX ones will cost ~$20, fixie ones twice that but are much more fashionable.
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You can also take a few links out of your chain and move your wheel all the way forward so it has nowhere left to slide forward. This is probably the least desirable solution, I highly suggest getting a chain tensioner.

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Search for chain tugs rather than a chain tensioner.

Chain tug

You want something to hold the wheel in place rather than to push the chain up or pull it down (Chain tensioner).

On a fixed gear, the latter will just break with the first back pressure on the pedals.

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