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I've got a geared bike back tyre that has a dent in the rim. I'm considering a fixed gear conversion. A few points of issue:

The bike has small vertical drop outs.

The skewer width on the current back tyre width is for a 7-speed block.

What are my options to deal with these issues?

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Are you dead set on fixed, or are you willing to go single speed with freewheel? Freewheel will give you the option of adding chain tensioners. –  Mac Mar 23 '12 at 0:32
    
Pretty dead set on fixed. I've seen some drop out conversion kits but I'm a little dubious of them. Then again they may be my only option if I do not want a slack chain –  will Mar 23 '12 at 10:52
    
You might want to consider this conversion kit: surlybikes.com/parts/fixxer. It is attached directly to the star inside the hub body on shimano cassette hubs, thus converting it to fixed in a totally reliable way. You remove the cassette (with a 10mm allen key) and screw the Fixxer in place. –  heltonbiker Mar 23 '12 at 21:53
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4 Answers 4

No EBB, vertical dropouts, and 130mm spacing in the rear. You have a few options. Here they are, from worst to best, and most likely cheapest to most expensive.

  • Ghost ring. Basically, you get your chain length as close as you can then cram an old chainring in the chain inside the chainstay. Scary solution, especially if you don't run (all of your) brakes.
  • Magic Gear. Find a gear combination and chain length that gets the chain respectably tight. May require halflinks, and can be a PITA. If if works, it works great for a short time, then the drivetrain wears and the chain becomes loose and you have to do it all over again. Not a great permanent solution.
  • White Industries ENO eccentric rear hub. This is the way to go if you're willing to spend the cash. Comes in a variety of spacing, free or fixed threading. Works basically the same way an Eccentric Bottom Bracket does. Dropout bolts are offset from the axle so it allows you to adjust the distance from the bottom bracket to the rear axle. White Industries makes bombproof components as well.

My recommendation is the ENO, hands down. Don't bother with your current rear wheel. It's more trouble than it's worth.

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I think this conversion depends on where you live. Currently, a lot of niche market factories are producing small parts specifically engineered for fixed gear conversions.

I can see the value of the ghost chainring, but I think it's dangerous, and the ring would be dancing up and down all the time while you accelerate/deccelerate via the pedals, and bob violently on fast downhill, when it is very hard to catch up with the pedals, and when it's most dangerous if you have any surprise.

The magic gear has its value, and would give a very very nice setup: easy wheel assembly and reassembly, use a regular skewer (no bulky 15mm spanner to bring along), BUT I think it would last only for a few miles. Slack develops very fast, and you couldn't adjust it with the same chain (but honestly, I'm talking from theory, never used that either).

But I think the solutions that would give you more satisfaction are those that allow you to solidly compensate for chainslack, and most of them were already mentioned:

  1. Eccentric bottom bracket;
  2. Eccentric rear hub;
  3. Custom-made chain "tensioner".

That third option would be a metal pulley held in place below the chainstay by some solid structure rigidly attached (welded, clamped) to the chainstay, with some kind of adjustment (a slot would be perfect). It would be necessary to attach it so solidly because, when deccelerating or skidding, the chain would compress this pulley against the chainstay with what might be a hard force. Some frames might not be good candidates for doing this.

Anything you chose, keep in mind that:

  • Fixies are DEFINITELY not toys. The chance you get killed (or kill yourself) on a fixie in traffic is much greater than on those free-ride bikes in steep trails;
  • Fixies are so cheap that perhaps you assemble one as a second bike, and just "fix" your old bike back to what it was: geared, freewheel. Most likely a decent frame or even a whole bike wouldn't cost so much as you would spend with all these boutique components, which in the end are a bit like fancy workarounds.
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You can purchase a new skewer or add a ton of washers. There are eccentric bottom brackets you can use to provide chain tension in the absence of a horizontal dropouts.

enter image description here The big hole (notice it is not in the center of the cartridge) accepts the cranks. Depending on the adjustable orientation of the hole you gain or loose a couple inches to the front/back up/down. These small adjustments will tension the chain.

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Or use Heltonbiker's formula to figure out the exact chain length. (VBG) –  Daniel R Hicks Mar 22 '12 at 21:35
    
can you elaborate on eccentric bottom bracket and how it provides tension –  Will Mar 22 '12 at 21:56
    
@Will -- It's basically an eccentric adapter for a smaller diameter BB. Rotating the adapter causes the BB spindle to move relative to the dropouts. Assuming you're facing the right side of the bike, insert the adapter and BB with that top notch facing right. Install the shortest chain that will fit the sprockets. Then rotate the adapter until the chain is taut. –  Daniel R Hicks Mar 23 '12 at 0:13
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@Will An EBB is only an option if the frame was designed with one. –  joelmdev Mar 23 '12 at 1:55
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An eccentric bottom bracket is not a converter. Your frame must be designed to accept it. –  zenbike Mar 23 '12 at 6:50
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Due to the following reasons, I can't recommend converting this bike to a fixed gear:
a) Vertical Dropouts (making chain tension adjustment difficult)
b) Dented wheel (Probably don't want to rely on this, it could fail more easily or cause the tire bead to pop out when skidding)
c) Existing wheel has a freewheel, and is not going to accept a fixed cog. (You need a new wheel to accept a fixed cog and lock ring)

You'll spend way more money getting this bike converted to a fixed gear than it's worth.
Really, it's probably easiest to either a) purchase a new or used fixed gear bike or b) buy another bike with semi-horizontal or track dropouts and get a new rear wheel with a flip flop hub, fixed cog, and lock-ring.

Otherwise, the cheapest solution to having a working bike is probably to just buy a new geared wheel and put it on your bike and leave it as a geared setup.

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