special feature

The Ask GeWilli Morning Edition.

To preface, i have a few friends who ask advice on occasion. It doesn't happen often, #1 cause i only have wicked smart friends, and #2 who knows if what i will offer up is right (sarcastic negative humility). There are probably a few more #s, like i don't have any friends, or they know better than to ask a question that could lead to a 1000 word email essay and prefer to call or what ever reason there is. Or like gluing tubulars. I ain't going there, more than i did already.

So.

On to the question for the day.

This is from A down in the Carolinas,

Can you run a fixed gear rear wheel on a bike with a derailleur?
Seems cheaper to buy a fixed gear rear wheel and throw it on your
beater road bike or cross bike than to purchase a fixie. Is this
possible or would the slack in the chain as it runs through the
derailleur cause the chain to skip off the cogs when meeting the
resistance of the fixed gear?

You are my Leonard Zinn.

A

Your Leonard Zinn? I'm flattered. But i think the only similarities between me and Zinn are in vertical stature and a passion for bikes. That well i think we are both better mechanics than we are racers (he's i think a bit better than me in both areas - something to strive for on my part, no?).

To the answer
single speed... yes, fixed gear... no (you can but it'd not really work as you point out with the slack)
If you had a double derailleur, one on top, one on bottom... it might just work if not for the next problem:

problem with fixed gear wheels is they generally have track spacing
ie 120mm and that no work on 130 spaced road bikes.

In general though. With a bit of futzing with cog/chainring sizes and chain length you can make most vertical drop out bikes work as a fixie. Just look at fixed gear gallery for "ideas" assuming the axle spacing is 130 on the hub. Many shops can convert a fixed gear track wheel over to a 130 drop out. But then ya looking at buying a new axle, spacers and the labor involved in it.

Bottom line Fixed can have no slack. The chain needs roughly equal tension on both sides. Think about it symmetrically. Normal geared or singlespeed bikes apply force only on the top so there is always a slack side. On a fixed gear bike you apply force equally (biased significantly to the top but not as much as you'd think).

Why ya want to fixie your road or cross bike anyway? Hell you can buy a cheap ass complete one for under $500, it won't be light but it'll last at least a couple years of winter beating. Probably 10 down in your neck of the woods.

So there ya go AC in the Carolinas...

Hope that helps
GeWilli