Re: Fixed Gear (Fixie) vs Single Speed Gearing

On Mon, Feb 7, 2011 at 2:22 PM, Andy Goodell <[email protected]> wrote:
>
> I think I remembered the flaw in my plan. With a rear derailleur
> applying tension, if the wheel spins faster than one pedals, it will
> throw any extra chain on the top piling up by the chainring. I think
> there would need to be an additional tensioner on the top in order to
> solve that.
>

I think a  tensioner on the top would be questionable at best and I'd
still be worried about ripping off/mangling it or the rear derailer if
I tried to coast on a fixed multispeed bike.  Also, part of the
benefit of going fixed/single speed is that the drivetrain efficiency
increases noticeably (at least, it did for me when I converted an old
12-speed to SS).

Here's Sheldon Brown's take on the subject:
http://www.sheldonbrown.com/fixed-conversion.html

"You CanNOT use any sort of pulley type chain tensioner on a fixed gear bike!

You cannot use a derailer on a fixed gear bike, even as a chain
tensioner, because when you resist the rotation of the pedals, you
would bend the derailer. This presents a problem if you want to use a
frame with vertical dropouts as a fixed gear, because there's no easy
way to adjust the chain tension. This is also true of chain tensioners
sold for singlespeed coasting bikes, such as the Surly Singleator.

Even the chain tensioners used for downhill mountain bike racing are
not strong enough to withstand the stress of resisting the pedals.
These tensioners have to clamp on to the chain stay, which is more or
less round. There is no way to make one that would be secure, short of
installing some sort of brazed-on fitting."