Dave Reckoning? said:What happens when you put a pair of spring loaded chain tensioners
on your chain, both above and below the chainstay on a fixed gear
rig? So that the top one would take up the slack during braking and
the lower one to suck up the extra chain during forward drive.
Oops! Chain tensioners take up slack in chains up to a certain
tension, that tension being just enough to keep slop and sag of the
span to stable limits. Since a fixed gear puts many times that much
tension in either chain run, a spring loaded tensioner cannot be used
because it will yield all the slack there is and cause a large
backlash from pedaling to back-pedaling or even from neutral (no force
on the pedals). That is why tandems generally don't have such devices
and use an eccentric BB to adjust chain slack.
Quoted message said:Assume that you have a vertical dropout and that you would never
have more than one link length of slack to contend with. Also
assume that you are using a "big" ring and cog (52 - 20)to maximize
the distance the chain moves per unit of tire travel. In my feeble,
untrained mind this looks like a near perfect solution save for the
problem of slop going from drive to braking.
Quoted message said:I know this sounds crazy, and probably has a fatal flaw but, has
anyone here ever tried it and lived to tell?
You may be surprised how much sag .99 of a link (one inch) will cause.
Anyone who has gone that far as trying it got out of there after just
sitting on the bicycle to test it and didn't talk about it again. Of
course if you have just the right spacing, you can do it and have no
tensioner, especially on both runs. I have had a derailleur break
when a "derailleur stick" flipped up off the road I was on and into
the chain. I took the derailleur parts off and put them with my patch
kit etc. and was able to shorten the chain so that the 50-15 and 46-17
worked with practically no sag. I was lucky since those two gears got
me home from the far side of the Santa Cruz Mts. (CA).
Jobst Brandt
[email hidden]
