Friday, April 25, 2008

Singlespeed on the Super-Cheap and Easy

Boyfriend Scott's bike was making the telltale pop-pop-pop sound whenever he pedaled hard. Pop-pop-pop means "Replace my drive train! Pronto!"

I told him what was happening - the gears wear out and the chain stretches, and eventually you get the popping sound 'cause they don't fit together right any more. If you only replace the chain instead of both together, you'll still get the pop-pop sound because the new chain won't mesh right with the old gears. has a whole article about it, of course.

Scott asked me if I could switch it to a singlespeed, too. He's the "I only use the highest gear of my hybrid bike, anyway" version of singlespeed. So we pulled off his 7-speed freewheel, and switched in the not-very-worn 16-tooth freewheel that had just been sitting on the other side of the flip-flop hub on my fixie. And we did the ceremonial snipping of the cables and denuding of deraillers. His bike (a Raleigh C-30) has vertical dropouts, so I couldn't get the chain tension right, and the chainline (going from the big ring to where the little ring had been) was wack, so it kept throwing the chain. Ugh! I broke my boyfriend's bike! I sent him to BikeWorks for a half link, but that didn't resolve the problem.

There's a standard way around this, which is to re-space and re-dish the wheel from having room for a whole 7-speed freewheel to just enough room for a onesie. That seemed like way too much work for this bike. So I got him another chain, and came up with this hack. I'm sure this has been done before, because it's one of those things that feels so obvious when you stumble on it, but here it is for the taking:

Here's what I did: I put his derailler back on to use as a makeshift chain tensioner. For this to work, the derailler has to be locked in the right place. Ideally, you could do this with the limit screws, by dialing in the top and bottom limit screws so that the derailler won't budge in either direction. But limit screws are designed to keep the chain from falling off either end of the freewheel cluster, not to lock it in place somewhere in the middle. The lower limit will reach, but the top won't. So I dialed in the lower limit screw to hold the derailler in the right spot. Then I dropped a shortened piece of brake cable through the derailler and locked it in place by snugging the anchor bolt.

The result: A derailler with a hot second of cable that stays put inside the derailler itself. Neat-o, huh?

This could be way more simple and elegant if you have a decent hardware store handy. Get a screw or bolt that matches the diameter and pitch of your limit screws, but is about a centimeter longer. Replace your top limit with this one - you can put your derailler wherever you want it with no cables at all!

Purists, take note: I know I could take a few links out of the chain. I'm trying to convince Scott to use 42/16 instead of 52/16 because I want his knees to last. I'll pull the links if it works for him, otherwise he'll be rocking the big ring.


Emily said...

Wait... wait. WAIT! Say that again, but more of it.
I was just trying to fix someones bike with a slightly bent rear dropout on tuesday. I was trying to figure out how to keep the rear derailleur from ever hopping up to the biggest gear, where it would start rubbing spokes. I adjusted the derailleur but it was still able to get up there-- finally we decided we would have to just tell the guy to never shift up there unless he wanted broken spokes.
But now you tell me you have this way to force it to be so. But I don't get it! Ya do what now? Does this just restrict the derailleur's range of movement, or make it immovable?
I am always jerry-rigging/fixing messed up old bikes that people use but don't want to spend any money on-- and would love a way to work around this kind of problem without a total rebuild.
This may be more of an in-depth question than a comment section can stand. Also: more bike-fixing posts! I will start posting more bike-fixing posts too... bike fixing: its like knitting, but greasier.

Daniel Yuhas said...

Okay, here goes - the high and low limit screws are what keeps the chain from jumping off the gears when you shift the whole way up or the whole way down. The more screwed in they are, the less range of movement the derailler has. If the limit screws were long enough, you could immobilize the derailler that way by holding it where you want it to be and then tightening the screws down so it wouldn't budge any more.

In my case, I didn't want it to move any more because I'm using it as a chain tensioner and to correct the chainline.

For your friend's bike, you might be able to keep him from shifting up to the big ring by replacing the lower limit screw with one that's the same size, but longer. Then basically you'll be able to screw it in further and his derailler won't hit his spokes any more.

Did that make any more sense?

Someday I'm going to open a bike shop and knitting store all in one. There will be some sort of impermeable degreasing airlock thing between between the bike half and the knitting half.

Emily said...

Oh... a longer limit screw. That is a great solution! Thanks for the answer.
Unfortunately, since the bike was at this bike co-op I work at, it has probably been taken back by the owner by now. But its good to know for the next messed up rear derailleur I run into. I spend a lot of time fixing very weird old bikes through this co-op, so I probably will encounter this problem again soon!