gif4445

Not sure where to ask this question, so it goes here. Have you ever had a rear derailleur break and were forced to single speed it to the next town or whatever? I nearly had that "opportunity", but hitched a ride 20 miles to a bike shop instead. This was on a Coast to Coast Bike race in eastern Missouri last June. I had contemplated the chance of something like this happening and thought I was prepared with chain breaker and necessary links. But not having done it before gets you to asking questions. What combinations of front/back gears would be best? I'm sure that depends upon how far you need to go and what the climbing requirements are. Luckily, at the present time, I need to replace my chain and thinking it's a good time to experiment with this scenario. I have a 50/34 front and an 11-40 rear cassette. The 11-40 breaks down individual gear-wise to 11-13-15-17-19-21-24-27-31-35-40. I assume that chain alignment will be almost or more important than gear combination. Before I try all of this, I would like to hear from those that have did such or have some thoughts. Thanks.

ThermionicScott 

The most important thing for me would be the gear combination. Chain alignment isn't as critical as it was in the olde days, but I'd still try to find a gear combination that was relatively straight. My preference for single-speed is around 65", so it would be 50/21 for me.

phughes

It would really depend on your load, the hills you will encounter, and whether or not you want to ride up them, or walk the bike, and of course your preference.

I might go with the 34/21, or the 50/21 depending on which combination had the straighter chainline. Once again though, it all depends on the terrain, and load. Whatever you chose it would be a compromise.

A guy did a world tour on a single speed, using 32/18 on a Surly Ogre, which is close to the ratios you get with the combinations I suggested. . https://bikepacking.com/plog/around-...d-singlespeed/

dsaul

Chainline is very important to singlespeeding a multispeed bike after a derailleur or hanger failure. I have done it and seen it done numerous times and the chainline needs to be very straight or the chain will try to climb up onto the next larger cog on the cassette. When that happens, something will break. Usually the chain breaks, but QR wheels can pull out of the dropouts. I saw one case, with a thru axle wheel, where the chain was able to climb onto the next larger cog and put so much tension on the axle that it was extremely difficult to remove the axle.

79pmooney

50-19. Good chainline on your bike, good all around gear. You might have to walk a hill but you are only doing this once. (And you can ride a hill in a much bigger gear than you ever dreamed possible once you throw out the concept of a proper RPM. Breathing hard? Slow down. RPM's only 30 and still breathing hard, Ride 20 RPM.)

Ben

Leinster

I've done it on 2 occasions. Getting chainline right is important; I had a wheel try to pop out descending the Col de Peyresourde in 39x14.

One of my bikes is now permanently converted to SS. Even after taking the other sprockets off, it would still occasionally jump off the 16, and it took several attempts at chainline and link count to get it consistently right.

gif4445

Thanks for the replies and suggestions! I will aim for the 50-21/50-19 area and see what works best. Sounds like it will take a little trial and error.

Happy Feet

I would also add to pay attention to what combinations you tend to spend the most time in. If you had to go SS you would probably fair best overall with something close to that.

c_m_shooter

I have tried to do that a few times and it doesn't work unless you can straighten the derailer enough to lock it with the end point adjustments. The ramps on the cogs of the cassette always cause the chain to try and shift under heavy pedaling. I end up removing the chain and walking up hill and coasting down. It is best to just start with a single speed to begin with.

rosefarts

Depending on the damage to the derailleur or hanger, itight be possible to use the derailleur as a chain tensioner. This mostly eliminates the need to get the perfect line or chain length.

Happy Feet

If you have a chain breaker, as the op says, you can just bypass the derailer and take out enough chain length to turn it into a SS.

That's why some are suggesting chainline is important. If the chain wants to walk up the cassette the tension will either break the chain or pull the wheel out of the dropouts.

Otherwise, if you can still route the chain through the derailer it's a more common failure such as a cable breaking. The chain lands on whatever cog it lands on. You can alter that somewhat with the limiter screws or tying off the cable and still have the limited range of the front derailer to work with.

livedarklions

I got pretty much stuck on a flat MUP in a 53 x 11 combination when the shifter crapped out. Wasn't too bad except for the stop signs, but I'm a high gear freak. OTOH, when I replaced the shifter, I felt like Superman able to leap tall stop signs in a reasonable number of spins.

woodcraft

I've done it twice. One time it worked OK and I was able to continue on for the remaining 40 miles of the ride.

The other time was 5 miles or more out a dirt road. I didn't get the chainline right, and the chain went off to a smaller cog under load,

so ended up walking up the hills & pedaling the flats & downhills.

So IME, chainline is the important thing. If the RD was intact, there would be no point in this discussion- it would just need tape, zip tie, or tieing off the cable to get a usable gear.

I haven't tried this, but you could probably run the slack chain with the bike on the stand and see what cogs it would stay in,

but it's unlikely that it would be remembered during a roadside event.

mr_bill

Just for future reference, if the problem is the shifter or broken shift cable (or groan broken cable stop) you often can play with the hi limit to move the derailleur up from the small sprocket to a few higher. Less Super.

For those bypassing the rear derailleur, chain line is indeed most important (modern chainwheels and cassettes want to shift).

Warnings - go easy, no standing, even walk up steep hills. This is limp home mode only.

And disable the front derailleur, especially if you size the chain to the small front chainwheel. (Make it impossible to click-f-me.)

-mr. bill

rm -rf

A rider had a broken rear shift cable on a group ride a few years ago. I had previously worked around a broken cable by tying it off on my bottle cage. I tried this again, and it just slipped back to the 11 cog.

The limit screws often only move a shift or two.

But one of the other riders knew what to do:
How to move to the middle of the cassette with a broken shift cable

This is easier with two people, one to push on the rear derailleur body, one the crank and set the bottle cage bolt.
1. Crank the pedals and push the rear derailleur by hand to the biggest cog. Then stop moving the chain.
2. with the chain on the biggest cog:
3. loosen a bottle cage bolt on the down tube.
4. wrap the broken cable around the bottle cage bolt, and pull it tight!
5. tighten the bolt.
There will be enough slack in the cable to move the chain to one of the middle cogs.
Now you have a two speed! Shift the front for flats or for easy hills.

So inventive!

gif4445

So I tried the SS route today. I ended up taking 12 links off of my 114 link chain to fit it on the 50-19. A little loose, so rode it up on the 21 tooth gear. Tight. I plan on taking the chain off later this afternoon and see if there might be any problems due to chain being too tight. Anyway, I went for a 4 mile gravel ride with the 50-21 and the chain stayed on. The ride included a couple 6-8% grade hills. I was reluctant to get out of the saddle until the 8% grade close to home. I did so then, and everything held. It would be interesting to see what would happen if I needed to go 100 miles on this setup. I know for sure, I wouldn't want it to be in the Missouri Ozarks or Kentucky hills!

gif4445

I've stored my info in the notes section of my iPhone. That's the problem with mechanicals that do not happen that frequently. I tend to forget what I did exactly.

gif4445

When I had the problem in Missouri, the DR just broke just beyond the base of attachment to the hanger. Nothing to salvage or use.

63rickert

If you have a Campagnolo 1020 derailleur insert pinky finger inside the parallelogram and disengage the spring. You may now put the chain on any cog you wish and it will stay there. And you wonder why some of us are still using sixty year old shifters.

Happy Feet

Because you anticipate them breaking?

Pratt

When I did it, about 50 years ago, the chain wouldn't get tight enough on the cog with the good chainline. It would climb the next larger cog from time to time, due to bumps. That would then pull the wheel out of alignment. Dismount, release the quick release, remount the chain, tighten QR, ride on. Happened eery few miles. Ever since, I have been very attentive to limit screws

gif4445

Took the shortened chain off today and inspected everything. Looks good IMO. The bigger question for me as I look at doing some more ultra-distance races in the future? Do I want this for my plan in case I have another derailleur break? Derailleur failure was not uncommon on the Trans Am race. I'm considering it might be a good idea to take a spare DR with me. Adding to it, the fact that the long cage DR I use, may not be available at all bike shops. (I was lucky that in the shop I went to in Farmington MO, an employee had a bike at home with a long cage DR). An Ultegra DR weights around 250 grams. How many minutes would an additional 250 g slow me down over a 4200 mile race? Probably not many and certainly not close to the 2/3 of a day I lost dealing with the problem. Maybe I'll just vow to weigh a half pound less than normal target weight at the start of the race.