Vertical dropout single speed without tensioner

[tigoat]

The bike shown probably has more than 10,000 miles as a single speedster with many thousand feet of climbing. I usually ride at least 2 centuries a week during warmer months and with many fast weekday club rides so I am not your ordinary grocery shopping rider. I have used Surly single speed rings and cogs without any issue whatsoever. I probably only dropped a chain once or twice with a worn out ring in the last 6 years of single speed riding. I have used many single speed 3/32"x 1/2" chains over the years and most of them last at least three to four thousand miles. My favorite are KMC K810SL chains which usually last more than five thousand miles. If you don't believe me then you could place a bet so I can show you my Strava and Garmin Connect accounts with my millage in the last 5 years.

For the OP, make sure you know precisely your chain stay length, as that will dictate your chain length and gear combo that fit.

[11.4]

A slightly different perspective: On the track, you don't try for maximum tension on the chain. You get a smoother ride with less equipment wear and fewer failures overall if you set the chain as loosely as you can but where the chain won't derail when pushed with a wrench or screwdriver or similar implement. Rotate the chainring slowly while pushing the chain from the side; if it won't come off, it won't come off while riding. If a chain has come off using this method, it's because the wheel slipped in the horizontal stay-ends, not because the chain stretched or somehow derailed when it was unable to while testing it at slow speed.

Now, what's significant for this discussion is that this tensioning method (a) takes up quite a bit of chain (at least a half link if not more), and (b) that's a lot more than any chain wear could amount to. (Remember that you measure a whole road chain and look for more than an eighth inch of stretch, but a chain half link is a half inch, so stretch isn't going to amount to all that much -- and if you still worry, it's a cheap chain and you replace it if the chain feels slack to you). The point is that you don't have to use only a completely tensioned chain but instead allow for some slack built in.

As a result, if you have three or four chainrings and an assortment of cogs, plus a couple half links, you can experiment with different combinations so that you're at a tension you like. If it slackens slightly with use, simply test from time to time whether you can push the chain off with a tool while rotating the cranks. (And there are trackies who prefer to hold the bike up and simply shake it -- if it doesn't come off, it's ok. I prefer the push-it-off approach because I feel it's a little more demanding, but you don't have to be obsessive about it. I'm a careful track rider and track mechanic and with over 50 years' experience on the track, I've never ever thrown a chain this way.)

[mtechnica]

If it’s a singlespeed a tensioner works because it can take up slack on the side that isn’t under tension so there’s no downside to using one since you can actually adjust the tension properly instead of compromising. Fixed you need the dropouts or eccentric.

[astroturf]

+1 for eccentric hub or bb. However I am not sure how much an eccentric bb will affect your crank to saddle positioning.

[rustychisel]

Late to this party, so here's just another opinion to add to many excellent suggestions (SoCal Steve) ... get an ENO hub.

Have tried with 2 or 3 bikes using vertical dropouts and 'magic gear' filing dropouts, etc and they all can work until they don't, generally due to chain stretch. Half link is too coarse an adjustment for many situations. Get an ENO hub.

[cribbit]

Originally Posted by rustychisel

Late to this party, so here's just another opinion to add to many excellent suggestions (SoCal Steve) ... get an ENO hub.

Have tried with 2 or 3 bikes using vertical dropouts and 'magic gear' filing dropouts, etc and they all can work until they don't, generally due to chain stretch. Half link is too coarse an adjustment for many situations. Get an ENO hub.

How does this have any fewer points of failure than an ec bb?

[rustychisel]

TBH, I doubt that it does, since it's been a very long time since I serviced a bike with an eccentric BB.

So here's a few unscientific thoughts. ENO hubs seem a more 'elegant' solution, perhaps, with more range of adjustment, and allows you to use the very common UN-55 and UN-72 bottom brackets (your flavour may vary), and since we're discussing a fixed gear it may be that you don't much care for a rear brake. That, as I see it, may be the only real shortcoming to an ENO hub, since the adjustment if done sloppily might alter the brake track enough such it becomes an issue.

[tigoat]

Good track insight, 11.4. Fortunately, track bikes have an adjustable horizontal dropout, which is too easy to adjust the chain, no challenge at all. The challenge of making a regular dropout work with a single speed without a tensioner is a wow worthy accomplishment .

[JStonebarger]

Question: I seemed to get lucky finding the "magic gear" for my single speed cx bike, but the chain is quite tight. How tight is too tight?

[Jaybee]

Originally Posted by JStonebarger

Question: I seemed to get lucky finding the "magic gear" for my single speed cx bike, but the chain is quite tight. How tight is too tight?

can you still turn the cranks? no binding?

if you can't dial in perfect velodrome-worthy chain slack, you can get a teensy bit more by loosening the chainring bolts, going through a couple rotations to allow the chainring to find the best spot, then re-tightening the bolts. If you have a direct mount chainring, this won't work. sorry. another hack is to use an older chain that already has some stretch in it.

all these rigged half-measures are why magic gear is "magic" and requires just the right circumstances to work.

[JStonebarger]

No binding at all. (I actually rode my first sscx race ever on it at Nationals in Louisville.) It feels great, but seems a bit louder than I'd expect if I spin the cranks unloaded.

[SoCalSteve]

Just an FYI: https://forums.thepaceline.net/showthread.php?t=236886

[11.4]

Originally Posted by tigoat

Good track insight, 11.4. Fortunately, track bikes have an adjustable horizontal dropout, which is too easy to adjust the chain, no challenge at all. The challenge of making a regular dropout work with a single speed without a tensioner is a wow worthy accomplishment .

Actually, the point is that with three consecutive-toothed chainrings and a set of cogs to give the same ultimate gearing, you can get so close that the amount of slack is not a risk.

This whole kind of discussion often gets started with a vision of tightly tensioned chains. That's not the way to do it, so you start to gain degrees of freedom. An ENO hub is great, but if you have what you have and want to make it work, that bit of slack isn't an issue if you monitor it properly when you put the rig together.

[jbay]

My friend Eric put this neat page together years ago. It allows you to figure out the optimal chainring and sprocket combinations for a given chainstay length:

http://www.eehouse.org/fixin/fixmeup.php

— John