Tips for proper tension on a fixed

[Acotts]

I had my first "I almost died on my fixed" moment this weekend. It turns out the hill I spoke of on my last post is not that bad to climb up, but is pretty hariy going down.

Thank god the chain jumped off and locked up the cranks instead of the rear wheel. Thank god I had a front brake. Otherwise Acotts would not get to 400 posts!

Anyway, any folks no a good way to make sure the tension is perfect?

Also, my single speed MTB that I used to ride had some sort of device on the dropouts that looked like it helped keep the wheel set. (I have no idea what it is called) Anyways, do I need one of those devices for my Fixed roadbike? If so, what kind would I need? (how do I make sure it is compatable?)

...on a good note. I was not to far from my house. I reset the chain and wheel and ended up having an awesome ride. 2 hours on the fixed and I have to say that I have not had a bike ride that was that enjoyable in a looong time.

[mister]

if you use 1/8" drivetrain the chain will have a harder time coming off, so you can run a looser tension with it. you need to have a good chainline, unworn cog and chainring and you should be fine.
no need to make the chain really tight.
after you get the tension set where you think it is ok, push the chain sideways with a wrench while you turn the wheel. if it doesn't come off when you do this then you're good to go.

[Fixed]

what mister said
there is a trick to setting your chain ring a little tap here and there to make it round
cheers imho

[Joel]

It's interesting that you bring this up. Yesterday I was at a light and applying pressure to go forward after slowing. I felt some "give" in the chain.

After 800 miles or so on the new chain, it had definitely stretched some. I don't think enough to come off, but I stopped and slid the rear wheel back enough so it was tight again.

I'm not certain exactly how tight is tight enough...one of the experts I'm sure will chime in, but for me I just pull the wheel back by hand and tighten so that there is no vertical play.

Happy to hear there was no damage done...throwing a fixed chain can really mess up your day!

Joel

[TimB]

Acotts - does your road fixed have track tips, or are you running a Eno or some such other device?

If it has track tips, and you want something to help tension the chain, Surley makes something they call Tugnuts, or check out these:

http://www.benscycle.net/index.php?main_page=product_info&products_id=1420

In order to get my rack to fit I had to ditch the Tugnuts in favor of these from MKS.

A chain tensioner is not really necessary, but if you're concerned, or, like me, just have a hard time to get the wheel in straight (important on my fixie with canti brakes) they can be helpful.

[Tobias]

Chain tension is a function of catenary. Best way for me to tell is to lift chain at center and see how far I can lift from very bottom to top.
As chain wears the amount you can lift is noticeably more. A small amount of chain stretch makes a big difference in catenary.
Since chainrings are not perfectly concentric, I do this a few times while indexing the cranks 30 to 45 degree at a time until I find where chain is tightest.

[Acotts]

Acotts - does your road fixed have track tips, or are you running a Eno or some such other device?

If it has track tips, and you want something to help tension the chain, Surley makes something they call Tugnuts, or check out these:

http://www.benscycle.net/index.php?main_page=product_info&products_id=1420

In order to get my rack to fit I had to ditch the Tugnuts in favor of these from MKS.

A chain tensioner is not really necessary, but if you're concerned, or, like me, just have a hard time to get the wheel in straight (important on my fixie with canti brakes) they can be helpful.

The drop outs are track tips. It is ver7y easy to get the wheel in and straight.

I clicked on the URL, I cant really tell what exactly I am looking at. Are these just locknuts with little handles on them?

As for the tapping, are you tightening the locknuts lightly and then tapping them back with a rubber hammer until the chain is taut, then tightening the nuts some more?

[WadePatton]

what mister said
there is a trick to setting your chain ring a little tap here and there to make it round
cheers imho
Pretty sure Sheldon has an article on this trick of centering the chain ring. The purpose is have the chain tension remain most constant. Slight out-of-roundness in the chain ring and cog usually cause variations in chain tension. Spider-mounted rings can be tinkered with.

Chainline. Measure it and get it right. My SS atb was quite a ways off from the factory. I fixed it with a longer spindle in the BB.

Brakes are good. ;)

[mister]

i ride mine with a little visible droop in the chain. it is smoothest that way.

[WadePatton]

The drop outs are track tips. It is ver7y easy to get the wheel in and straight.

I clicked on the URL, I cant really tell what exactly I am looking at. Are these just locknuts with little handles on them?

As for the tapping, are you tightening the locknuts lightly and then tapping them back with a rubber hammer until the chain is taut, then tightening the nuts some more?

snipped from: http://www.sheldonbrown.com/fixed.html
Chain Tension

The chain tension on a fixed gear is quite critical, and is regulated by moving the rear axle back and forth in the fork ends. If the chain is too tight, the drive train will bind, perhaps only at one angle of the pedals (chainwheels are not usually perfectly concentric). It should be tight as it can be without binding. If the chain is too loose, it can fall off, which is quite dangerous on a fixed gear.

Set the rear axle so that the chain pulls taut at the tightest part of the cranks' rotation. One at a time, loosen up each of the stack bolts, and tighten it back just finger tight. Spin the crank slowly and watch for the chain to get to its tightest point. Strike the taut chain lightly with a convenient tool to make the chain ring move a bit on its spider. Then rotate the crank some more, finding the new tightest spot, and repeat as necessary.

This takes a little bit of your hands learning how hard to hit the chain, and how loose to set the stack bolts, but it is really quite easy to learn.

Tighten up the stack bolts a bit and re-check. Tighten the stack bolts in a regular pattern, like the lug nuts on a car wheel. My standard pattern is to start by tightening the bolt opposite the crank, then move clockwise 2 bolts (144 degrees), tighten that one, clockwise 2 more, and so on. Never tighten two neighboring bolts in a row. You may prefer to go counterclockwise, but try to get in the habit of always starting at the same place and always going the same way. This reduces the chances of accidentally missing a bolt.

Once you have the chainrings centered and secured, adjust the position of the rear axle to make the chain as nearly tight as possible without binding. Notice how freely the drive train turns when the chain is too loose. That is how freely it should turn when you are done, but with as little chain droop as possible.

[TimB]

They "washer" part goes on the axle, the other "handle" part fits over the end of the track tip. It uses a 3mm hex nut to pull back on the washer to tighten the chain.

Not sure what you're talking about with the rubber hammer. That's related more to getting a more consistent chain tension given the imperfect roundness of chainrings.

[fixednwinter]

Acotts;

Glad you're OK - that's a heart-attack inducing incident, for sure.

The other posters have all better tips that I can contribute, so you'll want to listen to them. Going 1/8th (if you haven't already) is a definite advantage.

Since I only ever use my fixed for road use (have never done track), I tend to tighten my chain on the tight rather than loose side, due to the bumps and potholes. About the only time I've managed to derail my fixed chain is on a pretty big speed bump, during a fast pedal interval. Normally, if I wasn't doing an interval, I'd take it easy over a speed bump.

[11.4]

The real issue here is why your chain derailed in the first place. Even with extremely sloppy chain tension a derailment is very hard to do unless you have another problem, most usually either chainline or a rear cog that spun off and threw the whole chain. On the track, it's increasingly the trend to loosen the chain more, going to 1 to 1.5 inches of vertical compliance in the chain -- this buys you smoother pedaling, less equipment wear, and overall more speed. Chain derailments are essentially unheard of at high-level track events.

The basic rule applied here is to run the chain as loose as possible and use any handy tool to push the chain off the chainring while rotating the pedals. If it doesn't catch on the teeth, it won't derail. I routinely run over 1 inch of vertical compliance and have zero problems on road or track.

I'm guessing you have a chainline or alignment problem. This can arise from many causes, some of which aren't entirely obvious (a misaligned bottom bracket, a front triangle not aligned with the rear triangle, etc.) as well as the obvious problems of different chain offset between a particular hub and particular crankset. Your cog didn't spin off in the rear (that's the 100% certain way to throw a chain)?

I'd try to diagnose the real source of the problem, because just tightening the chain with an alignment problem can just increase the risk of breaking a chain or having other problems.

[Acotts]

"Your cog didn't spin off in the rear (that's the 100% certain way to throw a chain)?"

What do you mean here?

For some additional info. I am running an Iro BB, Iro Crankset, and Iro Hub on an Iro frame. Not to say that manufacturers cant make mistakes, but it is unlikely that there are compability issues. Would misalignment issues arise from the installation.

[mister]

he means, you didn't apply a little backpressure and then have the cog start spinning on the hub until it was completely unthreaded from the hub...a lockring is supposed to prevent this...and will unless the threads get stripped.

you should check your chainline. some cranks/bottom brackets don't work well is other hubs sometimes.

[goonster]

Chain tension is a function of catenary. Best way for me to tell is to lift chain at center and see how far I can lift from very bottom to top.
As chain wears the amount you can lift is noticeably more. A small amount of chain stretch makes a big difference in catenary.
Since chainrings are not perfectly concentric, I do this a few times while indexing the cranks 30 to 45 degree at a time until I find where chain is tightest.

Please clarify for those of us who only have undergrad degrees. ;)

Are you saying that (relatively) small deviations in chainring concentricity result in (relatively) large differences in catenary angle or "shape"?

Is not the converse of the highlighted statement actually true, i.e. "catenary is a function of chain tension", since (for constant chain weight) the catenary is a direct function of variable chain tension*?

(* = actually, distance between "anchoring points")

Just trying to wrap my head around this . . .

[Ti Designs]

I had no idea fixed gears were that complicated. The only rule I play by is "keep your fingers away from a moving fixed gear drivetrain if you want to keep them"

[Fixed]

bro try to get it to do it again on a repair stand
i have had a chain break but never had one just come off by its self
check your lock ring try and see what's goin on
cheers if you listen they talk to you

[Fixed]

I had no idea fixed gears were that complicated. The only rule I play by is "keep your fingers away from a moving fixed gear drivetrain if you want to keep them"
that's why i like em even a dope like me can work on them
cheers :beer:

[regularguy412]

Is it possible that frame flex combined with some of the other, aforementioned, factors could cause the chain to derail? It seems to me that standing to accelerate from a stop would be the mostly likely time for the frame to flex. If the chain line was a bit off and the chain too slack, all these factors might contribute to a dropped chain.

Mike in AR

[Acotts]

Is it possible that frame flex combined with some of the other, aforementioned, factors could cause the chain to derail? It seems to me that standing to accelerate from a stop would be the mostly likely time for the frame to flex. If the chain line was a bit off and the chain too slack, all these factors might contribute to a dropped chain.

Mike in AR


No, there is much more crazyness going on when you are shooting downhill and your legs get away from you and a car pulls out of a drive way 20 yards ahead. I was realy jamming back on the pedals to stop becuase my front brake wasn't cutting it at all.

There was a good amount of adrenelin involved.

i am positive that the stresses I unleased on my drive train were greater than anything anyone could do by simply accellerating.

[11.4]

Hard for frame flex to do it. Well nigh impossible in fact.

It's not unheard of for bikes to arrive from a manufacturer with chain alignment issues. Plus some cogs have different offsets and different total threading depths -- that can easily be worth a couple millimeters -- but cranksets are usually the worst culprit. I've had problems from time to time with a couple friends' IROs -- the equipment isn't always a perfect match in chainline. Check it yourself - you want to put a straightedge on the side of the cog and the side of the chainring and have everything lie perfectly flat (no chain in place, of course).

The chainring concentricity issue is probably not the source of the problem here. There are a number of machining steps in producing even an inexpensive chainring, and they involve jigging the chainring first to cut the teeth and then rejigging it to cut the bolt holes and countersinks. Crankarms are also a culprit -- the center spline may not be concentric with the chainring bolt holes. Usually the holes themselves are drilled in a proper circle so you don't have problems mounting a ring on a crankarm -- the ring just isn't perfectly centered around the spline it rotates on. It's usual that some brands have wildly inaccurate machining, and even the best tend to be off a little. It's normal and acceptable to try out a high end chainring (Dura Ace or top-end Sugino) and return it if it's really not round. You'll tell right away on a track ring because as you rotate the pedals through one revolution, the chain will be tighter at one point, looser at another (typically 180 degrees opposite). Since part of the machining problem lies in how the crankarms are machined, you can SOMETIMES rotate the ring to match a high spot on the ring with a low spot on the arms. SOMETIMES this works -- it depends on both crankarm and ring being out-of-round. Frankly, if arms or ring are out of round, I simply return them immediately and try another. Even inexpensive equipment like IRO should manage to be round. Road equipment has the same problems but the rear derailleur takes up any chain slack so you don't notice it. And yes, track equipment can get quite tricky because while simple, it's also unforgiving. I see far more badly designed track frames than badly designed road frames, and more bad components for track than for road. Your IRO stuff should be working OK, although no one ever can be certain about chainline til you verify it yourself.

[11.4]

No, there is much more crazyness going on when you are shooting downhill and your legs get away from you and a car pulls out of a drive way 20 yards ahead. I was realy jamming back on the pedals to stop becuase my front brake wasn't cutting it at all.

There was a good amount of adrenelin involved.

i am positive that the stresses I unleased on my drive train were greater than anything anyone could do by simply accellerating.

This does sound like rear-cog alignment. A frame without perfect alignment will often sound quiet and smooth in a service stand while you rotate the pedals forward, but you'll hear a little clicking at the rear cog when you pedal backwards. That's an alignment problem.

[Tobias]

Please clarify for those of us who only have undergrad degrees. ;)

Are you saying that (relatively) small deviations in chainring concentricity result in (relatively) large differences in catenary angle or "shape"?
Is not the converse of the highlighted statement actually true, i.e. "catenary is a function of chain tension", since (for constant chain weight) the catenary is a direct function of variable chain tension*?

(* = actually, distance between "anchoring points")

Just trying to wrap my head around this . . .Yes, the greater the tension the straighter the chain; or the straighter the chain the tighter (for a given chainstay length). Kind of one and the same in my way of looking at it.

When the chain is relatively tight, a small amount of eccentricity can create too much tension. My only point was to check and set chain tension where chainring makes it tightest.

If a chain is very long, a small amount of eccentricity will make very little difference. It's mostly an issue when the chain is tight.