Track Folks: Chain Tension Question

[Lewis Moon]

For some reason something is out of whack in my drivetrain. I have the dreaded tighter looser tighter looser tighter looser tighter looser.

The chainwheel is a Dura Ace (yes, you read that correctly) 1/8 track pitch, but I'm running it on a Suntour Superbe road crankset. Could the crankset be out of whack?

[stien]

Try loosening the chainring bolts a tad, giving it a spin, then retightening? I seem to recall someone having the chainring slightly off "center" in the holes.

[nooneline]

Do what Stein recommends. When I see this phenomenon, it can be helped by loosening the bolts, spinning the wheel, tapping the chain with a wrench to help "center" the chain on the spider. When you tighten, tighten the CR bolts by tightening every other one - not going sequentially around..

Or, maybe you need to get a track crankset. I'd guess that there's a greater possibility that an old road crankset was produced nonconcentrically than modern track cranks are.

[darkmother]

You can often correct this situation by loosening the chainring bolts and moving the ring into a more concentric position. I squeeze the upper and lower runs of chain together with my hand to pull the ring towards the rear axle.

I seem to remember an article on Sheldon Brown's site that talks about this technique.

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[Hindmost]

A natural phenomena with chain drives. Adjust so the tight is not overly-tensioned. Something about how the chain is taken up by the rear cog, exaggerated by small cogs.

What cog are you running?

[spinarelli]

Since using a road crank measure your chainline to see if it's correnct for your rear hub and the chain/cog/ring is not used/worn and stretched. I always run a new cog and a new chain just so they wear out together.

Take the chainring off and put it on a flat surface to check if the ring is not warped. Then put it back and tighten the rings in an even pattern, alternating so it is evenly seated. Don't tighten one bolt all the way and then the next.

[ultraman6970]

The problem could be the cog or the chainring, if you are using a good brand of cog then sure the chainring is the problem. Tracker here... dont worry about it ok? Just set the tension in one of the tight spots and good to go. It is what it is my friend, even using campagnolo and shimano (and other brands) specific cranksets I never seen chainrings 100% flat. Seen cogs perfectly straight but that doesnt mean arent tad oval... and that will bring the problem you have.

Just set the tension in the tight spot and good to go.

[oldpotatoe]

Originally Posted by Lewis Moon

For some reason something is out of whack in my drivetrain. I have the dreaded tighter looser tighter looser tighter looser tighter looser.

The chainwheel is a Dura Ace (yes, you read that correctly) 1/8 track pitch, but I'm running it on a Suntour Superbe road crankset. Could the crankset be out of whack?

Yes, loosening the CR bolts and spinning wheel helps to 'center' chainring but all fixed gear/track setups have a little tight-loose-tight phenomenon. Make sure 'tight' isn't too tight. Break chain or at least wear stuff out. Also have the ring on the inside of the spider if the frame has clearance, Clarence.

[11.4]

Modern chainrings and cranksets are made pretty much always with full concentricity so this happens less. It's easy to do right when you are using CNC controls and are doing more of the process on one fixturing.

In the older days, aka Suntour Superbe days (whether track or road), the machinist had to cut the shelves on the crank arm spider, then had to drill the bolt holes, then had to mill the square taper in at least three steps, and so on and so on. You may have a square taper slightly out of concentricity, or a host of other potential problems. With older crank arms I've often put them on a CNC'd mill and found three or four different errors, that sometimes offset each other and sometimes didn't. I've also always found more track problems with some of the lesser brands. Dura Ace is pretty consistent now but wasn't a few years ago so you ideally want the newer grey-finished rings, and Sugino Zen track rings are generally the best on a consistent basis.

You can rotate the chainring a couple holes worth and reinstall, to see if it evens things out. If that doesn't work, try a couple different rotation amounts. If that never works, try to exchange the chainring and see if that makes it go away. The odds, though, are that it's in the crank arm or even in the bottom bracket.

Your Dura Ace cog, by the way, is probably not a problem (assuming it's current production and not an older model).

Many track setups have a little bit of unevenness in chain tension. I try to avoid it because it can feel tiring on your legs and it can sometimes make your bike more prone to dropping a chain. Use a high quality chain and set the tension so you're not running out of play at the tight spots. But at the loose spots, you likewise don't want to so loose that you can push the chain off the chainring with the edge of a spanner as you rotate the crank a bit.

Trackies who used to have tension problems would test equipment upon purchasing it and would immediately return pieces that didn't support concentricity. You still have to think that way if you choose to use older equipment.

[Greyfox]

Hello 11.4 - very helpful information as always.

You commented about the chainring concentricity. What about rear cog concentricity?

I ask because the Niner ti cogs in 3/32 look great and would be good for winter riding, but there’s not much point in riding it if it’s not truly round.

Is there any easy way other than installing it and running the chain over it to check for cog concentric?

Thanks in advance for your insights and perspective.

Greyfox

[11.4]

Originally Posted by Greyfox

Hello 11.4 - very helpful information as always.

You commented about the chainring concentricity. What about rear cog concentricity?

I ask because the Niner ti cogs in 3/32 look great and would be good for winter riding, but there’s not much point in riding it if it’s not truly round.

Is there any easy way other than installing it and running the chain over it to check for cog concentric?

Thanks in advance for your insights and perspective.

Greyfox

There's a lot more room for inaccuracy in a chainring than there is in a cog. The cog would have to be really eccentric to make as much difference in chain tension. Also, they are basically very simply made -- one pressed or machined cog that's then threaded. I've occasionally seen a badly threaded one or a very old pressed steel cog that was kattywompus, but they aren't common. You can swap the cog and see if it's the problem, but it rarely is.

[smead]

I didn't see anyone mention the most obvious so I'll add it - when chains stretch and wear, they usually exhibit this (tight spot). If your chain isn't new, try a new chain first.

[11.4]

Originally Posted by smead

I didn't see anyone mention the most obvious so I'll add it - when chains stretch and wear, they usually exhibit this (tight spot). If your chain isn't new, try a new chain first.

I've seen chains wear but never unevenly so as to create a problem like this. They may not seat as well on the chainring, but wear typically doesn't create uneven lengths from one link to the next.

[93KgBike]

Could we see photos of your setup, illustrating the tension and slack in the revolution, please?