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Technical FAQ with Lennard Zinn: Fixie chain tension and nipples threads

  • By Lennard Zinn
  • Published Oct. 18, 2011

You can get chain tension perfect without a tensioner.

Q. Dear Lennard,
What’s the best way to ensure correct chain tension (and secure rear wheel) on a track bike that doesn’t have a built-in adjuster in the rear dropouts? A separate chain tensioner?
— Martin

A.Dear Martin,
You certainly do not need a separate chain tensioner; people have been getting chain tension right on fixed gear bikes for well over a hundred years without them.

With standard, long-slot track dropouts and axle nuts, you tension your chain properly by “walking” the hub back in the dropouts: by alternating tightening one axle nut at a time and loosening the opposite one and alternately pulling the rim over toward the chainstay opposite the tightened nut.

As for getting the tension exactly right, you can’t improve on Sheldon Brown on this one. If you’re anal about it, you will first make sure that your chainring is centered on the bottom bracket as he suggests. Then your chain will have consistent tension as the crank rotates.

From Sheldon Brown:

Centering Chainwheels
The chain tension on a fixed gear is quite critical, and is regulated by moving the rear axle back and forth in the forkends. If the chain is too tight, the drivetrain 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.
Rear Wheel Installation
When your install the rear wheel, there are basically three things you need to adjust simultaneously:

  • The wheel needs to be straight. This basically means that the tire needs to be centered between the frame’s chainstays. If you get it centered between the chainstays, it is properly aligned.
  • The chain tension needs to be correct. (See previous section )
  • The axle nuts or quick release skewer need to be tight. Note: if you have a nutted axle, it is vitally important that the threads be properly lubricated with grease or oil. You should also have grease or oil on the contact surface where the axle nut presses against the washer that contacts the frame.

Some folks who are used to derailleur bikes find it frustrating, especially with a nutted hub. This is usually because they don’t know the technique of “walking” the wheel back and forth in the fork ends.

Start by installing the wheel at approximately the correct position and tightening the axle nuts. They don’t need to be super tight at this stage, but should more than finger tight. Check the chain tension and wheel alignment.

Most likely, the chain will be a bit loose, but perhaps the wheel is correctly aligned. Loosen one of the axle nuts and push the tire to the side so that the loose side of the axle moves to the rear, then tighten the axle nut you loosened.

Now the chain tension should be better, but the wheel is no longer centered between the chainstays. Loosen the other axle nut and re-center the wheel in the frame. This will actually tighten the chain a little bit more.

The key is to keep one or the other of the axle nuts tight at all times, and “walk” the wheel forward and back.

This takes a bit of practice and getting used to how much axle movement is needed to adjust a given amount of chain droop, but it isn’t really hard as long as you keep one side secured at all times.

[I like to leave the right-side axle nut a bit loose, get the chain a too tight, and tap the chain with the wrench as Sheldon describes for centering chainwheels. This way, I can move the rear wheel forward just the tiny bit needed to make the chain run smoothly. The wheel will then be skewed, and I need to readjust the left end of the axle, but this has little effect on the chain. — John Allen]”

Alles klar?
— Lennard

Q.Dear Lennard,
Thought I’d shoot you a quick email and pose a question to you being as you’ve helped me out in the past.

Stan's rim.

Question is: Can you use Wheelsmith nipples on DT Swiss spokes? I never have during my dozens and dozens of wheel builds, because I was told that there were slight differences in the threads and you’d have issues later on. I accepted that answer, but now I’m curious if that’s true or if it’s just another “urban legend” of the bicycle mechanic. What say you?
— Brian

A. Dear Brian,
They are compatible. Here is an eloquent answer from Ric Hjertberg of Wheel Fanatyk and Mad Fiber (and before that FSA and Wheelsmith):

“While nipples vary a lot (long, short, hidden, spline drive, various materials, etc.), spoke threading is stable. For bicycles, all nipples are compatible with all spokes as long as you match gauges.

Spoke threading is rolled on a 2.0mm wire (for 14g) at 56 threads per inch. Standards:

(1) DIN 79012 (also described as FG 2.3) = major thread diameter of 2.299mm x 56tpi.

(2) JIS (BC 2) = 2.27mm x 56tpi.

(3) In Asia = M2.5×0.45.

(4) In the US = 0.093″-56.

All of these threads are fully interchangeable. So much surface area in the spoke-nipple interface means there’s no worry.

As you well know, 15g spokes (1.8mm diameter) use the same thread pitch, 56. So one must always be careful not to use a 14g nipple on a 15g spoke. It’s loose but the thread seems to work until tension is high. This is a needless hazard but we’re stuck with it.

As one can tell, the “56tpi” harkens back to the 19th century when England (and its Whitworth standards) were the backbone of engineering. Not today, but the standard remains.

Recently, in an engineering forum, someone recently asked what is the world’s most common thread. Some said “M6″ and others “1/4-20.” The winner was the bicycle spoke thread. After all, 1+ billion bikes X 72 spokes/bike = more than any other threaded application.”

So there you go. It’s an urban legend. Interchange brands, but don’t interchange gauges.
— Lennard

FILED UNDER: Bikes and Tech / Technical FAQ TAGS: / /

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, as well as Zinn and the Art of Triathlon Bikes and Zinn's Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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