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Technical FAQ with Lennard Zinn: Spoke tension

  • By Lennard Zinn
  • Published Nov. 22, 2011

Q. Dear Lennard,

Have you ever seen a rear wheel stay perfectly true, yet go out of dish? I have two Mavic rear wheels that over time the rims have migrated towards the cassette at both the brake and chain stays. I took the wheel in and it was indeed very true, yet about 1/16 inch towards the cassette. The mechanic tightened up the non-drive side and Loctited them, but I have not tried it out yet. I am a 200-pounder that has a very steep hill coming home, and I try to pedal smoothly, but maybe that is a contribution?

—Gordon

A. Dear Gordon,

What I certainly have seen is a true and dished rear wheel maintain its true but lose its dish when a tire is installed and pumped up. When the air pressure in the tire pushes inward on the rim and decreases the spoke tension as the rim diameter decreases, the wheel pulls more to the drive side because those spokes are under higher tension. Are you sure this isn’t what happened to your wheel? Otherwise, I think that the likelihood of each non-drive spoke loosening the same amount so that the wheel stays true and loses dish would be low.

Normally, the amount that the dish drifts is dependent on tire pressure as well as vertical rim stiffness. The lighter the rim, the greater is the spoke de-tensioning effect of a given amount of tire pressure. Ideally, a rear wheel would be dished more toward the non-drive side so that when it has a tire on it, it becomes centered. Either that or the dishing would best be performed after the tire is mounted and inflated.

Finally, your greater weight sitting on the bike de-tensions the spokes at the bottom more than a lighter rider, resulting in perhaps the non-drive spokes loosening as you ride.

—Lennard

Reader follow-up

Following are three comments regarding losing spoke tension on a PowerTap/NoTubes Alpha 340 rear wheel:

Q. Dear Lennard,

I just saw my last e-mail online and wanted to follow up. I have since sold my Alpha 340 wheelset because I couldn’t keep tires on it.

Regarding your writer with the vanishing spoke tension: I had a similar problem when initially building my Alpha 340/Ultegra hub wheelset. I lost 25 percent of the spoke tension upon installation and inflation of the tubeless tire. Simply put, tension was down and dish was off when a tire was on and inflated, and dish and tension were perfectly normal when the tire was off — weird and dramatic with some serious head-scratching.

Once I deduced that the ERD was compressed by the tire I called Stan’s and was told that this is common to varying degrees depending on the hub design. They suggested installing a tire and re-dishing and re-tensioning with the tire in place and inflated. Exactly, but what about the resulting spoke tension without the tire on? It was super high and beyond their suggested limits. Weird.

So what is my conclusion? Loved my old Shimano/Hutchinson tubeless set-up. Loved it and miss it. The Alpha 340 wheelset was light and rode great when I was able to keep tubeless tires on, but a pain in the butt to build with no real sense of how long they would last considering spoke tension.

—Justin

Q. Dear Lennard,

The “friendly mechanic” in your article laced the wheel 2x on both sides because you have to on a PowerTap hub. If you lace the non-drive radial, then you don’t get an accurate power reading.

This is what the CycleOps manual has to say (PDF):

Important: For your safety, the non-drive side of the PowerTap hub must be built with at least a 2x lacing pattern. Because of the patented PowerTap design, torque is transferred through the hub to the non-drive side. Failure to adhere to this precaution will void the warranty.”

—Tim

Q. Dear Lennard,

I had problems with a PowerTap wheel I built using DT Revolutions and a Mavic Open Pro rim. Did 3x drive and radial non-drive. Radial spokes wouldn’t stay tight. Re-laced with 3x both sides, per Saris recommendations (PDF):

Wheel-building: Contact a wheel building professional or dealer for assistance in building the PowerTap SL wheel if not purchased as a complete wheel. Both sides of the PowerTap should be built using only a 3x spoke lacing pattern. Due to the design of the hub, the load pattern is not the same as a conventional hub.”

The wheel has been fine for years.

— Phil

A. Dear Tim and Phil,

In my haste to answer Eric’s question, I did not pay attention to the fact that it was a PowerTap hub. Indeed, you must have a crossing pattern on both sides of that hub. I also discounted how much spoke de-tensioning effect you get with the Alpha 340 rims, as I have only used them at low pressure with tubeless cyclocross tires. But clearly, Justin’s letter indicates that this could be a very significant effect. I still stand behind my DT ProLock nipple suggestion.

— Lennard

Q. Dear Lennard,

In your November 1 FAQ, you responded to a rider who recently had a wheel built by a local bike shop. It seems his non-drive side spokes (reportedly, Wheelsmith with alloy nipples) had lost a great deal of tension. You suggested that perhaps an alternate lacing pattern and/or slightly higher spoke tension may have helped prevent this problem. You also stated, “He should have used DT ProLock nipples. …” Does this assertion have to do with something specific about the nature of tubeless rims?

I build with Wheelsmith Spoke Prep, because it is a requirement for wheels built at the shop where I am employed, but several of my personal wheelsets were built with the spokes’ threads treated only with Phil Wood Tenacious Oil. One such set has rolled over more miles than any of the rest and has seen perhaps one or two quarter turns of a spoke nipple or two over the years. That is how I was taught as I came up. That properly tensioned and trued, a wheel shouldn’t need thread-locking compound in order to hold tension. Were these merely the misguided teachings of retro-grouches?

—Martin

A. Dear Martin,

Using oil to lubricate the threads (and under the nipple head) is far better than having dry threads. The lubricant prevents the nipples from binding for smoother tightening. It allows greater and more uniform tension to be achieved with less torque applied to the nipple, hence resulting in a longer-lasting wheel build.

Wheelsmith Spoke Prep and DT ProLock nipples both provide lubrication and thus the same effect, but they also subsequently grip the threads after setting up, making it harder for the nipples to unscrew. The two-part epoxy threadlock compound in the ProLock nipples is a stronger set than the drip-on Spoke Prep (which needs to stay liquid in the bottle), and there are unburst spheres of the two components left inside the nipple after initial wheelbuilding, so a couple of further truings are possible. Turning the nipple breaks more spheres and adds some fresh threadlock compound to the threads.

Finally, the assertion does not have specifically to do with tubeless vs. non-tubeless rims, but it does apply more the lighter and less vertically stiff a rim is.

— Lennard

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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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