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Tech FAQ: 29er Big-Guy Wheels

  • By Lennard Zinn
  • Published Dec. 9, 2009
  • Updated Oct. 12, 2012 at 12:50 PM EDT

Dear Lennard,
What are your thoughts on the relative “safety” of 29er wheels? I’ve read a few commentaries (some even from people who may be qualified to pass an opinion) claiming that many 29er wheels may struggle to provide the structural robustness of their smaller cousins.

All rim and spoke thicknesses being equal, I can see the point to a degree. Maybe this was more of an issue when people were first building such wheels, and maybe these comments are concerned primarily with wheels being subjected to particularly rough/vigorous riding.

However, as a 6-foot-6, 220-pound rider contemplating a move to a 29er format, the engineering behind making a 29er wheel stand up in the long term has me thinking. Beyond subjecting a lightly built wheel to use for which it was not intended under an overly heavy rider, have you any reason to believe (with evidence) that 29er wheels might actually put a rider at increased risk of a structural failure in the real world?

If so, are there pre-built wheels or hub/spoke/rim combinations that you particularly advocate?
-Paul

Dear Paul,
This is a subject that is near and dear to my heart. As essentially all of our mountain bike production for at least the past five years has been 29ers — both hardtail and full suspension — I’ve tried many 29er wheels. Furthermore, while we build custom frames and cranks for riders of any size, the vast majority of my customers are taller than 6-foot-4 and well over 200 pounds, so I have a lot of experience with 29er wheels under somebody of your size.

When we first started making 29ers early in the decade, the only rims you could get for it were road rims (I assume you know that the rim size of a 29er is the same as a 700C road rim). And I was building bikes for big riders then, just as now, so I was understandably worried about wheel strength. Initially, we only used Mavic A719 and DT Swiss TK7.1 rims, both 24mm-wide road trekking rims of around 550 grams, and we only built 36-hole wheels for big riders.

We had no problems with wheel failures, even under 6-foot, 8-inch, 250-pound North Shore riders. However, we had a lot of problems with pinch flats, as the rims were narrow and the available tires only had thin, cross-country casings. We found the Kris Holm Unicycle.com rims, which are 38mm wide and around 900 grams. That solved a lot of the pinch flat problems and eliminated wheel failures even off of big drops with big riders.

I am certainly aware of some people writing on the Internet about 29er wheels being weak, even making scary statements warning about the rider possibly ending up as a quadriplegic. But as with any wheel, the quality of the build is critical, and the rim, spokes and spoke count must be chosen appropriately for the end user.

At 6-foot-5 and 175 pounds and an aggressive rider, I cannot ride the same wheels for long that I select for my 5-foot-4, 130-pound wife, be they road or mountain-bike wheels. Even though they are good wheels, they just are not appropriate for me and for the way I would use them.

While it should be obvious that with the same spoke count and type as well as the same rim thickness, material and construction, a smaller wheel will be stronger. That’s not to say that you still can’t make the big wheel strong enough. And I believe that you can trust most of the name-brand, pre-built wheels to be safe, even at your weight.

That said, most of them will have far too much lateral flex for you to be able to sprint confidently or steer precisely on sharp downhill turns at speed. And you will get rim cracking in short order at each spoke hole on the rear wheel, probably appearing just after the 6-month warranty has expired. And spoke breakage will likely also be an issue.

I believe that a guy your size, assuming an aggressive riding style, ought to not buy factory pre-built 29er wheels at this stage of their development. If you were riding a 26er hard at your weight and height, you would not be on a cross-country wheel either, and that is what most pre-built 29er wheels are made for.

In 26ers, you have a wide range of pre-built options for downhill, freeride, all-mountain and other categories people keep coining names for. For you, I would always recommend through-axle hubs in both the front and rear. Both ends will track better by virtue of the stiff axles tying the fork legs and swingarm members together. And the rear axle will prevent the hogging out of the right rear dropout that can happen with a big, strong rider under high torque in low gear. You will know about this if you cannot keep your rear wheel from pulling over to the left chainstay, no matter how tight you keep your quick-release skewer.

Secondly, I would recommend high spoke counts – at least 32, and preferably 36. I would recommend high-quality, double-butted 2.0/1.8mm (14/15-gauge) stainless steel spokes with thread-locked nipples to prevent them from loosening up (we use DT Competition spokes with DT Pro Lock nipples).

The double-butted spokes actually make for a longer-lasting wheel than would straight-gauge 2.0mm (14-gauge) spokes of the same quality. They stretch a bit more, allowing the nipples to stay in contact with the rim under the high wheel deformations that often occur under somebody your size, and they remove some of the stress concentration from the breakage points at the elbow and nipple. For somebody your size, I see no reason to use aluminum nipples; brass will allow more truing over the years of spokes under high tension without rounding off the nipples.

I would recommend a 27-30mm-wide all-mountain rim, something like a Sun Ringlé MTX 29 (585-gram) or Equalizer 29 (540-gram). The Mavic A719 has been replaced by the TN719 disc-brake specific rim, and the DT TK7.1d is also a disc-brake version; these rims are still narrower than I think is ideal for you, but they are plenty strong if built up well with 36 spokes and through-axle hubs.

Even though higher spoke tension makes the wheel neither stronger nor laterally stiffer, it is usually necessary to go up in tension with larger rider size to avoid so much deformation of the wheel while rolling that the bottom spoke becomes completely de-tensioned, leading to nipple loosening and rim and spoke fatigue. The lifetime of the wheel is higher the more uniform the tension as well. I think it is important to go to a professional wheelbuilder with a lot of experience who will stand behind the wheel.

If you insist on a pre-built wheel, I’d recommend the Sun Ringlé Charger 29 with the 20mm through-axle option. It has the narrower and lighter (27mm, 490-gram) Equalizer 27 rim and 32 spokes, but it should still hold up very well as long as you’re not doing a lot of hucking. I imagine the 28mm-wide Bontrager Rhythm Pro TLR Disc 29 all-mountain wheel might be good for you, but I haven’t tried it, and I don’t know if it comes in a through-axle version.
-Lennard

Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, 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.”

Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

Follow Lennard on Twitter.

FILED UNDER: 29er / Bikes and Tech / MTB / 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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