Gear
Photo: Caley Fretz | VeloNews.com

Technical FAQ: Clydesdale road wheels

Lennard Zinn explains the fundamentals of why wheels fail when ridden hard by heavier riders and how to build a stronger wheel.

Dear Lennard,
I took my bike in for its break-in tune-up and was told that the back wheel already needed some re-truing. I did some homework and found a few articles saying that riders over certain weights should seek out certain wheels. I wanted to know if you give any “weight” to this argument. I emailed Rol wheels, since they advertised wheels for Clydesdale riders and found that their upper limit was 240 pounds. While I am on my way there, and should be around that weight by the start of next season, the guys at Rol recommended I look at Wheelbuilder.com and get a 32-spoke rear wheel. Is this, in your opinion, something I should look into? Just looking for a set of alloy wheels that are built for a larger individual that will still be fun to ride.

That being said, would you have a recommended starting point on the site? When looking through Wheelbuilder.com I had been looking at the Pacenti SL23 Rim since it was a wider rim that created a bit wider tire profile.
— Mat

Dear Mat,
Yes, I’d give some “weight” to this argument! It’s not just weight but also riding style that’s important.

An obvious wear factor on a wheel is impact — a guy who unweights the bike for train tracks or potholes will have less impact damage than the guy who bangs into everything fully weighted on the saddle. And, of course, the greater the weight (force) on the wheel on impact, the greater the damage it will sustain.

But often, more important than impacts for wheel durability, is fatigue, and that is dependent on weight and also on smoothness of the pedal stroke. At least half of the customers buying bikes or cranks from my company are over 250 pounds, and the ones with a hitch in their pedal stroke crack rear rims on factory-built wheels at every drive-side spoke nipple in short order. We have some 300-pound customers who get quite decent wheel wear, and some who break everything in no time — they break the hub flanges, as well as the spokes, and crack their rims.

The spokes loosen up because, as the wheel rolls, the section at the bottom becomes flattened (D-shaped). If you’re heavy enough, that flat spot is deep enough that it totally de-tensions the spoke that is at the bottom, since the nipple has lost contact with the rim. This allows each spoke to jiggle during that moment it’s at the bottom without tension and, over time, consequently unscrew.

Furthermore, as the wheel continues rolling, the flattened section of rim snaps back to its original shape, abruptly bringing that spoke that had been at the bottom back to full tension. If the spoke had been completely de-tensioned, the bang-bang-bang of the impact of the rim snapping back against the nipple with every single wheel rotation will fatigue not only the spoke, but also the rim at that spoke nipple. This will cause the rim to crack over time at each spoke nipple.

Rim cracking at each nipple is a bigger issue with aluminum spokes, because aluminum has less elasticity; an aluminum spoke is not stretched as much as a thin, steel spoke would be, so its nipple loses contact with the rim with less deformation of the rim when it is at the bottom. Thus, it requires less load on the wheel for that bang-bang-bang fatigue process to crack the rim if it’s built with aluminum spokes than if it’s built with steel spokes.

This is also why a double-butted steel spoke will result in longer life of both the rim and the spoke than will a straight-gauge steel spoke — because its thinner center section will stretch more at the same overall spoke tension. This keeps the nipple in contact with the rim better as it rolls, and its thicker ends will still protect it where the stress is most concentrated.

In general, higher spoke counts and stiffer rims are friends of a heavy rider.

Rich Sawiris at Wheelbuilder.com is indeed fantastic at making wheels for big guys, and he wrote this in response to your question.

“The Velocity Dyad is a better option than the SL23 from Pacenti. The Pacenti has a relatively thin cross section across the nipple bed and we have started using load-distribution washers to prevent cracking. Another rim that would do a good job for a heavier rider is the Hed Belgium Plus in a 32H drilling. If weight is not a factor, the strongest rim I can think of would be a Velocity Chukker. The Chukker will do the trick for sure, but many people are turned off by its 640g rim weight.

For hubs, I recommend using something with the largest-possible axle diameter. Some popular options would include Chris King R45, Industry Nine Road Torch, White Industries MI5, and the DT 350 hubs. The 350 hub uses larger bearings than the 240S, which makes it a better candidate for heavier loads.
— Richard Sawiris, P.E.
Wheelbuilder.com”

I agree wholeheartedly with Rich. We build lots of wheels with Velocity Dyad rims; it has been our go-to wheel for big guys for a couple of years, and we have yet to hear a single complaint from any of the 250-pound-plus riders we’ve sold them to.
― Lennard

Dear Lennard,
When I read this article, I remember you discussing a cleat position moved farther back toward the middle of the sole.

According to me, this would help keep the Q-factor in check, as despite still having the need to increase the Q-factor, it could be considerable less.
It also might mitigate some of the physical distress to the body as described.
— Reginald

Dear Reginald,
Wow, you have a good memory. That goes way back. I imagine you mean articles I’ve written regarding the center-cleat theory of Götz Heine. They were so long ago, I can’t even find them in my hard drive.

Yes, I imagine you are right; Colin could get his foot angled farther outward with fewer issues of heel clearance and further forward stagger of his right leg relative to his left if his cleat were centered on the shoe sole.
― Lennard