I received a good question about a common bike part that can fail, from Mark Pryor of Alameda, California, who’s the co-founder of the Alameda Velo bike club.
Mark wrote, “I’m proficient at breaking and loosening rear spokes. I never have problems with fronts; only rear wheels. I’m a 195-pound roadie who climbs a lot of the steep hills in the Bay Area and is mid-pack in events like the Death Ride.
“I broke several spokes on my Trek Madone’s stock Bontrager Race Lite wheel and the LBS/Trek rep replaced those with 32-spoke Bontrager Classics. And, I have loosened spokes on a hand-built 32-spoke rear wheel with a Mavic Open Pro rim, so my bike shop rebuilt it with a Velocity Fusion rim (supposedly it’s drilled differently to provide better spoke tension). So far, I have 300 very true miles on the wheel with LOTS of steep climbing.
“Obviously, low spoke-count wheels are out of the question for me. Maybe Jim can explain what’s happening when bigger guys stand on climbs (steep or not) and what sort of forces stress wheels – like my LBS said that the newer hubs are narrower, making it harder for the spokes to remain tight. To me, it almost seems like rear wheels are one of those things you can’t live with or without!”
Thanks for the great question, Mark. It sounds to me like you’ve found a pro bike shop that really knows their wheels because the way they handled the broken spokes on the stock wheelset was spot on. And fixing your spoke-loosening problem on your 32-hole wheel by replacing the lightweight rim with a stouter model, and one with offset holes, was also exactly the right solution.
Bicycle wheels are amazing. They’re nothing more than a hoop, a hub and a handful of wires. Yet they must withstand the weight of the rider, plus the bike and any gear; the road surface that can vary greatly; and all the thrashing that roadies give them, from powering down the blacktop, to standing and rocking your bike to scale steep climbs, to bunny hopping potholes and jumping away from stoplights or sprinting for the town line sign.
Tip: If you want to learn all about bicycle wheels, I recommend my late cycling engineer friend Jobst Brandt’s fine book on the topic The Bicycle Wheel.
I started fixing wheels in the early ’70s when wheel problems were commonplace and you were lost if you didn’t carry a spoke wrench in your seat bag if not bring some spare spokes along. Today we have much better rims, spokes and hubs, but the biggest difference is the vast selection of wheel companies making wheelsets engineered for specific purposes.
In most cases, the problems I see today are the result of someone riding wheels that aren’t right for them, which was the case with both of your wheels. I was happy to hear that your Trek dealer replaced your first wheels with a model with more spokes, because for bigger riders, those extra few spokes make all the difference.
Tip: If you’re shopping for a new bicycle, be sure to ask the salesperson if the wheels on the bike you’re looking at are suited to you and how you ride. They may be able to upgrade the wheels for a slight additional fee and that would be better than having problems down the road. Also ask if the wheels are guaranteed, so you’re covered if you end up having issues.
On your other wheel, they upgraded you to a rim with a more triangular cross section and with offset spoke drilling. The triangular rim is stiffer than the rim you had before. And the special drilling allows more balanced spoke tensioning. This really helps with 10+ cogs, which makes the right-side spokes have to do even more work than on rear wheels with fewer cogs. The offset drilling gets the left-side spokes more into the act strengthening the wheel.
As you pedal down the road, your spokes are constantly getting a workout because all rims flex slightly vertically and laterally. When you stand to climb you lean the bike, flexing the rims sideways even more. Because the spokes are held in tension, this rim flexing changes the tension, which stresses the spokes.
Only if the rim is strong enough for you and how you ride, and if the spokes are tensioned adequately for the job you’re asking them to do, will the wheel hold up and remain tight, true and round.
The bigger and more powerful a rider you are, the rougher the roads you ride, and how smooth or hard you ride, all affect how the wheels hold up. For the best results you want a wheel that can take just about anything. And that’s where a wheelsmith comes in, like your LBS that correctly diagnosed your issues and got you rolling on more suitable wheels.
Dealing with spoke breakage
It’s not as much of a problem as it once was, but if you find yourself on a wheel that breaks spokes, the most likely cause is inferior spokes. That’s because one of the best ways to cut the price of wheels is to build them with cheap spokes. They may work fine for lighter riders on smooth roads who don’t ride that much. But put some miles on them, and they can quickly become a liability.
If you’re breaking spokes, look at their heads (the round part that’s at the hub) and see if you can spot a logo. What you want are stainless-steel spokes from great brands like DT Swiss, Wheelsmith or Sapim. DT spoke heads have the initials DT stamped in the spoke head and Wheelsmith’s have W on them. Sapims may be marked on the side of the spoke with SAP and SAPIM.
The only way to fix a wheel that breaks spokes is to rebuild it with quality spokes. But it’s not worth it if the hub and rim are poor quality, too. It would be better to purchase a pre-built wheel composed of nice components, since there are so many available at lower prices, than if you bought the parts and built the wheel yourself.