Showing posts with label spoke failure. Show all posts
Showing posts with label spoke failure. Show all posts

Monday, October 25, 2021

What if your wheel collapsed?

 Back around 1980, a once-promising racer in the Maryland scene supposedly had lost a lot of his nerve when his low spoke count front wheel folded up in a sprint, sending him down from 30 to zero in the length of his own body. For you metric users, that's 48 to zero in less than two meters. When the front wheel disappears, the glide path is pretty abrupt.

Back then, low spoke count could mean 28, or maybe 24, and lightweight spokes were called "piano wires." I wasn't around before this rider had that crash, so I never knew him at his best. He was still plenty strong and skillful, but pretty good is not good enough for national-level competition. In a strong district, it isn't even good enough for regional prominence. You have to be willing to ride to die. On top of that, you need the genetics and the training to have the motor just to stay with a field of top riders. Anything that makes you the least bit hesitant is going to cripple you.

Nasty crashes can happen to anyone, for a wide variety of reasons. Equipment failure is not limited to high performance equipment built to thin margins of safety. On the plus side, incipient equipment failures can be detected by inspecting a bike regularly. Sometimes these failures make themselves obvious, as with previous cases of spontaneous spoke or nipple failure I've reported here.

The worst case scenario is that someone hops on their recreational bike that's been sitting in storage and pedals away without noticing that a couple of spokes have failed, and manages to get up to a moderate speed -- down a hill for instance -- before the wheel folds up. Of the two, a rear wheel is only slightly preferable, since it's not going to lead directly to a face plant. You'll still hit the ground abruptly and hard. Fortunately, most of the time, other issues will prompt a person to bring their bike in for a check up before they go out, or will stop them early in their shakedown cruise, as rusted chain links or some other drive train interference make the bike too hard to ride.

One case of spoke failure this summer showed up on a Schwinn recreational bike with an internally-geared hub. It had a couple of broken spokes. This can happen in storage if something gets shoved into the bike, or it can happen when several bikes are stacked on a rack on a car, or in a crowded parking situation, or a crash.

Closer examination revealed that the spokes had simply come apart. Every spoke in the wheel was banded with rings of rust that had eaten most of the way through them, except for the ones that had already disintegrated.


If you look closely, you can see a piece of spoke at an angle, impersonating a normal bend. You could crumble these spokes in your hand, into little fragments. They had no tensile strength at all.

With the current problems getting parts, my only choice was to respoke the wheel with a different cross pattern to match the lengths of spokes available. It went from three-cross to four-cross, which will just provide a cushier ride. I built my first touring wheels four-cross because it was supposed to be better for long hauls at moderate speeds, with a load. It was all right. I've had to depart from basic three-cross on other occasions as well. It's all legit. I generally don't go below three-cross except by customer request.

Stripped down, the hub felt like something you could use to train for the shot put. It weighs 4 1/2 pounds.

My wife, who competed in the shot put as part of her track and field career in school, informed me that the women's shot is almost nine pounds, and the men's is 16. But we could have a "hub put" category added to the Huffy Toss if we ever have a bike shop field day. Regulation weight could be whatever we say. This hub was still a hefty handful. Holding it up to load the spokes, my arm started to get pumped.

Within a day or two, another wheel job came in and I reflexively wrote it up for respoking, even though we could have replaced the wheel with a complete pre-built wheel. This is another example of how cheap labor has led to replacing rather than rebuilding something because parts and labor cost more than a new unit of low to modest quality.  In the wheel department, this is nothing new. My friend in Florida worked as a contract wheel builder in the 1970s, paid by the piece. I don't know if any US supplier uses American workers for that sort of thing anymore. She also wasn't trying to support herself on the income. It was supplemental in a variety of gig jobs, in a duo with her talented and enterprising husband before he finished his aircraft mechanic certifications.

The wheel I built was better than mass-produced, and it saved a complete wheel for someone who might need it more. It's good to stay in practice. I'd observed early in the season that people don't have much use for wheel builders anymore, and promptly started getting wheel repairs and complete builds.

A conventional build doesn't take too long, which might make it seem cheap and easy, but you do need to know how to make it efficient as well as quick. Proper tensioning takes most of the building and truing time. That's the part that takes experience. It's easy to get into trouble by rushing the tensioning phase. 

Novice builders will make two common mistakes: go for lateral trueness before roundness, and stop with too little tension once the wheel is as close to perfectly true as they can get it. After they've had a few of their creations develop the wobblies because of inadequate tension, they might move on to the intermediate mistake of too much tension. You can buy a tensiometer to check whether tension is sufficient and even, but after a while you will develop a feel for it by squeezing and by how the spoke wrench feels when you turn it. Check your calibration with the tensiometer occasionally.

A big part of the cost of custom wheel building is that we only get parts at wholesale, whereas most mass-production builders get a price that is at least one tier lower, and probably even better than that. They can take a margin on parts and labor that compensates them well, and still undercut us for the same parts on the same build pattern. When we have unrestricted access to supplies, we will often spec a pre-built wheel that matches what we would have done anyway. Reputable production suppliers have become pretty good at spitting out consistently acceptable wheels. And if you want something tweaky and modern, super light and fashionable, you will have to buy complete wheels. If you want something a little more tailored, based on rim width or a preferred brand, then you have to find someone to put that together for you.

Monday, August 10, 2020

The Woman with Exploding Nipples

 It could happen to anyone with a low-spoke-count, highly tensioned wheel with trendy alloy nipples. They start popping without warning. This customer had come in a couple of times already for single incidents of nipple failure.

This rear wheel had 27 spokes: nine on the left side, 18 on the right. The rims were a little deep, but not hard to work with. Weird-looking wheels are part of what makes a bike look modern.

To begin, I had to remove the tire. Because it wasn't a punctured tire, I went to remove it without tools. When I pushed down on the wheel to work the bead around, another nipple exploded. I called the customer to let her know we were going to do a complete nipple transplant, not just an individual replacement.

On the stand, two more nipples popped when I put a wrench on them to start loosening them. This wheel had been a real time bomb. Imagine ripping down a bumpy descent when one spoke after another detaches from the rim.

Fortunately, the diameter and thread on the bladed spokes matched the DT brass nipples I was planning to use. And the low spoke count made the swap less time consuming. I would never ride a low-count wheel myself, but I appreciate the time I save on jobs like this.

This has also been the Summer of Forgotten Through Axles. We've had several in a row. A rider calls up and asks if we have through axles in stock. We explain that there are different kinds (of course). They're not sure of the brand and type. We figure it out. We had one kicking around from a previous customer's special order that they then declined to pick up. We've accumulated one or two more, to try to cover some of the possibilities.

Next up on the list of modern problems, a mother and daughter had to forgo their bike ride because they had forgotten the keys to their ebikes, turning them into nothing more than immensely heavy regular pedal bikes. You can just ride them that way. It's a common claim in the advertising. But who would? No one, actually, unless they get caught out with a dead battery and have no one to call to pick them up.

Problems like this are right up there with forgetting the charger for your shifters. If you have electronic derailleurs and a dead battery, you got nothin'. 

There's still plenty of good old abuse and neglect to keep us busy. I figured out that the handlebar tape on these bars was about 15 years old when I removed it the other day.

The bars themselves were old enough and had been through enough rough use that I recommended replacement. The last bars I saw that had that much salt and oxidation encrusting them had been on a bike that had lived in Singapore for a year or two. Those bars were so deteriorated that I could poke a screwdriver right through them. These bars were nowhere near that level of deterioration, but still a risk according to most manufacturer recommendations. Better to be safe. It also gave us a good opportunity to put on a much shorter stem for the new rider of the bike.

Accidents will happen. One of the local ebike aficionados took a digger on their chunky steed. The owner called to see if we would work on it. To make it easier, he had contacted the president of the company that made the bike to hook us up with a direct pipeline to parts and advice. With clout like that, ebike ownership is smooth sailing indeed. When a bike weighs upwards of 60 pounds, it hits the ground with more force than a bike weighing less than 30. It also hits a rider with more force, should you happen to get on the wrong side of things as they're going every which way. The rider was apparently not hurt badly enough to be worth mentioning, so that's good. I was just musing about it as I looked at what was scuffed and tweaked.

The trickiest part will be replacing the battery case, which is cleverly inserted into the welded rear rack on this Pedego bike. It has thick cabling inserted into it, and has an irregular shape that does not appear to slide easily out of either end of the framework of the rack. The screws that hold it in place broke loose when the bike crashed, because they were never designed to restrain such a heavy piece of equipment in an impact at an angle. The good news is that the owner of the bike doesn't need it fixed instantaneously. We can put it off for at least a week or two before getting mired in its complexities.

Tuesday, June 09, 2015

Exploding Spokes

The season of urgent repairs has arrived. People come to town for the weekend. Something goes wrong with the bike. They plead for emergency care.

Last Thursday it was two guys carrying a Specialized Secteur. It was 4:30 p.m. The shop would close in one hour.

"The bike was hanging in storage all winter," said the owner. "When I brought it out, a bunch of spokes were broken in the rear wheel."

I asked about the usual things: could a car have hit it, could a heavy object have fallen against it, do any people have access to the storage area who might be pissed off at him? He dismissed each of those possibilities. That left us with four broken spokes on the drive side, cause unknown.

The owner said that the bike had been hanging by the front wheel from a storage hook, in an unheated space during last winter's phenomenal cold spell in Boston. I had never encountered spoke failure due to cold, but there's a lot I haven't encountered. Still, I would have expected the rim to fail before the spokes. Or, more likely, the rim would contract more than the spokes, relieving tension on them.

I said I could not adequately investigate this mystery in what remained of the day. I would need a few hours to see if this thing would be safe to fly, even with the broken spokes replaced.

The spokes were all in a row. The rim is DT. The spokes are DT. The hub is one of those Specialized-labeled ones that look like they say SIXE if you read them upside down. It's "Axis." They've fixed the font now, but I liked it the old way. I can't remember what I read about those hubs, whether they're DT or Formula or some other generic maker. No matter.

The spokes had not broken at the bend or the threads. They had snapped somewhere in the middle. The edges of the breaks showed no pinching, as they would if a cutter had been used.

A cruise through the Internet turned up some forum posts about bad OEM spokes of Asian origin a few years ago. I had seen failure of various OEM spokes myself, but never DTs. Another forum thread mentioned corrosive environments that weakened spokes. The spokes on this bike did show signs of that. They had a black finish. On close examination you could see cracks in that, and some crusty residue. I sanded away the black around one, carefully and gradually, to see if the crack extended into the metal beneath. In my test area it did not appear to.

I determined the proper length for replacement spokes and installed four. Put the wheel on the stand and tensioned the new spokes. Straight, smooth, round, the wheel looked good. I stepped away to work on something else before I put the bike back together.

BANG! A black spoke snapped, sending the nipple-end across the room.

That's annoying. Glad I didn't have my eyeball down there, sighting along the truing stand calipers.

To me, that was the end of any stop-gap repair. This wheel needs to be rebuilt. To complicate the problem further, the non-drive-side spoke holes in the rim all showed little stress bulges. Nothing had cracked yet, but it made the rim a questionable candidate for the investment of parts and labor to respoke it. I don't know why the non-drive side would show stress that the drive side did not, but this wheel was clearly weird.

BANG! Another spoke fired off. That's it. This thing is dead. I took our spokes back out of it and set the remains by the rest of the bike, with some cloth draped over it as blast matting in case any other spokes decided to blow. It was less likely now that the tension had been reduced. Still, I didn't want any of us to have to dig a spoke fragment out of our leg.

While the front wheel had not misbehaved at all, its spokes had been in the same environment as the rear ones, and there are only 24 of them between the rider and a screaming face plant. Low spoke count wheels are technically strong enough for the stresses of performance riding, but they sacrifice most of their margin of safety by putting more and more load on fewer and fewer parts. When one part fails, the structure deviates much more than it would if more parts were carrying the load to begin with. Are you really going to rip down some exhilarating descent, congratulating yourself on the money you saved by not rebuilding or replacing that front wheel?

Not my decision. I did advise the owner to think about getting both wheels redone or replaced. Because he claimed -- as do they all -- that the bike barely had any miles on it, he was going to take up the matter with the shop where he bought it.

Barely any miles. Not that old. We hear that all the time. Your average ten-year-old bike is between fifteen and twenty years old. A guy brought us his 15-year-old Cannondales on Sunday, and they are 23 years old. Bikes we "just tuned up" show up in the repair records from two years ago.

Sunday started with barely enough work for the number of people on the schedule. We did not get a wave of check-ins, but the couple we did get kept us turning wrenches and looking useful until closing time. Summer has shrunk from the cheerful chaos of the 1990s and early 2000s to a brittle, somewhat desperate couple of months at best, starting on the Fourth of July weekend and not quite making it to Labor Day. But the warm weather can bring us little waves of business any time from now until the fall foliage fades.