Serious Injury or Death

Danger is all around us. An almost infinite number of things could go wrong at any moment. Some computer program might be able to measure the probabilities in something close to real time, but most of us just have to live on our luck. By and large that luck is surprisingly good, considering the massive risks people take all the time and get away with it.

Bicycles are seen as safe, stupid little machines. Bike mechanics aren't considered "real" mechanics, because we don't have to deal with powerful engines. Bike riders are contemptible, wobbling along slowly. Adults on bikes need to "grow up." Bikes are toys. Bike crashes are slapstick comedy, unless it's you, skimming along the tarmac, feeling skin burn away, or feeling the snap of bone and ligament from a more vertical landing.

Bikes are also seen as terribly dangerous, the act of balancing on two wheels an affront to the laws of nature. A bike rider is a daredevil, especially riding on the road. And there are the obvious daredevils on mountain bikes, launching sick tricks off of every available drop.

Bikes themselves might as well be made out of stone, the way most people treat them. They leave them out in the weather, neglect maintenance, and basically treat them they way they treat cars. But a car has its house with it all the time, like a turtle has its shell. And the mechanical parts of a motor vehicle can be made more robustly, because even a small car has power to spare, compared to the .25 hp of a human engine pushing the pedals.

Serious component failures are rare. The massive crank recall of 1997, when Shimano had to replace millions of cranks on bikes sold worldwide, was the last -- and the first -- really enormous safety crisis, created by Shimano's design aesthetic favoring skinnier and skinnier alloy crank arms. But cracking cranks have always been a problem. My first experience with them was back in the early 1980s, when Campagnolo Super Record cranks were cracking, as were any other brands trying to make their cranks look like Campy's. Stress concentrates at the spider, where too thin a web of aluminum between the crank arm and the spider can start to crack in non-structural metal. If you spot the nascent crack soon enough, you can file away the material with the crack in it, and prevent it from traveling into the load-bearing metal. If you know the problem could occur, you can file away the web before a crack even starts, rounding out the radius to remove the stress riser. Wait too long, and the crack gets into real meat. Then the crank is doomed.

Here is an example of a web crack that got away:

You have to look really closely to spot them. That's where you benefit from the vigilant eye of an experienced not-a-real-mechanic who has seen quite a few of these over the years of a misspent life. This particular crank, a Sugino made for Specialized, could never have been saved, because of the shape of the back side of the crank arm. It's hollowed out back there, and has casting residues that create permanent stress risers immune to filing. Too bad, too. It's a pretty crank. The cracks only revealed themselves by the pattern of the oily grime that had adhered to them, hidden in the rest of the oily grime that had accumulated on the surface of the crank.

We play the game "Scratch or Crack?" a lot in the workshop. For instance, here is a Shimano Ultegra Hollowtech crank belonging to a rider who should be concerned about the load-bearing capability of his components:

Rubbing against a badly adjusted front derailleur cage, the arm has been scored, but hasn't cracked...yet. Hollowtech cranks are breaking, but Shimano has yet to acknowledge it with an official bulletin or recall. It's just street knowledge among not-real-mechanics.

Any lightweight component subjected to vigorous riding can eventually fail. As manufacturers try to make parts as light as possible, they will shave down the margin of safety, slap on warning labels, and call it good. You, the consumer, have the ultimate responsibility to accept or reject their creation. It gets much harder when the manufacturers stop making anything nicely finished but a bit more robust, and you have to keep up with the latest number of cogs in order to buy top of the line parts. We have some poor bastard who wants to put Di2 shifting on his "old" bike with mechanical 10-speed Dura Ace. Haaaa! You're what... five years too late? Three years? I don't keep up with the ephemeral crap the way I should, because we don't sell much of it in our market area, and I keep hoping that it will just go away. And it does go away, but only to be replaced by worse ephemeral crap.

Here is another entry in Scratch or Crack:

This one was just a scratch. But you have to take every one seriously.

Rims are another common site for cracks. But you can't ignore hub flanges, handlebars, stems...you can't ignore anything, really. I've found frame cracks and fork cracks as well. I spotted cracks in the crown of a guy's Cannondale Lefty fork that would have led to a nasty face plant. Aluminum and carbon fiber each fail more quickly and more abruptly than steel or titanium, so spotting cracks becomes more urgent with these inescapably common materials. Carbon in particular will just disappear when it reaches its load limit. It doesn't bend. It breaks. Properly designed and manufactured, it will function perfectly well for an almost indefinite period. Parts that can be made more ruggedly, like crank arms and stems, can hide a little reserve strength under a negligible bit of extra weight. Frames present greater design challenges, because a shape and wall thickness amply strong to stand up to the normal loads of hard riding will still be vulnerable to highly probable mishaps like collisions or simply having the bike fall over against something with a hard corner to it. Sure, a nice metal frame might dent in a case like that, but small dents are only a cosmetic problem. It takes a pretty deep dent to render the bike unridable.

Any time you are dependent on a machine, you could end up stranded. The simpler the machine, the better the odds that it will continue to function, provided it was well enough designed and built in the first place. But it has to do what you want it to do, which invites complexity. And even a fixed gear has plenty of parts that can break. Whatever you ride just remember to take a close look at it from time to time. Good luck out there.