Why Things Fail: From Tires to Helicopter Blades, Everything Breaks Eventually

Robert Capps with a great article in WIRED on some of the tradeoffs involved in product engineering.

Product failure is deceptively difficult to understand. It depends not just on how customers use a product but on the intrinsic properties of each part—what it’s made of and how those materials respond to wildly varying conditions. Estimating a product’s lifespan is an art that even the most sophisticated manufacturers still struggle with. And it’s getting harder. In our Moore’s law-driven age, we expect devices to continuously be getting smaller, lighter, more powerful, and more efficient. This thinking has seeped into our expectations about lots of product categories: Cars must get better gas mileage. Bicycles must get lighter. Washing machines need to get clothes cleaner with less water. Almost every industry is expected to make major advances every year. To do this they are constantly reaching for new materials and design techniques. All this is great for innovation, but it’s terrible for reliability. …

On tradeoffs:

It’s actually not hard to make a hinge that will last for a really, really long time. All you have to do is make it a tough, heavy hinge. But that creates several problems. First, a burly hinge will be stiffer and less sensitive than a small, thin hinge, so the pedal won’t feel right. Second, and worse, is the excess weight. Slap a big hinge onto the gas pedal and you may add only a couple of ounces and a few cents of overhead to the truck. But multiply that across hundreds of hinges, bolts, handles, door locks, latches, and so on, and suddenly you have a bloated truck that is slow, sluggish, gas-hungry, and expensive. A truck that is, in the parlance of reliability testers, overengineered.

The amount of overengineering a product can tolerate depends on what the product is. Airplanes, for example, are a classic example of overengineering because the cost of even minor failure is so high. But with this overengineering comes excess weight—and the resulting loss in fuel efficiency makes flights more expensive than they otherwise could be while also causing them to generate greater carbon emissions. On the other hand, some products—like carbon-fiber racing bicycles of the sort you’d see in the Tour de France—are almost entirely about performance, and so they’re consciously underengineered. Obviously, the makers of such bikes don’t want them to shatter going up l’Alpe d’Huez. But having a few frames that crack earlier than expected is better than adding even a few ounces to a bike.