When tension is a good thing

Okay, so there are a lot of forums and discussions out there about “hanging bikes by the rims”, and if you read them all carefully, like I did, you will discover two things: 1) There are a lot of paranoid people out there. 2) No one ever responds that their rims or bikes were damaged by doing this.

Being an experienced bike mechanic, an engineer with a BS in Mechanical Engineering from NYU Polytechnic, and having over 25 years’ experience in industrial machine design (automated machinery/vacuum chamber/pressure vessels), I can tell you one thing for certain, “Tension, in certain circumstances, is a good thing”. Without getting too technical, try this easy experiment: take a thin wire, like a spoke of a bike rim, and push on both ends with your fingers, and you will see that it will try and bow and buckle immediately. Now try pulling on both ends and you will see that you cannot change its shape. Most people do not realize that the spokes of a bicycle are all under tension. They are fighting each other and keeping the hub in the center of the rim in a “circular tug-of-war”. That is why when you see a mechanic “truing” a bike rim; he/she is constantly tightening the spokes as they go around. Hanging the bikes by the rim, is keeping this force in the same direction, and these spokes are incredibly strong in this direction. When you are riding your bike, all your weight and forces developed going over bumps and curbs are pushing down on the wheel hubs, which in turn are “hanging” by the spokes that are above them. Those spokes and rim were designed for the weight of the rider, plus all those dynamic forces. Hanging a bike by the rim and subjecting it to the weight of the bike alone is nothing for the wheel to handle. Here is another little experiment that shows the strength of a circular shape in tension (like the rim of a bicycle); Take an empty plastic 2 liter soda bottle and blow into it as hard as you can. You may see it flex out a little. This is why when designing pressure vessels, designers always try to use round or tubular shapes. This is also why airplanes (pressurized for high altitudes) have cylindrical body shapes, as do propane tanks and gas cylinders. Now try blowing into a square bottle. You will see that the side walls will bow out and the square bottle will try to become round. This same shape is great for external forces as well. This is why submarines are always cylindrical or round in shape as well. Bottom line is: It is perfectly safe and acceptable to hang a bike by its wheel, and that’s why every bike shop in the world has been doing this forever.