What Bike Spokes Do and How They Function

Bike spokes

Rachel Johnson / Flickr / CC by 2.0

The spokes on your bike's wheels are like the busboys at the restaurant. They're quiet and out of the way, and it's pretty much a thankless job. No one ever notices them when everything is working well, but without proper setup and operation, all sorts of trouble will break lose.

What Spokes Do

The spokes on your bike may look like little more than metal toothpicks that fill space between the axle and wheel but, really, these mighty little dudes have some important jobs: 

  • Add strength to your rim
  • Transfer your leg power from the hub to the wheel
  • Support your weight on the wheel

How Spokes Work

How do the spokes accomplish these terrific and heroic feats? First, spokes don't push outward, holding the rim at bay, like it might seem. Rather, the rim is evenly pulled inward by the spokes, which are laced through the hub, the center part of the wheel that rotates around the axle. Tension between the hub and rim is applied evenly in all directions, making the assembly extraordinarily strong and also somewhat flexible and resistant to shock. This uniformly applied tension is what supports your weight on the wheels.

The other key role of the spokes is transferring the power from your legs to the rim to make the bike go. Enormous force gets applied to the hub of a rear wheel by the chain and gearing when you pedal down hard, and together the spokes carry the power that has gone from your legs to the chain then out to the wheel. This force driving the bike forward is distributed among many spokes so that there is not too much stress on any single spoke.

Keeping Rims True

Starting at the hub in the center of the wheel, spokes radiate outward to the rim, where they attach to nipples, which are like little nuts that screw onto the spoke ends. Turning the nipple increases or decreases the tension of the spoke and also pulls the rim slightly to the left or right. Wheel builders and bike mechanics must balance this tension so that the rim is perfectly flat, or "true."

Rims become warped, or out of true, when the spoke tension is out of balance. This results simply from using the bike, from spokes loosening on their own or from damage to the rim such as when the wheel hits something hard and deforms the rim slightly, throwing off the spoke tension. Straitening—called truing—a wheel is a tricky task that's best left to a mechanic. If your bike has a loose spoke or two, you should tighten it just until it's snug and plan to have the wheel trued soon. Overtightening a single spoke can pull a wheel out of true.