How Much Lighter Is a Carbon Bicycle Frame Than an Aluminum One?

There's a reason carbon fiber bikes are ubiquitous at the top levels of cycling competition. No other material can match carbon fiber's strength to weight ratio, or its ability to be molded into the most aerodynamic shape. The difficulty of manufacturing a carbon fiber bike makes these frames much more expensive than aluminum. If you're choosing a material for your bike frame, understanding the differences between these materials makes your decision a lot easier.

Carbon fiber is a unique material made from individual carbon strands. These strands are woven and glued together to form plies, which can be shaped and heated to form almost any shape. Sandwiched together, the resulting frame for a bicycle is extremely lightweight and stiff. Carbon fiber has a strength to weight ratio that is 18 percent higher than aluminum and 14 percent higher than steel. The drawback to carbon fiber is that it is mostly irreparable; if you experience a bad crash, the frame may splinter and break apart, and it cannot be fixed. The Union Cycliste Internationale, or UCI, enacted a rule to require a bike's weight to be 15 pounds or above. This rule ensures bikes are strong enough not to break during normal race conditions.

Aluminum makes great material for a racing bike because the frame can be built with thicker aluminum tubing for stiffness and strength compared to steel. It's not as light or as strong as carbon fiber, but aluminum is much less expensive to produce and manufacture, reducing the price of a racing bike by as much as a few thousand dollars. An aluminum bike cannot be welded like steel in the event of an accident, but aluminum can tolerate a bit more abuse than carbon fiber before it fails. Aluminum is also an ideal material for wheels, since a broken rim will be much less expensive to replace.

The weight of a bike frame matters, but not as much as you might think. Assistant professor for the department of exercise and sport science at the University of Utah James C. Martin, Ph.D, put the weight of a bicycle to the test by measuring a rider's time on a 7 percent incline over 5 kilometers using a 15-pound bike (the minimum for racing as per the UCI rules) and the same bike with 5 pounds added. The difference in the climbing averages was about six seconds. Those seconds can be crucial for a professional cyclist, but for the average rider, the difference won't be of consequence. Tire width and aerodynamics have a much greater effect on speed than bicycle weight.

A carbon fiber bike can be built under the 15-pound weight limit of the UCI rules, but most are produced at just 15 pounds so they're legal for competition. In comparison, an aluminum bike can get very close to that weight limit. Different factors like frame size, manufacturer, components and wheels have a big effect on weight, but most aluminum bikes come in at around 18 pounds or lighter, while still costing far less than a carbon fiber bike. For the best bike for your dollar, see if an aluminum bike will satisfy your need for speed.