Ask a Mechanic | Life & Care of a Carbon Frame

Susan wants to know: “What should I be wary of when buying a carbon frame? Do they last as long and are they as strong as aluminum frames?”

Thanks for the question Susan. Both materials have their advantages and drawbacks. When it comes to longevity, it’s generally accepted that aluminum frames have a five-year fatigue life, while the fatigue life of a carbon frame is unlimited. In reality, things aren’t quite as simple. I’ve seen aluminum frames still in use after decades of riding, and carbon frames that have to be repaired after a year.

The downfall of carbon fiber is an impact force highly concentrated on a small area. Modern carbon frames can essentially be ridden forever if they are not involved in a crash. Even then, current carbon fiber is very strong, and a large impact force would have to be sustained, enough to badly dent an aluminum frame. Luckily, damage to carbon frames can usually be repaired, whereas re-welding or patching a cracked aluminum frame is not safe. UV damage is essentially non-existent to reputable-brand’s carbon frames.

Mostly, the difference between carbon and aluminum comes down to weight and ride quality. Carbon frames are usually a bit lighter than aluminum—up to a pound for mountain frames and up to a half-pound on road frames. Ride quality is more noticeable on road frames than mountain frames, with vibrations being damped by carbon more so than aluminum. Torsional stiffness is often greater on carbon frames than aluminum frames these days, although carbon frames that are as stiff or stiffer than aluminum frames have less of a weight advantage.

If you choose to go carbon, here are some suggestions and things to look for. Besides the aforementioned impact force, areas where carbon frames have been know to fail are at bonded junctions and glued inserts. Junctions are where two tubes join, such as the seat tube and head tube, although modified monocoque construction has made junction failure extremely rare on modern carbon frames. Glued inserts include headset races, bottom bracket threads or sleeves, and rear drop-outs. Again, modern construction and materials make failure at these points very uncommon.

As with any bike, regular cleaning helps keep your drivetrain and suspension pivots in good shape and gives you the time to inspect your frame for cracks and damage. Pay attention to tube junctions, the bottom bracket area, the top and bottom surfaces of the head tube, and the chain stays and seat stays at the rear dropouts, and the area around the seat post clamp. Rocks are often kicked up into the down tube, so inspect there for cracks and chips in the bike’s finish. We suggest applying frame protection on this vulnerable area if there isn’t already. Be absolutely sure to use a torque wrench and adhere to specifications when installing components.

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