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 Bike Frame Materials Explained
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home » bike frame materials explained

It seems like everyone has to have a composite bike frame now so here's an explanation of the differences between composite frame options and metal.

Many times I've heard athletes tell me they need a composite frame because they want a smoother ride. Yet I ride a composite TT bike and feel the road surface just as I do on my aluminum road frame. The fatigue I get riding the metal and composite frames is the same.

The difference between composite and metal frames is mostly about damping which is just one component of road feel.

A car has springs that allows the level of the vehicle to change as it moves over high spots and low spots. A spring responds to a bump in the road with compression of the spring. Problem is, the spring also wants to move with equal force in the other direction (extend), pushing the weight of the car up to an even higher level after the compression. This is called oscillation. What you would feel is the car bouncing up and down in ever smaller moments, but shock absorbers stop this oscillation movement.

Without shock absorbers the car would continue bouncing up and down for a long time after the initial compression over the bump. Damping from shock absorbers resists this movement, and this is what a composite frame does well, absorb oscillation energy.

The ability to absorb bumps in the road is called vertical compliance, and it's determined by frame design, wheels, and tire pressure. A metal frame is more like a spring than composite, it can give good initial shock absorption, but a bouncy/springy feel after. Composite frames can also give good shock absorption but there is virtually no bounce after the initial hit.

Those of you who ride a high a end mountain bike where suspension qualities can be set understand this as rebound. Metal road frames have lots of rebound, while composite frames almost none.

A composite frame can be made several different ways. Composite tubes can be glued into metal lugs. This gives good size variation possibilities. Similar to this, composite tubes can be glued into composite lugs which also gives good size variation, and also usually lighter weight than metal lugs. A composite frame can also be made in a mold with no lugs, but with this type one mold makes one size frame.

The lugged composite frames usually have composite tubes of uniform shape. They are cut to length and glued into the lugged joints. It is a less expensive way to make a composite frame and gives the possibility of more frame sizes.

A composite frame made in a mold gives infinite possibilities for frame shape, but one mold makes one size and the mold is very expensive. A mold is essentially a negative (female) version of the frame split in half. What eventually becomes the solid composite frame begins as cloth and resin. The cloth is cut and placed in the mold then combined with resin. A catalyst is added to the resin so it hardens. The cloth becomes rigid when the resin sets.

The quality of the cloth determines the finished weight and stiffness of the frame. A matt cloth is the least expensive and yields a relatively thick and heavy finished product. Woven cloth gives a better strength to weight ratio. Modulus refers the quality than the cloth. Generally a finer weave is referred to as high modulus. Fine weave gives a better quality finished product much like it does for tires.

A benefit if composite frames it the ease with which you can add and reduce stiffness by varying the material and layers. The key ares like near the frame's head tube and bottom bracket control the ride quality that is difficult to do with metal frames.

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