To understand the myth of modulus, we must first think about two characteristics which direct material choice. They are Strength and Stiffness. Strength is defined here as the amount of force that can be applied to material before it breaks (fails). Often mistakenly interchanged with strength, think about stiffness as the amount a material deforms when a given force is applied. A stiffer material will deform less under the same force compared to a less stiff material. Think of the rubber band as low modulus and the spaghetti as high modulus carbon fibres. The bragging rights associated with the use of high modulus fibres suggest that the bike is super stiff. However; remember what happened to the spaghetti noodle? High modulus carbon fibre may be stiff, but it is not very strong and thus–like the pasta–breaks with less force than lower modulus fibres. Simply put: fibres that are higher modulus (stiffer) are also weaker, and ones that are lower modulus generally offer higher strength (harder to break). It is also important to note that higher modulus fibres cost much more than lower modulus fibres, over 10 times more in some cases.
For most serious cyclists, a carbon fibre road bike is a must-have piece of kit. But the composite material famed for its light weight, high stiffness and crash resistance starts its raw life as threads woven from thousands of filaments, each a tenth of the width of a human hair. Bike construction differs from a typical bicycle in many ways. The most noticeable differences are the inclusion of suspension on the frame and fork, larger knobby tires, more durable heavy duty wheels, more powerful brakes, and lower gear ratios needed for steep grades with poor traction. Downhill (DH) bikes typically have eight or more inches (200 mm) of suspension travel. They are built with frames that are strong, yet light, which often requires the use of more expensive alloys and very recently, carbon fibre. In the past few years, lighter downhill bikes have been getting below the 40 lbs mark (18 kg).