What to look for in a frame
Frame materials are often compared based on the qualities of strength, stiffness, and weight:
✓ Strength: Strength refers to the durability of the frame. If you crashed, a stronger frame would be more likely to survive the crash intact. For a mountain bike that’s going to be put through some challenging trail rides, strength is important.
✓ Stiffness: Stiffness describes how much the frame material flexes under a force. For example, when you pedal, you’re applying a force to the frame; around the bottom bracket, it’ll flex slightly depending on the frame material.
✓ Weight: Weight is an important factor with frame materials. In an ideal world, you’d have the lightest frame possible so on your next climb
it wouldn’t feel like you were hauling a sack of potatoes with you. Of course, lighter frames require more expensive materials, which makes them cost prohibitive for some riders.
Types of frame materials
The most common frame materials are
✓ Steel: Steel frames have been around for a long time, and the best of them can still compete with some of today’s frames fashioned from fancier materials. The higher-end steels or steel/alloy blends (such as chrome-moly) are very strong, offer significant stiffness, and are long lasting, all for decent prices. Cheaper, mild steels or high-tensile steel are found on lower-end bikes where the frames are thick and heavy.
The downside to steel, other than the weight, is that it can rust. Also, high-tensile or mild steel is very uncomfortable — all the road vibrations are transferred through the frame to your butt. The better-quality chrome-moly frames with butted tubing are much more comfortable than the mild steel.
✓ Aluminum: Aluminum has become the most popular choice for manufacturers of bike frames. It’s lighter than steel, has better stiffness, and, unlike steel, it doesn’t rust. The other benefit of aluminum is that it can be easily formed into different shapes to improve the performance and aerodynamics of the frame. The downside of aluminum is that it’s not as strong as steel, so a big-time crash could leave your frame mangled beyond repair. The other factor with aluminum is that it fatigues over time, increasing the chances that the frame could break. Aluminum also transmits road vibration far more severely then steel or carbon fiber.
✓ Carbon fiber: Carbon-fiber frames are made by gluing, with an epoxy resin, individual carbon-fiber sheets together in patterns that enhance its strength. Manufacturers use this technique to customize frame strength by adding layers of fibers to the parts of the frame that require greater strength, and removing layers of fibers from the parts of the frame that doesn’t need as much strength.
The fact that carbon is strong and light makes it a desirable material for frames. However, carbon fiber is expensive. Carbon-fiber frames offer the most comfortable ride with the most efficient use of energy. The other nice thing about carbon fiber is that the frame can be made in almost any shape or size. Manufacturers aren’t limited to the standard tube sizes or the typical rounded shape of a frame tube.
✓ Titanium: Titanium, like carbon, is on every serious biker’s wish list when it comes to frame materials. Titanium is light, it doesn’t rust, and it’s as strong as most steels. It’s less stiff than steel and flexes to give a comfortable ride. Unfortunately, titanium is very expensive and out of reach for most bikers.