Bicycle Frame Materials, Demystified

(CCN) For many, buying a bicycle comes down to price. But for others, the quality of the build takes priority over price. One thing that we can all agree upon, is that you really don’t want a bicycle that weighs a ‘ton’. Of course no bike does, however years ago the primary material used to build bicycle frames was steel. Even though alloy has been around since the very early 1900s.

A bicycle frame is the backbone of any bike. The goal of any frame is to offer extraordinary strength with minimum weight. However, frame strength is determined by many factors. The material used in frame construction is chosen for may qualities, and the weight is only one of them. Depending on the riders weight; the type of riding is even more important than weight. In many cases a steel frame offers a more comfortable ride than an alloy frame, taking in frame geometry, tubing and the butting method to mind. But in this article, we will only explain the different materials used, and how to identify them.

The most common frame construction materials are: (Heaviest to Lightest)

  • Carbon Steel (High-Tensile)

  • Chromoly Steel (Chrome Molybdenum)

  • Aluminum Alloy

  • Titanium

  • Carbon Fibre

Carbon Steel is the most common material used. It offers great strength and durability. Many long distance touring riders prefer this because of the terrain they may travel. However, the game changer was chromoly steel. Technology created a steel that produces light frames and still offers the brutal strength of carbon steel. Chromoly is very responsive and provide good flex making it the preferred material for many manufacturers.

Today Aluminum Alloy is taking over the industry. With double triple butted building techniques, alloys offer great strength and extremely light frames. So light that the differences are negligible when compared to a titanium frame. Alloys are very stiff, so frame geometry is very important when it comes to ride comfort.

By far the most expensive materials are titanium and even more so, carbon fibre. Extremely light but as tough as steel, titanium can be found on road and cross country bikes. The top of the heap is carbon fibre. Compiled in laminated parallel fibres to create strength, much like plywood, this is one tough material. Of all the materials, carbon fibre frames are the most expensive and because they can become brittle, heavier riders are cautioned look to alloys.

By far alloys and chromoly have won the day. They produce excellent bicycles but to many without build experience, it is hard to know at a glance what the bike is made of. Luckily, manufactures are required to identify the materials using a numerical system. (See image above) These four digits numbers are the key in understanding both the principle alloy elements and the carbon content.

If you look at your bicycle frame, you may see a four digit number on a decal. The most common are 4130, 6061 and 7005.

The first two numbers indicate the principle alloying elements. For example “4130” tells us that 41 makes it chromium and molybdenum (Chromoly). The last two numbers, 30, represents the carbon content of the steel in one hundredth of a percent. Therefore, 4130 contains 0.30% carbon.

The amount of carbon determines a compromise between strength and ease of weldability. Steels with less carbon aren’t as strong, but steels with more carbon don’t join as well.

Aluminum alloy tubing is designated by the numbers ranging from 6061 to 7075. Typically we see frames stamped 6061 and 7005. Taking in our understanding the following can be determined from these numbers:

  • 60 – Aluminum alloy with magnesium and silicon
  • 70 – Aluminum alloy with magnesium and zinc

Both of these alloys have similar chemicals used in different proportions, which include chromium, copper, iron, manganese, silicon and titanium. It can be argued that the differences between the two are negligible.

Of course from these number we know the carbon content. (.60% and .05%)

So what do we take away from this?

We can at least know what frame is either steel or an alloy. But then again, if you pick the bike up, you can pretty much figure that out. Price-wise we find bicycles made with 7005 alloy a bit pricier. Why depends on how the frame is constructed.

When it comes to frame materials, consider you own weight, and type of riding. Make sure that the material can take the stress you will be subjecting the bike to. Frame construction technology has been developed over 100 years and today we have such a range to choose from.

Personally, I enjoy how a carbon steel frame takes in the road. But then again, it just a preference.

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