Steel Bicycle Tubing
Steel is the choice of material for bicycles produced at Peyto Design Works. Bicycles have been produced out of steel for the past hundred years, in fact much longer than any other material (Alumnium, Titanium) used to produce frames.
It wasn’t until the 1970s that aluminum was used in bicycle frames, and in the 80s we saw the first frames being made out of titanium. The bicycle industry has recently seen the use of various blends of Carbon Fiber and aluminum. While all of these alternative materials have been used with a measure of success, it is steel that has been around forever, and continues to be the custom frame builders choice of tubing for bicycle production.
The steel is an iron and arbon alloy that, with the addition of several elements such as chrome, nickel, manganese, molybdenum, and vanadium. It develops specific characteristics such as higher strength, corrosion resistance, greater fatigue life, and toughness.
Properties that are important for bicycle frame considerations are often misquoted, and even worst, misrepresented by marketing hype. Below is a quick run down of materials and the properties that make up a bicycle frame in relation to the rider.
Density of Steel Bicycle Tubing
Chromoly steel has a density of 0.283 pounds per square inch compared to aluminum 0.098, and titanium 0.160. Looking at these numbers steel is the heaviest material to build a frame out of, however this information alone is not enough to make a decision on material since various tubes are used to change the weight of a bicycle frame.
Steel Bicycle Tubing Stiffness
Younge’s Modulus (modulus of elasticity) for steel is approximately 30 million pounds for square inch. The titanium alloy Ti3Al-2V is 15.5 million psi, and 6061 aluminum is approximately 10 million psi. When comparing these ratios to density, bikes made out steel and aluminum have a close stiffness to weight ratio (or specific stiffness). Titanium on the otherhand has a slightly lower specific stiffness. However when tubes are increased in diameter, wall thickness of the tube can decrease, (oversize tubing is common on aluminum bicycle frames) and the stiffness increases, while the overall weight can remain low. This is why aluminum frames stay light while tube diameter increases, however the end result for the cyclist is a stiff harsh and unforgiving ride. Also as tube diameter increases, the wall thickness decreases, leaving the frame susceptible to denting, and when an aluminum frame is dented the frame will brake or crack.
Elongation of Steel
Measures how far a material will stretch before it breaks. It’s also referred to as ductility, the ability of a material to deform plastically without fracturing. Plastic deformation occurs when a load is applied to a material, and the material deforms, and remains deformed after the load is released. A material that bends before it breaks has more ductility than one that will just break. This is a good thing for a cyclist to recognize, it could help avoid catastrophic failure of the frame, and hence a very messy crash. Ductility is measured as a percentage, and steel frames come in around 15%. Aluminum frames ductility falls below 9%. Basically bent aluminum is not good, if an aluminum frame is bent or has a dent it should be considered garbage. It cannot be repaired. Steel on the other hand can be repaired, and depending on where the bend or dent is it can sometimes cause very little to no damage at all. As a matter of fact some framebuilders rely on this plasticity to properly align the frame after it’s been built. Titanium’ ductility is about twice that of steel.
Tensile Strength of Steel Tubing
Tensile strength testing, is done by pulling the sample apart (applying tension) and measuring the load/defection relationship. The tensile strength of the steels used to produce bicycles is between 100ksi for normalized 4130 chromoly steel to 140KSI for alloys such as columbus nivachrome, 175ksi for heat treated 4130 and up to the 200ksi range for air hardening steels such as Reynolds 853 and True Temper Platinum OX. Alternatively aluminum strength is approximately 1/3 of this value. The titanium used in bicycle production 3/2.5 has a tensile strength of about 130,000 KSI. Does this mean that an aluminum frame is going to pull apart during riding, no not really, but tensile strength combined with elongation should demonstrate steels long-term reliability, and quality of ride.
Fatigue Strength - Steel Bicycle Tubing
Fatigue describes a frame’s resilience to weakening over constant use. There is not a definitive measurement of fatigue strength that will tell us how the material will last in a bicycle frame. Bicycles are subjected to forces of varying amounts in a random, cyclic fashion. As long as these loads are kept below a certain level, titanium and steel both have thresholds below, which they will never fail. Almost none of the aluminum (including the metal matrix composites), magnesium used in bicycle fabrication has a defined endurance limit.
Steel is Real
Steel is a wonderfully reliable material for building bikes. It’s safe to say that there’s no more successful material ever used. It’s relatively easy to work with, can be easily welded or brazed and repaired, requires simple tools for fabrication, and creates a smooth comfortable ride. Titanium on the otherhand is very expensive, and more difficult to work with.
Steel Tubing Information
True Temper Steel Bicycle Tubing
Custom Mountain Bikes, Cyclocross, Road, Street, Road, Trials bikes, Dirt Jump, Freeride, Single Speed, and 29er Bicycles.
More information on Steel Bicycle Tubing.