Reynolds 531 steel tubing was originally developed for the aircraft industry, but it also became one of the most sought-after materials for building the frames of high-performance bicycles. To this day, it is still considered a premium material for bicycle frame construction, though aluminum alloys and carbon fiber composites have displaced 531 as the material of choice by many high-end bicycle builders since the 1980s. Reynolds 531 is a mix of the following alloying materials:

Carbon: .23-0.29%
Sulfur: 0.045% max
Silicon: 0.15-0.35%
Phosphorous: 0.045% max
Manganese: 1.25-1.45%
Molybdenum: 0.15-0.25%

Reynolds 531 Steel tubing is seamless, and also butted, which means that the wall thickness of the tubing is greater on the ends than it is in the middle.

History of Reynolds Tubing

Use of Reynolds tubing in bicycles started in 1902, and the tubing was considered to be the best material available for building a bicycle frame. World War 1 provided Reynolds with contracts to manufacture tubing for bicycles and aircraft for the military, and continued to serve the aviation market after the war. The War brought advances in Metallurgy, and in 1923 they introduced the first High Manganese tubing for the aircraft and bicycle markets. Reynolds 531 was introduced in 1935, originally intended for use in aircraft, but specifications were modified for use in bicycle frames. The advanced material was an immediate hit, and 531 frames are still popular today, despite the widespread adoption of other frame materials, such as carbon fiber, titanium, and aluminum alloys. In 1976, Reynolds introduced 753 tubing, a special heat treated alloy which was much stronger than 531, but must be worked with extreme care. 853 tubing has been introduced since, and has a strength to weight ratio approaching that of Titanium. For comparison, Reynolds 531 has an ultimate tensile strength of about 120,000 psi, and 753 has an ultimate tensile strength of about 180,000 psi.

Characteristics of Reynolds 531

A bicycle frame made of Reynolds 531 is lightweight and springy, and fitted with lightweight wheels and tires, seems to become a part of the rider himself or herself. A Reynolds 531 frame itself weighs about 4 pounds, and a complete road bike, less than 25 pounds, depending a lot on the tires and wheels, cranksets, and handlebars used. Reynolds 531 tubing is available in a number of variations tailored to road racing, track racing, and touring bikes, and I even saw a reference to motorcycle frames being built of the stuff. A complete Reynolds 531 bicycle frame will still command close to 500 USD today. I rode a Peugeot PX-10 built with a 531 frame in college extensively. It pretty much ruined me for inferior bicycles to this day. Sadly, I had to park it outside on the bike rack at college, and after several years corrosion found its way into a stress point where the butting ended near the bottom bracket, and the frame developed a crack. I was preparing to rebuild the bike, starting with a clear coat metallic paint job, when I discovered the crack. I even looked into getting a new seat tube brazed in, but the oddball French size led to the frame getting scrapped.


Links:
http://www.bretonbikes.com/reynolds.htm
http://www.sheldonbrown.com/harris/waterford/const.htm
www.reynoldsusa.com/history/history.html
www.reynoldsusa.com/tubing/tubing.html

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