In 1941 the average weight of a bicycle designed for adults was 57 pounds. A 57 pound bike was not considered heavy, but simply an average sized bicycle for the time. In 1942 the government ordered the bicycle manufacturers to make some mandatory cut-backs to preserve valuable metals so they could be used for the War effort.
World War 2 caused a lot of manufacturers to either drastically cut back their production, cease manufacturing, or even to change the product they manufactured. Metals, along with many other items were needed for the War effort. At the time people did not look at our Government as being intrusive or Socialistic, they were honored to help out with the War effort by contributing in any way they can. Oftentimes contributing to the War effort meant sacrificing many common items. Rationing during World War II, although forced upon the people, was seen as a patriotic duty.
In 1942 the Government instituted certain demands on bicycle manufacturers. The average weight of a bicycle was 57 pounds but new rationing laws meant that bicycles could no longer weigh more than 47 pounds. 47 pounds is considered a heavy bicycle by today's standards, but in 1942 a 47 pound bike could be considered a light-weight bike as it was 10 pounds less than the current average weight of an adult bicycle.
In addition to restricting the weight of bicycles, the Government also ordered bicycle manufacturers to cease production on children's bicycles. The only bikes that could be made were designed for men and women. The government knew that with all of the new industries and factories that were built to support the war effort the workers would need a mode of transportation to get to the factories, and in 1942 many of these workers used bicycles to commute to the factory.
In addition to these restrictions the Government also imposed tighter regulations between April 1st and June 30th 1942. During this period bicycles manufactured had to meet strict guidelines that demanded bicycles manufactured weigh 31 pounds or less. Bicycle makes were also forced to use a 20 inch frame size minimum which eradicated the production of all children's bicycles during this period. During this period it was also mandated that all men's bicycles be made with a diamond shaped frame so that no excess metal would be needed for bikes.
The bikes that were produced during the Government imposed rationing were designed to be lightweight to conserve metal and to be a simple bike with no flashy designs or non-essential "gadgets".
Because of the Government imposed rationing during World War 2, the design of bicycles was forever altered. Bicycle manufacturers learned that people preferred the lighter weight bikes and they began to try and produce lighter yet stronger bikes each year. This tradition with bicycle manufacturers continues to this day, and we see many evolutions of the bicycle such as Titanium and Carbon Fiber frames that are extremely lightweight, yet very strong.