R36 question

Why did the R36's have a lighter, thinner steel than their predecessers did? Cost saving measure?

The R36's weighed about 69,000 pounds as delivered in 1964. They used St. Louis' all-welded unit construction method. St. Louis used somewhat lighter construction than on the previous R33, and this would be troublesome in later years as water and rust were able to seep through the lighter, thinner body, endangering the body structure's intergrity.

7 Train wrote:...this would be troublesome in later years as water and rust were able to seep through the lighter, thinner body, endangering the body structure's intergrity.

That never stopped the MTA from keeping them in revenue service, lol

7 Train wrote:The R36's weighed about 69,000 pounds as delivered in 1964. They used St. Louis' all-welded unit construction method. St. Louis used somewhat lighter construction than on the previous R33, and this would be troublesome in later years as water and rust were able to seep through the lighter, thinner body, endangering the body structure's intergrity.

Well why did St. Louis use lighter construction for the R36's?