I am designing a seat mast for one of my customers and this is the first time I have done this style and was hoping for some input as I want to be sure this has sufficient strength. I wanted to get some different ideas about testing methods to find out what type of load the seat tube can withstand under the weight of a rider. What type of formula would I use to calculate the amount of stress on the seat tube? I am gonna be using a 73 degree seat tube angle with an externally butted seat tube. Any info would be appreciated.