I will be starting a project bike within the next month. I have a 1973 rigid shovelhead frame. I want to cut a little weight. So, I was thinking about building an exact replica of the frame I already have, but I was going to use aluminum tubing. I plan on using 1 O.D. .5 I.D. tubing. From an engineers point of view, would the aluminum frame hold up to the weight and stress as well as the steel frame? Or at least hold up just fine?
Aluminum frames are used in racing bikes but they have heavy castings and the correct grades of aluminum. many street bikes have aluminum parts however they are carefully engineered for strength. I would not duplicate a frame made of steel out of aluminum. The welding would have to be perfect as would be the correct material. Steel is easier to weld and less prone to cracking. Would you really save that much weight that it is worth the effort and possible danger? A rigid frame suffers more impact stress which makes it less a candidate for your project. Titanium would be perfect but the cost is prohibitive.
Aluminum tends to work harden from flexing. A frame made from aluminum would have to be super rigid to prevent this. That is something that is pretty difficult to do with tubing. Secondly, have you done the math? I am not sure you will really be saving that much weight.
First in 1973 Harley did not make a rigid frame, so please double check your year. Aluminum is a bad idea, it won't hold up. We recommend Steel .125 wall, DOM (seamless) Or if you have Ex. welding skills, Chrome Moly tubing is much lighter and stronger.
