I'm 5'11", ~175 lbs., so I'm not big, but I'm also not small. For a step-through Spaceliner frame that required the seat post to stick way out from the top of the seat tube for me to fit on it, what I did was take a cheap Wald 13/16" steel post (only post I could find long enough) and hammer an aluminum rod inside of it. I greased it and had to do a little grinding down to get it to fit, but it's in there forever (or until electrolytic corrosion dissolves it). I also cut some spirals along its length to help it flex to fit and hold some grease. Anyway, it's very solid now. Problem then was that the clamp couldn't flex the post enough to get a grip on it and hold it in place, stripping the regular hardware before it would bind tight. Grade 8 replacements fixed that problem.