Originally Posted by
guy153
Looks about right to me but your builder will have taken more detailed measurements.
If I were building it I would consider going "double oversize" on the tubes to achieve required stiffness given your relatively high weight and that it's a large frame.
I would also make the seat tube longer (and the top tube closer to horizontal) so you have less seatpost sticking out. (Unless you want a dropper post). It's fashionable to have a lot of seat post sticking out nowadays,.and it gives you a bit of suspension, but it puts a lot of strain on the top of the seat tube especially with a heavier rider. It will probably be absolutely fine I'm just sharing my thinking here! Maybe some things to discuss with the builder.
+5. Absolutely good advice. I ride a folder with an ultra-long seatpost and have seen multiple frames fatigue crack right there, front of seat tube above the top tube. This bike is not a folder, but with the rider weight, and just good practice for durability in general, I would go with a level top tube. In this day and age, it also gives a nice retro-style vibe to things. There was a darned good reason for level top tubes for so many decades, it was only when they started counting grams and/or wanted to build fewer frame sizes, that sloping top tubes came into vogue. Go level, go strong, provided you have enough standing crotch clearance with the other dimensions of the frame fitting you. Some folder frames also put a welded gusset in that area, usually on aluminum, but certainly can't hurt on steel either, for what may be the highest stressed part of the frame, in tension, which is where fatigue failures happen, not compression stress. Oh, and simply extending the seat tube above the top tube, only reduces stress on the seat post, but does not reduce the bending moment on the weld zone of the aft top tube weld. Moving that weld higher with a level top tube, does reduce the moment on that weld.