Originally Posted by
vintagebicycle
Something I've been leery about lately when switching to upright bars is how the frame takes the new directions of stress. I've had a few taller frames exhibit some pretty noticeable frame flex when converted to IGH and North Road bar bikes. I never saw any real data on how rider position affects frame stress, but I did have a down tube break off at the BB shell on one bike with Champion
#2 tubing, and had a Schwinn Volare frame loose a right chainstay at the BB shell. both were tall 26 and 25cm frames.
I tend to look at 23" frames as the ideal upright conversion size for me because they're just a more rigid frame in most cases.
While I realize all we have to base our theories on is personal observation, I don't think this is enough to suggest the upright conversions were the cause. IGHs often come with North Road conversions, so it's difficult to rule one out from the other, and we're talking about a size which is likely to be ridden by fairly powerful riders if only by size alone.
I have a hard time seeing where a lugged frame - if built correctly - should break because of an upright configuration. If we are to assume rider distribution of weight and force lead to lugged joint failure, one could theorize that a drop bar configuration results in a higher possibility of the headlugs or seatlug cracking from weight tearing the headtube forward and out from the top to the bottom (with similar forces applied whenever the fork hits a rough patch of road, etc).
It may work for you, but I don't see where 23" converted for upright bar duty would somehow be stronger when set up for a rider that should be on a 25" frame. If there's anything where empirical data could come into play, take a look on Amazon at how many supposedly decent, aftermarket aluminum seatposts break in two once you have more than 300mm of post sticking out of a frame.
-Kurt