Originally Posted by
oldbear63
I rode a 2004 Lemond road bike for about 12 years until it wore out and I just replaced it with a new Fuji. My new bike has 31.8 mm handlebars that are flattened on the top and I noticed that I have had significantly less hand pain with the new bars. When I reconditioned my old bike and tried riding it I found that the old 26 mm handlebars are much too painful. When I replaced them with a modern handlebar (and a shorter stem) I found my old bike was also quite comfortable. The modern brake / shifters are also much more ergonomic and comfortable on long rides.
31.8mm and 26mm are the diameter where the stem clamps the handlebar, not the diameter of the handlebar where you hold it. Nearly all road drop handlebars, vintage and modern, use a 23.8mm diameter for the areas with circular cross-section everywhere except the stem clamp.