“Superdave is right. An unfinished weld leaves more material at the weld joint for a theoretically stronger weld. Finished welds are also a good way to hide an ugly weld.”
when i was building bikes we didn’t fatigue test this, but one of our contract builders, kinesis, did. they said their smooth welded bikes lasted twice as many cycles as did their beaded welds, which backed up the conventional thinking.
mind you, this was kinesys USA, the portland factory. it did this study because marcus storck’s bikes were smooth welded, and marcus wanted to know.
but there’s a flip side, as you point out. it depends on how thick the wall is, and who’s doing the grinding. i’m riding scandium bikes right now, and i’d never grind a scandium weld, because the wall’s so thin. with steel it was different, you could lay down a fillet braze and you’d hardly need to grind anything, plus it was easy to see what was fillet material (gold color) versus the silver color of the tube. nowadays, grinding thinwall aluminum to get a smooth weld, it’s hard to tell how much tube you’re hogging out, esp if you’re on an asian assembly line.
so i don’t think you can make a blanket statement about smooth v beaded. depends on the builder, the material, the wall thickness, and of course the price. smooth joints cost money. if it’s a cheap smooth weld, it’s possibly also a shoddy smooth weld. it also depends on what joint you’re talking about. for example, grinding around seatstay-to-seattube joint is really, really hard. likewise dropouts, really anything in the rear triangle.
all things equal, i would guess it’s not to felt’s interest to grind the welds, and if i was them i certainly wouldn’t. but if i was cervelo, with the way its tubes are extruded, the ability to control wall thickness, and the higher price of bikes like the P2K and P3, you bet i’d grind those.