This modern new fangled stuff....

[mattr]

I've had the old square taper cartridge BB last more than half a decade,

I topped out at about 16 months of racing and training.

while most external systems have struggled to last a year.

The "usual" method of execution is either bearings that aren't parallel or concentric. Or too much end load. If you get all these right, they last 3 or 4 years of race/training......

 

[al-onestare]

Hollowtech approach is very nice in theory, but I am not convinced by the longevity of the external bearing setup. I've had the old square taper cartridge BB last more than half a decade, while most external systems have struggled to last a year. I do now have Hope external BBs on most of my bikes, and they seem to be lasting OK though.

I've had a Hope one for over 2 years on the daily commuter with zero issues other than the usual servicing. The Shimano ones barely lasted 6 months so as ever it boils down to manufacturers and price.

 

[gradeAfailure]

The difference between HT2 and GXP is that with HT2 you preload the bearings using the plastic tool on the NDS crank, then nip the crank bolts up - exactly like a horizontal Aheadset - whereas GXP cranks have a shoulder on the axle that butts up against the inner face of the NDS bearing and the NDS crank then tightens onto the outer face of the same bearing, meaning the DS bearing is effectively a floating bearing, and there's no sideways preload on the bearings. I prefer GXP as it's all too easy for ham-fisted mechanics to overload a HT2 BB and kill it rather quickly..