What makes some external bottom brackets run with a plastic 'spacer' between the left and right cups (FSA, GXP, Shimano, Chris King and many others), while others do it without the plastic sleeve (Campy for example). In another topic there was stated that the sleeve just is an extra protection for the bearings for water and stuff that enters in the frame via seat tube and other openings. Are the bearings without a sleeve in the bottom bracket better sealed or is the sleeve just an unnecessary part for all bottom brackets?

_________________
I Will make the leap

Unnecessary; extra weight.

If you ride in the rain often or your frame is prone to internal leakage, they are helpful in that they will protect the inner side of the bearing seals from contamination.

Otherwise unnecessary.

_________________
Exp001

if your bike takes on water, make sure you have a drain hole. with a drain hole, the center sleeve is superfluous. without a drain hole (and with a way for water to get in), the center sleeve is worthwhile. without it, bearings can be spinning while essentially submerged. in these cases, though, it's really a need for a drain hole and not for the sleeve...

If you are running or will be running DI 2 then it will keep the wires from rubbing against the crank spindle. At least that is why I put them in.

It's just an extra layer of protection. Water tends to get everywhere, but pretty much all frames have drainage holes somewhere around the BB region.

I use Shimano Hollowtech II sleeves on all my external BBs since they are paper thin, very light (~10g) and I like it more than pulling cranks off to clean.

Some of them are very, very weighty.

_________________
BMC SLC01

Visiting South West Australia? Visit Crank n' Cycles!