The real reason for press fit BBs is to allow a stiffer but lighter frame.

By widening the frame at the BB you get stiffness for little extra weight, but you have to set the bearings into the frame, hence the press fit.

Press fit BBs are all about frames, not BBs.

http://www.slowtwitch.com/Tech/Bottom_Bracket_Standards_2573.html

an explanation of the move away from BB30 or even the threaded Iso/English shell (both using metal shells)

to PF30, OSBB and other “plastic cup” systems is that it does away with a problem that has affected a good number of older carbon fibre frames

manufacturers using metallic (aluminium alloy) components integrated into carbon fibre frames were finding after several hard seasons of use that corrosion was causing the frame to crack around the metal insert, typically the BB shell, but also dropouts and head tube parts

I’ve worked as a workshop manager for several big shops doing lots of warranty work and have seen this many times, first hand. Seen a good number of big brand and small brand frames with a hairline crack in the carbon fibre around the entire metallic BB shell

since moving to the the press-fit plastic cup systems I’ve seen more issues with the cups moving in the frame (which is why many are now bonded), or bearings heating up or moving in the cups

these issues are generally from poor initial fitment, poor repair or from abuse where bearings have started to seize and then rotate in the cups

Yes, so it makes sense for carbon frames. It makes no sense for metal frames, where the metal can happily take a thread.

I can see a case* for a larger threaded bottom bracket standard! or perhaps a standard which allows both threaded and thread less cups depending on the frame.

*though not really a very good one. The percentage of riders who found square taper 68mm to be too flexy or fragile was pretty small, for most riders in most conditions it’s a good system.

The real reason for press fit BBs is to allow a stiffer but lighter frame.

By widening the frame at the BB you get stiffness for little extra weight, but you have to set the bearings into the frame, hence the press fit.
For carbon maybe it helps make a stiffer shape in that area and as ben says, the main reason for pressfit is fitting BBs into carbon. But not all pressfits are wider, BB/PF30 still has a shell width of 68mm so you have bigger bearings but they’re closer to the bike centreline than HT2, so the leverage from the crank on the bearing is potentially greater. BB386 is wider but also a bulkier crank at the axle area. Cervelos system is better designed than BB/PF30 imo.

I think BB/PF30 is great, if your frame material is unsuitable for threading. (edit, as ben said above)

best advice for BB30?

don’t use “grease” its for lubricating bearing races, not fitting metal parts to metal parts

clean shell with iso alcohol

apply good smear of shimano anti-seize around inside of shell where bearing contacts shell, including the metal circlip the bearings sit againstI’m replacing a bb90 bottom bracket atm – do you know if it is recommended to grease the cups for insertion into a carbon frame?

I tried to just knock the old bearings out but damaged the bb shell – it was only made of plastic so seemed like you’d need to gently caress the bearings out to avoid any damage.

Holy thread bump.
I “own” the Cyclescheme bike I posted about now 🙂
BB has been fine since its first service.