I almost never hear of a square taper cartridge bearing bottom bracket failing.  And I do not think I know anyone personally that has ever had one fail.

I have spares on the shelf, not because I am fearful of them going bad in the near future, it is more of a fear that I will not be able to find the size I need later if I need one.  Thus, I saw it more as an insurance policy.

I did a group tour in 2012 with a dozen other riders for a week.  One rider had an external bottom bracket fail, the bike was still under warranty, the manufacturer sent a new bottom bracket to a bike shop on our planned route.

I have four friends that have bought Trek Checkpoint bikes, all bought shortly before or during Covid.  Now a second one has had an external bottom bracket bearing fail. 

When I first built up my Nomad Mk II a decade ago, I was nervous about bottom bracket enough that I considered buying the cup and cone parts so that I could clean and re-grease it any time I felt that it was warranted, but now a decade later I am no longer worried about the Shimano cartridge bearing ones.  I have the cup and cone parts with spindle on the shelf, but it probably will never get installed.

Yeah, the UN55 BB's did last well. I have also been mighty impressed with the long lasting bearings in the FSA headsets Thorn fitted as standard.

Curious how headsets became an "install it and forget about it part" (a Chris King headset, or even those's FSA headsets, will probably last, without any maintenance, for longer than the average bicycle-traveler’s travel career), but BBs remain a source of worry. Of course, BBs are more susceptible to road salt, or water ingress during water crossings.

I got about 25,000 km out of the Shimano UN55 on my expedition bike before I ended up switching to different cranks and BB (Shimano XT and Hope, respectively). I then installed the Shimano BB on a bike for local use that probably did about 3,000 km before being sold.

My Raven has 31,000km and it’s still on the original.

I enquired and size added to listing (536S)

I have flat bars with a high angled stem, and a handlebar bag with a Rixan Kaul fitting that would keep it well out of the way of the rack.

I hadn't considered the v-brake cable getting in the way, so am very grateful for your advice!