This more curiosity than help but I really do want to know.
I’ve been taking my bike apart and putting them back together, I lose my mind in the winter. It’s forcing me to notice parts that are not doing well, that’s good because i never notice anything until it embarrassing.
My road bike with a Praxis T47 bb that’s 2 years old wasn’t embarrassing but it was well past it’s prime. I’m not sure if that’s a good or bad lifespan.
My gravel bike’s bottom bracket on the other hand has the same Shimano Ultegra bottom bracket it came with in 2019 and it’s as smooth as new. It’s survived obsessive pandemic gravel riding in the worst conditions. It’s got at least 25,000km on it.
Which of these is normal? Is the difference due to brands or luck, or does it come down to T47 vs English threaded bottom brackets?
Bearing design: how well it’s sealed, the type of bearing, how well the bearing is lubed
Assembly: were the appropriate surfaces lubed when the BB and bearings were installed?
Riding conditions and care of the bike after riding in foul conditions.
Frequency of bearing checks/service.
Whether the bearings are internal or external could make a difference, with internal bearings possibly being better protected. BSA vs T47? I think it’s more about the other factors I mentioned as well as bearing size than it is any difference between those two BB “standards”. I’ve only had experience on my bikes, so I’m sure there are a lot of folks with way more experience that likely know more.
That’s a good start, and I’ll add a less common one–alignment. If that 2-yr old BB is already trashed, and no crazy miles or abusive conditions, then it could be that one of the cups is slightly tilted. Most mechanics would check that as part of servicing, rechase the threads, etc. though. Mine used to work for a big bike retailer and had to assemble all the new bikes and he was often finding manufacturing defects in the frames that lead to either BB problems or disc caliper mount problems.
On the road I’ve generally had good luck with Shimano bb’s, they’ve tended to last with a lot wet winter riding and no service. I just replaced one that had 35k kms on it with no major issues. The replacement is a wheels mfg angular contact thread-together, but only about 5k kms on it so far, but I expect it’ll last the rest of the lifespan of the bike.
Cross bikes I’ve had ones that died in one season (sram dub, creaked almost straight out of the box and was dead after a few rough months) and even one race (FSA, to be fair to them it was a very sandy race and I went down in the sand multiple times). Currently have a wolf tooth on my cross bike, but only 1,200kms and a couple of races on it at the moment, but no complaints so far.
The frame interface (T47, PF, BSA, etc) shouldn’t really matter, as long as the cups are square.
I’ll add a square BB shell face is very important. Remove paint and ensure the faces are parallel. Design can affect lifespan in terms of spindle diameter, bearing spacing, tolerances. Excessive leverage on the bearing can increase wear.
I will say we can all thank Shimano for the cartridge BBs that came out of the MTB evolution. Before that many BBs were hopeless. The cartridge BB was cheap, durable and easy to change.
I recently bought a Crux DSW frameset with BSA BB to move away from the BB86.5 on a 2019 Trek ALR5 that wouldn’t stay quiet even with a Token thread together BB and obsessive cleaning and re-greasing. Having the metal axle directly contacting the metal inner bearing surface is not a good engineering solution in a high load area (in my opinion). Having said that, the bearings have lasted ~20,000 km before I noticed some increased resistance when spun with a finger.
Before swapping parts over I had the Crux DSW frame faced at head tube, BSA BB (including tapping the threads), and disc brake mounting tabs. You can see the freshly cut surfaces in those areas indicating material was removed and therefore, faces were not square. Would I notice in day-to-day riding, probably not, but I would like bikes and bearings to last as long as possible and stay quiet.
I think the biggest BB killers are alignment, and preload, followed by riding conditions and water ingress.
The more the BB cup/bearing alignment is out (or if a cup is loose in the frame, or with press fit the frame shell is undersized) the less time a BB will last, to the point that a BB could die in just a few rides.
If the alignment is good, you ride in good conditions, and don’t overdo the preload, all but the most bargain basement BBs will last for a really long time. Even if the bearings don’t feel like new, but spin ok, in a frame that provides good alignment the BB will still likely last for long time.
After the above, it would be riding conditions, or specifically how likely water is to get into the BB, whether down the seat tube or past the external seals.
My summer road bike was on original BB after over a decade (not sure distance, but not small) and only changed due to crankset change. My MTB is on third BB in five years. Road bike alignment looks to be spot on, and bike isn’t ridden in rain or washed very often. Not convinced MTB alignment is quite as good, but the mud and regular washing won’t be helping at all.
100%. People slag off pressfit for alignment issues causing wear and creaking or loose BB cups, but I’ve seen all three with threaded cups, all thanks to the same poor build quality/QC that cause issues with press fit. The difference is that the tools to mitigate/resolve the issues are more readily available, techniques more broadly known, and can mostly be done in a normal cycle workshop.
Always, but it’s much more important with the new style of BB where the cups hold the bearings.
In the old style cartridge BB (introduced by Phil Wood), the BB shell held the bearings and the cups held the shell. The bearings were aligned ex factory, misaligning the cup threads could create enough force to throw this out but problems were smaller. With the new style, the cup thread alignment is the bearing alignment so facing and chasing the threads is absolutely necessary IMO.
I learnt this the hard way when a client specced a Praxis T47 BB on a frameset and it effed up very quickly, despite the threads having been chased and faced with the tooling I then had. This was absolutely due to my installation not being good enough: I learnt from the experience and improved my frame prep practices (including new, better tools) so all good in the end.
On the other hand it seemed to me to be an incredibly finicky bit of kit; I subsequently refused to use a Praxis BB on any frame.
My go-to became C Bear which, in my opinion, are a much better design: more robust, much easier installation, worth every penny of the extra cost.
C Bear are also a dream to work with, their tech support is incredibly good.
IMHO, facing and chasing BB’s falls into the same category as properly facing disc brake mounts: it’s something every single manufacturer should be doing. Unfortunately far too many of them seem to either leave it up to an LBS to fix or don’t consider it much of a concern at all.
All I can says is that lifespan of a BB varies wildly. Current record for me is a BSA Shimano XT full cartridge square taper BB installed in 2001, still smooth as butter, installed in 1996 GT Zaskar that serves as a commuter, all with little to no maintenance. Not even sure if I’ll be able to pry it out of the aluminium frame ever again.
On the opposite spectrum the horrendous GXP press fit. And race face press fit BBs. The worst one lasted a few months of admittedly heavy off road MTB abuse. So I guess it depends.
As mentioned above, bearing size, bearing spacing and sealing matter a great deal. The Shimano external cup bearing for road and MTB BB with BSA thread generally last a very long time.
My old Canyon road bike had Shimano pressfit BB, still fine when I sold it after 7 years and 35t km. My current road bike has CeramicSpeed BB, I service it every year (clean and relube the bearings), ther’s 14k on it after 2 years and it’s like new, totally smooth. Both road bikes were ridden in nice weather mostly.
Then I have a year old gravel bike with 8k km on it, SRAM Red BB and it’s definitely not as smooth as new now, but still fine to use it. This bike is ridden whole year in all conditions, lots of mud and snow now in winter
Adding to all the other points here on BB alignment, etc. If you ride outside in the winter, you really should consider full fenders. They are a PITA to install, but not only do they make riding in the wet better for you and the person on your wheel (with a long enough tire flap imop) but it saves the BB and lower headset bearings.
For those able to do the N+1, a winter fender bike with cheap (or older) parts is the way to go.
One point worth considering: you don’t have to junk the whole praxis BB - the bearings can be removed and replaced, keeping the existing cups and seals. Those Praxis BBs are ok, but they lack the complex labyrinth sealing of the Shimano units.
Replace the bearings, whack a generous amount of grease under the dust cover seals, and you should be ok - 2 years is probably longer than you would expect if there were any alignment issues.
I’m loving my retro look Fairlight in part cause I can run awesome metal wrap around guards (albeit cut down so they do enough to protect me and the bike - anyone riding behind will get covered, but tough). They make winter riding so much more pleasant, massively reduces issue of water increase via seat tube, and stops spray towards the lower headset bearing.
Mudguards will be removed in summer for stripped back, lighter weight, go fast mode.
Have a winter road bike with full guards for sealed road only rides for same reason.
In my limited experience I’ve found that the smaller 24 mm axle Shimano BBs seem to have a significantly longer lifespan than the DUB standard I’ve used on the same bike (Shimano PF92 press fit system).
As noted by others it is likely the additional sealing (does feel notably more drag on a free spin than the SRAM DUB ones) probably has a huge influence on the winter riding, but the plastic internal/external housing does appear to be a lot more conforming than the smaller bearing SRAM ones which likely helps with minor misalignment.
Helps they also tend to be cheaper locally for me.
