Having recently re joined the world of riding and also the world of stw, I've been wondering how you lot seemingly get thro countless bottom brackets amongst other rotating items. Are these things so poorly built or does it just come with the territory?
We have pumps at work that run for months on much higher revolutions that never seem to fail. Explanation please.

Calderdale grit destroys everything in no time. Especially in winter…

When you pay a bit more you get better results. Most of us here skimp on the BB so we can complain here. It's ever so simple 😀

External BBs such as HT11 have poor sealing and the bearings are thus vulnerable to grit entry. also vulnerable to miss alignment as the bearing cups screw into each side of the frame. I had an HT11 get gritty after a few hundred miles, HT1 / octalink where the bearings are more inboard thus are less vulnerable to grit and are held in alignment last thousands and thousands of miles.

MTBers seem to put up with poor design and engineering and frequent replacements for reasons I can't understand. When the HT11 BB I have dies completely the whole crankset will be replaced with older but more reliable tech. I think a part of it is that the UK is one of the few places in the world where you ride your MTB in foul conditions so stuff is not built for this.

As TJ – poor sealing & bearings not parallel. Factor in they're cheaper to produce than older styles but the end user will pay more for them, quicker to install and also the suppliers can make money 'cos you have to buy replacements more often.

The way it went as I understand it was that square tapered BB axles, being skinnier, were supposed to be more likely to snap & so needed to be heavier i.e. not hollow, or not so hollow. They last ages without wearing out because the individual ball bearings are bigger, due to the smaller axle giving more room for bearings. Not that bigger diameter balls are stronger or more wear resistant in themselves, just that it makes the tolerances of the whole unit less crucial. What also made the whole idea work well on the Shimano sealed units (possibly others) was that the whole thing was a sealed unit, and didn't rely on cartridge bearings as such, which again would have resulted in smaller balls & less room for error. The balls ran directly on the axle & the inside of the shell, as far as I remember, so it was a bit like a sealed in, non serviceable version of the really old units.

But then it was decided that the axles should be bigger diameter, because then they could be lighter without snapping (some did though..)
So Octalink & ISIS BBs came out that had stronger axles. Alignment isn't an issue as they are 1 unit, but the ISIS ones at least used cartridge bearings, probably for ease of manufacture. Nothing wrong with cartridge bearings, except that when a unit has to be a certain size to fit in a certain size frame tube, the bearings again have to be smaller. So ISIS BBs have a bad rep for wearing out. However, at least some units are made with bearings of good enough quality to last a reasonable time. I had an FSA DH unit on my regular bike that I got over a year of hard use out of. This replaced an external crankset. External types could again be lighter in theory because the design allows for a larger axle again, which can be thinner walled & just as strong. The disadvantage is the BB shell has to be faced to make sure the surfaces are parallel with each other & directly square to the frame. If not, the bearings won't be lined up & they'll wear out quick. Also, even though the bearings are on the outside the individual balls are still quite small. It looks like he sealing can't be too good, although the ones I've had seem to have kept all the dirt out. But the most I ever got from a set was 6 months. The worst was 3 rides before seizing.

Superstar have an ISIS unit that I'm using at the moment. The design looks sound as it uses the integrated approach where the bearings run like the square taper sealed units. So far so good, no problems with it.
As for weight, Middleburn RS7 cranks are very light & still guaranteed for life for DH & jumping, so they'll do me. So, I'll use them until it's no longer possible to buy an ISIS BB.

The cynical approach just says that they change things to sell new products & there must be an element of that, but sometimes mistakes are made as well, I guess. Who knows? If anyone's still awake, I'd just say you're better off buying stuff that you know a mate has got lots of miles out of, rather than believing the hype…

…and I'm happy to be corrected on anything here if I've got anything wrong

Have to say I've no issue with the longevity of my XT ones, especially when compared to my Raceface one which has lasted, oh, 1/4 as long as my current XT one. If I was bothered by the lifespan I'd service the things but instead I'll just replace the one slightly graunchy bearing and carry on.

The HT2 XT doesn't last as well as my old square tapers did but then the cranks are better so I'll accept that. If the lifespan was terribly short I doubt I would but in my experience it's not, with a faced frame and a properly set bearing tension.

I'm sticking with square taper. I'm 16 stone or more. ST works reliably for me. If it ain't broke, don't fix it.

Tj, that was my thought, why, and I'm yet to experience it do we put up with inferior products such as this. Obviously you get what you pay for in any aspect of machinery but it seems even some of the top end stuff is subject to the same failings!

Oh and O5 excellent explanation!

The only point I would make is it's absolute boll0x about facing frames for external bearings, the torques involved will not distort the cup and hence misalign the bearings, the only factor involved is the quality of the threads, only been riding 6 years so only experience is with ISIS and external, ISIS = rubbish, external = good. Quality of bearings/sealing in external is where the problems lie.

The reason your pumps run and run and run is that they are designed, built, installed and maintained to do so.

I use a good quality (Hope) BB, installed as per instructions and i maintain it depending on use. Its on its 4th bike and is used in all weathers. Its also (along with the chainset) a lighter setup than any previous 'method'.

Look after your stuff and it'll last longer. I've never killed a bottom bracket of any design. Although I've never used ISIS

I'm one of those odd people that gets far more milage out of HT2 then I ever did out of SQ Taper or Octalink…. I also scour the classifides and other places for cheap replacements, so it's not expensive either. I like HT2, I think it's a great system…. Very easy to fit, just as easy to transfer between frames (Where SQ Taper often needs a new axle length) stiff, well made. I have learned a lesson with FSA cranks though, and now stick to Shimanos, which I don't think can really be beaten. 🙂

I'm one of those odd people that gets far more milage out of HT2 then I ever did out of SQ Taper or Octalink

Same here, I'm also on of those seemingly odd people that enjoy maintaining/fettling my bike, understand how to fasten bolts correctly and the importance of correct lubrication….

….I know bike parts can fail JRA but I'm pretty sure many of the problems people wail about are compounded by either incorrect use or poor maintenance ❗

I know this is a massively varied situation but again look at the durability of say a landrover wheel bearing, millions of rotations in all kinds of sh¥t muck water and salty british roads, last for years. And then not expensive to replace, ( pain in the arse to change granted) so it just goes back TJ's point of why do we put up with it?

I know this is a massively varied situation but again look at the durability of say a landrover wheel bearing, millions of rotations in all kinds of sh¥t muck water and salty british roads, last for years. And then not expensive to replace, ( pain in the arse to change granted) so it just goes back TJ's point of why do we put up with it?

Good luck jamming a pair of those big (heavy) bastards into your bb shell!

Fair point concisely made ha ha 🙂

Doesn't the problem just go back to the size of the BB shell (something designed about a hundred years ago if manufacturers could come up with common standard (they've tried with BB30) that would allow bigger bearings and axles more suitable for the stresses encountered by modern bikes.
One of my bikes has BB30 and, so far its been trouble free for a year (touch wood).

but then the cranks are better

better in what way ??

Look after your stuff and it'll last longer

square taper cartridge BBs are zero maintenance and can only be opened with a saw…

simonfbarnes – Member

but then the cranks are better

better in what way ??

More durable, stiffer, lighter. Oh and I know you'll say none of this is relevant to you.

More durable

like the ST ones wear away ? And lighter because the hole through the end is bigger ?

I can't be the only person who only ever got 12 months form a square taper BB and lass if it snapped/bent?

"And lighter because the hole through the end is bigger ?"

Lighter because they're lighter. Middleburn RS7 + UN52 BB + spider is 784g without rings, to give one example, and costs about £150. A set of rings is around 200 grams. How favourably does that compare to XT? Not very- 850g with 3 rings and all bolts and BB. And more expensive to boot.

my UN26 was £5.50 and the steel chainset £29 🙂

poor maintenance

You aren't supposed to maintain HT2 BB's though, at least not shimano ones, they have "do not disassemble" written on them!

And how much did that weigh sfb? Less than a typical HT2 crankset? My Alivio crankset might have been cheap but then the cranks without BB weighed almost as much as a Deore M590 crank does complete.

pypdjl, yes they do say that. But then lots of bikes come with "Not for downhill use" written on them yet we ride them down hills 😉 Shimano BBs are servicable, you can clean and repack the bearings or replace the bearings entirely should you choose. Which is more than I can say for any of the ST BBs I had 😉 Most people choose not to of course since they're fairly disposably priced.

Yeah I know, just saying it seems harsh to blame poor maintenance when it's supposedly a maintenance free part! In my experience they are very vulnerable to water getting in from inside the frame, which a cartridge type BB is obviously not going to suffer from.

Yeah, that's a fair comment.