Bottom brackets old style vs new, what's it all about

[rogerzilla]

The only issue with the UN55 is its weight. Shimano have reverted to solid spindles, probably to make the product less attractive so you "upgrade" to HT2. Tange BBs still have hollow spindles.

 

[fossyant]

The only issue with the UN55 is its weight. Shimano have reverted to solid spindles, probably to make the product less attractive so you "upgrade" to HT2. Tange BBs still have hollow spindles.

And.... more reliable. They always had solid spindles on square taper - yep heavier, but I'd swap the small weight penalty for fit and forget.

 

[rogerzilla]

A hollow spindle is perfectly strong and stiff enough but does need to be made from a better grade of steel. Solid ones are just cheaper to make, no other advantage.

 

[Smokin Joe]

Bog standard Shimano UN52 square taper bb cartridge would last at least 3 years of everyday, all-weather commuting.

I'm referring to older stuff in general, not specifically bottom brackets. Where they are concerned I'll have square taper any day.

 

[raleighnut]

C'mon. Just don't buy crappy ones.

Hopefully I'll never need to buy a square taper BB again, I'll probably have to buy new external bearings for the 4 bikes equipped with those so far ( I've got 2 spare cranks in the shed a 105 with bearings and an FSA without) but due to the leg I'm not hammering out the mileage I used to before the accident.

 

[Yellow Saddle]

A hollow spindle is perfectly strong and stiff enough but does need to be made from a better grade of steel. Solid ones are just cheaper to make, no other advantage.

There's good reason for solid spindles. Bunny-hopping and landing with that force taken up by the spindle in torsion is tough on hollow spindles. It has nothing to do with the grade of steel.

 

[derrick]

Have seen a couple of snapped hollow axles. Has anyone seen a snapped sold axle?

 

[Shearwater Missile]

I have a square taper bb on my Claude Butler bought new in 2010 and has done 14000 miles and still going strong. It may be old hat to some but if it works then why not ? I am not sure who made my bb as I have never had it out. If I get a creak then it must be my joints !

 

[rogerzilla]

Square taper has a few problems, which rarely apply to most riders:

1. Chainline is inexact due to tolerances and wear - you never quite know where the crank will end up. This is only really an issue for SS or fixed.

2. Really big and heavy riders (I mean 15 stone+) can break cranks at the BB end because the square hole (despite being an octagon really) weakens the crank.

3. The bearings of sealed units aren't really big enough and are too far inboard to give optimum support and stiffness. Largely theoretical.

 

[Yellow Saddle]

Square taper has a few problems, which rarely apply to most riders:


2. Really big and heavy riders (I mean 15 stone+) can break cranks at the BB end because the square hole (despite being an octagon really) weakens the crank.

3. The bearings of sealed units aren't really big enough and are too far inboard to give optimum support and stiffness. Largely theoretical.

2. It isn't the weight or the power of the rider that cracks a crank knuckle but the fact that people feel they have to continually tighten those cranks. The really strange thing about a taper is once it is on and tightened, and the bolt that holds it in (the crank bolt) remains in place, the taper will squirm upwards onto the taper. That is, the crank will tighten itself. The result of this is that the bolt is no longer tight, which leads people to re-tighten it, which leads to more upwards squirm and so on, until the knuckle cracks.
Many people think some loctite will solve the loose bolt problem, but if you understand why it becomes loose, you'll see that threadlock compound isn't the answer.

3. The bearings on square taper BBs with cartridge are big enough and last a very long time. It is the large hollow BSA BBs that are problematic, the ISIS and Octalink styles. These have a large OD and force the manufacturers to use undersized bearings with predictable results. As for stiffness, it is a function of the frame, not the BB. No matter how wide you make the BB, the flex is taken up and resisted by the frame in the downtube, seat tube and two chainstays. Ironically, the outboard bearings as in Shimano Hollowtech, Campag Ultratorque and SRAM GXP has a stiffness problem in the design itself. These bearings rely on the shoulder of the bearing cup to sit firmly, squarely and evenly against the edge of the BB shell. This requires a very precisely reamed BB shell, so precise that even paint can spoil the face and lead to premature bearing wear. What happens here is that the cup moves on its own threads with pedal cycles. This causes the bearing balls to run out of alignment with their races and gall. Still on that topic, the flex in the hollow shaft on the left side of the crank exacerbates this out-of-line running of the bearing and left cups fail long before right cups. To the casual eye it may seems that both sides receive the same forces but they don't. The left end of the axle is subject to torsion whilst the right side not at all.

 

[rogerzilla]

Chalo on the old rec.bike.technology newsgroup used to crack ST cranks (and knew what he was doing when fitting them) but he was a self-confessed claymore.

I've only ever seen cranks go at the pedal eye.

 

[Yellow Saddle]

Chalo on the old rec.bike.technology newsgroup used to crack ST cranks (and knew what he was doing when fitting them) but he was a self-confessed claymore.

I've only ever seen cranks go at the pedal eye.

Yes, but he was 7'4" and weighed 310 pounds @ 15% body fat. Hardly your average fat 5'10"er. Outliers like that aren't valid when used as examples of design weakness.

 

[Profpointy]

Have seen a couple of snapped hollow axles. Has anyone seen a snapped sold axle?

I've bent one. Admittedly it may not have been the highest quality, but bent it was. Couldn't work out why the chainrings had a wobble till I took it to bits, and rolled the axle on the table - surprised me as it was nearly 1/2" thick bar, and I'm hardly Eddie Merckx !

 

[derrick]

I've bent one. Admittedly it may not have been the highest quality, but bent it was. Couldn't work out why the chainrings had a wobble till I took it to bits, and rolled the axle on the table - surprised me as it was nearly 1/2" thick bar, and I'm hardly Eddie Merckx !

As you say it may have been a cheap one. You get what you pay for.

 

[Ming the Merciless]

My old square bicycle wheels are still running, can't see the issue.