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Square taper BB's

Old 08-14-19, 11:59 PM
  #26  
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Originally Posted by terrymorse
Just say "no" to square taper. It's junk technology that eats crank arms, and possibly injures the rider.

If the crank arm becomes loose, which happens when the fixing bolt gets loose or falls out, the crank arm is ruined.

If the fixing bolt is over tightened, which happens a lot, the crank arm "walks" up the taper. The crank arm develops a crack from being overstressed, then it breaks off without warning—usually when the rider is standing on the pedals—sending the rider to the ground.

Just. Say. No.
That‘s why i like cottered cranks the most. The weakest part is the cotter. Simple and cheap to replace.
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Old 08-15-19, 02:08 PM
  #27  
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Originally Posted by terrymorse
Please note that I stated "if the fixing bolt is over tightened". I stand by my statement. Even a crank arm assembled with the specified fixing bolt torque will walk up the taper, as evidenced by the looseness of the fixing bolt after some use. The bolt becomes loose because the arm has moved up the taper during use. If the cyclist is lucky, that will not be enough to initiate a fatigue crack.

As you state, re-tightening the fixing bolt will continue the crank arm's journey up the taper, increasing the possibility of a fracture.

And believe it or not, I do "have a clue". Would you like to compare CVs?



Two words: proprietary & patents.
I can't agree with your statements here. Based on my knowledge of theory and the practical experience:

If a square taper crank is properly installed (lubed, then torqued with appropriate force), it will stay put and bolt will not come loose.

Lubing the interface before the installation (axle and the bolt) and using a proper torque guarantees that the crank will move all the way up it can go (without getting damaged) and will from then on keep supporting the tightening bolt with a proper preload to prevent it from loosening... while the tightening bolt prevents the crank from sliding off. You could consider it a sort of "mechanical knot". Using the force created by the elastic deformation of the crank, axle and bolt, ass well as the spindle "angle" (narrowing down towards the ends and widening towards the mid part) to make it all work.

I am yet to have a properly installed square tapper crank come loose - unless the crank, axle, or both have already been damaged by improper installation and coming loose once already during riding.

The problem with square taper cranks is the failure mode. They crack at the place that is covered with the crank. While they are not practical for regular inspection.
In those terms, newest Shimano MTB XTR M9100 cranks and BBs offer both the proper bearing preload adjustment (unlike Hollowtech) and, at least in theory, no such risky, sudden failure mode. As long as one doesn't ride with worn bearings that keep binding, the axle should be fine (though modern "superlight" craze does tend to make those axle-tube walls as thin as possible, so I'm not sure of practical durability of the sold items, time will tell).

I would go as far as to say that most cycling stuff from this century does not benefit neither a casual rider, nor a high-mileage rider. It is made to make more money. Perhaps useful for racing as well. But when it comes to robustness, durability and even safety - older stuff is often just as good, if not better. With BBs perhaps being an exception - if they ever really get it right.
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Old 08-15-19, 02:08 PM
  #28  
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Originally Posted by Kovkov
That‘s why i like cottered cranks the most. The weakest part is the cotter. Simple and cheap to replace.
But hard as hell to install and remove without a special tool.
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Old 08-15-19, 03:09 PM
  #29  
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Originally Posted by San Rensho
But hard as hell to install and remove without a special tool.
That‘s one disadvantage. The other being the possibility the cotter catches a shoelace.
On the other hand, square taper bb‘s need special tools too. Puller and torque wrench.
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Old 08-15-19, 03:26 PM
  #30  
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I love that you can come on BF and find people who claim with a straight face that cottered cranks are in any way desirable.
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Old 08-15-19, 06:20 PM
  #31  
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Looky here now ksryder,
As an ancient mechanic and one who still has all the stuff to work on them they aren't that bad. The difference is that the weak part is not the aluminium arm but the cotter which was soft steel. And was that way by design so the arm could be removed by drilling if necessary. The hardest part of the cotter system was being sure the cotters were of exactly the same taper. I spent a bunch of hours filing those down to match back in the early 70's. Same goes for the improper installation as over-tightening the aluminium arms, they could be damaged. With the correct installation they worked quite nicely. When mechanics hammered them in, instead of pressing them with a C-clamp is when they failed. Smiles, MH
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Old 08-15-19, 07:15 PM
  #32  
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Originally Posted by Mad Honk
Looky here now ksryder,
With the correct installation they worked quite nicely. When mechanics hammered them in, instead of pressing them with a C-clamp is when they failed. Smiles, MH
And you get even pressure on both sides when using a C-clamp.
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Old 08-16-19, 08:16 AM
  #33  
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Originally Posted by Mad Honk
Looky here now ksryder,
As an ancient mechanic and one who still has all the stuff to work on them they aren't that bad. The difference is that the weak part is not the aluminium arm but the cotter which was soft steel. And was that way by design so the arm could be removed by drilling if necessary. The hardest part of the cotter system was being sure the cotters were of exactly the same taper. I spent a bunch of hours filing those down to match back in the early 70's. Same goes for the improper installation as over-tightening the aluminium arms, they could be damaged. With the correct installation they worked quite nicely. When mechanics hammered them in, instead of pressing them with a C-clamp is when they failed. Smiles, MH
Bold of you to assume I've never worked on them. Which is why I can unequivocally say that they're awful. Have fun with filing those cotters, I'll be over here spending less than five minutes swapping out a new cartridge or outboard bearing BB.

(I hope you realize this is all in fun.)
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Old 08-16-19, 03:56 PM
  #34  
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Originally Posted by ksryder
I love that you can come on BF and find people who claim with a straight face that cottered cranks are in any way desirable.
...if you look at what the pro peleton was riding way back when square taper was first coming into vogue, you'll quickly discover that cottered cranks hung on for quite a while. People did not trust them and felt that cottered cranks were more durable, and were willing to accept the small weight penalty Not making this up (even though I still have a number of bikes with cottered cranks. )
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Old 08-16-19, 05:01 PM
  #35  
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Once again ksryder,
I haven't assumed anything. I just said I was an ancient mechanic who has those tools and has worked on those my self. I didn't question your creds, or even your street cred! (Smiles) Now if you would like for me to start speculating about yer skills just lemme know. As for all of this being in jest I get it! And am not trying to flame anyone or discredit them. I just said they work quite when well done correctly. Smiles, MH
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Old 08-16-19, 07:39 PM
  #36  
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In all my years of cycling, maintaining numerous bikes at a time, I have never had a problem with square taper BBs. My (now college-aged) son's friends will bring their bikes (mostly MTBs) to me for various maintenance. A kid in the neighborhood brought his over last week. He said "The pedal is loose." Turns out that one of the teeth, or splines, on the splined crank (non-drive side) had broken off completely. A couple others were half broken. As a result...the crank won't secure at exactly 180° from the drive-side crank. I never had that issue with square tapers. The bike is only a couple of years old. So like 'dsbrantjr' alluded to...what good is it?
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Old 08-17-19, 08:23 AM
  #37  
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I have bikes with cottered cranks, square taper, HTII.
None of them are a problem.
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Old 08-17-19, 01:52 PM
  #38  
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Square taper is what many of us are making do with until something better comes along. Still waiting for that to happen.
Or to paraphrase a famous person from history, it's the absolute worst system ever, except for all the rest.
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Old 08-17-19, 05:33 PM
  #39  
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Of the 10 or so bikes purchased in my household in the past 35 years, 8 have been square taper with no problems, 1 Ashtabula again with no problems. The last one, an external BB was a mess that ended up with the spindle/spider interface breaking apart. Nothing wrong with square taper IMO. Robust, proven design. Newer designs are all for the benefit of the manufacturer, not the consumer.
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Old 09-06-19, 03:51 PM
  #40  
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Originally Posted by Bike Gremlin
I can't agree with your statements here. Based on my knowledge of theory and the practical experience:

If a square taper crank is properly installed (lubed, then torqued with appropriate force), it will stay put and bolt will not come loose.

Lubing the interface before the installation (axle and the bolt) and using a proper torque guarantees that the crank will move all the way up it can go (without getting damaged) and will from then on keep supporting the tightening bolt with a proper preload to prevent it from loosening... while the tightening bolt prevents the crank from sliding off. You could consider it a sort of "mechanical knot". Using the force created by the elastic deformation of the crank, axle and bolt, ass well as the spindle "angle" (narrowing down towards the ends and widening towards the mid part) to make it all work.

I am yet to have a properly installed square tapper crank come loose - unless the crank, axle, or both have already been damaged by improper installation and coming loose once already during riding.

The problem with square taper cranks is the failure mode. They crack at the place that is covered with the crank. While they are not practical for regular inspection.
In those terms, newest Shimano MTB XTR M9100 cranks and BBs offer both the proper bearing preload adjustment (unlike Hollowtech) and, at least in theory, no such risky, sudden failure mode. As long as one doesn't ride with worn bearings that keep binding, the axle should be fine (though modern "superlight" craze does tend to make those axle-tube walls as thin as possible, so I'm not sure of practical durability of the sold items, time will tell).

I would go as far as to say that most cycling stuff from this century does not benefit neither a casual rider, nor a high-mileage rider. It is made to make more money. Perhaps useful for racing as well. But when it comes to robustness, durability and even safety - older stuff is often just as good, if not better. With BBs perhaps being an exception - if they ever really get it right.
one argument against using some lubricant is that the friction is not predictable. it depends on the lube being used.
therefore the manufacturer who published the torque to use on the bolt advised against using lube on the bolt or the tapered interface for that reason.
i care not which manufacturer advised against using lube and when did so. i'm too lazy to find out what the situation is today.

the bottom brackets i bought for new were already greasy when i took them out of the plastic they were in.
the friction coefficient on the bolt can be even lower than 0.1 if you use the best wax lubricant you could find.
the friction of high grade steels that the bolt and bottom bracket should be made of is about 0.15.

using wax lubricant can have those unpredictable consequences as either too high preload or too low. i mentioned wax lubricant just to give the picture of what would work too well for this cranks/BB interface. it's more useful as a lubricant for bicycle chains and for spokes/nipples threads. there are many kinds of waxes as to their chain length and melting point. there is straight paraffin and there's also the less biodegradeable kind which are described by these terms: branched, isoparaffins and microcrystalline wax.

"In Soviet terminology, “ceresin” denotes any relatively high-melting microcrystalline wax, here, specifically, petroleum-derived microcrystalline wax"

back to the cranks/BB discussion: some recommend using a light oil just to ensure there will be no corrosion/galling of the threads in time. that's because a light oil film will not have the bolt in too high preload as the people are used to a certain torque when assembling the cranks. and a thicker grease can take more time to flow so in that case you need to torque it again a bit later or in stages if the grease is not so easily squashed/moved.

the most important thing to do is use a torque wrench or use a certain amount of weight for a certain amount of length if no torque wrench is available.

if i were to assemble some tapered cranks right now i'd use some concoction with high temperature melting microcrystalline wax to which i'd add some lanolin and talcum powder... and do my calculation as to the equivalent torque for the same preload. then i'd go a bit over that and then unscrew the bolt a bit and have a final measurement for the tightening torque. it's the same stuff i use for chains now.

i'd use grease only if having polyurea as a thickener because it does not incorporate water in it but protects better against corrosion by preventing the water from getting in. calcium greases tend to emulsify water so that corrosion would become an issue in time.

take care not to leave the bike vulnerable to the morning dew because with each cycle of raising and lowering of temperature the bottom bracket will breath and condensate water inside it. i't a good way to minimize it by slapping some grease over the seals.
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Old 09-06-19, 04:00 PM
  #41  
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Originally Posted by oldschoolbike
I realize this may be a hypothetical or even rhetorical question, but here goes:

If square taper bottom brackets are so heavy, flexible, and crude compared to modern hollow axle systems, why does square taper still seem to dominate the track and single speed worlds? I would have thought track and single speed riders would most want the claimed improvements, especially in stiffness, but uptake seems minimal to zero compared to road and MTB riders.
2 reasons:
1. low q factor
2. cheap

the second one is meant to mean that the differences in performance are really small and the small added weight is not too much of an issue for most folks.
low q factor with BB other than this tapered standard is only achievable by press fit etc. not cheap.
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Old 09-06-19, 06:17 PM
  #42  
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I use campy square taper on all my bikes to great success. I prefer the q-factor, and reliability compared to the failures in through axle bearings my friends suffer from. I use campy record 102mm bb's on my road, mtb, touring bikes, and gravel bikes. Perhaps, every once and a while, a bearing might go out (After about 5-10k). This is very rare compared to the bearing failures my friends with the latest incarnation of through axles experience. In my 49 years of riding, I have never experienced (or heard of) a catastrophic square taper failure of any sort in either the cranks or spindle. I did snap a hollow single piece bmx crank when I was a kid. Tonight is the first time I have heard of such square taper failures. I have experienced bent square taper axles from jumping off large drop offs back in the late 1980's using cheap long spindles.

Never a crank or spindle failure.

I have also worked in a number of bike shops in my life. I never saw a failure come through any of those shops either.

Also a teenager, I even have REEMED out the square taper portion of cranks to cinch them in tighter on the spindles (not recommended). Never a failure there either- granted, some could never be tightened enough and would work loose because of my "engineering", but never a failure.

G@# help us all.
R

Last edited by dualresponse; 09-06-19 at 06:29 PM.
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Old 09-07-19, 10:11 AM
  #43  
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Originally Posted by terrymorse
Just say "no" to square taper. It's junk technology that eats crank arms, and possibly injures the rider.

If the crank arm becomes loose, which happens when the fixing bolt gets loose or falls out, the crank arm is ruined.

If the fixing bolt is over tightened, which happens a lot, the crank arm "walks" up the taper. The crank arm develops a crack from being overstressed, then it breaks off without warning—usually when the rider is standing on the pedals—sending the rider to the ground.

Just. Say. No.

No seriously...
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Old 09-07-19, 10:12 AM
  #44  
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Originally Posted by terrymorse
Luck.
Or, proper installation, and maintenance.
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Old 09-07-19, 10:14 AM
  #45  
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Originally Posted by HTupolev
The crank arm "walks up" the taper with every installation, even if it was torqued properly. This is a form of long-term wear for square-taper cranks. But, it typically takes a very large number of installations for a failure to occur, either from a bottom-out of the taper or a fatigue crack.

Excessive torque will move the starting point for that installation cycle slightly farther up the taper, which means that the crank will suffer more of that permanent wear than it should have. In today's cartridge-BB world of very infrequent re-installations, this almost never becomes a problem in the first place.
To cause a problematic amount of added walk-up on a single installation from overtorque, you'd have to go really nuts. Like "bust out a huge cheater bar for no reason" nuts. The kind of behavior that will wreck any kind of crank interface.

(What is a big problem for taper interface wear is when someone misinterprets the walk-up as loosening of the fixing bolt, and repeatedly re-tightens the bolt after every few rides. Each time this is done, it restarts the walk-up cycle and puts a re-installation worth of wear on the interface.)
I shall run out in a panic and remove the cranks from my 1984 Ross Mt. Rainier today. Had you never told me this, I could have died. Thanks. The have been hiding their catastrophic failure form me for years.
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Old 09-08-19, 09:19 AM
  #46  
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I see all this hate for square taper cranks and wonder why. I think the square taper design does take some mechanical finesse to disassemble / reassemble if you're not familiar with how they work.

the current issue Shimano / Campy outboard bearing cranks with the large diameter axle and easy disassembly with simple tools has a lot to be said for it, but as somebody has posted above the bearings are poorly sealed and can require frequent replacement if used in adverse conditions, since they are "out in the weather" so to speak.

I find the Stronglight cranks (49D, 57, 93, 99) and the TA cyclotouriste cranks to be fragile and requiring some care, however the current Campy and Shimano square taper cranks are very reliable and should last a lifetime with reasonable care. I am also a huge fan of Phil bottom brackets. Again, all of these require specialized tools to install and maintain.

Kind of like leather saddles and other old school accoutrements in this modern age, it's something of an acquired taste, but can be used and enjoyed if you believe the journey is the reward !

Mark Petry
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Old 09-08-19, 11:05 AM
  #47  
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Originally Posted by phughes
I shall run out in a panic and remove the cranks from my 1984 Ross Mt. Rainier today. Had you never told me this, I could have died. Thanks. The have been hiding their catastrophic failure form me for years.
Huh?

My post was basically saying that square taper is fine, and you're unlikely to run into issues unless you do something silly with it

...Most of my bikes have square-taper crank interfaces.
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Old 09-09-19, 05:56 AM
  #48  
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i hate riding with too high (taper has only 140mm) q factor for light bikes with the seat - and narrow bars - mounted for high cadence.
it's not only aerodynamics but also the biomechanics. some people could have larger butts and therefore tolerate more q factor and also need wider seats. that would go along with lower cadence.

you might need a bit more width in q factor to better maneuver when offroad at the cost of pedals more closer to hitting the ground.
taper is of not much benefit other than being cheap/available as the 150mm q factor for the external BB with CX/road cranks can be too low for frame (heel) clearance and riders don't feel the need to go as low as possible q factor when offroad.

for road bikes the lowest q factor is only available with square taper or with the very expensive alternatives to the external bottom bracket.
square taper is just fine for regular road use. just a bit heavier than external BB but cheap and easy to work with.

when offroad the main advantage of the external bottom bracket (like hollowtech II) is the weight being reduced and/or the durability when doing stuff like high drops etc - octalink or isis cranks being not lighter than taper but somehow more durable as an interface. most of the usual cranks have 175-180 (they are so because most want them being wide enough) which is too high for my liking. i would install an external bottom bracket and road/cx cranks because i am used to ride high cadences and hate doing so with 175-180mm if the frame can take less.

have in mind that installing external BB cranks can get you problems with an older frame that has not proper facing - not built in order to have that. it's not easy to face the surfaces of the frame for the external BB to press on uniformly.

so, there, elaborated on the initial reply... cheap, easier to work with... and lower q factor compared to what most people think is always better - which is the external BB.
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Old 09-09-19, 06:07 AM
  #49  
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Originally Posted by dualresponse
I use campy square taper on all my bikes to great success. I prefer the q-factor, and reliability compared to the failures in through axle bearings my friends suffer from. I use campy record 102mm bb's on my road, mtb, touring bikes, and gravel bikes. Perhaps, every once and a while, a bearing might go out (After about 5-10k). This is very rare compared to the bearing failures my friends with the latest incarnation of through axles experience. In my 49 years of riding, I have never experienced (or heard of) a catastrophic square taper failure of any sort in either the cranks or spindle. I did snap a hollow single piece bmx crank when I was a kid. Tonight is the first time I have heard of such square taper failures. I have experienced bent square taper axles from jumping off large drop offs back in the late 1980's using cheap long spindles.

Never a crank or spindle failure.

I have also worked in a number of bike shops in my life. I never saw a failure come through any of those shops either.

Also a teenager, I even have REEMED out the square taper portion of cranks to cinch them in tighter on the spindles (not recommended). Never a failure there either- granted, some could never be tightened enough and would work loose because of my "engineering", but never a failure.

G@# help us all.
R
I have been riding much less than you have (31 years, 22 of those with square taper BB's), but I had the spindle break once on my MTB, non-drive side. I wasn't doing anything particularly extreme on it, just the odd small jump, pretty sure I never went higher than 1 ft, but mostly commuting. Probably the spindle was faulty from the beginning, I don't know. The failure wasn't exactly catastrophic - there was some minor creaking, and then I noticed some weird feel on the pedal while pushing uphill, and a few revolutions later the crank broke off. The mechanic at the LBS seemed to be surprised as well.
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Old 09-09-19, 11:41 AM
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phughes
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Originally Posted by HTupolev
Huh?

My post was basically saying that square taper is fine, and you're unlikely to run into issues unless you do something silly with it

...Most of my bikes have square-taper crank interfaces.
Sorry, I got carried away reading all the other ridiculous dire warnings regarding square taper BBs.
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