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Does square tapered bb really last longer than isis bb?

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SingleTrackHound

· on my 3rd wind...
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Discussion starter · #1 ·
I use both integrated bb/crankset and isis bb/crankset on my bikes. I keep hearing/reading, especially from ss forum, that the old school square tapered bb design last longer than isis bb. I am trying to understand how this is so.

If I understand the difference in two designs correctly, it's in the spindle where crankarm attaches to. ISIS spindle is splined and square bb is squared, obviously. As a result, isis has stronger interface between the crankarm and spindle due to greater contact surface. As far as the bearing goes, both designs are inside the bb bracket. There may be some difference in type or # bearings in the bb due to mfg design philosophy but ultimately they are all inside the bb...and size of the bearing can't not change whole lot since they are all cramped inside the standard bb shell/size. So how can squared bb design outlast isis? Now if someone are indeed experiencing a longer bearing life on Phil Wood square tapered bb verses isis brand, isn't it because you are paying bigger $$$ for higher quality bearing, tolerance, & seal? Not necessarily because somehow square bb design has this unknown design advantage in making the bearing last longer?
 
#2 ·
In short... yes.... in fact the bearings used in square-taper bottom brackets can last YEARS longer than anything in an ISIS bottom bracket, even ones costing far more.

Splined bottom brackets weren't adopted to be a better interface, but to be a gimmick to justify increasing the spindle diameter for a strength/stiffness perspective of the spindle itself (which is amusing as BMX bikes used splined spindles with MANY more splines on a spindle a lot closer to the diameter of square-taper cranks, and also for that matter, still use square taper cranks on many models). Once they committed to using a larger spindle diameter, it was just as easy to adopt a splined end than a new square-taper size, and a lot less confusing too.

Anyways, with the exception of one of my bikes which has a 1996 XTR M950 Octalink splined bottom bracket (which has serviceable ball and needle bearing sets in it, and thus far superior bearings to anything ISIS setups have used) matched to an adventure components crankset, all the others are square taper setups, most with titanium spindles, double adjustable cups (so I can easily handle chainline changes), and replaceable sealed cartridge bearings available from numerous brands off-the-shelf at any good bearing supply store. Some are the disposable shimano-style cartridge BB units too with CrMo spindles, but heck even with those the bearings are still so durable that you can find bikes that have been in regular service for a decade where the BB is only just NOW becomming crunchy as the bearings and races inside are pitted, and the hardest part of replacing them is that the cups may be seized into the frames. I've had to pull TWO such BB's out this year where both bikes dated from 1993/94 and had low-end shimano square-taper cartridge BBs in them. On my oldest syncros titanium square-taper BB which I bought in 1993, I'm onto only my second set of bearings.
 
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#3 ·
DeeEight explained the politics behind it very well, but just to clarify...

Yes non-external BBs are constrained to the same shell diameter, but square-taper spindles are a smaller diameter than splined ones - leaving more room for larger bearings around them. That's why they tend to last longer.

As far as anecdotal evidence, I went through 2.5 ISIS BBs in about 2 years before switching back to square-taper. At which point I pulled an old Shimano UN-52 BB out of the parts bin that has been running smooth for about 4 years now. I wonder if the problem is more than just bearing size though. I don't know of that many people complaining about bearing failure in the shimano splined BBs and those have about the same spindle and bearing size as ISIS.
 
#4 · (Edited)
Bearing size....

All other things being equal it's the bearing size that makes the big difference. Square taper spindles have a smaller diameter and thus allow larger bearings to be squeezed into the relatively small BB area. I'm pretty sure that's really what it comes down to. I have a relatively cheap Shimano square taper BB that I've used for over five years and only now is it dying. On the other hand I've gone through very pricey ISIS BBs in less than three months.

Now SKF has done something really nice. They've put roller bearings into their ISIS BBs which I hear makes a huge difference in how the BB bearings can handle loads. I've been using one all last year and it shows no sign of failure. It's as smooth as the day I got it. It really is super nice. Personally I think the ISIS interface is probably more robust than the square taper set up and we now finally have an ISIS BB that's suppose to last a few years. Crank Bros also makes an ISIS BB that is suppose to be very good as well. The SKF BB is very nice. It seems to be very well sealed. It also uses the 8-point Shimano spider tool for instalation for both "cups". That is great because it's a very solid connection and makes instalation very easy.

Shimano's splinned BB-cranks that were around just before the external BB seem to be very good. From what I hear the bearing size in those BBs were not as small as the ISIS versions. I personally have four of those cranksets. Two I got used and two on blowout sales (two are 180s). They've all been in service for years on everything from DH bikes to SS bikes. All still function perfectly. I also have an assortment of BBs for them and maybe one BB is just starting to get a bit notchy. It's really a shame they moved away from this design as it worked very well for me.

I've installed Shimono's XT external type crankset and it was easy to set up. The best idea is that you can remove your cranks easily should you need to remove or work on your chain rings. Seems like I'm always pulling my cranks off my bikes for one reason or another and I worry that I'm wearing out the splined or square taper interface. You don't have that worry with the external BB setups. You also don't have to worry about getting different BBs for different shell widths. As we've all heard the big problem is having you external bearings exposed to the elements resulting in premature wear. I don't know if there is a way around this. I wish there was because otherwise I like the design.

So with all that said, I must say the ISIS system is still my favorite provided you have a good BB that will last, like an SKF.

Mike
 
Discussion starter · #5 ·
Interesting...

I didn't realize the square tapered bb spindle has a smaller diameter than isis. I can see how that could make a difference in longer bearing life since larger bearing can be used on square bb.

If so, there has to be definite stiffness advantage on isis due to a larger spindle diameter, correct? I am sure it can't be just a gimmick or false advertising. More "beef" equates to stronger and stiffer component provided that the material it is made out of is same. Just like larger bearing on sqaure bb last longer than smaller bearing on isis.

I have been thinking about buying some SKF 300 & 600 series bb. They would make a long lasting mate to my isis crankset. A bit pricey, though.

What is consensus on isis bb that has a larger bearing on the outside bb shell (much like the external bb)? I have seen these in CrMo spindle version for cheaper price as well.
http://www.bikesomewhere.com/bikesomewhere.cfm/product/19/95/5394
 
#6 ·
I have a UN-72(I think) that I originally used in my first ground up bike build around 1996. And that particular BB has seen its way through four frames, has been raced, used in a half-assed trials/freeride bike, and for most of its life been a part of a commuter/fixie mtb. And to this day it is like butta. In that same time 3 ISIS, 2 Octalink, 2 Race Face Outboard bearings have died. If this BB ever dies I'll have an excuse to get the Phill Wood I've always wanted.
 
#7 ·
The other point to consider, is that manufacturing a splined interface is far more complex than a square taper. Even considering computer controlled machine centres. As we all know and regret most bike products are built to a price. If manufacturing one piece costs more then another must be bought cheaper to make the price point. I think it is fair to suggest that bearing quality has been sacrificed to pay for those nice shiny splines. If bearing quality was the highest priority they would all use a combination of ball and roller bearings. But then bbs wouldn't wear out and we wouldn't have to buy knew ones...
 
#8 ·
DeeEight said:
In short... yes.... in fact the bearings used in square-taper bottom brackets can last YEARS longer than anything in an ISIS bottom bracket, even ones costing far more.

....

On my oldest syncros titanium square-taper BB which I bought in 1993, I'm onto only my second set of bearings.
Click to expand...
I am on my second set of bearings in my RaceFace Taperloc BB. I got it in '98. At that time it came with the cheapo Enduro bearings. Now it is loaded with SKF's and should be good for several more years....
 
#9 ·
Syncros spec'ed SKF originally... I think my current ones are INA or NTN. Anyways there's really nothing wrong with square taper spindles, and it takes a major whoopsies to break one even in titanium (like landing a jump with your pedal into a rock, curb or stair...that'll bend a spindle at least, if not shear it off right at the bearings). Hell middleburn still makes square-taper cranks and they're quite respected among singlespeeders. And square-taper setups are usually a lot lighter, especially for the money.
 
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#10 · (Edited)
Square taper lasts longer, as d8 mentioned, because the bearings are larger. I've only had a problem with a square taper BB once, and that was a gradual deterioration of one had seen almost 10 years of regular service, much if it in bad weather. Other than that I've had square on almost all my bikes and have never had any other problems. (I do have an outboard-bearing splined crank on my FS, but only because that's what it came with.) A UN-73 BB will outlast several ISIS BBs, is only very marginally heavier and costs $20. Done.

And despite the popularity of expensive Middleburn, WI, Cook Bros. and soon Surly cranks, a perfectly good and reasonably light square taper crank can be had for under $100, brand new.

Some people claim to feel a difference in stiffness with splined interfaces. That may well be, but there is no evidence whatsoever that that results in more power being transmitted to the wheels. The flip side of the extra stiffness is many say that splined transmits more vibration to your feet, a significant consideration for hardtails. In any event, frame and wheel flex probably far exceeds crank/BB flex.
 
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Discussion starter · #11 ·
I for one have never experienced the squared tapered bb and its crankset. Well, I did but it was so long ago that I can't seem to remember the detail as far as the stiffness and how long it lasted based on number of miles I rode. I did use and remember quite clearly what the stiffness feels like and how long the bearings lasted on Shimano Octalink w/ cartridge bearing. It lasted me about one season of 2000-3000 miles of hard usage before I began to notice the creak and play on the crank. I always thought it served me well. Then I remember the first day when I made the switch to XTR M960 crankset w/ ext bb. When I turned the first pedal over at the TH, it was amazing! Stiffness was by far the greater than anything I felt in my life. As I pressed the on the steep and steady climb, I was feeling the stiffness everywhere...on the handlebar, legs, and frame. Hard to believe but the difference was so drastic that my entire bike felt stiffer. It's been over two+ years and has yet to replace ext bb on my XTR. Other owners may have gone through 2-3 sets by now but not me. Since then I have built few more bikes for myself (ss mostly) and have equipped them with ISIS setup...they were readily available and relatively cheap. I keep waiting for them to creak or cease but they have not…neither XTR M960 bb on my susser nor ISIS setup on others. I mainly contribute this long lasting bb life to my shared ride time on several bikes I own. I am sure ext bb and isis bb will fail at some point. When they do, I will prolly go with SKF isis but stick with shimano ext bb. But I am intrigued by how older technology can out last the new. As far as unmistakable stiffness felt at the crankarm, nothing surpasses integrated crankset...bar none!
 
#12 ·
1% vs 2%

SingleTrackHound said:
I use both integrated bb/crankset and isis bb/crankset on my bikes. I keep hearing/reading, especially from ss forum, that the old school square tapered bb design last longer than isis bb. I am trying to understand how this is so.
Not necessarily because somehow square bb design has this unknown design advantage in making the bearing last longer?
Click to expand...
There another issue that your post didn't address that has also contibuted to the failure rate of ISIS; why does Shimnao Octalink have a much less failure rate? To be sure they did not violate Shimano's Octalink patent, the ISIS designers went with a 1% taper, opposed to the tried and true 2% taper. Once the ISIS BB went into production, something became apparent; the 1% taper meant stricker quality control. Any time you have tapered mating surfaces, than you will have metal deformation. With square taper (also 2%), the metal deformation meant that the crank arms would continually ride farther up the spindle. With both ISIS and Octalink, the crank arms seat at a pre-determined point, so evertime it seats, the metal deformation will be less, hense a looser fit. With a 1% taper of ISIS, the tolerances appear to be nearly twice that of Shimano's 2% taper. Since by definition ISIS will cost more per unit than Octalink due to the shear volume produced by Shimano, the qulity control will be at best equal to and probably less with ISIS. Hense the failure rate of ISIS is almost guanteed higher than that of Shimano Octalink.

1G1G, Brad
 
#13 ·
1% or 2% has nothing to do with the quality of tolerances, its just the slope angle of the taper. And actually as far as squares go, the cranks do NOT seat further and further up the spindle each time you reinstall the cranks, because its NOT plastic deformation of the metal that's occuring during a proper installation but ELASTIC deformation. What's the difference? Elastic is temporary and Plastic is permanent. Elastic deformation is the metal compresses and deforms under a load that's lower than its yeild strength, which then rebounds to its original shape when the load is removed (as when you pull the cranks off). Plastic deformation is the metal compressing and deforming under a load that exceeds its yeild strength.

In 16 years I've only ever achieved plastic deformation ONCE with square taper cranks (and I've installed hundreds of them) and that was by deliberately exceeded the torque specs on the crank bolts. Proper installation bolt torque on most square taper cranks is in the 25 to 35 ft-Ibs (depends on manufacturer) range, but to get plastic deformation took about 75 ft-Ibs on the shimano altus crankarm I was using as a guinea pig. Other than doing it deliberately, the only other time it'll occur is when you have someone who doesn't understand crank assembly very well, and does it improperly (a dry installation without a torque wrench for example) who just keeps cranking on the bolt until the arm bottoms out on the spindle.
 
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Discussion starter · #14 ·
A bit different subject than bb bearing life on diff brand but interesting never the last. Plastic wear on isis, octalink, or square on the spindle should be that big of deal since they are all tapered. Correct? The crankarm is going to mount slightly higher up in the spindle anyways. I am sure there will be point when it will bottom out after repeated removal/install of the crankarm, but does it even happen when crankarm don't get reinstalled all that many times?

I think I typically pull the non-integrated crankarm about two times per year for various reasons.
 
#15 ·
We often have talks around this at our shop and our consensus is that a good quality 3 piece square tapered axle combined made with good quality bearings, cups, and races will outlast and out perform most cartridge bottom brackets.

Not only do you have a lighter setup but you have larger bearings to distribute the load and if you remove the ring bearings and add a few more loose bearings, it gets even better. If you can add one ceramic ball to the rest of the bearings the lifespan of the assembly will get even better as the ceramic bearing purges the unit of crud and keeps things polished.

Cartridge BB's are easy to install, zero maintainence, and have a service life that makes them a good money maker for parts manufacturers as they need more frequent replacement.

There's also this predilection to make bikes as light as possible as this appeals to buyers and makes the end product far more expensive even though some of the new parts are cheaper to manufacture and require less materials. The parts also wear out far more quickly.

There's always been a lot of marketting and hype driving things in the industry... people were once convinced that steel was only good for making cheap bikes and aluminum was the best material for building bikes since it was lighter and stiffer.

Many are now going back to steel as they realize that all the hype around aluminum was just that... aluminum bikes are great but you have to buy them knowing there's an expiry date.

One of my favourite bikes (it's a steelie) just turned 20 and is going as strong as it was the day it was new... most of it's parts are original.
 
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#16 ·
No hijack here..

SingleTrackHound said:
A bit different subject than bb bearing life on diff brand but interesting never the last
Click to expand...
You asked

SingleTrackHound said:
I use both integrated bb/crankset and isis bb/crankset on my bikes. I keep hearing/reading, especially from ss forum, that the old school square tapered bb design last longer than isis bb. I am trying to understand how this is so.
If I understand the difference in two designs correctly, it's in the spindle where crankarm attaches to. ISIS spindle is splined and square bb is squared, obviously. As a result, isis has stronger interface between the crankarm and spindle due to greater contact surface.
Click to expand...
DeeEight said:
1% or 2% has nothing to do with the quality of tolerances, its just the slope angle of the taper. And actually as far as squares go, the cranks do NOT seat further and further up the spindle each time you reinstall the cranks, because its NOT plastic deformation of the metal that's occuring during a proper installation but ELASTIC deformation. What's the difference? Elastic is temporary and Plastic is permanent. Elastic deformation is the metal compresses and deforms under a load that's lower than its yeild strength, which then rebounds to its original shape when the load is removed (as when you pull the cranks off). Plastic deformation is the metal compressing and deforming under a load that exceeds its yeild strength.

In 16 years I've only ever achieved plastic deformation ONCE with square taper cranks (and I've installed hundreds of them) and that was by deliberately exceeded the torque specs on the crank bolts. Proper installation bolt torque on most square taper cranks is in the 25 to 35 ft-Ibs (depends on manufacturer) range, but to get plastic deformation took about 75 ft-Ibs on the shimano altus crankarm I was using as a guinea pig. Other than doing it deliberately, the only other time it'll occur is when you have someone who doesn't understand crank assembly very well, and does it improperly (a dry installation without a torque wrench for example) who just keeps cranking on the bolt until the arm bottoms out on the spindle.
Click to expand...
Nowhere did I say that the crank arm would ride up the spindle during repetitive R&R. As you rightfully said, the forces of installing a crank are not within the realm of causing plastic metal deformation. It is due to the improper installation and repetitive tightening..

From Jobst Brandt (the bain of dry spindle installation advocates)

"Because cranks squirm farther up the taper when stressed highly, the
unwitting mechanic believes the screw got loose, rather than that the
crank got tighter. By pursuing the crank with its every move up the
spindle, ultimately the crank will split. It is this splitting that
has been incorrectly diagnosed as being caused by lubrication. I have
never seen a warning against re-tightening cranks after having been
installed with a proper press fit. It is here where the warning
belongs, not with lubrication.

For the press fit to work properly, the pressure must be great enough
to prevent elastic separation between the crank and spindle under
torque, bending, and shear loads. This means that no gap between
crank and spindle should open when pedaling forcefully. Friction
has no effect on the transmission of torque because the crank creeps
into a position of equilibrium on the spindle in a few hard strokes.

Failure of this interface occurs when the press fit is too loose
allowing a gap open between spindle and crank. Torque is transmitted
by the entire face of the press fit, both the leading edge whose
contact pressure increases and the trailing edge whose contact
pressure decreases. If lift-off occurs, the entire force bears only
on the leading edge and plastic failure ensues (loose crank syndrome).
Tightening the retaining screw afterward cannot re-establish a square
hole in the crank because the retaining screw will break before the
spindle can exert sufficient stress to reshape the bore. Beyond that,
the crank would split before any plastic deformation could occur even
if the screw were sufficiently strong."

As far as the quality control issue, this was brought up on this board due to the high failure rate of ISIS BBs. The issue included the fact that the quality control of TruVativ ISIS Cranks and BBs did not seem to be at same level of Shimano. It is my opinion that the QC was similar but the 1% of taper was to blame. Since the ISIS relies on a 1% taper, this means that the elastic deformation will occur within less space than 2% taper. Since there is also a termination point to the press fit, any variation in the tolerances will have greater effect on the 1% taper resulting in a higher degree of failure. At least that's my take. If you think I'm wrong, lets talk ;) ;) ;)

Brad
 
Discussion starter · #17 ·
Thx for sharing your insight, Brad.:thumbsup: Lets not turn this thread into heated debate over nothing. I am not sure whose reply or what statement caused you to be less than happy. My thread was inteded to undertand the bearing durability between the different brands mainly isis and square type. BB spindle type and crankarm interface only brought up since I didn't see how that could make the bearing last longer than the other. Since I am a info junky, I enjoy reading about other aspect of bb not related to bearing. Who cares if thread is hijacked.
 
#18 ·
Well now you tell me..

SingleTrackHound said:
Thx for sharing your insight, Brad.:thumbsup: Lets not turn this thread into heated debate over nothing. I am not sure whose reply or what statement caused you to be less than happy. My thread was inteded to undertand the bearing durability between the different brands mainly isis and square type. BB spindle type and crankarm interface only brought up since I didn't see how that could make the bearing last longer than the other. Since I am a info junky, I enjoy reading about other aspect of bb not related to bearing. Who cares if thread is hijacked.
Click to expand...
I think when we look back the splined spindle cartridge BB will be just a hiccup on the way to outboard bearings. I have one bike with a ISIS BB and that's only because I received the cranks gratis. Saying that I expect the BB to last as least as long as the warranty; two years.

As far as our heated debates go, it would seem most folks spend a lot of time, using so called science to prove their opinions. It's an interesting choice of avenues, as the scientific or hypothesis method is designed to find the faults in opinions. Still it makes for an interesting show..

1G1G, Brad
 
Discussion starter · #20 ·
aka brad said:
I think when we look back the splined spindle cartridge BB will be just a hiccup on the way to outboard bearings.
Click to expand...
I am a believer in external bb and its crankset and they are definitely here to stay. Even with all those positive experiences on square tapered bb, I am not quite ready to part with isis. It would be too costly anyways. Once my current set RF isis bb goes, I am going to give SKF isis bb a try. With its needle bearing design and better seal, I think it has a fighting chance. Reading OP's experience with SKF is very encouraging.
 
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