Recently there has been some discussion about bottom brackets and specifically the superiority of external bottom brackets (bb). While researching why Shimano and Campagnolo did not have external bb in their Track/Pista gruppo, some interesting facts came up regarding the weaknesses of external bb. The first is the fact that external bb are not supported by the inside of the bb shell. External bb bearing are in cups outside the bb shell. This causes the spindle to wobble, reducing smooth pedaling and bearing life. Further, the whole point of external bb are larger bearings for larger dia spindles. Unfortunately larger bearing also mean there are less points supporting the spindle; this also increases the tendency of the spindle to wobble. My take on this is there is a point of diminishing returns with bearing size and the old square taper seemed to have gotten right. Another issue with external bb is the tightness of the seals, which causes more drag on the spindle of internal bb. Keirin racers are known to still use loose ball bb, even though Octalink is NJS certified. They do this because the loose ball are not sealed and they can use oil instead of grease when they race, both reducing bb drag. I have said this before, that I believe that the BB30 will probably replace external bb, as it still supports the bb bearings inside the shell and still allows for a larger dia spindle. If there is a weakness with square taper, it might be its inability to withstand some 10'+ drops. Yes, the larger dia spindle will withstand the drop, but it's only a matter of time before the poorly supported bearings fail. So you might want to think twice before you upgrade to to external bb. The only reason I can think of is to use the uber cool Forward Components EBB converter.
Some Inherent Weaknesses of External Bottom Brackets
aka brad
21 - 40 of 65 Posts
Joined
·
655 Posts
External bbs are really easy to manufacture (compared to any other bb). Two identical aluminum cups that just have to be threaded different ways (compared to a cartridge bb). Kinda like threadless headsets vs threaded headsets, regardless of which you think is better, its just easier for manufacturers to make/use threadless headsets (which is why they've been the 'standard' for years).
Joined
·
4,133 Posts
You never mentioned that you were talking about BBs for singlespeeds, I thought you were just talking MTBs in general. Even among the SS riders on this forum, there are plenty of people that swear by each system, be it square taper, Octolink, ISIS, or external BB. I personally still use Octolink V1 on my singlespeed, and it has proven to be very reliable for me. I'm sure there will be others who have had bad experiences with it. In the end, choices are good, and just be happy you can still get quality square taper cranks and bottom brackets. You should actually be a happy camper, as there are more quality square taper offerings right now than there were 5 years ago, so obviously there are more people that think like you.aka brad said:
Mark
Joined
·
10,053 Posts
Please don't throw around ridiculous exaggerations like that; silly biases get stuck in people's heads after it gets passed around second and third hand. It isn't a problem at all; probably happens just as often as it does with 26ers. To back up my retort, I just searched the 29er board for any instances of "ovalized" or "ovalization" and found one person who mentioned an ovalized headtube on a custom 29er frame over two years ago. Since then we have had more aggressive 29ers with longer forks becoming much more common and yet the problem hasn't grown. I have definitely heard of many people having their King's start to creak when they moved it to a rigid 29er, but that is related to a design weakness and the same people had zero problems after switching to a Cane Creek or something elseaka brad said:
I'm not saying there isn't more stress on the average 29er headset, just saying it isn't a problem so please don't yell fire.
Now back to your regularly scheduled programming....
And that coupled with the short headtubes only increases it furtherforwardcomponents said:
Anyways... bigger spindle, bigger ID for the bearings, more bearings, more surface area support of the spindle. If the bearings are larger, they'll spin slower, thus wear less. Threading the cups into the frame and torque them to spec produces at most a teeny tiny bit of play completely unable to be felt by the rider. Perhaps if the threads were poorly manufactured and did not have a tight fit it could be an issue. But with the quantity of the threads and the pitch and considering the relatively low load of a cyclist it would basically completely transfer all force to the shell.
Joined
·
137 Posts
Not quite all. The majority of the force on the bottom bracket is vertical. What is supporting vertical loads on a standard outboard bearing cup? A thin aluminum shell. It has to flex and deform under all that load, especially under off road conditions. The bearing races themselves are thin, so if their supporting shell is thin as well, then you are going to experience some deformation of the bearing geometry under severe vertical loading. The bearing as a whole is kept reasonably round by the large spindle that it is supporting, but it must be deforming more than a bearing that is supported within a thick bottom bracket shell. Again, I find it interesting that a Phil Wood outboard bottom bracket is made from stainless steel rather than aluminum. The material supporting the bearing looks to be about as thick as the aluminum found on most bearing cups, but is presumably far stronger. I doubt that Phil Wood's customers are willing to pay a premium for that weight penalty if there is no gain to be made in terms of performance and longevity.Schmucker said:
Joined
·
2,080 Posts
You are right; my bad. I was remembering the King Creaking Thread and had a senor moment. To all reading this thread, 29ers do not have an issues with ovalising head tubes, some just don't play well with King headsets. Now back to your regularly scheduled programming....boomn said:
Joined
·
242 Posts
I like most of the ideas for the ultimate bb thrown out there by Bikeny. As a singlespeeder, and freerider who has destroyed sq, taper, Isis and external bbs, I have always thought the ultimate would be an oversized bb shell and sqaure taper style bb (possibly splined). Sort of a cross between square taper and American/BMX.
I have a ss 29er with an eccentric bb that I'm dabbling in hardtail downhilling with, and after destroying the external bb bearings (can barely turn them, I think some of the balls are broken) I tried to come up with an American bb system that would fit in the eccentric shell and still take up chain slack. It's a full 3.25" wide (83mm outside to outside) and uses 6004 bearings.
![]()
So far so good. Obviously, the weight wouldn't sit well with most , but I'm liking the big ol' cheap, off the shelf bearings that probably won't have to be replaced for years. The other nice thing was to make the bb a press fit into the shell, so the shell wouldn't get ovalized (but that's another subject all together).
I have a ss 29er with an eccentric bb that I'm dabbling in hardtail downhilling with, and after destroying the external bb bearings (can barely turn them, I think some of the balls are broken) I tried to come up with an American bb system that would fit in the eccentric shell and still take up chain slack. It's a full 3.25" wide (83mm outside to outside) and uses 6004 bearings.
So far so good. Obviously, the weight wouldn't sit well with most , but I'm liking the big ol' cheap, off the shelf bearings that probably won't have to be replaced for years. The other nice thing was to make the bb a press fit into the shell, so the shell wouldn't get ovalized (but that's another subject all together).
Joined
·
137 Posts
That looks like a fairly indestructable bearing system and housing. You could probably get the weight down by removing more material from the center. The core is basically hollow, so it is probably lighter than it looks.KeylessChuck said:
Joined
·
469 Posts
Terrible connection. Terrible logic.j e SS e said:
Joined
·
242 Posts
Yeah, I could have taken quite a bit more material off of this thing, but by the time I got to that phase, I was getting tired of standing at the mill (rotary table) and weight isn't a big concern with this bike.forwardcomponents said:
Joined
·
9,514 Posts
I've used square taper, ISIS, Octalink, and now Octalink II in a mix of XC and DH. My favorite so far is Octalink II, and I plan to stay with it for one simple reason: the crank arm to spindle interface is by far the best of all the systems (excluding the new XTR system). It's simple, foolproof, and doesn't need adjustment and checking once set. When's the last time you heard of someone rounding out a Octalink II crank arm?
At first my cranks didn't spin as easily as with my cartridge BBs, but after switching to Enduro bearings they're nearly as good. I'll take that trade off for the more robust design.
At first my cranks didn't spin as easily as with my cartridge BBs, but after switching to Enduro bearings they're nearly as good. I'll take that trade off for the more robust design.
from a geared standpoint, all the cool shifting advances are coming in the external form. such as the new xt. also not all externals are created equally. ive had nothing but problems with race face and truvativ. i suspect that is because of the lack of bearing preloading. with the shimano and a few of the fsa cranks there is a separate preload adjustment. IVE only had external bb success stories when using that system. i believe companies like phil wood and chris king acknowledge that because they only support the shimano cranks. the only reason i sometimes use a bontrager(truvativ) crank is because i got it for free and working in a shop i can buy the bb's on closeout for around $2 a piece.
Joined
·
2,419 Posts
Sorry, but you're a bit off.
External bearings use a larger diameter bearings, meaning that there are more balls, and more contact area. Also, the bearings are farther apart, giving more support.
As an Engineer, external bearing cranks are a far superior concept, but they need a bit of work in the seal department. That's their downfall.
You will never catch me on square taper as i've destroyed more crank arms than i could count, even when i was 140lbs. And yes, they were properly torqued.
I'd rather replace a $20 set of bearings than a crank arm.
External bearings use a larger diameter bearings, meaning that there are more balls, and more contact area. Also, the bearings are farther apart, giving more support.
As an Engineer, external bearing cranks are a far superior concept, but they need a bit of work in the seal department. That's their downfall.
You will never catch me on square taper as i've destroyed more crank arms than i could count, even when i was 140lbs. And yes, they were properly torqued.
I'd rather replace a $20 set of bearings than a crank arm.
Joined
·
14 Posts
Well I like square taper for my Keirin track bike only because that is what it takes. but for all intensive purposes the external bb is fine TRUST ME! smooth as butter if installed correctly. Frame facing ECT.ECT.
I'm a very large dude (300lbs 6.1) that can break any bike part you want
Bottom brackets are going to fail in time it's kinda the nature of the beast unless you have one that can be maintained in some sort of fashion. ( This is also why All Keirin NJS track bikes use loose ball because they can be maintained quickly. Do that with any other bottom bracket. Also nihon jitensha shikokoai (njs) is a sanctioning body to keep the bikes the same for betting purposes as the Japanese people bet well over a million Yen on these races per year.
I've worked on bikes for most of my life and I can tell you the only parts i've seen that were worn out or broken are the one's that were on bikes that were A. doing things they weren't designed to do. Or B. poorly maintained. There are also manufacturer blunders no doubt but for the most part A&B are the main reasons these parts fail.
I'm a very large dude (300lbs 6.1) that can break any bike part you want
Bottom brackets are going to fail in time it's kinda the nature of the beast unless you have one that can be maintained in some sort of fashion. ( This is also why All Keirin NJS track bikes use loose ball because they can be maintained quickly. Do that with any other bottom bracket. Also nihon jitensha shikokoai (njs) is a sanctioning body to keep the bikes the same for betting purposes as the Japanese people bet well over a million Yen on these races per year.
I've worked on bikes for most of my life and I can tell you the only parts i've seen that were worn out or broken are the one's that were on bikes that were A. doing things they weren't designed to do. Or B. poorly maintained. There are also manufacturer blunders no doubt but for the most part A&B are the main reasons these parts fail.
Joined
·
469 Posts
1,000,000 yen = 10,000 dollars.BEEZLEBOSS said:
21 - 40 of 65 Posts
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
