JC 911

Can someone help explain to me the benefits of having external bearings on a crankset?

Chad's Colnago

I think part of the idea of using external bearings was that they could increase the size of the spindle since the internal diameter of the bearings is bigger, thus increase the crank stiffness.

cuda2k

Bigger axels, bigger bearings = siffer, longer life. Keeping the bearings on the inside meant smaller bearings for larger axels which greatly reduced their life. Bigger bearings required thinner axels (think older square taper) which flexed more. It was a trade off situation that external bearings solved to a large degree, or at the very least elevated the baseline for the trade off.

derath

I would also guess by being external, they are further to the outside. This puts the bearing contact closer to the cranks, helping to increase stiffness.

-D

merlinextraligh

Or you could just increase the size of the BB shell ala Canondale. But then you've got the non standard problem.

Ramjm_2000

IMO this is the way to go. I've had two external bearing cranks (FSA and Truvativ) and had less than steller results. They are much more sensitive to misalignment of a frame and the bearings lasted significantly less time than even the worse ISIS I ever owned. I'm on the fence about campy's new system, really just waiting to see if these issues occur with ultra-torque. Just my two cents...

Psimet2001 

While I agree that you can run into frame issues (well really just 1 issue - non-parallel BB shell faces that are also not perpendicular to the thread centerline), they can be easily fixed with proper frame prep (chase and face).

The external bearing BB is one of the innovations that I have enjoyed greatly.

As for alignment issues...you get that with Campy's UT as well. At least it reared it's head during my last build.

Grasschopper

Um if the BB is properly faced where are any misalignments coming from? Prep the frame properly before a build guys.

Psimet2001 

Echo-echo-echo....

biker7

+1...size and location are the two principle benefits. Bigger size translates to lower bearing stress...and outboard location reduces the bending moment applied to the crank. A great design. Yes, moving the bearings outboard slightly does make the system sensitive to misalignment but if the frame is prepped properly...no issue. I love the new Campy UT...a clean, sweet design with excellent power transfer.
George

DocRay

While externals in theory should be better, many have reported problems. The bearings in externals are cheaper to produce.
Internal designs are fine, it just costs more to get good bearing cartridges, and now with ceramics, wear will likely be a non-issue.

To start new, I'd likely go for the Campy UT design, and eventually swap to ceramic bearings.

Heron Todd

External bearings provide manufacturers the opportunity to present something new. They are the answer to a question that nobody asked. Yes, stiffness can be increased, but there are no data currently available to show that the square taper design was insufficiently stiff or that increasing stiffness will increase efficiency. Durability might theoretically be improved, but the designs produced to date have not been any better than the square taper design in this regard.

This is not to say that improvements cannot be made. However, it appears that much development is directed towards improvement in marketing, not performance.

jamiewilson3

I agree, with one addendum or exception. There is a molivation, in that the external BB are much easier and cheaper to manufacture. They do pass some of it on in pricing. An octalink BB is allot cheaper than a 7800 BB.

nitropowered

Much like everyone else has said, the exteral bearings increase stiffess. I have rode 7700 Dura Ace, 7800 Dura Ace, Truvativ Rouleur Carbon, Campy UT Centaur, Campy UT Record Carbon.

The older Dura Ace has a noticeable flex. All the External systems I have ridden all are noticeably stiffer. In terms of installation and maintenance, I'd say the new external systems are simpler. However, the BB shells should be faced.

quattrotom

I am of the opinion that the external bearing design has superior marketing over the square taper design in 2007 - I am unconvinced that it is a better mechanical design. It seems to me that the bearings are supported by a thin sleeve that threads into the BB shell. The "standard" type were positioned inside of the BB shell which kept everything nice and "tight". It seems that the external design would allow for a lot more displacement of the bearings under load. The standard design would require the BB shell to deform for misalignment of the bearings under load - now you only need that thin sleeve that threads into the BB shell to deform. Am I seeing this incorrectly?

Unlike others - I'll be honest in saying that my degrees are in engineering, but my concentration is not mechanical design and my formal education is limited to a handful of ME classes.

I don't want to start a flame war - but I'd love to hear some intelligent arguments for both sides of this debate.

Patriot

It looks neat.

LWaB

That is after the start-up costs of a new design (Octalink) have been covered. Cotterless cranks were expensive when they were first brought out.

Remember when CDs cost more than the records they replaced? The actual production costs for CDs are minimal.

marcelinyc

Last week Cannondale rep said they stoped manufacturing external bearings in new bikes. Now, he said, they think external bearings aren't stiffer at all! lol

banerjek

On a board frequented by weight weenies, I can't believe no one has mentioned that they are significantly lighter than the alternatives.

I have external BB's on two of my bikes. I have mixed feelings about them. I like the weight reduction and they work well. However, they seem more prone to making noise and requiring adjustments than the BB's on my other bikes. Fortunately, they are extremely easy to work with.

They don't cost much and they work, so I like them overall.

Grasschopper

It isn't the bearing that is stiffer it is the larger BB axle that is stiffer...you don't HAVE to have the BB externally to do that but you do have to have one of two things. A) larger BB Shell to maintain bearing size or B) smaller bearings. Both have been done. B) was done with ISIS and Octalink BBs and these designs had a lot of early bearing failure due to the reduced size of the bearings. Cannondale on the other hand likes the larger BB shell plan and for quite some time now has been using it...first on CAAD7 bikes, then the Six13 and now the SystemSIX and Synapse. They have a great design that keeps the bearings internal while still having an oversized BB axle and a VERY stiff setup...so of course they would tell you that internal is better. IMO it may be and in fact I wish more than just Cannondale, Specialized and Pinarello would go with the oversized standard (it is called BB30)...it also helps stiffen the bike because there is more area on the BB to make your joint to other tubes.

briscoelab

This isn't true at all. A good square taper or ISIS bb and crank can be just as light, or lighter than external designs. (Other than the external cranks using a carbon fiber axle and chainrings) For example, the Zipp ISIS crankset is VERY light.... Stronglight Pulsion ISIS cranks, heck even Campy Record cranks are just as light as the new UT design if paired with a good lightweight bottom bracket. (Like a Token Ti or Phil Wood).