The Square Taper vs. External Bearing Bottom Bracket Debate

Some time ago, on our local board we had a “discussion” on the pros and cons of square taper bottom brackets vs. external bearing bottom brackets.  The mountain biking crowd has basically split into two camps.

  1. Square Taper Devotees
  2. External Bearing (X-Type) Riders

Others, use some of both, but I think everyone has pretty much ruled out ISIS as an option over the past couple of years.



I am all in on the external bottom bracket technology.  I have been running this style of bottom bracket since it’s introduction for several reasons.

  • Stiffer – Larger axle and bearings
  • Trail-side Maintenance – You can actually get the cranks off if you have to. A friend of mine blew up a granny ring at Dupont once and it would have been a long walk back to the car if it wouldn’t have been for externals
  • Cheap BB’s
  • Drag is unnoticeable on the trail – For me, this is a case of what you see on the stand does not translate to the trail…just my opinion.

It all boils down to personal preference and I think the pluses of externals far outweigh the minuses. There are people that can argue either way…but the industry is going the way of externals…so all of you square taper guys better start buying up the inventory.

Manufacturers also have to produce products to the widest possible audience. The racer/pure xc riders is arguably the smallest group of riders these days due to increased bike technology and market trends. 10 years ago…that was basically all there was, but that is not the case now. XT cranks see everything from xc to dh, so why would a company manufacture several product lines when one will eventually win out due to market demand?

The AM 5″ trail bike is the fastest growing market in mtn biking. Even now we are seeing larger travel bikes marketed towards more xc oriented riders because of light weight parts/frames that can also take long term abuse. External BB’s are a better fit for these types of riding styles and frames.

Phil Wood also makes some great replacement bearings for the external cups…but like everything Phil Wood, they aren’t cheap.

Probikewrench on the local forum had this to say:

I guess I’m a technology buff. Personally, I’d rather use the newer style cranks with an outboard bearing set-up (ceramic or not) than revert back to a square taper that is over two technological generations removed. No manufacturers are spec’ing it on completes… there’s definitely a reason for that. I’ll still run ST on my single-speed beater, but not on anything else. If you are doing it with some trick cranks or just in it to be a little different, by all means, go for it. It’s your bike. You have the final decision. Good luck!

Bikephan’s Statements:

weight is a small factor when comparing st to external. external bb weight lighter but then you have to add some weight to crank due to spindle. why a bike company would switch is how the market looks. it is the what is new that sells. you can put a $300 dollar st bb on A bike and most people would not care because it is not current. unless you have a knowlegeable staff it would be a hard sell. a st is only proven in regular riding or racing xc conditions.

the true problem with st is that is a press fitting, not an interface. there will be some slight alignment issues(maybe a white industry crank to deda bb, the companies will have slightly different margins of errors) but for the most part it is not an issue. a st will never be perfectly aligned(we are talking mm) due to factors of manufactoring. it does have a smaller q factor but now we have bikes with 83-100mm shells for strength. q will help with narrow hip people etc(most racers)

the orginal design of the external was to run a larger bearing with more surface contact for strength in crank/bearing interface. a external drive crankset is a stiffer design. you are not dependent on a m12/m10 bolt. now does the strength come from just riding xc or hucking mountains. that design came about to improve the strength to weight ratio due to cranks failures in the dh scene. when running a square taper i was blowing up bearings or with a heavy impact on bashguard could and has started to move my cranks due to a 4 piont press engagement. not the cranks or bb faults, it was the fact i was on 46lb dh bike with 10 inches of rear travel. this was a new area for mtb. people went looking for solutions.

the issues with bearings on x drive is that the oe bb companies use plastic shims to “help seal bearings”. that is why i prefer the enduro bearings since they design a metal to metal interface with their bearings. ceramic bearings have been used for quite a while, it was how to cut manufactoring cost to get it where it will sell. issues i have noticed with x drive is you can get water through the seatpost etc that can get to bearings on the inside where that is not possible on standard st designs.


Duckman had this to say:

Proven design.

I use an Action Tec titanium square taper BB(Cambria) on the race XTC. I wish all my bikes had the same setup. 145gms. Been in 4 frames to date since late 02. Spins about 25 times with new bearings(yes, they are replaceable. About $20 per set every yr or so if you race alot with some mud events).

Anyone can get ST cranks off on a trail plus a decent multi tool and self extracting bolts. Why is that so hard on a ST crank? And I’ve NEVER needed to pull a crank on a ride regardless. Thats not even a concern either way.

I bet most can’t flex or detect it on a ST crank. Thats crap. Theres LOTS of super strong roadie and mtb racers that are animals that still use ST with zero “flex” issues. I think thats a non issue for 99.9% of racers. Maybe Lance.. :roll:

XT ST BBs can be had real cheap. And last way longer then “cheap” external BBs ever dreamed of. All the while performing better as well as lighter.

Speaking of “generations removed”…one could say that the Racer X is an “old” (but proven) design(like my Spider for that matter) also…and could also be argued a couple generations removed from current tech(again, like my Spider :wink: ) itself. Somethings just don’t need “improving” much imo. But in BB design…that apparently means going to heavier, slower, wider(Q-factor), and apparently less reliable x-cranks(unless much more $ bearings are had).

Kokopelli said:

Okay, I have been giving this a lot of thought over the last few days (obviously). I think there are pros and cons of both designs, but I still question whether the pros of external BBs outweight the cons.

Then it hit me: The manufacturers are not making external BBs for the beneift of the riders, it is for their OWN benefit. The big advantage is ONE SIZE FITS ALL. Instead of making two (or more) different shell sizes and multiple axle lengths, they just package up one unit with a bunch of spacers and let the wrench sort it all out.

Now, this does give the bike owner one small advantage in that you can move your spacers around to get the perfect chainline for your rig, and eliminate some of the vagaries of internal BB manufacturing. But I know that at least RaceFace admits in their instruction manual that the spacers might create further drag on the bearings (they suggest you move or remove spacers if your cranks are not spinning smoothly upon installation).

edited to add: I guess another advantage is that they are easier to install and remove, which is good because you have to replace them so often

Some riders wanted bigger axels, and now they have them, but so does everyone else. While 5″ trail bikes are apparently a huge market, I question how many of those owners are actually using the 5″ of travel in a way that necessitates a larger axel. I know some of them clearly are, but what percentage?

I don’t mean to sound like I’m whining, I just question whether the “new” technology is “better” technology. I have ridden bikes my whole life, and I have been riding mountain bikes for 12 years. I never gave my bottom bracket a single thought until 2004, when I bought an ISIS crankset and the BB seized up after only 6 weeks of use.


herein lies the problem…i’ve got square tapers that are over 10 yrs old that still rock. they’re the king headsets of the bb world. i’ve been through 3 or 4 isis though i am now using the crank bros that has a 5yr warranty. no true experience w/ the outboard stuff, i’ll admit, so perhaps i was a bit hasty in judgement. of course, there are those that would never run carbon cranks and i’ve been rockin the same set on the titus since oct ’03 and i’ve hit some fairly big stuff w/ them.

what exactly are the problems w/ sq t other than their being an older design? the only things i can think of are perhaps rounding them off – which i’ve never done – or possibly flex.

The square taper devotees seem to find the Turbine’s from Race Face as the holy grail of hard to find cranks these days.


A solution that I think would make everyone happy is for frame builders to start building in the external bottom bracket bearings into the frame.  The roadies have seen this for awhile and we are starting to see this style move over into the custom steel mountain biking market.  Overall, I truly believe that the external sets are a step up from the older square taper design.  The advantages they have over the traditional square taper bb’s far out weigh any minuses they might have.  What do you guys think?


BARRY June 5, 2020 - 4:15 am

the only reason for changing to external BB is because no square taper option is available. the only real benefit of external is that its easier to remove / install with a basic tool. having said that i now have a square taper tool that screws into the crank and is more solid than my external BB wrench. but i replace external BB far more often than square taper. i have never replaced a square taper due to it wearing out, but my current external BB is creaking and grinding after only 2500 miles.


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