Why Square Taper Bottom Brackets?

Why Square Taper Bottom Brackets?

Square taper bottom brackets may seem like anachronisms dating from the last century, and yet they remain the best option for metal cranks. Here is why our Rene Herse cranks use square tapers and will continue to do so in the future.

Modern bottom brackets have larger spindles, so they can use thinner walls. The result is a lighter bottom bracket – but the larger spindle requires more material on the crank.

No problem on a carbon crank (above), which needs to be large anyhow, because carbon is very light, but also bulky. Just don’t try to replicate the massive shape of a carbon crank in aluminum: It will get very heavy.

Our Rene Herse cranks are so incredibly light – just 490 grams for the 42/24 shown above – because they use only as much material as necessary. We’ve optimized the shape using Finite Element Analysis to remove all material that isn’t needed, but keeping aluminum where it’s needed for strength. The photo above shows that there is just enough material to fit a slender square taper spindle. Imagine how much material we’d have to add to make room for a massive oversized spindle!

The light weight doesn’t come at the expense of durability or safety: Our cranks pass the most stringent EN ‘Racing Bike’ test for fatigue resistance. Few other aluminum cranks are as light and as strong.

There is another benefit of square tapers: The taper reforms itself every time you install the crank. You can remove and install the cranks dozens (or hundreds) of times, yet the square tapers will not develop play. And even if a crank comes loose by accident because the crank bolt wasn’t tightened enough, you can usually reform the taper: Tighten the crank bolt as much as you can, ride the bike for 5 miles, then retighten the bolt. Do this five times, and the taper will usually be fine, unless it’s really been damaged beyond repair.

The smaller spindle of a square taper has another advantage: It leaves more room for the bearings. Above is an SKF bottom bracket that I cut open after years of use. The large ball in the center shows the size of the balls used in the SKF bottom bracket. On the right is a typical, much smaller, ball from a modern bottom bracket.

Bike makers now work around that problem with new standards that use bigger bottom bracket shells. For carbon frames, this works fine, since you have a lot of material in the BB region anyhow. A steel frame built to a ‘modern’ BB standard will be quite heavy, as the oversize bottom bracket shell adds a lot of material. Bottom bracket shells are the heaviest part of a metal frame, so keeping them as small as possible is useful for keeping the frame weight down.

And then there is the issue of the ever-changing standards, because none work as well as the old square taper. It didn’t come as a complete surprise when Allied, the US-based maker of high-end carbon frames, decided to return to the BSC/BSA bottom bracket standard. Their web site explains: “After more than a decade of changing bottom bracket standards, we are happily back to BSA. No more creaking, easy to service and just as light as any other bottom bracket standard. Your mechanic will thank you.”

Aren’t there performance advantages with bigger spindles? In theory, the bigger spindles are stiffer. In practice, all spindles are stiff enough. Your frame flexes far more than your bottom bracket spindle. The reason why we haven’t done a double-blind test of crank stiffness is simple: It’s so pointless that it isn’t worth the effort. Eddy Merckx used square tapers, and so do the Japanese Keirin track sprinters. If they can’t flex them, neither can you and I! In fact, I’ve raced our square taper cranks in Japan’s toughest gravel race (above) – without any issues.

It’s only for mountain biking with huge jumps – especially downhill – where the higher impact strength of larger spindles is useful. That is why we don’t recommend Rene Herse cranks for mountain bikes. On the road, cranks don’t fail due to impact, but they fatigue after many miles of use. To resist those forces, we forge our cranks. This aligns the grain structure to make them more resistant to fatigue.

We give a 10-year warranty on our Rene Herse cranks as well as on our SKF bottom brackets. Few makers are prepared to stand behind their products for that long. This illustrates how much confidence we have in our square tapers (and the rest of our cranks and bottom brackets). We’ve spared no expense to make them as good as they could possibly be.

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Comments (57)

  • David Snyder

    There is also the matter of being able to tailor the bottom bracket spindle length to the drivetrain requirements, something that seems to have been lost to all of the newer, oversized designs.

    July 5, 2019 at 12:41 pm
    • Jan Heine

      Easy to forget that one! It was a life-saver on my Firefly. The massive chainstays are probably one reason why the bike performs so well, but they don’t quite clear a ‘road’ crank. With a 6 mm longer BB spindle (116 mm), I have a perfect chainline (since the rear is spaced to 135 mm instead of 130), and the Q factor is still under 150 mm.

      July 5, 2019 at 12:44 pm
  • gajett

    So, uh, why are you showing an ISIS spindle in a story on square tapers?

    July 5, 2019 at 12:45 pm
    • Jan Heine

      Good catch! I replaced it with a photo of a cut-open square taper SKF bottom bracket.;-)

      July 5, 2019 at 12:56 pm
      • Larry Leveen

        Maybe redo the caption too so that it not only makes more sense but also communicates why roller bearings are (apparently) used as well? #squaretaperfan

        July 8, 2019 at 7:41 pm
        • Jan Heine

          Yes, there are roller bearings on the driveside, since they can take much greater loads. You need a ball bearing on the other side to handle the side loads (roller bearings can’t).

          July 12, 2019 at 1:09 pm
  • Bert Platzer

    Interesting story, but how is reintroducing BSA thread a vote for square taper bottom brackets? It is just as much a vote for (also creakless) Shimano Hollowtech.

    Sure square taper bb’s are extremely durable, but they can also be extremely difficult to replace. I remember at couple of occasions with crank threads being damaged because of corrosion. No problems like that with modern standards (of which there are far to much, I agree!).

    July 5, 2019 at 1:01 pm
    • Jan Heine

      Allied’s reintroduction of the BSA threading was quoted to show that we are not alone in wondering about all these new BB standards.

      Crank threads can get damaged by corrosion with dust caps that keep water inside. Rene Herse cranks don’t use dust caps, so that isn’t a problem. If your crank threads are really dirty, clean them with a toothbrush before you screw in the extractor. Also lightly grease the tapers to get a good seat of the cranks and prevent galvanic corrosion between (aluminum) crank and (steel) spindle…

      July 5, 2019 at 2:12 pm
      • mtbvfr

        Should Titanium spindles be lightly greased also?

        Some people say the spindles should not be greased.

        What is your definition of “lightly greased”?


        July 5, 2019 at 4:32 pm
        • Jan Heine

          It doesn’t really matter how much grease you put on the spindle – the excess will be wiped off as the crank goes on. I usually wipe off the spindle before I install the crank to get just a very thin film.

          Yes, Campagnolo used to recommend installing spindles dry. However, our own research, as well as that by Race Face (when they were an independent company and I worked for them) show that grease is useful to seat the crank evenly on the spindle.

          July 6, 2019 at 9:25 pm
      • marmotte27

        I’m not so sure about the grease. I did it to install the 70th anniversary TA cyclotouriste cranks on my bike, and I finished getting ticking noises from the cranks that now reappear systematically even if I retighten the cranks (installed without grease meanwhile). Hence my question about reforming the square taper.

        July 8, 2019 at 7:33 pm
        • Jan Heine

          Clicking noises are frustrating. We’ve found that more often than not, they originate from chainring bolts that aren’t quite tight. Of course, with the Cyclotouriste (Pro 5 vis), the bolts are a bit underdimensioned, so it’s difficult to tighten them enough without breaking them…

          July 12, 2019 at 1:10 pm
  • Eric Peterson

    I may be looking for a replacement compact crank. On all my bikes save one, crank length has been 175 (it’s 172.5 on my Rambouillet).
    But the choices for your cranks are 177 and 171.
    What’s a fella to do?

    July 5, 2019 at 1:02 pm
    • Jan Heine

      We size our cranks in 6 mm increments, because that is the smallest difference (3.5%) you’ll conceivably notice. The 2.5 mm increments that were used in the past make little sense – the tolerance of the machining on many cranks is 1 mm or more. So if you measure your 175 mm cranks carefully, they may well be 174 or 176 mm. You’ll never notice a difference of less than one percent!

      July 5, 2019 at 2:15 pm
      • designrecruit

        When you start to think about all the other elements which can influence your position on the bike I’m not entirely convinced you can ever duplicate a position to the millimeter. Even something as simple as chamois thickness could effective alter things by more than a millimeter – especially with the bulky, diaper like chamois that come in so many shorts these days!

        July 5, 2019 at 2:58 pm
  • Ben

    Now what if there were square taper bottom brackets for press fit frames available so that one could use “old-fashioned” cranks in modern carbon frames… Are there any technical limitations that make it hard to develop a press-fit BB with square taper axle? Or is the market for such odd parts not worth it?

    July 5, 2019 at 1:04 pm
    • Jan Heine

      We’ve been thinking about this. It would be nice to run a Rene Herse crank on an Open, for example. However, if we do this, we also want to solve the other problems of squeaking, etc. It makes little sense to develop a new part that doesn’t fix the problems that exist with the current ones.

      July 5, 2019 at 2:16 pm
      • jasonmiles31

        I think it will be difficult to fit a JIS crank to a 86.5mm wide BB. With a 110 spindle ~10mm of the taper would end up inside of the BB shell.

        July 8, 2019 at 10:07 am
  • Owen

    Your mechanic will DEFINITELY thank you! Mine did when I recently needed a new square taper BB on my touring rig, indeed he even smiled while replacing it. This from a shop that mainly caters to mountain bikers and as such deals with the multitude of new BB standards. He said even the cheap Shimano square tapers last 4-5x as long as the current external bearing designs–it’s a mystery to me why this system was even developed.

    July 5, 2019 at 1:07 pm
    • Paul

      Owen, they were developed entirely to sell more replacement parts. Manufacturers absolutely know they don’t last nearly as long as square taper bb’s.

      July 6, 2019 at 12:49 pm
  • philip

    You have missed a critical element in your analysis. With modern 2-piece cranks and external bearing designs, nothing prevents the spindle from lateral movement causing wear and bearing failure. Ask any bike shop mechanic how many bearing cartridges he’s changed because they’re worn out. With square taper crank arms they are bolted onto the spindle, with a torque wrench. NO comparison. And your feet are closer together. And yes the spindle on 2-piece cranks does move. End of story.

    July 5, 2019 at 1:33 pm
    • Jan Heine

      I mostly agree, except don’t use a torque wrench to bolt on the cranks. Many consumer-grade torque wrenches are too inaccurate. Traditional crank wrenches like our Rene Herse crank bolt wrench are sized and shaped that you get just the right amount of torque if you tighten the crank hard, but not so hard that the wrench hurts your hand. With cranks (unlike most other bike parts), it’s almost impossible to overtighten them. We’ve tested them with 3x the torque spec that we used to recommend, and neither crank nor bolt showed any problems even after repeated installations.

      July 5, 2019 at 2:19 pm
      • John C. Wilson

        I know a shop where the mechanics decided they were going to end the plague of crank bolts loosening up after first few rides. And end the need to include checking crank bolts in the 30-day free service. For two seasons they tightened cranks with two and three foot cheater bars. Near end of second season they moved to 4 foot cheater bars and really leaned full weight into it. A surprising number of cranks survived this. Difficult to remove the bolts and of course a lot of cranks did crack. Most survived and remained in service. That was at ten and twenty and thirty times recommended torque. With the René Herse wrench or the old standard Campy peanut butter wrench it would be very unlikely anyone could get it so wrong as to make a difference. The cranks will tolerate quite a lot.

        July 5, 2019 at 3:22 pm
        • Jan Heine

          Yes, like everything, we don’t recommend to overdo it. That is why the Rene Herse crank wrench is relatively thin – you won’t be able to damage the crank using it unless you are of truly Herculean build. And even then, your hands would hurt. Traditional hand tools were dimensioned for the torque that was correct – that is why a 20 mm wrench is much longer than a 10 mm.

          July 5, 2019 at 9:05 pm
  • Jon Spangler

    The other advantage of continuing to design and sell square-taper BBs and cranksets is the ability to replace those parts on a classic bike (like an Alex Singer or Rene Herse) with new BB cartridges and change the axle length if either changing one’s drive train or installing cranks on a different frame. A big plus — those of us who have finally figured out square-tapered BBs do not have to learn how to handle a new technology! 😉

    July 5, 2019 at 2:43 pm
    • Jan Heine

      I’m all for new technology when it works better. For example, I can’t imagine going back to pre-LED lights for night-time riding…

      But yes, we love the classics and support them where we can. So we’re even offering French-threaded bottom brackets for those who need them.

      July 5, 2019 at 9:01 pm
  • vintagebicyclefixer

    As a bike mechanic i applauded the ht2 system from shimano , although i do still use old stronglight and TA cranks on all my old bikes i have fallen in love with the campagnolo ultra torque system . For the sake of being pedantic the bearings in square taper cartridge systems have fewer and sometimes smaller balls than in external ht2 or ultra torque bb’s . I agree whole heartedly about the number of different systems , we have two added this year that i know of . As for the moans about creaky systems that i hear all to often , all creaks can be solved with correct installation, press fit is a sin but redemption is at hand in the form of wakos brake grease , very expensive but you only need a tiny amount so lasts for ages , like all aspects of the current mass market bicycle evolution , the good stuff will stay , the crap will fall away .

    July 5, 2019 at 5:04 pm
    • Jan Heine

      square taper cartridge systems have fewer and sometimes smaller balls

      That is another problem when standards are mixed. The BSC bottom bracket shell was designed for cup-and-cone bearings. If you use standard bearings pressed into a cartridge – as so many aftermarket BBs do – there isn’t enough space for proper balls. That is why the SKF BB runs the bearings directly on the spindle and on the outer shell. That way, the bearings are much larger and last forever… There is more detail in this blog post.

      July 5, 2019 at 9:11 pm
  • Richard

    The phrase “Tighten the crank bolt as much as you can” made me cringe, even in the context of reforming a taper. It reminded me of a long-ago experience with a beat-up Schwinn a friend gave me. When I tried to remove the one-piece crank to service the bottom bracket, the left-hand pedal wouldn’t budge. In desperation I tried to turn it the “wrong” direction and, with great effort, it began to move. By the time I’d finished, the crank arm was too hot to touch. My friend, a person of sturdy build, had installed a right-hand thread pedal in a left-hand thread steel crank arm! He recalled that it was a little hard to turn, but was unaware why. Advising him to “tighten as much as you can” would likely have a bad outcome.

    Re crank bolt torque, some years ago I looked up major manufacturers’ specs and found that 25 lb-ft fell within every recommended range. Torquing to 25 lb-ft felt excessive at first, but I’ve never had a creak or any other problem. If you have a bench vise, it’s easy to performance test a torque wrench using a weight or even (don’t laugh) a bathroom scale.

    July 5, 2019 at 8:55 pm
    • Jan Heine

      Wow, forcing a left-hand threaded pedal into a right-hand threaded crank hole takes a) a lot of force and b) quite loose tolerances on the threads.

      Regarding crank torque specs, we found that many riders who own torque wrenches are so concerned to break bolts that they err on the side of less torque. With high-quality square-taper cranks, when in doubt, torque them more.

      July 5, 2019 at 9:15 pm
      • Richard

        Other than the lead-in, the thread tolerances were not loose, at least by Schwinn standards. I base that conclusion on the fact that the crank arm was too hot to touch from merely unscrewing the pedal. That was a unique experience. It took very high effort, but after an already sustained attempt with no results, I was determined to get it apart once it started moving.

        I could scarcely believe it at the time and remain astonished that my friend was able to install the pedal all the way into an opposite-threaded hole. I can only guess that it was analogous to cross-threading a fastener and persisting until it pulls up square against the surface surrounding the hole.

        Thank you for the explanatory note about bolt breakage concerns. It was a little bit intimidating the first time I torqued a crank bolt to 25 lb-ft – thinking to myself “this is too much, it’s going to break.” I’ve broken enough bolts that I have a sense of what a given diameter can withstand, but my experience with crank bolts is exactly as you describe. I learned not to worry about it and have never broken a crank bolt while torquing it.

        July 5, 2019 at 10:24 pm
  • Bertrand

    The SKF is so heavy (and overbuilt?) id goes a bit against your cranks.

    July 6, 2019 at 2:33 am
    • Jan Heine

      The SKF is a bit heavy, but for the most part, that is the price for properly dimensioned bearings. Bearings are heavy, but a failed bearing will end your ride. (Don’t ask how I know!)

      July 6, 2019 at 7:38 pm
  • Conrad

    Even on a mountain bike, did the square taper spindles ever fail? I have never seen it! I agree that the square taper is still the best system out there. Corrosion is not a problem if you properly grease the bottom bracket threads. I made the mistake of using Lanolube once. Bad idea.

    July 6, 2019 at 9:23 am
    • Jan Heine

      Yes, mountain bike spindles have failed. I know of one that failed for a 200-lb rider who liked to ride down stairs. First, he broke a bunch of forks, before finding one that worked. Then he went through bottom brackets…

      July 6, 2019 at 7:36 pm
  • Michael

    While I do not doubt the longevity of good square taper BBs, I am sceptical about the weight advantage (compared to Shimano Hollowtech II). At least by the numbers modern systems (BB and crank) seem to be lighter. But I might be missing something here…
    Also the SKF are pretty high quality. Maybe longevity will not differ much from external BBs of the same price category?
    Interesting to see you writing that modern BBs have smaller bearing balls. Beyond the marketing stuff it seemed logical to me that external bearings could have bigger balls leading to less wear. This is why I thought I could have long lasting BBs for little money with the new standards (especially those Shimano Hollowtech II ones). But in the end I am really lacking experience here.

    July 6, 2019 at 1:05 pm
    • Jan Heine

      All external bottom brackets I’ve taken apart had very small bearings. It’s the easiest way to save weight. On the plus side, they are usually easy to replace. On the minus side, if they go bad in mid-ride, you’re stranded, unless they are field-serviceable and you carry spares and the tools to install them.

      July 6, 2019 at 7:39 pm
      • Karl W

        If the races are further outboard on the newer designs, the bearings would experience less load. So they could be smaller and still meet the same performance criteria as the larger ones in the skf.

        I have no idea what the new external bb designs look like. I still ride a custom Panasonic road frame from about 1990. You should really do a story on those. They are still available as far as I know, factory direct with custom paint. Best road frame I have ever ridden. Tange prestige, internal cable routing. Super road feel. Website to order is in Japanese, though.

        July 7, 2019 at 9:01 am
        • Jan Heine

          You are right in theory. The problem with the external bearings is that they are in cups that are screwed into the standard BB shell. That means any alignment issues of the BB shell (which always will have tolerances in its facing) are magnified. A bigger BB shell is a better solution, as you can machine it to higher precision. With carbon, that is what most makers do, but with steel (or ti), a bigger BB shell adds a lot of weight…

          July 7, 2019 at 9:08 am
  • Drew

    “And even if a crank comes loose by accident because the crank bolt wasn’t tightened enough, you can usually reform the taper: Tighten the crank bolt as much as you can, then ride the bike for 5 miles, retighten the bolt, etc. Do this five times, and the taper will usually be fine, unless it’s really been damaged beyond repair.”

    I fixed a few worn/damaged tapered cranks by using brass shimming material. I cut a swiss cross shape out of the brass sheet and cut a hole in the middle (for the crank bolt) and formed it over the spindle taper. Then I put the crank on and got it really tight. It would end up assuming the normal position on the spindle. These fixes seemed to hold up just fine.

    My favorite crank came with my ’72 Mondia, a TA 3 arm 70mm, similar to (or a copy of) the Herse crank. Thanks for bringing this excellent design back into production, Jan.

    July 6, 2019 at 2:38 pm
  • marmotte27

    When reforming a taper the way you describe, how much further should one expect the cranks to slide onto the spindle afterwards?

    July 6, 2019 at 8:15 pm
    • Jan Heine

      Very, very little – maybe 0.5 mm – unless it’s a crank made from very soft aluminum.

      July 6, 2019 at 8:21 pm
  • Eric Peterson

    So back to my original question – given that I ride (mostly) 175, and 172.5 (one bike) cranks, any advice / experience as to whether 177 or 171 would be the best choice?

    July 7, 2019 at 1:32 pm
    • Jan Heine

      Either will work. It seems like there isn’t much difference for you between 172.5 and 175 mm – if you had a strong preference for one over the other, I’d choose the longer or shorter cranks. If it matters to you, the 177 mm are heavier, since they are intended for taller riders who push harder on the pedals and spin at a lower rpm…

      July 7, 2019 at 4:22 pm
      • Eric Peterson

        Thanks Jan.

        July 7, 2019 at 4:50 pm
      • Rick Thompson

        I’m glad I got the 177s just for this reason, as I am on the big side and more of a masher. It would be nice to put this in the general description, this feature seems more important than the small difference in length. It does say they are heavier in the technical description, but the intent of different riding style is not clear.

        July 8, 2019 at 3:05 pm
        • Jan Heine

          Good idea: We’ll update the description.

          July 8, 2019 at 6:35 pm
  • PStu

    Is there a big difference between entry-level square taper bottom brackets and better ones? My first commuter bike (a T— hybrid) had a STBB that didn’t last a year before it had to be replaced with a Shimano XT-level STBB.

    July 8, 2019 at 9:42 am
    • Conrad

      What was the first one? In my experience even a relatively cheap Shimano UN 53 or Origin 8 STBB is pretty durable, at least compared to the non-SKF ISIS or any of the newer so called bottom bracket standards. If it is was a truly low end STBB I wouldnt know, never used them.

      July 8, 2019 at 3:35 pm
    • Craig Lloyd

      Yes..not sure what the differences are but they are clear. On my fixed gear commuter I would barely get 6 months out of the cheaper Shimano UN26, but the UN55 was good for at least 2 years. The SKF is clearly in another league again with a 10 years warranty, but it would cost as much as that bike and risk of losing it to theft before it wears out is too high!

      July 9, 2019 at 3:31 am
    • Mike M

      My guess is that the better quality ones come with better seals for the bearings. Water is the enemy of BB bearings, and a better water seal makes a better product.

      July 9, 2019 at 8:54 am
  • Dann

    Jan, do ceramic bearings in square taper BBs make any difference?

    And do you have a preference for metal vs plastic non-drive cups?

    July 8, 2019 at 10:13 am
    • Jan Heine

      Ceramic bearings make little difference – the resistance of standard bearings is already almost zero. So there isn’t much you can save. As to different quality BBs, we recommend the SKF units – that is why we sell them!

      July 8, 2019 at 10:29 am
      • Mike M

        Ceramic bearings is one of those marginal gains that I’ve heard about in pro cycling. Jan wrote a post in the “Myths of cycling” series on marginal gains some time ago. In terms of improving the performance of you or your bike, it’s far down the list, way below other low- or no-cost options. A ceramic system will drain your wallet long before it makes any measureable difference in your riding.

        July 9, 2019 at 9:00 am
  • Dave

    I’m a bike mechanic in the Northwest. Square tapered bb’s keep the bearings sheltered inside the bottom bracket shell, not facing outward ready to be ruined by all of the water they can and will suck in

    July 8, 2019 at 9:12 pm
  • Bertrand

    What’s the point of square tapper BBs being in a shell? vs open designs like Spécialités TA Axix for example. So much simpler, lighter, bearings almost flush with the frame.

    July 9, 2019 at 3:19 am
    • Jan Heine

      The ‘open’ design relies of the threading and facing of the BB shell for alignment, and that is never very accurate. So the bearings tend to bind and not last very long. The shell adds very little weight – it’s a thin tube, but the machining is much more complex, so many makers prefer to do without it.

      July 12, 2019 at 10:19 am

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