Muddymoles mountain biking in the Surrey Hills and Mole Valley

DUB step – for bottom brackets and cranks

Posted by Matt | January 16, 2018 | 8 comments so far

SRAM DUB cranksets
Ah, standards! On the face of it, they sound so well-intentioned don’t they, when often their existence is more about protecting IP than serving customers.

Oh sure there’s a benefit to imposing some rigour into the process of producing bike parts. Making Part A fit with Part B, regardless of manufacturer is a Good Thing in my book, but the history of the frame/crank interface is littered with ever-changing designs with varying degrees of engineering integrity.

Just from my own experience, there’s the good old square taper bottom bracket, a design that was heavy, lasted for ages but suffered from cranks seizing on. Next came the notorious ISIS bottom bracket, a name that today is unlikely to ever get past a marketer’s initial brain-fart. Or an engineers either, unless the idea was to produce something that lasted five minutes and needed constant replacement.

After that, Shimano nailed it with Hollotech. End of story really, unless you were SRAM who have never been keen to pay royalties unless they have to. So they came up with GXP – basically, same, but different. Again, a reasonable, reliable design but with an inherent inferiority in axle diameter. Not much, but enough.

So, then came various oversized efforts – BB30 pressed directly into the frame which allowed up to 30mm axles, followed by Press Fit efforts – PF30, PF92 and other variations on a theme to try and engineer out bottom bracket variability in frame manufacture. Often creaky, rarely beneficial they had strong axles but a tendency to fail due to relatively limited space for bearings and seals. Oh and don’t forget the intriguing but weird e-thirteen triangular crank interface that is 30mm but not BB/PF30…

There are others that I haven’t listed but you get the idea. No-one makes us use this stuff but if you buy a bike with a certain type of bottom bracket, and it turns out you’ve backed the wrong horse on an otherwise great bike, then tough luck.

This sort of thing annoys consumers though.

Now SRAM has introduced another standard with it’s new bottom brackets. They have produced bottom brackets that take a… 28.99mm axle diameter and dubbed it (sorry) DUB – Durable, Unified Bottom Bracket. Which obviously need DUB compatible cranksets to go with them. The reasoning is to free up space for bigger bearings and better seals (both good), while getting almost but not quite to 30mm axles for stiffness. The claim, is lower weight and better reliability. Which I have heard before.

To be fair, the cranks available (and SRAM have brought out a whole slew of cranks) are very light – just 420g for a SRAM XX1 Eagle DUB SL at the top end (with bottom brackets that range in weight from 71g to 89g). That’s lighter than the Race Face Next SL, but you know, marginal gains. At the other end of the scale, a Stylo or Descendent will tip the scales around 717g with steel chainrings.

So there you go. This looks a worthwhile improvement- new supposedly reliable bottom brackets for almost everyone, and SRAM cranks for every pocket. It’s unlikely that Shimano will ever produce 28.99mm diameter axles for their cranks, but everyone else can reasonably be expected to move in this direction over the next couple of years.

And SRAM’s stranglehold over the big S appears to have tightened that little bit further.

Filed under 2018, News in January 2018


About the author

Matt is one of the founding Molefathers of the Muddymoles, and is the designer and main administrator of the website.

Having ridden a 2007 Orange Five for many years then a 2016 YT Industries Jeffsy 29er, he now rocks a Bird Aether 9 and a Pace RC-627.

An early On-One Inbred still lurks in the back of the stable as a reminder of how things have moved on. You can even find him on road bikes - currently a 2019 Cannondale Topstone 105 SE, a much-used 2011 Specialized Secteur and very niche belt drive Trek District 1.

If you've ever wondered how we got into mountain biking and how the MuddyMoles started, well wonder no more.

There are 8 comments on ‘DUB step – for bottom brackets and cranks’

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  1. Elliot says:

    What a bizarre measurement to have come up with!

    The main takeaway here is a 28.99 spindle gives them a measly 1.1mm more room to finally design a long lasting BB30 bottom bracket, but also means shaving 4.99mm off the space available for BSA and PF92. I look forward to hearing if Sram have pulled that one off…

    Not sure I understand the whole oversized spindle business anyway. I’ve never once felt my 24mm spindle needed stiffening up, even singlespeeding. Maybe it’s intended for fat ass Big Mac munching Americans?

    Biggest thing Sram could do to improve their cranks is switching to the Shimano/FSA/Surly pinch bolt mounting design rather than that single crummy lightweight aluminium cheese bolt.

    • Matt says:

      28.99mm?? I’m sure they can manufacture to these tolerances. And I’m also pretty sure there is an IP issue with going for 29mm as well!

      I think the oversize angle is about weight saving (thinner spindles with more air in the middle) as you’re right, stiffness is not the issue.

  2. Mat-S says:

    I like that they seem to be chasing a better all round solution. If they’d got a few other brands together and said ‘right, from here on in we’re going to sort it out so there are only these four bottom brackets and they’ll all work together’, then I could see some use to it.

    But we already had that- 24mm axle cranks in my experience run on other brands BBs (except SRAM with GXP, which is somewhat ironic) and ditto with 30mm.
    There are problems with running 30mm cranks in bb92 frames but I suspect a lot of people with those frame have bought a 24mm crank instead and the rest are a small enough number not to justify messing everyone else around.

    It could in theory reduce the number of BBs that shops have to stock. In practice I suspect it’s just added another four.

    • Matt says:

      I think this is all about squeezing Shimano further as most manufacturers will see this as a simple part swap on their production/assembly lines and further out, beyond the OEM market, many more companies will get on this ‘brandwagon’ because frames don’t need to change to accommodate it.

      • Elliot says:

        I’m not so sure Shimano will feel the squeeze. They’re a much bigger company, offering better value, often longer lasting parts and not built on a mountain of debt. Not that I’m against Sram, but this one looks like a brain fart to me! Be interesting to see if anyone else jumps on this bandwagon, their silly XD Driver idea seems to have been accepted.

        • Mat-S says:

          Of all the standards I actually don’t have that much of an issue with XD. It’s arguably a better way of making/mounting a cassette and does allow for a 10t cog. Backwards compatible too.

          Shimano has it’s own share of annoying ‘innovations’- see 15mm axles instead of 20, flat mount brakes (which incidentally use ever-so-slightly different pads to post- Sram, despite not inventing them managed to make their flat mount calipers take the same as their post).

          I guess we wouldn’t get some of the innovations that we’ve come to like without the ones that are a pain. At the very least this dub malarky isn’t a new BB standard.

          • Elliot says:

            I’ve had the misfortune of a Superfly with an XD type cassette seized in place, permanently, at a cost of almost £300. Besides that the main goal of the idea, to allow 9 or 10t cogs, is pointless because such small cogs are so inefficient.

            You’re right though, going from 20mm axles to 15 was a decidedly retrograde step!

  3. Jemster says:

    28.99? Why?

    Perhaps that’s the cost of the new bottom bracket, or thier milling machines don’t go up to 29!

    Anyway whatever the reason, think I will stick to 24mm spindles.

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