Today SRAM announces its new DUB crank/bottom bracket system. Standing for Durable, Unifying, Bottom Bracket, DUB is a new crank axle standard that is set to replace both BB30 and GXP.
By replacing two current crank axle standards with one new one, SRAM will also be drastically reducing the number of bottom brackets it needs to produce as well.
Although SRAM really, really doesn’t want to use the ‘S’ (for ‘standard’) word around DUB, there’s no denying that DUB is indeed a new crank axle standard. More importantly though, this isn’t a new bottom bracket standard – the DUB system is designed to work with all current mountain bike bottom bracket shells on the market including threaded (68/73mm), press-fit (BB92), BB30, and PF30.
However, you will need a DUB-specific bottom bracket to run a DUB crankset.
Before you get out the pitchforks, it’s worth acknowledging that there are several proprietary crank standards on the market already. And by proprietary, we mean cranks that require a specific bottom bracket design that isn’t shared with other crank brands. Praxis has its M30 axle and BB standard, and of course SRAM has its own GXP standard – as in you need a GXP bottom bracket to go with your GXP crankset.
So what is DUB?
DUB is made of two things; a DUB crankset, and a DUB bottom bracket. Its design is essentially a meeting point between GXP and BB30 – SRAM’s goal was to combine the lighter weight and stiffer performance of BB30, with the bearing reliability of GXP.
The crankset is built with an alloy spindle (like BB30), but instead of being a 30mm diameter spindle, DUB uses a slightly smaller 28.99mm diameter spindle. Doesn’t seem like a huge difference huh? Well, according to SRAM and Truvativ’s engineers, that extra 1.01mm of space provides crucial added room for improved sealing of the bottom bracket bearings.
For all intents and purposes, the DUB system works very similar to an existing BB30 crank, with a threaded preload collar on the non-drive side crank arm that allows you to preload the bearings correctly.
Less Grams
One of the main drivers pushing the DUB development was weight. The new XX1 Eagle DUB SL crankset comes in at 420g including a 32T chainring – about 50g lighter than the existing XX1 Eagle BB30 crankset, and 73g lighter than the XX1 Eagle GXP crankset. More importantly for SRAM though, that means the new XX1 Eagle DUB SL crankset is now lighter than its main rival – the Race Face Next SL G4 crankset (430g).
It’s easy to suspect that SRAM had been losing out on sales to Race Face because (other performance attributes aside) the Next SL crank has simply been lighter. And whether we like it or not, many people focus on the numbers – even if we’re only talking about the weight of a chocolate bar.
However, that’s changed with the new XX1 Eagle DUB SL crankset, which is now one of the lightest mountain bike cranksets in the world.
To achieve this low weight, SRAM had to use an alloy spindle. BB30 axles are great from a stiffness and weight perspective, and when paired with a quality PF30 bottom bracket and a frame with tight tolerances, the system typically works well. The problem arises when you try to stuff that 30mm diameter spindle into a smaller diameter bottom bracket shell – say with a threaded or PF92 bottom bracket. Other brands offer such bottom brackets to make this happen (Race Face and Praxis Works are two examples), but because that 30mm spindle takes up so much room inside the shell, there’s not a whole load of room for seals and ball bearings.
Instead of going down this route, SRAM decided to shrink the axle a little, to make more room for the bearings.
New Bearings
With all of its new DUB bottom brackets, the bearings sit on the outside of the frame (previous PF30 and BB30 bottom brackets put the bearings inside the frame). This ensures the bearings sit the same distance apart and are aligned correctly, while also being as big as possible. The bearings themselves feature a custom profile and custom seals, and SRAM states it has tightened up tolerances to improve sealing. For the PF92 bottom bracket, SRAM has actually turned the steel cups into the outer race of the bearing, therefore increasing room for all the gubbins. For those of us who frequently ride in wet conditions, there are additional o-ring seals that sit between the spindle and BB shields.
As for the size of the bearings? Well according to SRAM, it isn’t always the size of your balls that matters;
“In all of our development, lab testing and field evaluation of the DUB™ BB we found that the durability of the bearings on a bicycle bottom bracket are much more influenced by the sealing and contamination of the system vs. the size of the balls. We found that smaller ball sizes can far surpass the durability of larger ball sizes if the smaller balls are sealed better from contamination. It is the contamination that almost always is the cause of poor durability in a bicycle bottom bracket. And that is exactly why we did not follow some of our competitors and just use a 30mm system that limits sealing in certain configurations. We needed the extra room for proper sealing to ensure our BB durability” – SRAM.
Here’s the slick marketing video from SRAM to help further explain how it all works, and why the engineers decided it was a thing worth pursuing;
Aside from being able to produce a lighter and stiffer system, DUB was also developed to provide a more universal system that reduced the number of cranks and bottom brackets SRAM was offering – DUB will literally halve the number of stock units that SRAM has to offer. For the time being, SRAM will continue to offer BB30 and GXP cranks and BBs, but expect to see those phased out in the future.
As of right now, there are no other crank or bottom bracket brands looking to implement the DUB standard. However, it’s surely only a matter of time before we see existing bearing brands such as Wheels Manufacturing, Kogel, Praxis Works and Enduro offer up aftermarket DUB-specific bottom brackets. And although it’s extremely unlikely to see Shimano waver from its firm stance on steel 24mm diameter crank axles, it’ll be much more likely that we’ll see some smaller crank brands consider the DUB standard.
SRAM DUB Bottom Bracket
- Designed specifically for SRAM DUB cranksets
- Sealed cartridge bearings
- Four variants available: BSA (68/73/100mm threaded), PressFit (PF89/92/121), BB30 & PressFit 30 (68-92mm)
- Machined alloy cups (except for the PressFit version, which is made with steel cups)
- Claimed weight: 71-89g
- RRP: £32-£44
The new XX1 Eagle DUB SL crank is the showpiece of the new DUB range. It’s the lightest mountain bike crankset that SRAM has ever offered, coming in at 420g confirmed on our scales of doom. Aside from the new DUB SL spindle, the carbon crank arms have been reworked, and there’s a brand new Eagle SL chainring that has been CNC machined within an inch of its life to help chisel out grams.
SRAM XX1 Eagle DUB SL Crankset
- Hollow carbon fibre crank arms
- DUB SL alloy spindle
- Alloy CNC Eagle SL X-Sync 2 chainring
- Arm lengths: 170mm & 175mm
- Claimed weight: 422g (32t chainring, no BB)
- RRP: £520 – £530
SRAM X01 Eagle DUB Crankset
- Hollow carbon fibre crank arms
- DUB bonded alloy spindle
- Alloy CNC Eagle X-Sync 2 chainring
- Arm lengths: 170mm & 175mm
- Widths: Standard, Fat 4 & Fat 5
- Claimed weight: 471g (32t chainring, no BB)
- RRP: £480 – £490
SRAM Stylo Carbon DUB Crankset
- Carbon fibre crank arms
- DUB press-fit 7000-series alloy spindle
- Cold forged alloy Eagle X-Sync 2 chainring
- Arm lengths: 170mm & 175mm
- Widths: Standard, Fat 4 & Fat 5
- Claimed weight: 555g (32t chainring, no BB)
- RRP: £255-£305
SRAM Descendent Carbon DUB Crankset
- Carbon fibre crank arms
- DUB press-fit 7000-series alloy spindle
- Cold forged alloy Eagle X-Sync 2 chainring
- Arm lengths: 170mm & 175mm
- Widths: Standard, Fat 4 & Fat 5
- Claimed weight: 555g (32t chainring, no BB)
- RRP: £255
SRAM GX Eagle DUB Crankset
- Solid forged 7000-series alloy crank arms
- DUB press-fit 7000-series alloy spindle
- Cold forged alloy Eagle X-Sync 2 chainring
- Arm lengths: 165mm, 170mm & 175mm
- Widths: Standard, Fat 4 & Fat 5
- Claimed weight: 621g (32t chainring, no BB)
- RRP: £135 – £185
SRAM Stylo 6K DUB Crankset
- Solid forged 6000-series alloy crank arms
- DUB press-fit 6000-series alloy spindle
- Steel stamped Eagle X-Sync 2 chainring
- Arm lengths: 170mm & 175mm
- Widths: Standard, Fat 4 & Fat 5
- Claimed weight: 705g (32t chainring, no BB)
- RRP: £105
SRAM Descendent 6K DUB Crankset
- Solid forged 6000-series alloy crank arms
- DUB press-fit 6000-series alloy spindle
- Steel stamped Eagle X-Sync 2 chainring
- Arm lengths: 170mm & 175mm
- Widths: Standard, Fat 4 & Fat 5
- Claimed weight: 717g (32t chainring, no BB)
- RRP: £105
For more information on the new DUB crankset range, head to the SRAM website, or get in touch with UK distributor Zyro/Fisher.
Comments (18)
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Lets hope the DUB bottom brackets are more reliable than their GXP offerings.
Also speaking of Hope I eagerly await their version of this BB so I can continue to bling my bikes and keep running SRAM cranks in the future.
Ha ha ha.
And one day we’ll all realise the BMX standard Ashtabula size was the best option all along.
Do one SRAM.
I’ve a great idea lets make the bearings surfaces even smaller than the outgoing POS GXP BB. Great for OEM’s and bike shops, not such a great thing for customers. Just make the goddamn longest lasting bearings, that’s all we want.
FINALLY! A new crank axle diameter and bottom bracket standard that is 1.01mm smaller than the last one.
Oh fantastic, a new proprietary BB size/standard that isn’t compatible with any other cranks or BB’s on the market, yet will more than likely come fitted to a plethora of OEM bikes next year!
DUB uses a slightly smaller 28.99mm diameter spindle. Doesn’t seem like a huge difference huh? Well, according to SRAM and Truvativ’s accountants, that extra 1.01mm of space means every gullible suckers crank and BB becomes obsolete overnight
What a complete joke! 1.01mm difference!
God bless screw in BB! And balls to endless BB standards
https://xkcd.com/927/
“We’ve made BB just as inreliable as our other one, but made it evem less compatible”
Thank goodness I have a threaded BB in each of my bikes, into which a mega eliable Hope BB is screwed, with a Shimano crank running through the middle.
Bleeedin iphoney keboard too!
Filmed during Movember?
Haha I stopped reading when they stated they wanted the bearings to be a reliable as GXP. Currently on my third GXP BB on the road bike, compared to my second cheap Shimano BB on the MTB which gets far more abuse in terms of terrain covered.
Didn’t we have one unified standard……ah, it was the square taper bottom bracket that just kept going regardless of conditions.
Interesting to think that SRAM may have lost sales to Race Face due to weight difference. I’d have thought it was more about perception of the product. RaceFace have a long history of being an aftermarket kit provider (=bling) SRAM cranks are a groupset product (=boring).
but yes, not replacing a standard, but adding another.
wonder if the bearings are off the shelf available like HT2 BB’s 6805’s.
I stopped reading after this:
the DUB system is designed to work with all current mountain bike bottom bracket shells on the market including threaded (68/73mm), press-fit (BB92), BB30, and PF30.
However, you will need a DUB-specific bottom bracket to run a DUB crankset.
Of course, if they were interested in reliability they could have gone to 24mm which offers plenty of room for decent bearings and seals.
Me, I’ve recently bought two sets of Aeffect cranks which allow a wide choice of chainrings and as they’re 24mm are very good value.