Aftermarket Bottom Brackets with DUB Cranks?
I didn't intend to solve a problem when I started tinkering, because I wasn't yet aware a problem existed. At that point I just wanted to see if I could make an Enduro Bearing 30mm bottom bracket, that I already had tucked away in a drawer, work with a DUB crankset. I went to the web and found a couple of results for products to shim a 30mm inside diameter bearing down to the required 28.99mm to fit a SRAM DUB spindle. The Enduro Bearing PF92 BB has double row angle contact bearings that should be very durable, and I don't currently have a bike or cranks requiring a 30mm bottom bracket, and I wanted to put it to use. I hate it when products become prematurely obsolete, so I was on a mission.
The first Google result was from Chris King but it's stated that this solution is made to sleeve their own bottom brackets down to 28.99. I figured it would probably work fine with the Enduro BB, but I also found something from a Taiwanese company I'd never heard of; AEROZINE TW. Chris King's solution was 22 USD and Aerozine's was 6 so I went with door number cheap. After I purchased it online they emailed me saying they'd also need 23 bucks for shipping, so it was likely to be a wash, but I was committed at that point.*
*TBF when I told them I'd be writing about their product, they waived the shipping fee.
I'd been testing GX AXS and I wanted to go back to the XO1 version to see if I could notice any difference (I couldn't) and I decided to swap the cranks at the same time, because I'm not yet a fully recovered weight weenie. Unfortunately, my excellent Enduro BB tool doesn't work with 28.99mm so I used the hammer and punch method to remove the DUB bottom bracket that I've been using for the better part of a year. I managed to get one side out undamaged but I bodged the other side so it would no longer spin freely. The undamaged side was in excellent shape and both sides were still well-lubed; a considerable testament considering how aggressive I am with my spray nozzle, which I set to 'destroy' after almost every ride.
What I didn't know at that point was that DUB bottom brackets, at least on this side of the border, were becoming as rare as frankincense. Canadian retailers can't order SRAM or Shimano parts from across the border, neither directly from SRAM or from any distributor and the best news I've heard, from Lou Costa of Obsession Bikes here in North Van, is a September 15th delivery for popular sizes. That doesn't mean there won't be other orders trickling in during that time, it just means, according to Kevin Calhoun, who works for Hawley Lambert, a distribution company that trades on both sides of the 49th parallel, that you won't be able to place any additional orders until that time. If a shop booked those parts months ago they may very well be arriving this month, but they are likely all spoken for. Now my tinkering had purpose.
In the process of removing the DUB BB, I dislodged one of the plastic sleeves that keeps the DUB system from running the aluminum spindle against the stainless steel inner race of the bearing, and this got me wondering. I had a long conversation with SRAM drivetrain product manager Roberts Graudin when DUB was introduced, but I never thought to ask him about bearing sizes. I assumed at the time that the rationale for a 28.99 mm spindle was to accommodate a larger bearing. In fact it was to allow for the aforementioned plastic sleeve. Shimano bottom brackets use a 24mm spindle but they run on bearings with an inner diameter of 25mm, and they too use a plastic sleeve to prevent a metal on metal interface between bearing and axle. Other manufacturers, Raceface and Chris King being a couple of noteworthy examples, have no qualms about this, but there are some good reasons to provide this plastic buffer.
When exposed to moisture, the mixture of aluminum and steel can produce galvanic corrossion. That is asssuming there is wear on the aluminum to remove protective oxidization, and corrosion is much less likely when paired with stainless steel, as in this case. Another factor is that aluminum and steel expand and contract at different rates as temperatures change. Clearly in a perfect world they are best kept apart to prevent creaks and groans which was one goal of the slightly narrower spindle. The sleeves also have an o-ring which improves sealing. Since I've been riding DUB, I haven't had a creaking crank or any bottom bracket issues, but my stuff comes apart regularly to be inspected and cleaned as I roll through test parts, so I'm not a good sample for that evidence.
After taking apart the DUB bottom bracket, it was time to conduct an investigation. When I saw the measurements on my calipers I thought I'd uncovered a dirty secret; SRAM's been using 30mm bearings all along! Fortunately, it wasn't a secret at all, SRAM just kept that info a bit quiet for obvious reasons during the screams of 'another fucking new STANDARD!' Once I recovered my composure, I realized that getting a couple of tiny aluminum shims sent from Taiwan wasn't necessary at all. If you're careful, you can remove SRAM's plastic sleeves and reuse them on other bottom brackets, or some at least. The Enduro bearings with their double row of angular contact bearings were slightly wider and the inner flange didn't make it past the inner edge of the bearings. If you removed the inner flange of SRAM's plastic shims with an Exacto knife they would work fine, but I was too deep to turn back.
Thankfully I could use the Enduro PF86/92 installation and removal tool, which makes the process a pleasure, to press in the new bearings. When I'm working with a 30mm ID bottom bracket I actually look forward to any install or removal because it's so slick. Enduro also makes an adapter for DUB which is reverse compatible with 30mm bottom brackets. Once the cups were pressed in the rest was routine. I omitted the recommended spacers on the drive side to improve my Eagle chainline, and then installed the cranks, with a steaming glob of fresh grease applied to the aluminum spindle.
Before I go any further I need to tell you what SRAM feels about all this. I was told by Chris Mandell, SRAM's North American PR honcho, that it's important to understand that all the testing behind DUB in terms of durability, strength, and sealing apply only to DUB as a system. If you can imagine something that could happen to a set of cranks, including the load from a massive and unintended drop to flat, hundreds of thousands of loaded revolutions, side loads etc., SRAM has tested for these eventualities and built a system that exceeds the strength and durability of anything they'd made previously, all at lower weights. This system is apparently more interdependent than before, and the result is, "better wearing, higher performing products."
SRAM is confident that, when using a DUB bottom bracket with a DUB crank, you are getting the safest, most durable system possible. Once you start messing with that system, that confidence is gone. It's possible that axles will break prematurely, interfaces will creak, and all hell will break loose. After years of being able to mix and match cranks and bottom brackets without any real problems, I asked Mandell how he'd feel about riding a DUB crankset with a bottom bracket from another manufacturer. His reply was; "I wouldn't be comfortable.' His advice is to spend the time to call a few shops and source a genuine DUB BB, and if you're able to do that you're likely to save money and, it seems, get much of the performance and longevity SRAM is claiming.*
*Based on my intel talking to a few mechanics at different shops, this is legit, aside from some early DUB BBs that had premature wear issues.
Consider yourself warned. I haven't had any problems, and my Enduro Bearing/AEROZINE solution has been running silently, but it's only been a couple of weeks. I will update this article if things go to shit, but I don't share SRAM's fear that this system will cause issues with longevity and performance, and personally I'm pleased that some aftermarket solutions* exist considering how the pandemic has affected global demand and supply for the entire bike industry.
*Aside from Chris King and Aerozine TW, Wheels Mfg. and Enduro Bearing make solutions to adapt their bottom brackets for use with DUB cranks, or you can try reusing SRAM's plastic sleeves with the correct size 30mm bottom bracket for your frame, which SRAM doesn't recommend either