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Because lighter isn’t always better

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Weight has long been a driving factor in product development in the bike industry, with the ultimate goal obviously being to minimize it as much as possible. Let’s face it: all else being equal, lighter bikes are more entertaining to ride (and certainly more impressive to lift on the showroom floor). As a result, light metals such as aluminum and titanium are generally preferred over steel, for example, and if you can make something out of carbon fiber, of course you do so.

“All else being equal” is the key phrase here, however, and hardware is one area where weight shouldn’t be the primary consideration when deciding on a material.

When two threaded parts are tightened or loosened under tension, what’s supposed to happen is that the threads smoothly glide against each other — but as too many of us know, that isn’t how it always goes. Galling is the term used to describe a phenomenon when two threaded fasteners have seized to each other. Specifically, it’s what happens when one or both of those threaded parts start to shed microscopic bits of material. Those bits of material can create pits or raised bumps on those surfaces, and eventually, the tiny space that exists between the two gets jammed up with metallic gunk, binding up the whole system and preventing the two pieces from moving.

Large-diameter and relatively fine threads, a spindle and bolt both made from aluminum, and very high tightening torque all combine to create a scenario prone to galling.

In moderate cases, the parts can be removed from each other with a rather judicious use of torque — either a lot of it, such as what you can create with a breaker bar, or delivered very quickly, such as what you get with an impact driver. In more extreme cases, the threads are so damaged that the parts are no longer usable. And in the worst cases, the parts are basically welded together and it’s time to crack out the heavy-duty cutting tools.

It’s commonly accepted that galling can be prevented with several strategies, the most common of which are using proper lubricants (ideally some sort of anti-seize compound), designing the parts with coarser threads, avoiding softer materials (or at least avoiding using two softer materials together), applying torque more slowly, not exceeding recommended torque values, and the use of special surface treatments such as anodizing and electroplating.

Anti-seize is good.

For the most part, bicycle component brands have been pretty good about all of this, although in the name of saving weight, there are obvious exceptions.

One big one is the fixing bolt in SRAM’s higher-end DUB (and previously, PF/BB30) cranksets.

Leverage is your friend

If you look at those common recommendations for preventing galling, this situation violates several of them: the spindle and bolt are made of similarly soft aluminum, the recommended torque value is very high (54 Nm!), and the threads are relatively fine. Not surprisingly then, it’s not exactly uncommon for these bolts to require an inordinate amount of torque to remove them (Dave Rome and I have both experienced it ourselves on numerous occasions). Bicycle mechanic forums and boards are also littered with accounts not only detailing seized crank bolts and broken tools, but a variety of creative solutions for removing them, most of which involve some combination of breaker bars, impact wrenches, heat, cold, extra hands, and swearing. 

“I’ve had good luck putting the [non-driveside] crank on an elevated surface, then having someone sit on the bike,” read one suggestion. “Use a long, breaker bar with a pipe on the end for extra leverage. They usually break free. I’ve had more success with this method than with an impact wrench.”

“You can clamp the crankarm in the work stand and let the bike hang by it to lock it in place then use a big breaker bar for those that get really stuck,” read another.

“I have the Efficient Velo Tools stand,” said yet another mechanic. “I lower the bike until the wheels are on the floor, use a block or something solid under the non-drive arm to keep it at the 3 o’clock position, and then use the breaker bar/Allen socket to remove.” 

“Impact guns are your best friend. Way better than putting a big ol’ cheater bar on it.”

If you’re going to attempt to remove an aluminum SRAM crank fixing bolt that’s stuck in the spindle, you’d best be prepared. Photo: Dave Rome.

Regardless of the preferred method of extraction, anyone reading this who has experienced the issue themselves will likely be quite familiar with the telltale “gunsmoke” smell that often accompanies the sound of victory when the bolt finally breaks loose.

SRAM says it modified the thread geometry in DUB spindles a few months ago, but there are still countless other ones floating around that are apparently still prone to seizing. Better yet, there is one ultimate solution I discovered that takes care of the root cause — and not only has it proven to be highly effective, but it’s quite inexpensive, too. 

It turns out that SRAM also makes those bolts in steel, but only used them at stock equipment on the lower-end SX Eagle and X1 1000 Eagle mountain bike cranksets. A few months after some prodding on my end, though, the company decided to offer them aftermarket.

“We did spec the steel DUB bolt replacement assembly, based on a mountain bike crank spec, thanks to your request,” said SRAM road product manager JP McCarthy. “The part is in production, but it hasn’t been communicated to distributors, or even our own service centers yet.”

The stock aluminum bolt and self-extracting cap (at right) weigh just 18 grams, while the optional steel bolt and aluminum cap (at left) are nearly twice as heavy at 31 grams. It’s worth it.

This was back in July, mind you, and hopefully SRAM distributors and service centers have come up to speed since then. And now you can consider yourselves informed as well.

These steel DUB bolts are a straight replacement for the aluminum ones, tightening and loosening much more predictably and reliably, and they also retain the self-extracting function. What’s the retail price, you ask? Less than US$20 (it’s SRAM part number 11.6118.066.000, FYI). As a nice bonus, the self-extracting cap also sports a more reliable 10 mm hex fitting for installation and removal instead of the more finicky original version, which uses a pin spanner.

Switching to those steel bolts adds a bit of weight, of course — actual weight for the new assembly is 31 grams as compared to just 18 for the original aluminum one — and if you’re averse to lots of logos and call-outs, it’s perhaps worth mentioning that the laser etching on the replacement extractor cap is quite a bit bigger (though nothing that a good permanent marker can’t fix).

The folly of chasing grams

Although I was happy to discover this fix a few months ago, the fact that the issue exists at all is still troubling. Again, according to basic hardware principles, these high-torque aluminum crank bolts arguably shouldn’t exist at all. And yet SRAM not only uses them stock on all of its current higher-end cranksets with the 29 mm-diameter DUB system, but the company has also featured them for years on cranks with 30 mm aluminum spindles so who knows how many of these things are out there. Thousands? Hundreds of thousands? Millions?

Before you cast blame on SRAM, keep in mind that while the company has an outsized presence in the aftermarket world, the bulk of its revenue comes from OEM contracts (just like Shimano), with parts that are purchased by other brands for use on their complete bikes. Those contracts can be massive, so even if what the OEM brand wants isn’t what’s best for the end-user long-term, money talks, and SRAM has to listen.

OEM product managers can very easily request that SRAM provide its cranks with steel fixing bolts – but they either don’t know the option exists, or they’d rather save the handful of grams at the expense of serviceability.

According to industry sources I spoke to (who preferred to go unnamed), the issue, in this case, is weight. Specifically, bike brands are often so motivated by the consumer appeal of a lighter-weight bike in this cutthroat market that product managers will knowingly choose options that can trim the final tally by a few grams despite the possibility that it might sacrifice long-term serviceability. 

So what does that mean? Even if SRAM offers OEMs a version of its DUB and BB/PF30 cranks with steel fixing bolts — and seeing as the bolts exist, that’s almost certainly an option available to them — there’s a good chance product managers won’t choose them, simply because they’re a little heavier. But I sure wish they would.

Either way, the upside of all of this is that the situation is easily and inexpensively rectified, and the solution is also a cinch to install (provided you can get the original aluminum bolt out). 

To some, it might seem silly to spend money to make your bike heavier. But in this case, I’d say it’s weight (and money) well spent.

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