With the launch of its new Red XPLR AXS gravel groupset, SRAM has finally brought its Thread Mount chainring design to a non-MTB power meter spider.
In theory, this solves one of my biggest peeves about SRAM’s recent power meter spider designs – namely that, on its Red AXS and Force AXS power meters, the chainrings are integrated into the spider with no way to remove them.
Thanks to Thread Mount, though, chainrings can simply be screwed off and on the new Red XPLR AXS power meter.
Yet, while I’m glad SRAM has adopted this design with its latest gravel groupset, let’s not break out the champagne and declare this issue a thing of the past.
I also bristle at the idea of a brand taking something away from riders, only to add it back in later as a ‘feature’ – especially when the ‘new’ system is less functional than the one we already had.
Integrated chainrings were never worth it
SRAM’s spider-based power meters enjoy a well-earned reputation for accuracy and reliability.
It has always felt a shame, therefore, that the high-end Red AXS and Force AXS power meters featured such an annoying flaw.
SRAM’s argument for integrating the chainrings directly into the power meter spiders was that it made for a stiffer system (which improves front shifting) and lower weight.
Taken on their own merits, both of these things are true – chainring stiffness plays a role in front shifting performance, and getting rid of the bolts and threaded inserts will save some weight.
The problem, however, is the performance gains are intangibly small compared to what you lose – namely, the ability to replace chainrings, either for wear-related reasons or because you want to change your gear ratios.
Other brands have also shown it’s possible to create stiff chainrings and have excellent front shifting without needing to resort to impractical integrated designs.
I distinctly remember the first time I tried a Shimano HollowGlide outer chainring (on an Ultegra 6700 groupset), for example, and the improvement compared to traditional chainrings.
Shimano cranksets all use bolt-on chainrings, though, and don’t seem to suffer any reduction in front shifting speed or accuracy as a result. In fact, many – myself included – regard Shimano’s front shifting performance as class-leading.
To further prove the point, front shifting with a Quarq DFour DUB power meter (which is effectively the same as SRAM’s Red / Force AXS power meters but with a spider design that blends with interchangeable Shimano Dura-Ace R9100 chainrings) is also fantastic.
The argument that it makes the system lighter also feels like a stretch.
It's true that no bolts is lighter than four bolts, but the difference is miniscule – a set of four Shimano T30 chainring bolts weighs only 4.5g.
There are the threaded inserts on the outer chainring to consider too, but even so, we’re only talking about a few grams at worst.
Perhaps weight weenies will disagree, but unless you’re building a bike to win the UK national hill climb championships, I think every bike can afford an additional 10-20g to accommodate interchangeable chainrings.
Thread Mount is better, but it’s not the best of both worlds
With Thread Mount, SRAM effectively says riders get the best of both worlds – the lower weight of ditching bolts, plus the ability to change chainrings.
On paper, it looks as if it solves the problem, but in reality, its proprietary nature introduces another set of issues.
For a start, you’ll need SRAM’s proprietary tool (the SRAM Thread Mount Chainring Removal Tool) to remove and install a chainring, which costs £63 / $65 / €70 and can only be used for this one job.
That’s fine if you’re a tool fetishist like Oscar Huckle, but it can also just feel as though riders are being squeezed for yet more of their hard-earned cash.
Perhaps most obviously, though, while you can change chainrings, you’re stuck with only using SRAM’s own Thread Mount options.
For SRAM Red XPLR AXS, that means only five 1x chainring options from 38 to 46t (in 2t increments), with no third-party or 2x options as things stand.
While this likely won’t trouble many owners of the new 13-speed groupset, it means the new Red XPLR AXS power meter can’t be adapted easily for use on a road or time trial bike, or repurposed to work with a non-SRAM groupset, for example.
Of course, there’s no perfect power meter that can be used on all bikes and for all disciplines, but in this case the limitation isn’t inherent to power meter spiders in general – it’s something SRAM has designed in by choice.
As with the tool, I can see the potential benefits to SRAM here (it might sell more power meters if you need to buy a specific one for every type of bike you own) but the benefits for riders aren’t so obvious.
What was wrong with chainring bolts?
It’s frustrating to see SRAM highlighting the ability to change chainrings on the new Red XPLR AXS power meter as an exciting new feature, given it was SRAM that took away that ability in the first place.
It’s not as if Quarq power meters have always had this limitation. Prior to the launch of SRAM’s first AXS groupset (SRAM Red eTap AXS), the brand’s Red Quarq DZero power meter featured a five-bolt 110 BCD pattern with – you guessed it – interchangeable chainrings.
Thread Mount debuted on SRAM’s T-Type Eagle Transmission groupset, where you might think it was introduced due to the space limitations enforced by the smaller chainrings mountain bikes typically use (a smaller chainring necessitates a smaller BCD, which leaves less room for electronics in a power meter spider).
That wasn’t the case, though. The smallest chainring size available for the XX SL Eagle AXS Transmission power meter – 32t – is the same size as was available for SRAM’s previous XX1 Eagle power meter, which had a four-bolt 104 BCD with interchangeable chainrings.
Instead, SRAM says Thread Mount simply enabled it to “reduce weight without compromising reliability”. As already discussed, though, the weight savings are so negligible it isn’t worth it.
Just as standard bottle cages are perfect as they are, so is the practice of using standard fasteners to attach consumable parts such as chainrings.
Thread Mount is a slicker-looking design compared to exposed chainring bolts, which is important for high-end products. But hiding the chainring bolts, as Shimano does on its HollowGlide chainrings, achieves a similar effect without any loss of functionality.
It’s also clear SRAM knows how to do this.
Its previous-generation Force eTap AXS power meter (the PM-FRC-D1) featured hidden chainring bolts, and its AXS Power Meter Spider (the PM-AXS-SPDR-D1) almost ticks every box, except for the fact it uses a non-standard four-bolt 107 BCD, which significantly reduces its chainring compatibility.
I’m all for innovations that make our lives or rides better – heck, I even believe press-fit bottom brackets are better than threaded ones. But if an ‘upgrade’ or new feature doesn’t offer any tangible benefits then it’s fair to ask what the point of it is, and what was wrong with the old way of doing things.
