For many, Omloop Het Nieuwsblad is the true curtain-raiser for the new road season. Lidl-Trek turned heads at this year’s race by running a 54T 1X chainring with the new SRAM Red XPLR full-mount rear derailleur and its 13-speed 10-46 cassette. Or, in other words, part gravel groupset, part road, with a large 1X chainring.
The speculation as to why they’d have run such a setup has been as wide as the cassette range itself, with everything from aero gains to improved chainline touted as marginal gains such a 1X setup offers. The problem is, for every potential gain such a system offers, there’s also a similar potential loss. But that’s not to say Lidl-Trek’s decision was a poor choice, just that the potential benefits vary per use case and may lie elsewhere. In fact, I’d argue that Lidl-Trek didn’t go far enough.
Road 1X chainlines: marginal gain, a myth, or both?
One of the most frequently cited benefits of 1X drivetrains is a "better" chainline. This is true in time trials, where gearing can be optimised for sustained high-speed efforts. In short, you can be pretty sure you’ll spend most of your time in one narrow range of the cassette. But in road racing, where riders use a much wider gear range, the chainline can only be optimal for a limited portion of the cassette.
Across varied terrain and the stochastic nature of a road racing peloton, a 1X drivetrain will inevitably force the rider into cross-chaining more often than a 2X system would.
However, pro riders don’t typically utilise their front shifting on a 2X system to optimise for chainline. They cross-chain frequently, in fact, as the on/off nature of racing makes constant front shifting impractical. So while in most race scenarios a 1X system technically forces more cross-chaining, in practical usage, it may not result in any significant increase in cross-chaining compared to how pros actually use their 2x chainrings.
That said, the extreme gears used (e.g., 54:46 climbing gear) of a 1x, will result in greater cross-chaining stress on the chain than a more regular, smaller combination of chainring and sprocket.
Drivetrain efficiency: Does bigger mean better?
Larger chainrings generally improve drivetrain efficiency by reducing chain articulation angles and tension, thereby lowering friction losses. Conversely, smaller sprockets increase articulation, leading to additional friction and efficiency losses. Thus, a larger chainring, which in turn forces the rider to use a larger rear sprocket to maintain the same gear ratio (not to mention the larger pulley wheels on the XPLR rear derailleur), should all combine to improve drivetrain efficiency. How much are we talking? I’ve not personally tested it, but I’ve heard estimates of a 0.3-watt saving for every single tooth increase in chainring size.
That’s a marginal gain, and makes sense in a time trial scenario where teams are now opting for chainrings as large as 68 teeth. However, getting back to our first point, these benefits are potentially not only lost but outweighed by the significant cross-chaining.
Again, there are a select few sprockets in the middle of the cassette which do produce an optimal, straight chainline with either a 1X or 2X setup, but again it’s at the outer edges of the sprocket range with a 1X where the larger chainring and cassette combination forces more extreme chain angles, potentially negating the gains.
Where the use of the XPLR components differs, though, is in that the cassette range also plays a role. Until recently, 1X setups, as often used by SRAM teams, were limited in chainring size by the cassette range. The much greater low-gear range of the SRAM XPLR 10-46 cassette now allows for a larger front chainring, which again theoretically improves drivetrain efficiency. That larger ring does come at the cost of more frequent cross-chaining (because a rider has to use gears further up the cassette), potentially offsetting any gains.
As an additional benefit to the XPLR system, the extra sprocket within that 13-speed cassette means a slight reduction in the extreme gear-to-gear jumps typically associated with such wide-range cassettes.
It’s all ifs and buts. Again, in an ideal scenario, pairing a larger chainring with larger cassette sprockets would be optimal, but in real-world racing, cross-chaining and frequent shifting demands could make a 2X drivetrain the more practical choice for varied terrain. As we also already pointed out, though, if the racers aren’t using the smaller chainring, then they are still experiencing similar cross-chaining issues with their 2X setups.
The only true answer is: “It depends,” like so much in the world of optimising racing setups.
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