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by James Huang
January 20, 2020
Photography by Dave Rome
One of the key features of the current SRAM Red eTap AXS wireless electronic groupset is a 10-tooth sprocket on the cassette, which provides a generous amount of range without having to resort to very large sprockets at the other end. That 10-tooth sprocket also allows for smaller chainrings up front – typically 50/37T for SRAM-sponsored teams – which not only reduces the weight a bit, but also improves shifting performance thanks to the smaller gap between the inner and outer rings.
At the Santos Tour Down Under, though, Trek-Segafredo is taking a different approach. Instead of the 50/37T chainrings that would normally be used with SRAM Red eTap AXS in this environment, Trek-Segafredo is using 54/41T ones.
Commonly, SRAM-sponsored teams are running 10-28T and 10-33T cassettes, which would translate to 11-31T and 11-36T cassettes on a more conventional drivetrain with standard-sized chainrings. That sort of scenario would obviously make for a heavier cassette, though, and there’d also be additional weight from the longer chains and longer pulley cages that would have to go with them.
In terms of saving weight, then, SRAM’s 10-tooth sprockets and correspondingly smaller chainrings make a lot of sense. But from a drivetrain friction perspective, those smaller sprockets aren’t nearly as appealing. According to testing done for Velonews by CeramicSpeed, a 48x10T combination generates a substantial six watts more drag than the equivalent 53x11T at a fairly moderate 250-watt input. And given that drivetrain friction increases progressively with input power — not linearly — those losses would only be more dramatically magnified at typical WorldTour power outputs.
SRAM’s current Red eTap AXS drivetrain relies heavily on a 10-tooth cassette sprocket so to as to provide a wide gearing range without having to resort to a bigger cassette overall. However, the additional friction that comes with that smaller sprocket – and the smaller chainrings that go with it – seem to be giving some teams and riders pause.
Moreover, moving between the 10T and 11T sprockets represents either a 9% or 10% jump (depending on how you prefer to calculate it) in gear ratio, whereas a more conventional cassette would be more like 8% or 9%.
Neither of those are tremendously significant to average riders, of course, and regardless of who’s putting out the power, weight isn’t as big a factor as it’s long been believed to be when it comes to going faster. However, a growing body of data is demonstrating that drivetrain friction is a surprisingly significant factor in terms of overall performance, and in this modern age of marginal gains, that sort of thing is a very big deal when it comes to racing at the WorldTour level.
Every bike we inspected from the Trek-Segafredo team was fitted with special 54/41-tooth chainrings instead of the usual 50/37-tooth ones available at retail.
We noticed at last year’s Tour de France that Trek-Segafredo riders were using specially made individual chainrings on their SRAM Red cranksets that were larger than what’s normally available to everyday consumers, and things appear to have progressed further still, with SRAM now providing the team with oversized double chainrings using the same one-piece machined construction as production cranksets.
Larger-than-normal chainrings are nothing new to top-tier men’s road racing, of course, but Trek-Segafredo has been using them for everyday road events where unusually tall gears aren’t very useful. Consider this: Trek-Segafredo is still using the same 10-28T and 10-33T cassettes as usual, but that 54/10T top gear they have now is the equivalent of a truly massive 59/11T, which suggests that the team is running those bigger chainrings so that they can avoid using the 10T sprocket altogether.
Meanwhile, newly SRAM-sponsored team Movistar is using standard 50/37T chainrings at Tour Down Under.
“The chainring combo that some of the Trek-Segafredo riders are racing on is different than the 50-37 and 48-35 combos, but still has a 13T difference,” said SRAM global road communications manager Géraldine Bergeron when I asked about the reasoning behind the team’s chainring choices. “This specific chainring combo is part of our product development, and is also to give to some of the WorldTour riders, who have specific needs, extra gearing options.”
Take that as you will.