New Sram Red eTap AXS group

[yinzerniner]

Originally Posted by Mark McM

That's not really true at all. SRAM is claiming that this new gearing provides as wider or wider gear range, but with tighter spacing between gears - this is a physical impossibility. In fact, if you look closer, you'll find the opposite is true.

Let's compare SRAM's 10-33 12spd cassette (their widest range) with an 11-34 12 speed cassette. The 10-33 has a gearing range of 330% range, while the 11-34 has a gearing range of only 309%. SRAM did this changed the sizes of the smallest and largest by only 1 tooth each, which makes it appear that the gearing size differences would remain constant. But what matters isn't the absolute number of teeth between gear sizes, the relative change in sprocket sizes. The 10-33 cassette has an average of 11.5% difference in gear jumps, while the 11-34 has a difference of only 10.8%.

But SRAM didn't just change the cassette, they also changed the front chainrings. And the major change was to decrease the size differential between chainrings. So, instead of the 50-34 as the smallest 'compact' chainrings, SRAM has 46-33. Let's take a look at these:
When combined with 50-34 chainrings, an 11-34 cassette gives a high ratio of 4.54:1 and low ratio of 1:1. For SRAM, the 46-33 chainrings when combined with a 10-33 cassette gives a high ratio of 4.60:1 and a low ratio of 1:1. So both give the same low ratio, and nearly the same high ratio. So SRAM doesn't really give a wider total gear range. But while SRAM has a smaller jump between front chainrings, they have bigger jumps between rear sprockets. Since most people shift the rear more often the front, for most practical purposes SRAM has bigger jumps between gears, without any real increase in gearing range.

I'm sure there was a pretty big business decision to go to the XDr hub design instead of just sticking with 11 as the smallest sprocket. They probably could have accomplished the exact same goals in terms of drivetrain efficiency, cadence and range but it would have been more expensive on the manufacturing side since they'd have to make larger cassettes and chainrings, which leads to more material waste as both have a lot of one-piece construction. Also, the don't get to sell new freehubs to everyone.

That being said I'm also sure that the 2x FD with a clutch / damper RD works better with the smaller 13t max jumps at the front, so combining the improved FD shifting (which has always been a SRAM weakpoint) with the economic concerns it was a no-brainer from a business standpoint.

Originally Posted by Mark McM

They can claim all kinds of things, that doesn't make them true. It has been shown in many times and in many tests that smaller sprockets/chainrings have more losses. Given that this has been well established, it is up to SRAM to provide evidence of their claims, and they have not.

Addressed this in an earlier post, as the "larger sprockets/chainrings are more efficient" argument isn't necessarily true, just that all the test done with existing equipment shows that with that equipment the larger items test better. However that testing was done with non-clutch/damper RDs, current cassettes and typical 11s chains. All three of those variables have been changed with the new AXS group.

Not saying that it won't bear out that larger won't be better in terms of efficiency with AXS, just that it hasn't been tested yet.