Shimano Dura-Ace R9200 Groupset
Bringing an extra level of refinement to what was already a brilliant design, the shifting has somehow become smoother, the braking is marginally better, and the system as a whole is far more user-friendly. It might have taken Shimano a few years to catch up with the wireless competition, but it's done it very well.
Shimano has given the new groupset an extra sprocket while also taking away some of the wires, improving the connectivity and making the shifting smoother.
The front derailleur shows the biggest improvement in performance. The motor has been made stronger and the result is smooth movement of the chain between the chainrings, even under some pretty significant load. Changing when accelerating caused no issues.
The rear derailleur is also smoother across the cassette's range. Shimano was claiming a speed increase, but it is so hard to discern an incremental gain. What reviewer Liam Cahill could notice, again, was how good the shifting is under load. Want to flick up through the gears while smashing on the pedals? No problem. Need to bail out after a 40-second hill repeat? Easy.
The drivetrain runs a fair bit quieter than it used to, and while a lot of this can be attributed to the chain that Shimano has taken from its mountain bike groupsets, you'll get different results based on chain lube used and the quality of your indexing.
You can really feather the brakes when you need to be careful with your braking power, Liam loves what Shimano has done with the addition of the ServoWave tech from the GRX and mountain bike groupsets. There is now a smaller amount of lever travel before the pads contact the rotor, and as you pull the lever the power progresses with the lever travel - the feeling at the fingertips is brilliant.
The best gets a bit better, it's as simple as that.