The SRAM Rival AXS power meter upgrade adds power measurement to an existing AXS bike with just a left crank arm and spindle, so the right arm, bottom bracket, spider, and chainrings all stay exactly as they are. Quarq's spindle-based DUB-PWR unit measures left-side power and calculates total wattage from it, a proven method rather than a stripped-down compromise. It adds less than 40 grams over a standard crankset, keeping the upgrade close to invisible on the bike. What Our Gearhead(R) Experts Are Saying:"I've trained off these numbers for a full season and never once second-guessed them against a lab test or a friend's dual-sided setup. Left-side power from Quarq reads as real data, not an estimate I have to mentally discount."