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Originally Posted by Clean39T
The new arms are shaped differently and the new PM appears to basically be an SRM PM-10 .. a more advanced version with more strain gauges .. necessary? Of course not .. cool tech? Yep. And maybe it trickles down over time - alongside more crank lengths for those that want such things.
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Oddly, only the new left (NDS) SR WRL power meter crank appears to be shaped differently, the right (DS) crank appears to have the shape as previously used by other power meters. And that actually makes sense, as only the right crank needs to be special to accommodate the power meter spider. This points to the SR WRL power meter cranks being a bit of a hodge-podge, with a left crank specific to the SR WRL cranksets, but borrowing a right arm from an older OEM product.
As far as more strain gauges? That's not clear either. From the Bike Rumor article:
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Those Wheatstone bridges are a bit unique in that the most accurate in-arm power meters (E.g. Infocrank) tend to use 1 Wheatstone bridge per arm with 4 strain gauges to ensure accuracy & temperature compensation. The most accurate spider power meters (E.g. SRM) tend to have 1 or 2 Wheatstone bridges per arm with 4 strain gauges each to ensure accuracy. Campy has 4 Wheatstone bridges placed around the spider (presumably at each arm connecting to the chainrings) with 16 strain gauges in total.
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So, "the most accurate spider power meters (E.g. SRM) tend to have 1 or 2 Wheatsone bridges per arm with 4 strain gauges each", which means that (4 arms) x (1 or 2 bridges per arm) x (4 strain gauges each) = 16 to 32 strain gauges. It further says, "Campy has 4 Wheatstone bridges placed around the spider (presumably at each arm connecting to the chainrings) with 16 strain gauges in total," or in other words, the same or fewer bridges and strain gauges as other power meter spiders. Campagnolo claims +/-1% accuracy, but so do SRM and Power2Max.