I’ve used a Stages LR dura ace powermeter for several years without issues. Moved to shorter cranks and have been using a 4iii dual sided dura ace powermeter for the past several months as I couldn’t find a Stages LR in that crank length. I’m a bit frustrated with the number of dropouts I’m having with 4iii and thinking of moving back to Stages or a spider-based powermeter like Quarq or P2Max. I’ve read about the “inaccuracies” with Shimano based dual sided powermeters and can anecdotally relate - power is always lower when my left powermeter battery dies and I’m relying on just the right. My LR balance is also usually 55/45 which I read is common with Shimano but I don’t care about it so much as long as overall accuracy is ok.
I get there is concern with LR balance issues with shimano based dual sided powermeters. What about the overall accuracy of the powermeter? If that’s a concern, then I’m thinking of going spider-based powermeter.
I read your review and take it that the right PM reads low. What about the left? Does that mean the overall value reads low thus the concern with accuracy?
The left side is accurate. The problem arised because the right crankarm is asymmetric, and this asymmetry is hard, almost impossible to compensate for. This is not 4iii’s fault, it’s on Shimano. And it is shared by all right-side power meters based on modern DuraAce and Ultegra cranks, including Shimano’s own (courtesy of Pioneer).
Left usually tests within spec (also in the report published). To be blunt, don’t mess about with something you’re already questioning. There are a lot of great alternatives out there to choose from that work very well.
We get power meters because we hope they’ll help us answer hard questions that can’t be answered with a HRM or a speedometer or a stopwatch. When in that situation, trying to resolve a hard question, you don’t want the additional question, “Is this power meter right?” As long as there are alternatives available (and there are) why put yourself through that?
So do Shimano-based LR powermeters read lower? Or is it that they are less precise so you can’t depend on day to day consistency? I’m having trouble interpreting the said inaccuracies of the right sided crank.
Power meters based on the Dura Ace and Ultegra cranks are unpredictably accurate because of the right crank arm. That’s on top of any other any other problem you may be having, such as drop-outs, or in fact other inaccuracies because of the accelerometer-based cadence measurement. That is to say, crank-spider power meters may also have problems with drop-outs; or they may also have problems with cadence measurement – but they won’t have a problem caused by the Dura Ace or Ultegra right side crank design.
Thanks, everyone. I decided to go for a Quarq powermeter with Shimano 9100 chainrings. Hoping this will solve my drop out issues and also some peace of mind given the concerns about accuracy with Shimano-based powermeters.