Special Guest 4iiii’s Scott Cooper joins the team to discuss all things power meters, including how power meters are made, calibration, and what the future of power meters may look like. Tune in to hear Scott’s insights in episode 229 of the Ask a Cycling Coach Podcast!
I will admit I haven’t listened yet, so don’t know if this was talked about or not: any comment from 4iiii on the purported underlying power data unreliability for the right side given the current Shimano asymmetric crank arm design?
My 4iiii single side shimano XT on my hardtail is the best power meter I have owned. Fitted it and forgot it. calibrate every ride and change the battery as required
Previous PMs:
Stages gen 1 (x2) - battery killers
Powertap P1 - good but died, and would occasionally wander off
Vector 3 (still in use on road bike) - least said the better
My journey with my 4iiii is mixed: after (as best as I can tell correct) installation with bolts torqued to specs, power readings were high. After a few weeks, readings were normal, though. However, the battery unexpectedly failed before one race (going from 70 % to 0 % over night) and the Bluetooth connection crapped out in the beginning of a hill climb race (although perhaps iOS 13 is to blame here). Oh, and the app drives me nuts: they want to force me to create an account just so that I can update the firmware over my phone.
Nevertheless, given the price, I am mostly a happy customer.
Interesting thought. By that I guess you mean that everything is housed within the crank arm on the drive side prior to bonding the two halves of the arm together. This will allow the strain gauges to be moved much further away from the spider, which is what is causing the problems in the first place. Currently the sensor is very close to the spider because of the chainrings.
Following on the topic of zero offset, I’m wondering if anyone can help me. I have an older PowerTap G3 on a track bike. Worked great for several years then started reading too high. Only briefly did I entertain the idea that my FTP jumped to 400W. If I ride it on the trainer and do the zero offset “calibration” in the TR app, it’s all good. But as soon as I ride on the track, it’s too high. I can’t see any way to do a zero offset through my Wahoo head unit or the PowerTap app on my phone. Customer support at Quarq says there is no way to do zero offset and I need to send it to factory for calibration. I’m sceptical about this because the TR zero offset works. Any suggestions?
The way I understand Wakeham’s analysis, this would not eliminate the problem as other problems crop up once you move the strain gauges farther away from the crank.
I think what @gpl is something like Rotor’s InPower power meter, where the strain gauges are affixed to the crank spindle.
Have a look at Keith Wakeham’s video that @Aseldi posted in this thread. He compares four different scenarios, 2 cases with Shimano-style, asymmetric cranks and 2 cases with symmetric, SRAM-style cranks. The two variations differ by the distance to the crank axle.
Specifically, go to 14:00 of the video: while there is an improvement for the calibration curve, it is worse for the axial contribution which leads to manufacturers “fudging” with the curve. Or do you understand that differently?
