In an interesting bit of cooperation between a representative of the "gear reviewer" community and the nerdy, techy community, Shane Miller (GP Lama, gplama here) and Keith Wakeham (initial developer of the 4iiii power meter, kwakeham here) have come up with a convincing case that the asymmetric nature of the newer Shimano 4-bolt cranksets wreaks havoc on the accuracy of crank based powermeters using those cranksets.
Both have videos and write-ups on their findings:
The tl;dr of it is that due to the asymmetric nature of the 4-bolt pattern used by Shimano, the forces going through the chainring bolts are, well, asymmetric. This causes inaccuracies most easily seen in steady-state efforts (ERG or outside up steady gradients).
My takeaway: If you're in the market for a crank based powermeter, pick an FSA or Rotor crank, or another cranks that uses the traditional 5-bolt pattern.
Citizen of the world, former drunkard. Resident Traumatic Brain Injury advocate.
Both have videos and write-ups on their findings:
- GPLama (read and watch this if you don't know what 'Finite Element Software' means):
https://www.youtube.com/watch?v=M0tWTUwpt1k
https://gplama.com/...ankset-power-meters/ - Keith Wakeham (read and watch this if you want to see a mechanical engineer at work):
https://www.youtube.com/watch?v=Zwt4Bx_FGHU
https://titanlab.co/...rank-design-blunder/
The tl;dr of it is that due to the asymmetric nature of the 4-bolt pattern used by Shimano, the forces going through the chainring bolts are, well, asymmetric. This causes inaccuracies most easily seen in steady-state efforts (ERG or outside up steady gradients).
My takeaway: If you're in the market for a crank based powermeter, pick an FSA or Rotor crank, or another cranks that uses the traditional 5-bolt pattern.
Citizen of the world, former drunkard. Resident Traumatic Brain Injury advocate.