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I'm looking into placing a power2max powermeter on my bike, which is full Ultegra equipped (R8000). Now, the chainline specs of the crankset from p2m are either 45mm or 46mm (depending on the brand of the cranks), whereas Shimano's FC-R8000 specs at 43.5mm.

Are there any issues in swapping the cranksets, or am I facing some trouble or sketchy adjustments?

  • Something sounds off, 43.5mm is standard for road double. What p2m crankset are you looking at? – Rider_X Mar 27 '19 at 20:35
  • Which P2M crank are you looking at ? – Argenti Apparatus Mar 27 '19 at 20:38
  • I would be interested in the cheapest option, which is the FSA gossamer option. The axle diameter is 24mm and Q factor 146mm match my BB, it’s just the chain line that differs. The Rotor 3D24 is explicitly stated to be Shimano compatible on their site, but the chainline is also 45mm and Q factor is 147mm. It comes 150€ more expensive as well. I asked them for clear confirmation, but I’d rather double cross information. – Rwanou Mar 27 '19 at 21:08
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    Be careful with FSA-based cranksets. I have an FSA-based SRM, and the doggone thing has a 24.07 mm diameter spindle instead of the standard 24 mm. And FSA's 24.07 mm bottom brackets don't last long at all. It's also nowhere near as stiff nor does it shift anywhere near as well as a Campagnolo Record or Shimano Ultegra or DuraAce crankset. And when you're spending that much money on a crankset... – Andrew Henle Mar 28 '19 at 10:12
  • According to p2m support, only Rotor 3D24 and ALDHU 24 are compatible with existing Shimano components. Aldhu specs the chainline to 43.5mm (same as Ultegra R8000) whereas 3D specs to 45mm. Apparently Aldhu is specifically announced as Hollowtech II compatible. I wonder how the 1.5mm difference of chainline for 3D cranks affects the shifting performances on full Shimano drivetrains. It might not be noticeable as Nathan explains in the answer for longer chainstay lengths. – Rwanou Mar 28 '19 at 11:11
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Yes, that's enough to create situations where you may have chain rub that can't be adjusted out in some additional gears on most road bikes. There are other factors, namely chainstay length - bikes with "pushed" chainstay lengths, i.e. 405mm-ish or less, are notably more finicky about this kind of thing.

How important this is depends on your riding habits.

It sounds like you're looking at a power crank with a chainline that's either oriented more towards a road disc rear end (135mm as opposed to 130) or trying to do both with only one product.

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  • When you say “road disc rear end” are you talking about disc brake wheels vs rim brakes? I’m running disc brakes, so that can affect the chainline if I understand you right. – Rwanou Mar 27 '19 at 21:20
  • Yes. You should measure your existing rear chainline. – Nathan Knutson Mar 27 '19 at 22:02

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