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Newbie question here.
Im looking to replace my left crank arm with 4IIII PRECISION SHIMANO R7000 POWER METER. The thing is I dont know if is compatible.... but Im not sure I know what model of crank I have. I have a tiagra2018, and I attached a image of my back crank arm.This link is the powermeter arm


478551
E59D274E-2EFD-4708-99B3-ED5D17118E70.jpeg
 

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The compatibility is with the bottom bracket axle, not with the crank arm. I'm guessing (and very much only guessing) that your Tiagra crank is either square taper or one of the Shimano splined units. Pull off the dust cap on the crank arm where it attaches to the BB axle and see what you can see. Snap an in-focus picture if you can and share that. Others here probably know what the BB standard is for that crank.
 

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I would say they are not direct replacements:

24mm Spindle Crank (Shimano HollowTech II, etc.):
24mm spindle crank
478561


22mm/24mm Spindle Cranks (SRAM / Truvativ GXP):
GXP spindle cranks
478560

Your Crank Spindle and Attachment:
Cranksets - Fsa Omega - Nelo's Cycles


I've got one of each on different bikes, but you might understand that I don't really want to take them apart again to compare. :)
 

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I would say they are not direct replacements:

24mm Spindle Crank (Shimano HollowTech II, etc.):
24mm spindle crank
View attachment 478561

22mm/24mm Spindle Cranks (SRAM / Truvativ GXP):
GXP spindle cranks
View attachment 478560
I've got one of each on different bikes, but you might understand that I don't really want to take them apart again to compare. :)
The FSA Omega Crankset I'm pretty sure is a MegaExo which is a 17 mm shaft diameter. The Shimano R8000 or for that matter the DuraAce or the 105 have a 24 mm crank shaft. The MegaEvo cranks from FSA are 30 mm shaft diameter. The Shimano 24 mm shaft is plenty rigid enough. And they are about the same weight as the FSA Gossamer. (aluminum with MegaEvo shaft). So, no, you can't put an FSA power meter onto the Shimano shaft. Moreover it is getting pretty hard to find MegaExo bearings. Rather than try to install a power meter onto a mixed shaft arrangement do the entire thing properly.
 

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He's asking only if the left Shimano crank will attach to the FSA axle (not asking about the axle in the BB), but you are correct that the splined shaft attachment between the crank arm to axle is very different between the two, and cannot be substituted.
 

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He's asking only if the left Shimano crank will attach to the FSA axle (not asking about the axle in the BB), but you are correct that the splined shaft attachment between the crank arm to axle is very different between the two, and cannot be substituted.
You cannot put a 17 mm left crank on a 24 mm shaft regardless of the splines.
 
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