- The Q-factor is unusually large ~210-270mm, depending on who you ask and depending on the bottom bracket width.
- The offsets are asymetric due to the reduction gear, which puts the midpoint of the pedals to the right of the bike frame. This shift is ~18-30mm to the right (depending on who you ask)
- The length of 170mm is generally only suitable for non-e-bikes with tall on-road riders. The crank should be a shorter length for on-road riders shorter than 5'9", even shorter for off-road riders (who need clearance), and the motor makes the leverage of 170mm less important (and I'm not sure the leverage makes any difference at all on a geared bike in the first place anyway -- i.e. just as we know that increasing wheel size does not increase efficiency as gears render it moot). The stock size is therefore only optimum for a small minority of riders.
A problem remains: if there is zero angle on the right crank arm, and the left crank arm has the same length as the right (170mm) but it's angled (thus asymetric), then the left crank arm's lowest position will be higher than the right crank arm's lowest position. Time for a picture:
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/ | / | / | left crank arm => / | <= right crank arm ^ frame center
Is my math correct? Are my inputs correct?
I realize that the body adjusts amazingly well, and that riders don't even notice a significant problem with the factory cranks, but if someone is going to do custom mods anyway they might as well get it as close to perfect as there are available parts for.
I would appreciate it if someone could revew these numbers, so I don't end up creating more awkwardness than I'm starting with.