Crank arm length

[rydabent]

The length of crank arms seem to be somewhat problematic when you think about it. As we get older, we are told we should go to shorter crank arms, so we dont have to flex legs and hips so much. But OTOH, and we get older, we lose some strength, and shorter crank arms mean less torque. So what is the consensus here, short or long, for us old guys?

[Painkiller]

all personal, with your description it sounds like giving in and loss of range of motion if going for shorter crank arms for that reason. Who knows?

[meamoantonio]

A decent bike fit would really do the trick here, there's a lot of factors to consider

[Puppershep]

the torque/LEVERAGE increase mentioned earlier also requires added input to utilize...

too long of crank arms increases foot velocity for any given cadence (RPM)... it also ups the STRAIN on Knee and hip joints.

the trick is finding the PROPER CRANK LENGTH for you and your chosen riding style... most older folks aren't looking to win any races in the first twenty feet... BMX cranks are longer for that reason.,.. they Need to get out front or be left behind... most BMX bikes never race, and would be much more fun to ride with a 170 instead of 180 and 185mm cranksets.
personally, i'm now riding a 54cm road frame, and used to ride 56cm...
similarly, i'm now using a 165mm crankset, and wish i'd switched from 170mm a decade ago.
i use a bit higher cadence than most, and the shorter stroke makes that easier.

[ReapThaWhirlwind]

This is true, but there are bigger factors that contribute to your points of interest.

A shorter crank is better for spinning and maintaining momentum. It requires more direct force from your body, because there's less leverage. This will add more tension on your knees, and will make grinding in top gears more stressful on the body.

A longer crank gives you more leverage, which makes accelerating easier, and only stresses the body (in its own special way) when the length is so much greater that your connective tissues are greatly exerted by the stretch they experience.

In addition to this though, there's an even bigger contributing factor to these stresses, and that's the repetition of stroking the dead space on a circular chainring. The stroke on the dead space exponentially accentuates both these stresses (having to stretch out to reach—and also having to crunch down to apply more direct power transfer). You can adjust this factor by using an oval ring instead. Oval chainrings significantly lessen the dead space in the pedal stroke, making the power transfer on the body more fluid and continuous. The greater continuous motion alleviates the stressor factors of stop-and-go contractile activation that your muscles, joints, and connective tissues experience between the stroke the deadspace and the active zone.

Now, there is other big factor to note here, and that is the size of the chainring. Because shorter cranks offer greater power transfer dynamics, they compliment smaller chainrings better. An individual sticking to a round ring wouldn't want to just switch over to a shorter crankarm, but they would also want to step down a size or two on their chainring as well. This creates a more complimentary ratio for the dynamic factors at play.

Smaller chainrings mean more contact surface on the chain, so grinding will still be grinding. And if you insist on grinding in a larger ring, or require it for your style of riding, what you really want to do is switch to an oval chainring instead of adjusting your crankarm length.