Originally Posted by
prairiepedaler
Hi, I was talking with a fellow today about his Shimano XT cranks. He'd mentioned that crank arm flex is something that is minimized in much better cranks sets (i.e. they're stiffer) and thus better force transfer to the chain. Better transfer is good, but can a lighter crankset (i.e. XT vs. LX etc) offer that much more benefit other than weight? i know they lighten you're pocketbook but is this apparent reduction flex effect perceptable to most riders? He says he notices it. Some double blind, randomized, placebo controlled testing might be in order. Are the XT cranks that much stiffer than the old Sakae I have on my pack mule?
The stiffer cranksets aren't stiffer because they're light, they're stiffer because they use wider arm cross-sections. They're able to be lightweight because of advancements in material science and manufacturing methods.
As far as whether it matters: not really. The stiff stuff is stiffer, but you're not losing any significant amount of power. Even "noodly" cranks don't actually flex that much, and even if they did, there's a relevant question as to whether that flex would waste much energy; it's not going to be dampened much in aluminum, and for all the screaming that manufacturers have done about benefits of stiffer cranks and BB regions over the last several decades, they haven't published anything to show that there's actually meaningful losses either in the flexing of the bike or due to kick-back into the leg.