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.

i have a very cheap crank and square taper botom bracket on one of my bikes. i'm not a particularly strong rider, but notice the chain rubbing on the front der. some times when I really put everything I have into it while on the big ring. Can't say if it's the arms, rings or BB spindle that are flexing. Plus I can't say it affects 'efficiency' at all. But it's true, my other 'decent' cranks (Tiagara, Deore level and above) with modern-er BBs never do this.

The FSA-unbranded OEM supplied crankset that came with my bike, complete with FSA-unbranded rings, was downright noodly. The big ring would flex sufficiently on the downstroke as to make the chain go tck-tck-tck-tck when pedaling while standing. Stiffer rings (Praxis) fixed that, but I could still feel arm flex. The rest of the crankset got replaced with the el-cheapo Shimano CX50, and the difference was immediate.

So if you've got really really cheap OEM cranks, an upgrade can help. If you have anything name-branded or series (i.e. Shimano 5700, 5800, etc.) you'll probably never notice a difference.

Thanks for the input fellas. It kind of confirms my suspicions. Coincidentally, I was curious about this topic and after initiating this thread I performed a paraphrased search into Google resulting in many a similar question asked as mine. The fellow I have been talking with about his XT crankset is probably under the influence of a subjective psychosomatic effect. I didn't want this thread to get the lockdown like the other one I started about the feel of steel vs titanium. We could probably wrap it up here... tnxs.

I'd say it's some part of the frame flexing. Happens to me too when I wind it up.

I don't think so. This is a quality aluminum frame - Jamis's best aluminum cross frame about 10 years ago, a very nice, stiff frame. I had a good crank on it (Ultegra 6503 with Octalink BB) at first and the change was obvious when I switched to the cheap crank with square taper BB, but not before.

I bought the very low grade (cheap), used triple with the square taper BB to try out lower gears than my Ulgegra (46...26 vs 53...30) just to try it, thinking if I liked the gearing for hilly commuting w/ weight, I'd upgrade. I noticed the flexiness on the first ride and intended to upgrade asap, but that was 2 years ago! It doesn't bother me that much, and probably the aesthetics of the crank on an otherwise Ultegra/105 bike is more of a concern (vanity, but not much).

I have a budget set, Acera or summat on my touring bike, if I give them a hard time they flex a lot. Since I ride it loaded most of the time I tend to spin instead of stomp, so it doesn't matter.

If you are asking about current XT vs LX, I doubt you could tell. If you are comparing current XT to your old Sakae, I think you would notice a difference and not only in stiffness. Newer cranks shift better, are lighter and the Shimano external BB is soooo easy.

cold forged aluminum re aligns the grain structure of the metal, so its stronger than cast aluminum.

That question lies at the heart of a holy war. A bike's heart and soul are its frame. Nobody cares that much about cranks.

I doubt most put enough pressure on the crank arm to feel flex. But if you need to justify top of the line components, any reason is good enough. I for sure can't tell the difference between 105 and Red 22 at 200 watts...

I'm a crank fanboy.


Soon I am going to change the crank on my bike for two reasons.


1. I want a trouser guard
2. I don't like the look of my current crank(Acera Triple, Octalink)

Noticed a significant difference in stiffness and power transfer going from Al cranks to carbon fiber. So I say yes.

Agree, but does the stiffness (modulus of elasticity) change significantly?

Nooo... This is NOT a CF debate!! Don't start it please...

Who starting anything. I just gave an example from experience of lighter cranks that are stiffer.

I might be imagining it, but I believe that I can feel a significant difference between the different cranks on my bikes. The cranks that I perceive as stiffer feel much more efficient.

Honestly that's as good a reason as any.

I currently have an FSA Omega compact on a BB4000 and it flexes very noticeably. With that said, I"m almost 6' and 195lbs, and built like a sprinter. When I'm climbing hard or sprinting, it flexes a lot. I actually just today bought a lightly used Dura Ace 9000 mid compact crankset and new DA9000 BB and it is almost 300 grams lighter and noticeably stiffer, even in my hands. I can't wait to get it on the bike!

If by "wind it up" you mean spin at a high cadence, I would have to say I find the opposite to be true. I notice the flex the most under high torque situations, at lower cadence right after shifting before a sprint or when climbing. I had an el cheapo square taper crankset on my old single speed and I actually managed to bend the ring beyond repair from putting so much torque into it.

105 is in the realm of top line components in this day and age. And sure, nobody is flexing the crank at 200 watts, but when you can top 1000 or 1200 or more sprinting, you can absolutely feel it and hear it when the chain rubs the front DR.

Aesthetics aside, A bad crank is one that is damaged and so no Longer functions.

I went from OEM cranks and bottom bracket which came on a fixed gear bike to Dura Ace Octalink and could feel the difference in stiffness immediately. Much of that I attribute to the bottom bracket.



I have another bike which I just upgraded from 105 9-speed to 105 11-speed. I am an average rider and the newer 11 speed gear is not as stiff. It is noticeable when climbing.

you must be a stomper and a clyde like me. but the new 105 5800 11spd is VERY stiff and super nice. and for the price point it kills the market. I honestly don't know why you'd ride anything less if you were serious, and I've ridden everything from 5spd to 11spd this season alone. 105 5800 and up shimano is absolutely flawless, light, and stiff. if you don't like it, then personal preference is the only thing you have to fall back on. and FWIW, I personally HATE the sram double tap shift pattern, and the ergo of the hoods, and I know more than 1 rider who has thought their drivetrain was mal adjusted because the shifting is so counter intuitive and touchy.