smd4

Apparently for some people, any bike part that is black in color must be made of CF.

Polaris OBark

Shimano does not make carbon fiber cranks, crank-arms, etc.

The problem is galvanic corrosion: steel spindle attached to aluminum arms. If some water gets in there, or worse ... sweat, or salt water, you have a battery, and the aluminum oxidizes and degrades. This, combined with the two piece bonded (glued) construction, leads to these failures.

Hambini had a rant about this awhile back:

Eric F 

Add in curvy shapes, and it's a dead give-away for that new-fangled plastic stuff.

smd4

Curvy, black, and catastrophic failure. Has to be CF!

Eric F 

I need to check the cranks on my gravel bike (6800). Meanwhile, I can continue to pedal with confidence on the Campy Record, SRAM XX1, and FSA cranks on my other bikes - all CF!!

Polaris OBark

You probably won't see anything until it is too late. Have a look at the Hambini video. After the ranting, it gets informative.

It might be a good time to get a nice safe GRX crankset.


Ironically, if the CF crankarms were instead actual plastic, you would be safe from galvanic corrosion, since plastic is an insulator. Carbon Fiber, on the other hand, is a conductor, and has a redox potential. So you can still get galvanic corrosion with carbon fiber parts.

(Even if it was an insulator, I would still be afraid of CF crank-arms.)

Eric F 

Other than the inserts for pedals, BB spindle/chainring, the CF cranks that I've used - and continue to use - don't have sections bonded together, but are molded as one piece. IMO, crank arms are an excellent application for CF.

icemilkcoffee 

bikingshearer 

Yeah, you might want to have that one checked out.

terrymorse 

Shimano cranks are the first things I replace on a new bike, selling them as new "take of" to some other sucker.

Aluminum is not a great material for high stress, cyclically loaded structures. Making cranks two-piece and hollow only increases the risk of failure.

Maelochs

Yeah ... except it wasn't stress that killed them.

That is an excellent example of how smart people get information and completely ignore it, picking and choosing tiny bits to cobble together something which fits their a priori narrative to support their own ridiculous and unrealistic theories.

Those cranks did not fail due to stress ... they failed because they were not properly glued together, so that moisture could create a corrosive chemical reaction between steel and aluminum parts. This corrosive chemical reaction hastened the breakdown of the adhesive bonding the aluminum parts together. The glue is what failed ..... This has been explained repeatedly, in posts way before the recall was announced. In fact, pictures like the one above were posted years ago on a website which collected stories o crank failure ... which site was referenced here in an earlier thread (search and find.)

At no point did the aluminum crank fail because the intact crank was aluminum, and could not stand up to the stresses of being aluminum and being a bike crank. (If aluminum was not suitable for bike cranks the 105 cranks would also have been recalled. (https://handsonbike.blogspot.com/201...imano-105.html)

The cranks failed because the glue bonding the two sections together failed, and the remaining two parts, seperatley, could not function as a bicycle crank.

The All-Aluminum, one-piece, 105 cranks have No record of failure and are Not included in the recall.

This is a classic example of a smart person being deliberately stupid to support and inaccurate and dishonest theory. This is the same sort of lack of thinking or dishonest, actually psychotic (using information invented to replace actual information form reality) that allows people to hate CF ("Every CF frame and fork is a deadly accident waiting to happen," they have been saying for several decades, while the rest of us wait .... )

This is the kind of thinking that allows people to claim the Earth is flat and that technology doesn't work while driving computerized cars along routes suggested by GPS satellites while engaged in video-telephone calls with people in other countries,.
This si the kind of ridiculously pitiful failed thinking which is actually killing the human race.

Bravo.

smd4

Don't sugar-coat it, Maelochs. Tell us what you really think.

terrymorse 

What a load of nonsense!

Fatigue failure of solid aluminum cranks is a known phenomenon, and it has been happening since aluminum cranks were first made.

It does not take a leap of imagination to infer that a two part, hollow aluminum crank is even more susceptible to fatigue failure, whether or not this particular Shimano corporate announcement addressed a fatigue failure mode. There are many examples of Hollowtech cranks cracking, right around where stress concentration ought to be the highest.

Maelochs

Yeah ... you hate aluminum cranks, so you hate aluminum cranks.

As I noted ONLY the bonded aluminum cranks have been experiencing failures. None of the other Shimano Aluminum cranks have been failing .... the 105 cranks from the same two series (5800, 7000) are not even included in the recall because there are no reported failures.

Show us the data. Show the long list of Aluminum crank failures. We will wait.

And then ... list the ones from the past two decades. Because to propel who actually include some fact in their thinking, Al cranks work just fine and the technology has been solid (or hollow, single-piece) for decades.

Post your countervailing information please.

smd4

THAT'S IT! I'm swapping out my Dura Ace cranks for a steel one-piece!

terrymorse 

Funny, and it brings back a slightly amusing memory.

When I was growing up in my parents' bike shop, big, tall, and aggressive-riding Jobst Brandt was notorious for breaking his Campagnolo aluminum cranks. My dad stocked some steel Campy cranks just for Jobst, and that seemed to end his broken crank problem.

By the time I left for college, there was still an extra pair of steel Campy cranks in the shop's display case. I doubt they were ever sold to anyone else.

Eric F 

Good choice. I expect the weight of your sexy lightweight rig to double.

terrymorse 

As I noted, aluminum cranks of various designs and brands have had fatigue failures. Solid or hollow. A perfunctory web search will bring up several examples.

Fatigue failures are to be expected when you select a metal alloy with no fatigue limit, then subject it to cyclic stresses on every pedal revolution.

georges1

That is why I only swear by 7700 and 7800 Dura Ace since a long time

RCMoeur 

Jim Elliott (who raced RAAM in the 80s and rode a 70 cm frame) reportedly broke several Campagnolo cranks.

RCMoeur 

Mix up some JB Weld and that'll be fine.

Eric F 

Maybe that's what Shimano should have used to start with.

seypat

What's going on with the DT? Looks a little rusty.

Germany_chris

I have a set of these and they would look silly on a modern carbon or aluminum bike. The same applies to my square taper WI and TA Carminas.

Maelochs

Aluminum cranks have been working wonderfully for decades .... if 25 years ado some cranks were not sufficiently well-made as to withstand unusual amounts of force .... whatever. In the past 25 years aluminum cranks have been normal and perfectly functional.

As evidence I put forth the fact that even someone trying to prove the opposite could not list a single major mass recall of aluminum cranks withing the past two decades.

Seems to me the tech is working.

I am not interested in Luddites ord conspiracy theorists ... refuting them is pointless. Let them ride their Flat Earth where there are no satellites (but GPS still works) and NASA faked the Moon landing and all their steel cranks ... i simply do not care.