mkadam68

Background: I'm a clydesdale who races. I put out alot of power, and easily finish with the pack in local (SoCal) crit races (Pro/1-3 and Masters levels). My training regimen is such that I am in a big gear lots of the time. I use a 55x39/11x23 gearing.

About 3-4 years ago, I purchased a crank-based power meter (I won't say which company at this time) from a former Continental Pro. It came with carbon cranks. One would think that if anyone abused them, it would be a pro racer.

About 2 years ago (prior to my big gear training), I noticed the carbon layers, near the hole where the pedal spindle threads in, were peeling off. I contacted the manufacturer, and even though I had bought them 2nd hand, they sent me out a new crank/power meter (upgraded version!).

Now just yesterday, I noticed this (new & upgraded) crankset was doing the same thing. I've contacted manufacturer, and will be talking with them about their ideas, but I thought I'd try feedback from the BF community.

6+ years ago, I also had an Ultegra crank break right at the pedal spindle hole, tossing me onto the ground as I went through a corner. (The LBS owner looked at it and saw some dark greasy/oily discoloration along the break, so assumed it had cracked awhile before actually breaking, letting in road dirt.)


So now I have to assume it's me, perhaps a weird ankle/foot angle or awkward pedaling technique or something. I've checked with my coach and other students of his (national/international level track sprinters) and they've never heard/seen such a thing.

I'm curious

• If anyone has seen this type of behavior before, and
• What do you think is causing it?

pdedes

Two seasons ago, I broke two nds crank arms. A shimano da7800 stripped the splines, SRAM red cracked the aluminum insert that mates to the ds crank arm (bb30). I also can put out gobs of power and am not svelte.

hueyhoolihan

looking at the construction, compared to an all alloy crank, i'm surprised it doesn't happen more often. i'm serious. might want to ask on the track forum .

don't have to answer, but how much do you weigh? no cheating...

LifeCycles

I've never seen it but I don't think it's strange as there's often times more wear in that spot than there is any other place on a crank arm. A friend of mine has cut through the rubber bands on his Garmin cadence sensor from his shoes rubbing through it. Maybe you should try moving your cleat towards the inside of your foot so that your shoes is further away from the crank arm.

big john

The problem is, you're a beast.

TrojanHorse

If you're THAT big and THAT strong (and I say this with respect, not mockery!) you may need to treat crank arms as consumables. Unfortunately, the power meter versions are 2x-4x as expensive as the bare cranks, so that's not a pleasant thought.

If you've got clipless pedals, I can't imagine you could have a significantly awkward pedaling angle on your feet or your shoes would pop out.

Sounds like your power meter company is a stand up operation, so kudos to them for taking care of your issue.

GuitarBob

I've not seen that either, but I wonder if your natural foot position and rotation has you pressing more than average on the outside of the pedal rather than in the center -- I do that, at least a little. I'm thinking of supination:



Anyway, if you do, you are creating a slightly longer lever arm than average, which increases the force applied to the pedal threads. That would be no issue for many of us, but given your size and power, it might be.

Then again, it might be complete rubbish!

gsa103

Pro-racers put down a ton of power, but usually at high RPM, they also are usually light. A strong clyde could easily make more torque, that many pros. It's torque that breaks stuff not power. An over-tightened pedal might be able to crack the carbon like that.

mkadam68

Really? I hadn't thought of that. Would the over-tightened pedal just pinch the carbon, causing a weak spot? (But the pedal threads into an aluminum--I'm assuming--insert within the carbon arm.)

caloso

Did you use a pedal washer? I think Quarq/SRAM specifies that.

mkadam68

I did not. They haven't asked about that, either.

I thought of that also, but don't know how that would have made a difference. Wouldn't it have effectively made a longer pedal spindle, increasing the leverage against the crankarm, making it a faster failure?

MikeyBoyAz

I would suggest the alternate also, if the threads were NOT flush and tight, the torque would be uneven on the threads rather than loading the crown against the crank arm. The continual uneven loading could cause accelerated wear on the threads and lead to failure.