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Discussion Starter · #1 ·
A friend of mine broke his drive side crank yesterday. He is 230 pounds. The crank was Dura Ace, probably last years model. He was climbing a local hill and just snapped the thing clean off. about 4 inches towards the bottom bracket from the pedal. It ruined his ride.
What is the toughest crank set out there? Is titanium a better option than aluminum. I think at this point he doesn't care about weight. He just doesn't want to get stuck at the bottom of the mountain with only one side of his crankset working.
 

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... That is an unusual failure as DA cranks (at least back to the beginning of the 9 speed era) have been the standard by which others judge/compare their product lines.

Titanium is prolly unsuitable for a crankarm (depending on the alloy, titanium may have more flex within an application than aluminium... and it could be prohibitively expensive to manufacture when compared to Al or CF) and I'm unsure if anyone is making them in that material (aside from very limited/one-off offerings).

Aside from a manufacturing flaw (some problems in forging... or contamination in alloy) I'd call this a phreak incident.

Sound's like your friend stayed upright and suffered no other injuries?
 

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Agree with Akirasho. Cranks basically fail for two reasons only: faulty manufacturing or damage from use. The damage doesn't have to be much—a deeper surface scratch or an area of serious shoe rub is enough to start a crank on the road to failure. From the looks of the break surfaces, an expert can tell quickly whether the crank failed because a manufacturing problem or because of use damage.

I'd put my faith into another Dura-Ace crank. Titanium is not an option—it's not a good material choice for cranks.
 

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If it's a year old, he'll get a new one. (if he didn't break it in a crash)
Being able to tell the difference in stiffness in cranks from the major companies (Shimano/Campy) is a wet dream.
 

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Assuming it wasn't damaged in a crash, DA has a very good (3 year) warranty. Just have it warrantied and get another DA. The likelihood of a second failure is extremely low.
 

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wim said:
Agree with Akirasho. Cranks basically fail for two reasons only: faulty manufacturing or damage from use. The damage doesn't have to be much—a deeper surface scratch or an area of serious shoe rub is enough to start a crank on the road to failure. From the looks of the break surfaces, an expert can tell quickly whether the crank failed because a manufacturing problem or because of use damage.

I'd put my faith into another Dura-Ace crank. Titanium is not an option—it's not a good material choice for cranks.
Take a look at the inside of the broken crank arm to see if it was scored by rubbing against the front derailleur. A Dura Ace or Ultegra crank should be plenty strong unless it was somehow damaged.
 

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If you notice, there are no Shimano, of any modern (post 1996) Campy cranks, on this site.....(the old record cranks really sucked)
 

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MR_GRUMPY said:
If you notice, there are no Shimano, of any modern (post 1996) Campy cranks, on this site.....(the old record cranks really sucked)
Actually, there is a 7700 series Dura Ace crank. But it has been heavily abused based on the photos. Jobst Brandt claims to have broken DA cranks at the pedal threads, but I'm not sure what series. Seems Jobst can break anything, so I wouldn't place much stock in that as a quality indicator.
 

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I go 250-270 and have broken a DA crank twice. First time I bent the crank arm - same region it sounds like your friend's snapped. 2nd time I broke the spindle. Both times the vendor (SRM) repaired the crankset for free.

My view is as an "end of the bell curve" kinda guy I'm just going to do weird crap to bike equip.
 

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I have a 7410 DA crankset on my commuter. I bought it in 1995 and have put many tens of thousands of miles on it. It has rub marks and scratches and aftermarket rings. It has seen more abuse than any other crankset I own. Once a week I wipe down the frame and check everything including the crankset. If I ever suspected a crack I would replace it.

I broke a chunk out of a 7400 DA crankset at the pedal bolt hole about 15 years ago. I don't blame shimaNo, I blame me for being a criterium "pedal smacker". When the 7410 dies, I have a Record alloy waiting to replace it. I'll just have to send the PW bottom bracket back for a 102 spindle.
 

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Discussion Starter · #13 ·
Broken Crank

Here are a couple pics of the broken crank that made me start this thread. Apparently Shimano has a three year replacement policy on these cranks and this was just over three years old. So no new crank I guess.
 

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Even at 230lbs I bet he can't generate the forces a top rider can and they don't typically break DA cranks.

Hard to tell for sure but the black areas of the crack make me think that crack has been lurking for a while and he just finally snapped it on the latest ride. There definitely appear to be plenty of gouges and scratches for a 3 year old crank. Way more than my cranks ever get in more years than that. IMHO this one could have been avoided.
 

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BlackSteel said:
Here are a couple pics of the broken crank that made me start this thread. Apparently Shimano has a three year replacement policy on these cranks and this was just over three years old. So no new crank I guess.
That crank is a lot older than 3 years. It appears to be at least from the 9 speed generation, which puts it at 2002 or 2003 at the latest. (Not sure when DA went 10)

Anyway, I'm going to go check my cranks tomorrow. You guys got me spooked :D
 

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BlackSteel said:
A friend of mine broke his drive side crank yesterday. He is 230 pounds. The crank was Dura Ace, probably last years model. He was climbing a local hill and just snapped the thing clean off. about 4 inches towards the bottom bracket from the pedal. It ruined his ride.
What is the toughest crank set out there? Is titanium a better option than aluminum. I think at this point he doesn't care about weight. He just doesn't want to get stuck at the bottom of the mountain with only one side of his crankset working.
the consequences can be far worse...I broke one (an old Ofmega) while sprinting out of the saddle and hit the frame so hard I bent it, and hit the ground REALLY hard too...but fortunately no permanent damage to me. Long ago a coworker hit the top tube and lost a testicle, but don't know if equipment failure was the cause. Anyway, definitely worth researching, though as was said modern Shimano and Campy cranks are probably fine for big riders.
 

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Einstruzende said:
That crank is a lot older than 3 years. It appears to be at least from the 9 speed generation, which puts it at 2002 or 2003 at the latest. (Not sure when DA went 10)

Anyway, I'm going to go check my cranks tomorrow. You guys got me spooked :D

The chainring teeth are "sharkfinned" so they have a lot of miles. It really looks like the arm was cracked for a while before it snapped. I check mine weekly, but like previously posted, I have only broken one and I know the reason.
 

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Oh yeah, that's Aluminum fatigue...

No warnings, just gives out! It's rare but it happens with aluminum. Nothing you can do, it's not like it was a "bad crank" or anything else. If it passed QC which it did, any other DA crank would have done the same.

As for buying a stronger crank, errrr... I have no input as whatever you'll buy, if aluminum, will fatigue and fail eventually. Carbon will explode, and well everything else is iffy.
 

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Look at how dinged up that crank is. Any one of those gouges can create stress risers that will lead to it cracking like this. Too bad it broke, but it is obvious your friend does not care for his equipment at all. You have to take care of your stuff if you want it to take care of you.
 
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