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Clydesdales/Athenas (200+ lb / 91+ kg) Looking to lose that spare tire? Ideal weight 200+? Frustrated being a large cyclist in a sport geared for the ultra-light? Learn about the bikes and parts that can take the abuse of a heavier cyclist, how to keep your body going while losing the weight, and get support from others who've been successful.

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Old 02-21-09, 10:05 PM   #1
jh3xp
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Carbon Crank??

Do you guys think carbon cranks would be okay for a clyde?

specifically 230 lbs and up.
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Old 02-22-09, 06:57 AM   #2
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I don't see the point in them for a clyde. They might be a few grams lighter then Ultegra, but at that weight it doesn't much matter. Why risk it?
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Old 02-22-09, 07:47 AM   #3
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I don't see the point in them for a clyde. They might be a few grams lighter then Ultegra, but at that weight it doesn't much matter. Why risk it?
That about sums it up for me, too. Though, for me, it's not a safety issue--it's a money issue Of course, last year I did break an Ultegra crank, so it can happen to any.

That said, the Campy cranks do look really nice (better than the FSA stuff, I think). Just not worth the $$$ for looks.
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Old 02-22-09, 09:20 AM   #4
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Carbon cranks, like all carbon stuff, are rather sensitive to everyday kind of "abuse" (scratches,...). I guess they only make sense for somebody actually racing and needing to shave a few grams off. Why else add a part to your bike that needs checking on, worrying, careful treatment ......
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Old 02-22-09, 10:57 AM   #5
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My Red gruppo came with a carbon crank. So far, it seems every bit as durable as the Ultegra SL crank it replaced. Looks snazzy, too!
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Old 02-22-09, 11:30 AM   #6
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Do you guys think carbon cranks would be okay for a clyde?

specifically 230 lbs and up.
Pros: makes rider plus bike some .01% lighter then metal crank.
Cons: expen$ive, when damaged is subject to sudden failure.

If I were getting a new bike and it came with a carbon crank, I wouldn't replace it with a metal one. until it fails. If replacing a metal crank, I wouldn't bother with the expense of putting on carbon.
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Old 02-22-09, 11:50 AM   #7
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My Fuji came with a FSA SL-K carbon crank. It was replaced by the LBS with Ultegra after 250 miles when the NDS crank arm became loose.
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Old 02-22-09, 05:19 PM   #8
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I also thinks it depends on the type of rider you are. You can be 230+ spinning away and that will probably keep the pressure on the crank low. If you are a masher then you will put more pressure on the crank and that could cause failure.
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Old 02-22-09, 05:37 PM   #9
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I also thinks it depends on the type of rider you are. You can be 230+ spinning away and that will probably keep the pressure on the crank low. If you are a masher then you will put more pressure on the crank and that could cause failure.
The strength to weight ratio on carbon fibre reinforced plastic, is actually quite high, it's not mashing that damages the crank, it's the fact that if the fibres get damaged the strength can drop considerably, quickly. If you look at a metal crank that has been ridden hard under street conditions, you will see the metal is all nicked and beaten, this kind of damage can break the carbon fibres. The best place for using CF cranks would probably be a velodrome or a street race where the street is well swept before hand, so you do not get damaged cranks.
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Old 02-23-09, 06:10 PM   #10
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The possibility of sudden failure is what worries me. Several years ago, a neighbor of mine was the lead engineer for an airplane company doing work on carbon for fuselages. Part of the testing included doing pressure/depressurization cycles to failure--cycle pressure in and out of the fuselage until something broke, replicating multiple takeoffs, flights and landings.
I can't remember the numbers, but say the standard aluminum fuselage would go 50,000 cycles. At 50,001 it might develop a leak, a little crack or just show visible signs of fatigue, but could be flown safely for a long time before it became unusable. The same thing in carbon might go half a million cycles, but at 500,001, without warning, it exploded into little pieces. Probably materials and techniques are better now, but still...
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Old 02-23-09, 06:17 PM   #11
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I'd never spend the money but one thing that would scare me would be the carbon taking hits by road debris. I have no proof of damge or failure stats but just seems logical. But then agin they do make CF mtb frames too. I woudn't though!
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Old 02-23-09, 06:26 PM   #12
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The possibility of sudden failure is what worries me. Several years ago, a neighbor of mine was the lead engineer for an airplane company doing work on carbon for fuselages. Part of the testing included doing pressure/depressurization cycles to failure--cycle pressure in and out of the fuselage until something broke, replicating multiple takeoffs, flights and landings.
I can't remember the numbers, but say the standard aluminum fuselage would go 50,000 cycles. At 50,001 it might develop a leak, a little crack or just show visible signs of fatigue, but could be flown safely for a long time before it became unusable. The same thing in carbon might go half a million cycles, but at 500,001, without warning, it exploded into little pieces. Probably materials and techniques are better now, but still...
I think the normal process in engineering would be to run the test about 1000 times, and if it always failed at 500,001 then you simply scrap it after 250,001 cycles and that would be safe. Figuring that an airplane might take off 10 times a day, at that rate, every day, it would be good for 68 years.... Problem with CF Is that in actual use, hitting a Canada goose and breaking a few fibres might cause a crash. I think the best durability for CF would be to make a CF part, then cover it with a very thin layer of AL or steel to protect the fibres. Would give you the strength of CF without the fragility.
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Old 02-23-09, 07:34 PM   #13
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If carbon fiber was as delicate as some of you seem to think, I can't imagine that anyone would be making anything out of it! Product liability lawyers would see to that, if nothing else.

As long as you don't load it improperly (e.g. use it as a crow bar) or damage a significant number of fibers, a carbon fiber crank will probably out-last an aluminum crank.
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Old 02-23-09, 08:18 PM   #14
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Carbon Crank?

The full carbon FSA Pro I have works for me and I'm 225.
But then..I don't stand on the cranks. I'm more into spinning to achieve.
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Old 02-23-09, 09:57 PM   #15
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The SRAM Red group is sweet. A friend of mine put it on his bike and he is a clyde, about 260 and has not had any issues and has about 3000 miles on it so far.
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Old 02-23-09, 10:25 PM   #16
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If carbon fiber was as delicate as some of you seem to think, I can't imagine that anyone would be making anything out of it! Product liability lawyers would see to that, if nothing else.

As long as you don't load it improperly (e.g. use it as a crow bar) or damage a significant number of fibers, a carbon fiber crank will probably out-last an aluminum crank.
Question is how many fibres need to be damaged, and how that will cause a failure. CF tends to fail suddenly, AL tends to tear over time, which one would you rather bet your dentists new Lexus on?
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Old 02-23-09, 11:46 PM   #17
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Question is how many fibres need to be damaged, and how that will cause a failure. CF tends to fail suddenly, AL tends to tear over time, which one would you rather bet your dentists new Lexus on?
Me? Obviously, I'd bet on carbon fiber. Certainly not Bontrager or Dura-Ace aluminum cranks
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