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interesting conversation with a frame design engineer ...PART 2

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interesting conversation with a frame design engineer ...PART 2

Old 11-27-08, 09:02 AM
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bigtea
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interesting conversation with a frame design engineer ...PART 2

That thread devolved from the rational to the emotional in about six hours. Let me add some context to the conversation I had. Here is a copy/paste of the key point:

Yesterday he confirmed what I have believed for a while now: the market demand for increasingly lighter bikes has come at the cost of durability and useful life. In other words, generally speaking, a sub 900 gram CF frame will wear out much sooner and be more likely to fail than a heavier one.

We were discussing this in the context of the weight of non-professional cyclists compared to pros. In other words, the industry is selling a lot of ultralight carbon bikes used by pros to a much heavier consumer population. Let's be honest, few of us are in the 120-150lbs range yet we purchase sub 900gram frames as if we're one of the Schleck brothers.

To put this into perspective, of the top ten finishers in this year's Tour de France, Christian Vandevelde was the heaviest at 151.8 pounds. For American males between 20 and 30, 150 pounds is well below the 25th percentile of the population. Consider also that for American males age 40 the 50th percentile is 180 pounds.

There are many posts on BF that talk about the pursuit of the gossamer-weight bike, yet rarely does anyone question if that kind of bike is appropriate for their own weight.
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Old 11-27-08, 10:07 AM
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The desire to have the "best" plus rampant consumerism will enable manufacturers to sell these frames in perpetuity. Why can't bikes be disposable? Why do you hate America?
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Old 11-27-08, 10:10 AM
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Bikes are designed for both pro use and consumer use. There is a range with a recommended maximum rider weight for some manufacturers at 265 to 270 pounds. It is my understanding that under normal loading the lightweight versions of the same frame-set uses stronger carbon fiber or addition strategically placed carbon layups in critical areas with thinner carbon fiber in less strategic areas. The super lightweight frame-sets should be as strong as their cheaper cousins, however they are more expensive to make.
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Old 11-27-08, 10:37 AM
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Originally Posted by pharding View Post
Bikes are designed for both pro use and consumer use. There is a range with a recommended maximum rider weight for some manufacturers at 265 to 270 pounds. It is my understanding that under normal loading the lightweight versions of the same frame-set uses stronger carbon fiber or addition strategically placed carbon layups in critical areas with thinner carbon fiber in less strategic areas. The super lightweight frame-sets should be as strong as their cheaper cousins, however they are more expensive to make.
I think that is the very assumption in question.
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Old 11-27-08, 10:44 AM
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"There are many posts on BF that talk about the pursuit of the gossamer-weight bike, yet rarely does anyone question if that kind of bike is appropriate for their own weight."

If anyone ever spends much time on Peter White's website - especially with relation to heavyweights on lite wheels and race bikes - he has preached this for a very long time.
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Old 11-27-08, 10:49 AM
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Of course Peter white would say that in order to create a bigger market for his custom bikes. He is not an objective third party without a financial interest in the discussion.
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Old 11-27-08, 11:12 AM
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Originally Posted by Wanderer View Post
"There are many posts on BF that talk about the pursuit of the gossamer-weight bike, yet rarely does anyone question if that kind of bike is appropriate for their own weight."

If anyone ever spends much time on Peter White's website - especially with relation to heavyweights on lite wheels and race bikes - he has preached this for a very long time.
Do you have a URL or link for his website?
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Old 11-27-08, 11:22 AM
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Your argument shouldn't involve the weight of the riders, but how long these pros are actually riding these frames before getting brand new ones.. the answer? no longer than one year! pros only ride these feather light plastic babies for a year or less, and then they get brand new ones.. of course they are going to be a poor investment if you want to keep riding the same bike 8,000 mi a year for 5 years. in that time you'll probably drop or crash the thing and then it's toast.

this topic reminds me of how shimano says they COULD make their stuff as light as SRAM or Campy but they design their components to be a good investment to the consumer who wants to get 20,000 mi out of their parts without worrying about something disintegrating.. consumer and pro racer in mind.. why I like shimano.. but sad they went to carbon rear derailer just for the bling look.
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Old 11-27-08, 12:32 PM
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Nothing lasts forever- just ride it like you stole it till it breaks, then move on to the next one.
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Old 11-27-08, 12:58 PM
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Originally Posted by bigtea View Post
Do you have a URL or link for his website?
https://www.peterwhitecycles.com/
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Old 11-27-08, 01:50 PM
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Originally Posted by deadly downtube View Post
Your argument shouldn't involve the weight of the riders, but how long these pros are actually riding these frames before getting brand new ones.. the answer? no longer than one year! pros only ride these feather light plastic babies for a year or less, and then they get brand new ones.. of course they are going to be a poor investment if you want to keep riding the same bike 8,000 mi a year for 5 years. in that time you'll probably drop or crash the thing and then it's toast.

this topic reminds me of how shimano says they COULD make their stuff as light as SRAM or Campy but they design their components to be a good investment to the consumer who wants to get 20,000 mi out of their parts without worrying about something disintegrating.. consumer and pro racer in mind.. why I like shimano.. but sad they went to carbon rear derailer just for the bling look.
And what about the pros that put on 40,000 miles a year?
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Old 11-27-08, 01:54 PM
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Originally Posted by bigtea View Post
Do you have a URL or link for his website?
Here you go
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Old 11-27-08, 02:20 PM
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Originally Posted by the_mac View Post
And what about the pros that put on 40,000 miles a year?
Which pros are you referring to? the 140 pound pros or the 200 pound pros?
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Old 11-27-08, 02:36 PM
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OP...you need to listen a bit more to the technical cats on here. There are more than a few engineers on this board including me. I perform product development with composites. A 150 lb pro rider is a lot harder on a frame than a 180 lb recreational rider...plain and simple. Cyclic loading at much higher pedal pressures. Your assertion about weight relative to durability has an unfounded correlation and is design specific. You may not buy that but only because you haven't worked in the discipline which is based on liability i.e. not hurting people which will sink any company rapidly. Super light frames have extremely high modulus CF with not only very high ultimate strength but very high fatigue life. If they didn't, pros who are capable of 1300 watts or almost 2 horsepower would snap them in a sprint...especially after the 1000th repetition. Bicycle frames are tested on robotic fixtures with a safety factor of about 2X's which is true of just about any engineered product sold to the public that can cause death upon failure.
With respect...the average guy doesn't have a clue about design and what the implications are. The engineers on here get it and the others never will.

Last edited by Campag4life; 11-27-08 at 02:40 PM.
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Old 11-27-08, 02:39 PM
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Originally Posted by bigtea View Post
Which pros are you referring to? the 140 pound pros or the 200 pound pros?
Well, weight means many things, but if a pro is putting out huge wattage on a frame, it might be stressing it more than a 190lb person on the same frame. It depends on a lot of things.

The wheels, yeah they take the brunt of the load, so those have weight limits. I know frames do too, but I wonder if they've been tested by using weight loads or power loads and what difference that makes. 300 watts from a 145lb'er and a 190lb'er are the same amount of watts.
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Old 11-27-08, 02:48 PM
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Originally Posted by pharding View Post
Of course Peter white would say that in order to create a bigger market for his custom bikes. He is not an objective third party without a financial interest in the discussion.
I don't think PW has been building custom frames for a long time.
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Old 11-27-08, 03:31 PM
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Originally Posted by halfspeed View Post
I don't think PW has been building custom frames for a long time.
And he didn't make many when he did... That's not his bag. Moreover, the brands and models of bikes he has traditionally sold aren't exactly sport / recreational / bike-o-the-moment types.
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Old 11-27-08, 06:01 PM
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Well what do you expect a framebuilder to say?
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Old 11-27-08, 06:04 PM
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Oh no, so the Serotta Ottrot's CF tubes will break down?!
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Old 11-27-08, 06:18 PM
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this conversation is like the one with superbikes ... why would you manufacture and sell a 1000cc superbike that makes 180+hp and can top out near 190mph? manufactures make these bikes and shops sell them to teenagers because there is a market for them. no one holds a gun to your head and says ... you need to buy this bike, same with a bicycle.

it is up to you to determine the right bike for you the manufactures and bike shops are not to be blamed for anything.

oh yeah, i am 6ft and 158lbs in season and not a pro but a lowly cat 3. i am pretty sure there are more guys my size than say 180-190 pounder riding a CF bike like mine.
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Old 11-27-08, 06:24 PM
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Originally Posted by deadly downtube View Post
Your argument shouldn't involve the weight of the riders, but how long these pros are actually riding these frames before getting brand new ones.. the answer? no longer than one year! pros only ride these feather light plastic babies for a year or less, and then they get brand new ones.. of course they are going to be a poor investment if you want to keep riding the same bike 8,000 mi a year for 5 years. in that time you'll probably drop or crash the thing and then it's toast.

this topic reminds me of how shimano says they COULD make their stuff as light as SRAM or Campy but they design their components to be a good investment to the consumer who wants to get 20,000 mi out of their parts without worrying about something disintegrating.. consumer and pro racer in mind.. why I like shimano.. but sad they went to carbon rear derailer just for the bling look.
So you're suggesting that Campagnolo parts don't last? Even the carbon ones? That Shimano parts have a longer life span? Are you sure about this?
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Old 11-27-08, 08:21 PM
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Originally Posted by Campag4life View Post
OP...you need to listen a bit more to the technical cats on here. There are more than a few engineers on this board including me. I perform product development with composites. A 150 lb pro rider is a lot harder on a frame than a 180 lb recreational rider...plain and simple. Cyclic loading at much higher pedal pressures. Your assertion about weight relative to durability has an unfounded correlation and is design specific. You may not buy that but only because you haven't worked in the discipline which is based on liability i.e. not hurting people which will sink any company rapidly. Super light frames have extremely high modulus CF with not only very high ultimate strength but very high fatigue life. If they didn't, pros who are capable of 1300 watts or almost 2 horsepower would snap them in a sprint...especially after the 1000th repetition. Bicycle frames are tested on robotic fixtures with a safety factor of about 2X's which is true of just about any engineered product sold to the public that can cause death upon failure.
With respect...the average guy doesn't have a clue about design and what the implications are. The engineers on here get it and the others never will.
Just to let you know, my original comments were based on my conversation with an engineer who also has experience with composites...but specifically bicycle frame applications using carbon fiber. Sounds like there might be some disagreement among "technical cats".
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Old 11-27-08, 10:11 PM
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If carbon fiber is suitable for jet aircraft, I am sure that it will handle an overweight cyclist. Crashing is another matter altogether when unique, unanticipated forces may be encountered with the random nature of the event.
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Old 11-27-08, 10:15 PM
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You guys worry too much. Just buy the friggin bike, STFU, HTFU, and ride it.
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Old 11-28-08, 05:45 AM
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Originally Posted by patentcad View Post
You guys worry too much. Just buy the friggin bike, STFU, HTFU, and ride it.
What a genius.

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