Carbon Fibre and the riders weight?

DonDaddyD

How much wieght (of the rider/cyclist) can a carbon fibre bike hold/withstand?

This may sound silly but on a few occasions I've heard people say that they would love to get a carbon fibre bike but are either too heavy or want to loose more weight first. Is there a maximum or 'advised' weight a person buying a carbon fibre bike should be. If so what is it?

Serious question.

crankycrank

Each frame would have a different max weight depending on design. The beauty of CF is that it can be built to support as little or as much weight as needed. Generally it requires more CF material (and more weight) to strengthen a frame.

always_tyred

Cars and fighter plane wings are made out of carbon fibre.

Its not the carbon fibre, its the frame, and/or the manufacturers being conservative. I figure that if a bike, or a bike part has a weight limit, there's a concern. Were I a 65kg rider, I'd be worried that I might hit a pot hole that stresses the bike as much as the manufacturers think an 85kg rider would.

So, just as you used to be able to get superlight Al or steel frames like noodles that had rider weight limits, you can get cf parts and frames with weight limits. But unless there is a weight limit, I'd say that concerns are another example of "woooo, carbon, magiiiiic".

greg66_tri_v2.0

My view is that people (unless they're the manufacturer) who crap on about weight limits for CF frames don't know what they're talking about. More specifically, I think they equate carbon fibre with fancy fibre glass. Unless theyre structural engineers who work with CF and CF lay ups, and have examined the lay up of the frame in question, it's a bit like looking at a car in the road and saying "that would be a disaster in a crash".

They're also the same people who crap on with questions like "should I ride my CF frame in cold weather - it might snap". Yes, like the wings of an airbus. At -60 at 500 knots at 39000 feet. Nothing like the straing they put on their frames on a winter day, obviously. It's why every Airbus comes with a free dustpan and brush. To help with the clearing up.

So don't sweat CF frame weight limits.

FWIW, Campag did (and may still) have on its website a recommended weight limit for its components. Odd, since they're not on the whole weight bearing. And I'm on and off over it. No ill effects in more years than I care to count.

EDIT: I'm struggling to think of a frame - CF or otherwise - with a rider weight limit. Anyone? Wheels are a different matter. Quite a few there.

DonDaddyD

Edit.

nation

CF is a phenomenally strong material.

Check out thisvideo:

http://www.youtube.com/watch?v=GtUDtX2Tyfc

That's a 100kg weight.

Beeblebrox

DonDaddyD wrote:

Thanks Always Tyred. Though your post leaves me somewhat confused...

What I'm wondering is should a rider who is near 100kg be concerned that a carbon fibre bike won't withstand his weight (for long).

Certainly no issue on strength, fatigue life is a slightly different problem - but if there's no limit and you have a life time guarantee on the frame, then clearly the manufacturer doesn't think that any human weight can fatigue a CF frame to failure.

DonDaddyD

Greg66 wrote:

My view is that people (unless they're the manufacturer) who crap on about weight limits for CF frames don't know what they're talking about. More specifically, I think they equate carbon fibre with fancy fibre glass. Unless theyre structural engineers who work with CF and CF lay ups, and have examined the lay up of the frame in question, it's a bit like looking at a car in the road and saying "that would be a disaster in a crash".

They're also the same people who crap on with questions like "should I ride my CF frame in cold weather - it might snap". Yes, like the wings of an airbus. At -60 at 500 knots at 39000 feet. Nothing like the straing they put on their frames on a winter day, obviously. It's why every Airbus comes with a free dustpan and brush. To help with the clearing up.

So don't sweat CF frame weight limits.

FWIW, Campag did (and may still) have on its website a recommended weight limit for its components. Odd, since they're not on the whole weight bearing. And I'm on and off over it. No ill effects in more years than I care to count.

EDIT: I'm struggling to think of a frame - CF or otherwise - with a rider weight limit. Anyone? Wheels are a different matter. Quite a few there.

Thanks Greg. (Kharma or Fondriest it is).

Beeblebrox wrote:

Certainly no issue on strength, fatigue life is a slightly different problem

This is more a question out of curiousity, but how long can someone expect to have a carbon fibre bike?

I'm not overly hung up on this just curious.

always_tyred

DonDaddyD wrote:

Thanks Always Tyred. Though your post leaves me somewhat confused...

What I'm wondering is should a rider who is near 100kg be concerned that a carbon fibre bike won't withstand his weight (for long).

What I'm saying is that if a component, any component, has a weight limit, its because the manufacturer knows there is an issue with its strength, and if there isn't a weight limit, I can't see any particular reason for singling out a component because its carbon, and inventing one.

There is a LOT of bumkum floating around about cf. Carbon is no better or worse than Ti, Al, or Fe, its just newer.

100kg isn't terribly svelte for a cyclist, but I think that Magnus Backsted was well into the 90's and I'm sure that Paris Roubaix underneath a Magnus puts more stress on a bike than Croydon underneath a DDD.

greg66_tri_v2.0

Always Tyred wrote:

100kg isn't terribly svelte for a cyclist, but I think that Magnus Backsted was well into the 90's and I'm sure that Paris Roubaix underneath a Magnus puts more stress on a bike than Croydon underneath a DDD.

Hmm.

You haven't met DDD, have you? :twisted:

And as for Croydon...

DonDaddyD

Greg66 wrote:

Always Tyred wrote:

100kg isn't terribly svelte for a cyclist, but I think that Magnus Backsted was well into the 90's and I'm sure that Paris Roubaix underneath a Magnus puts more stress on a bike than Croydon underneath a DDD.

Hmm.

You haven't met DDD, have you? :twisted:

And as for Croydon...

Hey, I've moved up in the World, its Wimbledon now!!!

:evil: :evil: :evil:

The weight does piss me off though, no wonder I can't climb hills but sprint like the some speedforce embued speedster!

I'm heavier now than when I was when I first got the road bike in August. This, despite being healthier, fitter, faster, stronger and coming down a waist size. It's all in the thighs...

always_tyred

DonDaddyD wrote:

Greg66 wrote:

Always Tyred wrote:

100kg isn't terribly svelte for a cyclist, but I think that Magnus Backsted was well into the 90's and I'm sure that Paris Roubaix underneath a Magnus puts more stress on a bike than Croydon underneath a DDD.

Hmm.

You haven't met DDD, have you? :twisted:

And as for Croydon...

Hey, I've moved up in the World, its Wimbledon now!!!

:evil: :evil: :evil:

The weight does wee-wee me off though, no wonder I can't climb hills but sprint like the some speedforce embued speedster!

I'm heavier now than when I was when I first got the road bike in August. This, despite being healthier, fitter, faster, stronger and coming down a waist size. It's all in the thighs...

A lot of being able to climb is practice. It uses different musclesto riding on the flat - and it uses the muscles you normally use in different proportions. Being light helps, but its not everything (I'm not particularly light but because I seek them out, I am comparatively good at hills).

Its normall to get heavier before you get lighter when you take up sport. I suspect that by comparison to pre-cycle commuting, you are a lot less buoyant though.

lost_in_thought

I was told by the guys at epic that the heavier the rider the stiffer the frame has to be in order to minimise flex, so carbon of a stiffness which would be solid as hell to a 60kg rider would be more flexy to an 80kg rider, while a frame which is good and stiff to an 80kg rider would be uncomfortably stiff to a 60kg rider.

This made sense to me... I was talking myself into a custom bike at the time though. Pinch of salt, anyone?

roger_merriman

lost_in_thought wrote:

I was told by the guys at epic that the heavier the rider the stiffer the frame has to be in order to minimise flex, so carbon of a stiffness which would be solid as hell to a 60kg rider would be more flexy to an 80kg rider, while a frame which is good and stiff to an 80kg rider would be uncomfortably stiff to a 60kg rider.

This made sense to me... I was talking myself into a custom bike at the time though. Pinch of salt, anyone?

at that differnceces probably yes but yes once you get a big differnce yup.

normally smaller frames are stronger, so you have the problem that the larger more powerful rider has the all being equal weaker frame,

but to be honest unless your chris hoy etc probbly makes zip differnce.

Rich158

lost_in_thought wrote:

I was told by the guys at epic that the heavier the rider the stiffer the frame has to be in order to minimise flex, so carbon of a stiffness which would be solid as hell to a 60kg rider would be more flexy to an 80kg rider, while a frame which is good and stiff to an 80kg rider would be uncomfortably stiff to a 60kg rider.

This made sense to me... I was talking myself into a custom bike at the time though. Pinch of salt, anyone?

True to a certain degree, but then Cav has an ultra stiff frame made due to the amount of power he puts down, and he's certainly no heavyweight.

DDD, if it's an consolation I checked the specs sheet on my Madone ad Trek put a max rider weight on it of 275lbs, and I suspect most other carbon frames can handle about the same weight so you should be fine, there's always a margin of error in this as well to make sure they don't get sued.

Beeblebrox

DonDaddyD wrote:

Beeblebrox wrote:

Certainly no issue on strength, fatigue life is a slightly different problem

This is more a question out of curiousity, but how long can someone expect to have a carbon fibre bike?

I'm not overly hung up on this just curious.

I've no idea - probably years and years and years. I'm talking from a general materials science background, fatigue is the reason to be concerned, not maximum strength (which is known to be sufficient). When a CF aircraft wing fails, it's because it's been loaded on and off millions of times, not because an extra big gust of wind blew it off.

But really that's me subconsciously scaremongering, in the context of a human weight on a frame there's no worries and the only way you'll break it is getting a car to drive into you!

always_tyred

lost_in_thought wrote:

I was told by the guys at epic that the heavier the rider the stiffer the frame has to be in order to minimise flex, so carbon of a stiffness which would be solid as hell to a 60kg rider would be more flexy to an 80kg rider, while a frame which is good and stiff to an 80kg rider would be uncomfortably stiff to a 60kg rider.

This made sense to me... I was talking myself into a custom bike at the time though. Pinch of salt, anyone?

Okay, so point out which part of this statement doesn't apply to any other material.

Another poster raised the issue of fatigue life. Why? Because its carbon? Because you assume its not a problem with the aluminium bike in your garage?

There's nothing special about carbon. The technology is sound and really quite old now. Its essentially the same as fibreglass.

always_tyred

Rich158 wrote:

True to a certain degree, but then Cav has an ultra stiff frame made due to the amount of power he puts down, and he's certainly no heavyweight.

And his frame is sub 2lb. Tells you all you need to know really.

jedster

Cav has an ultra stiff frame made due to the amount of power he puts down

<pedant mode>
suspect that's torque or force rather than power
</pedant mode>

J

greg66_tri_v2.0

lost_in_thought wrote:

I was told by the guys at epic that the heavier the rider the stiffer the frame has to be in order to minimise flex, so carbon of a stiffness which would be solid as hell to a 60kg rider would be more flexy to an 80kg rider, while a frame which is good and stiff to an 80kg rider would be uncomfortably stiff to a 60kg rider.

I think this is confusing two distinct forces on a frame.

First: a rider can be heavy and weak or skinny and strong. The strong rider will generate a lot of power, thereby placing lateral force on the frame around the BB (he may also yank the bars around enough to stress the head tube). So he needs a frame that is torsionally/laterally stiff. That stiffness is irrespective of weight, because it's not the rider's weight that's distorting the frame.

Second: a heavy rider can stress a frame vertically - most typically at the seatpost/seattube junction, and around the chainstay/BB junction. This rider hits a pothole and puts a lot of downward force onto the frame, testing its vertical compliance. Here stiffness does relate to rider weight, because it *is* the rider's weight that's distorting the frame.

wgwarburton

Always Tyred wrote:

Another poster raised the issue of fatigue life. Why? Because its carbon? Because you assume its not a problem with the aluminium bike in your garage?

There's nothing special about carbon. The technology is sound and really quite old now. Its essentially the same as fibreglass.

Yup. Spot on. Most frames are made of one of three materials-

Steel - can rust, very light frames are vulnerable to dents due to thin walls.
Aluminium - will ultimately fail due to fatigue, as no endurance limit, can corrode.
Carbon Fibre- vulnerable to impact damage, which can compromise the structure.

A CF frame won't rust or fatigue (though I suppose integrated metal parts might) so should last indefinitely, if sufficiently well protected.

Cheers,
W.

always_tyred

Greg66 wrote:

Second: a heavy rider can stress a frame vertically - most typically at the seatpost/seattube junction

Ahh, so this is why your frame broke.......

greg66_tri_v2.0

Always Tyred wrote:

Greg66 wrote:

Second: a heavy rider can stress a frame vertically - most typically at the seatpost/seattube junction

Ahh, so this is why your frame broke.......

I dolly them up ... you wallop them...

singlespeedexplosif

I'm struggling to think of a frame - CF or otherwise - with a rider weight limit. Anyone?
Santa Cruz certainly used to put a 100kg limit on their Superlight. Not sure if that's the case any more. Not seen any others though.

lost_in_thought

@AT - you're right, that's notclearly specific to carbon.

And yes, there has to be an allowance for the heavy rider and/or the powerful rider - not necessarily one and the same!

In my case though, it's the weight...

always_tyred

lost_in_thought wrote:

In my case though, it's the weight...

Yes, that must be it. :roll:

Rich158

singlespeedexplosif wrote:

I'm struggling to think of a frame - CF or otherwise - with a rider weight limit. Anyone?
Santa Cruz certainly used to put a 100kg limit on their Superlight. Not sure if that's the case any more. Not seen any others though.

Trek have a weight limit of 275lbs on their CF frames

always_tyred

Rich158 wrote:

singlespeedexplosif wrote:

I'm struggling to think of a frame - CF or otherwise - with a rider weight limit. Anyone?
Santa Cruz certainly used to put a 100kg limit on their Superlight. Not sure if that's the case any more. Not seen any others though.

Trek have a weight limit of 275lbs on their CF frames

That's more of a health warning, surely?

Rich158

I did think that would be pretty much self regulating

DonDaddyD

lost_in_thought wrote:

In my case though, it's the weight...

That's what Epic told you to single handedly help the Country out of a recession....

What groupset and wheels did you go for?

Beeblebrox

Always Tyred wrote:

Another poster raised the issue of fatigue life. Why? Because its carbon? Because you assume its not a problem with the aluminium bike in your garage?

There's nothing special about carbon. The technology is sound and really quite old now. Its essentially the same as fibreglass.

What I posted had no significance to carbon, just pointing out that in terms of frame failure, it won't be (aside from crashes) the strength that limits the life, but the fatigue life. But then I went onto say that with the sorts of loadings a person can generate, there is a very long fatigue life from bicycle frames.