How strong should a frame be?

I feel for your mate but in my book this is just one of those things. Stuff can break when you drop it the wrong way and that can be the first time or the 1000th time you use it. 

Grahamd wrote:

 

MHO the design should be strong enough to cater for real world bike use, and a minor accident should not render a frame unuseable 

I believe cars are frequently written off after 'minor' accidents so I don't see why you'd expect that a bike frame would be indestructible. 

Mungecrundle wrote:

I lifted this straight from

http://www.sheldonbrown.com/frame-materials.html

It's a few years old now and things move on, but he seems to put together some technically knowledgeable articles.

 

"Carbon fiber is an increasingly popular frame material, but it is fundamentally different from metal tubing as a way to construct frames. Because of the fibrous nature of this material, it has a much more pronounced "grain" than metal does. A well-designed carbon fiber frame can have the fabric aligned in such a way as to provide maximum strength in the directions of maximum stress.

Unfortunately, in bicycle applications, carbon fiber is not a fully mature technology, as tubular-construction metal frames are. Bicycles are subjected to a very wide range of different stresses from many different directions. Even with computer modeling, the loads can't be entirely predicted. Carbon fiber has great potential, but contemporary carbon fiber frames have not demonstrated the level of reliability and durability that are desired for heavy-duty touring use. In particular, a weak point tends to be the areas where metal fitments, such as fork ends, bottom bracket shells, headsets, etc connect to the carbon frame. These areas can be weakened by corrosion over time, and lead to failure."

(Dated Aug 2010)

 

CF is still a maturing technology. I've seen those trail bike frame tests before and they really do put paid to the notion that CF is not a strong material. However the fact that very few touring bike specialists use it for frames at the present time is a good indicator that it is not 'better' as an overall package than other traditional materials for all applications.

Fingers crossed for a warranty frame replacement for your mate. Was it a brand new bike or new second hand? Giant may replace as a gesture of goodwill, especially if the alternative is an offer by your mate to post pictures of a cracked Giant frame all over the internet...

The main reason for not using cf for touring bikes is because it cannot be adequately repaired unless you are fortunate enough to be in a place where facilities are available.

However steel and other metals can usually be patched up or repaired by any competent village blacksmith even in remote areas of the world .

Batchy wrote:

Mungecrundle wrote:

I lifted this straight from

http://www.sheldonbrown.com/frame-materials.html

It's a few years old now and things move on, but he seems to put together some technically knowledgeable articles.

 

"Carbon fiber is an increasingly popular frame material, but it is fundamentally different from metal tubing as a way to construct frames. Because of the fibrous nature of this material, it has a much more pronounced "grain" than metal does. A well-designed carbon fiber frame can have the fabric aligned in such a way as to provide maximum strength in the directions of maximum stress.

Unfortunately, in bicycle applications, carbon fiber is not a fully mature technology, as tubular-construction metal frames are. Bicycles are subjected to a very wide range of different stresses from many different directions. Even with computer modeling, the loads can't be entirely predicted. Carbon fiber has great potential, but contemporary carbon fiber frames have not demonstrated the level of reliability and durability that are desired for heavy-duty touring use. In particular, a weak point tends to be the areas where metal fitments, such as fork ends, bottom bracket shells, headsets, etc connect to the carbon frame. These areas can be weakened by corrosion over time, and lead to failure."

(Dated Aug 2010)

 

CF is still a maturing technology. I've seen those trail bike frame tests before and they really do put paid to the notion that CF is not a strong material. However the fact that very few touring bike specialists use it for frames at the present time is a good indicator that it is not 'better' as an overall package than other traditional materials for all applications.

Fingers crossed for a warranty frame replacement for your mate. Was it a brand new bike or new second hand? Giant may replace as a gesture of goodwill, especially if the alternative is an offer by your mate to post pictures of a cracked Giant frame all over the internet...

The main reason for not using cf for touring bikes is because it cannot be adequately repaired unless you are fortunate enough to be in a place where facilities are available.

However steel and other metals can usually be patched up or repaired by any competent village blacksmith even in remote areas of the world .

Chances for repair in the wild would undoubtably be higher for steel frames in most places i'd warrant - i'd still hate to see your average village blacksmith put a flame anywhere near an aluminium or modern, performance steel/stainless one though. Also, much as I admire Sheldons site, i'd say that summary was nearly out of date at the time of writing - let alone now. I'd personally take a metal (probably non-exotic steel) frame for touring in out-of-the-way places, world circumnavigation and so on - otherwise i'd just go with whatever was to hand that took luggage and decent tyres.

AKH wrote:

Road bike frames are incredibly strong relative to their weight; but, they’re only designed to support that load in a certain plane. In a crash, all bets are off. Sorry to hear about your mate’s situation, but it doesn’t sound at all unreasonable to me.

Just a qualification: The above is true for carbon fiber. It's "anisotropic" so it doesn't support loads equally in all directions the way metal frames, made of an isotropic material, are.

In a sense, the anisotropic nature of carbon fiber makes it desirable because frame makers can tune the design and layup of the carbon to support loads in one direction and be compliant in another. The same characteristic doesn't do you any favors in crashes or for loaded touring though.