Carbon Fibre frame

[northwind]

Not true at all that, if you get a full break then sure, it's probably junk (though could be rebuilt over the break) but a crack will usually leave the fibres intact, and that can be repaired- just look to mountain bikes for real world proof, you can re-saturate the break and then simply "bandage" it, it's not even uncommon never mind impossible. Bike frames might be lighter but they have a much higher stress/mass ratio than a road or race motorbike frame.

[yorkie_chris]

Depends though, that will change the ratio in that area which won't do it any favours.

How pronounced is the difference between carbon and alloy in terms of strength/mass?

Originally Posted by northwind

Not true at all that.... you can re-saturate the break and then simply "bandage" it, it's not even uncommon never mind impossible....

What! Are we even talking about the same stuff? You might get away with that on a MTB that rarely exceeds 35mph, but not on a 180mph MC. As I said, fools errand.

....

Originally Posted by yorkie_chris

How pronounced is the difference between carbon and alloy in terms of strength/mass?

Roughly 1.5-2.5:1... lots of variables.

Cheers

[northwind]

Originally Posted by MattCo

What! Are we even talking about the same stuff? You might get away with that on a MTB that rarely exceeds 35mph, but not on a 180mph MC. As I said, fools errand.

....

What has top speed got to do with it Precisely nothing at all. As I said, a downhill mtb frame is more stressed than a road motorbike frame.

[yorkie_chris]

How do you know? They haven't built one yet, and to get as light as they can the thing will be as close to critical stress as possible.

Fall off at 35mph and it'll hurt... 180mph be a bit more serious though.

[northwind]

What I mean is, a mtb frame is more stressed than a motorbike frame regardless of material, because of the huge hits it has to take and the low volumes and small cross-sections, yet can still be repaired despite that higher stress. Carbon fishing rods are under gigantic flex stress compared to either, and can be repaired too. Motorbike frames really aren't under a huge amount of stress except when they're crashing.

A 35mph crash is less bad than a 180mph crash but a motorbike frame isn't really very stressed at 180mph, unless you hit something solid, at which point you've already crashed

[squirrel_hunter]

Originally Posted by MattCo

Glue? This is not some cheap wet layup or chopped glass structure that we are talking about. It is a critical structure. Any interruption to the continuity of the fibres or resin system and it becomes a throw away.

I only know of wet layup and prepreg CF techniques, in what way would the manufacture process differ for this type of application?

[Red Herring]

I seem to remember reading somewhere that it was far more likely to find a carbon road frame than a race one. The reason given was that race frames are always being tweaked and modified and it was much harder to do this with carbon than ally, you basically had to build a completely new frame each time. On road bikes they get the prototype frame right and then they can mass produce loads the same that never need to be changed.

[yorkie_chris]

You'd need lots of metal inserts to make a carbon frame work, can't really see it being possible to put a bearing into carbon. That would mean not much weight penalty to use adjustable headstock or what have you.