Originally Posted by
rekmeyata
But a race car chassis is about 2 to 10 mm thick (depending where on the chassis it's being used) vs a bicycle frame that is about 0.5 mm thick depending on the cost of the CF bike, and it's this thin CF in a tube set that I can make bend inward with my bare hands. Also keep in mind that one of the reasons race cars went with CF is due to its ability to break apart absorbing the crash energy instead of the person absorbing it, they didn't choose it for weight because race cars have to meet weight restrictions and requirements. Bike manufactures on the other hand could care less about how the material handles a crash, all they care about is shape and weight.
Since you use to be involved in motorsports, please correct my errors above concerning the race cars.
CF is used in motorsport for many varied applications, not just the chassis, and it is favoured primarily because of its superior stiffness/weight ratio and versatility in shaping - for example it's perfect for structural aero components like wings and suspension wishbones. Some of these components can also be very thin, just like a carbon bike frame.
It is true that you can also make a very effective crash structure out of carbon, but that's not the reason race car chassis are made out of carbon in the first place. That's more of a bonus. I used to oversee carbon chassis crash testing for one of the teams I was working for and that really just comes down to the nosecone design, which is specifically designed to fold up on itself in a frontal impact. Then there's the roll hoop which has to undergo a specific vertical compression test. Again carbon is perfect for that. Now they also have the Halo in F1. Even though there are minimum weight regulations in motorsport, it doesn't mean that weight saving is not important. We used to run around 50 kg of tungsten ballast on our F1 cars to meet the min weight and it was useful for fine tuning front/rear weight distribution. Plus of course it was bolted as low down on the floor as possible for minimum CofG height. So in motorsport you still design for minimum weight for the stiffness you require in any component.
But coming back to bike frames, I agree thin walled carbon frames are more vulnerable to damage than metal equivalents. But in my experience it's not usually a major issue even with mtbs that take a fair old beating. If you are not particularly bothered about weight and/or aero then a carbon frame doesn't really make much sense over a simple steel frame. But then neither does a Ti frame. It's just another option in the realm of marginal gains. I think the main reason people really choose Ti frames is for the looks and exclusivity. Nothing wrong with that of course!