This is what remains of the Cannondale CAAD7 that one of our shop junior rider’s was aboard at Junior Nationals a few weeks ago. 5 miles in there was a huge crash… as you can see, David didn’t fair well! Fortunately he was not injured. Unfortunately he ran smack into the rear of another one of our shop riders at 30mph and destroyed both bikes! Both riders escaped with only minor scrapes and bruises and were back on bikes (albeit different ones) within days.
Taking a look at the Cannondale frame really gives you an appreciation for the strength of these frames. It is amazing how thin the aluminum tubing really is, yet it took an immense impact at 30mph to do this sort of damage. And, even with the front half of the triangle missing, the frame is still incredibly stiff!
Today we stripped Dave’s old frame to build up his new Orbea Lobular frame. He is very excited!
It is interesting to see how different materials react differently to the same (or similar) situations. On this Cannondale the aluminum looks like it just snapped. It is a very “clean” break, with little tearing or deformation of the tube.
Last year we got a Cervelo Super Prodigy in the shop that had been in a similar accident with similar damages, but the steal tubing of the Cervelo showed much more disfiguration.
The steel *should *undergo more plastic deformation before failing. The Aluminum even if designed to be stiffer will not have the same ability typically to bend. Even with a higher ultimate strength, it will usually fail exactly as you’ve described.
I had something similar happen to a Cannondale a few years back. Caad3 frame with aluminium forks (not a bike for riding bad roads…), and went into the side of a car at 30mph (his fault). The frame stayed on one side of the car, I ended up on the other side of the car and the front wheel and bottom half of the forks ended up off to the side somewhere. Forks were sheared clean through, but the rest of the frame was still true and apart from a few bumps and bruises I was fine.
I have the forks mounted on the wall in my garage as a memento.
I know that’s how things are supposed to work. I have been a bike mechanic for a very long time… I just think it is interesting to see it first hand in real world circumstances.
You’re right. Stiffer aluminum=brittle material=catastrophic failure at the “breaking point.”
I’m more amazed at the amount of brute force it took to snap a tube with a wall thickness of less than 1mm!
