My CE28N's have been through a lot of abuse by some very aggressive co-drivers, and I can say that they will bend before ever breaking. I also tried deliberately bending an old one with a sledge hammer and I couldn't cause more than surface scratches (no I am not a masochist).

 

I think that Fongu did a good job summarizing the effects of unsprung mass and rotating mass. I'll add that the effect of rotating mass is felt only during acceleration and deceleration. A wheel/tire combination acts as if it is 1-2 times as heavy as the true weight for the purposes of acceleration or deceleration. It does not affect cornering any differently than non-rotating weight.

For a wheel, the factor is probably between 1.2-1.4. For a tire, the factor is probably closer to 1.9. Both wheel and tire contribute equally to unsprung weight. The tire weight is much more important than the wheel when it comes to rotating weight.

 

Hm, that's strange. A forged rim should never be more ductile than a cast one. A forged rim should crack instead of bending. Usually forging work hardens the metal to the point where it is stronger but more brittle and less ductile than a cast one.

Right?

I'm not a metallurgist, and am pulling this out of memory so don't shoot me if I'm wrong.

 

Aluminum and steel are two different animals. Plus, that sort of thing depends on a lot of factors like the alloy, the heat tempering, etc.

 

hm, interesting. I know Alloy A356.0 is typical of cast car wheels. It has pretty high ductility. But in a forged application the grain structure is going to guarantee higher strength at the cost of ductility, no? Like a 6061 alloy... I guess the heat treating makes all the difference.

 

It makes a huge difference in aerospace Al, anyway.

 

Proof is in the pudding.

Here is one of my old Ce28N's after an "incident". The first pic shows a major bend, but it did not crack or break. The surface marring is from me hitting it with a small sledge hammer to see if I could bend it (a test procedure before attempting to straighten another slightly bent rim), but to no success. The second pic shows a hole torn in the rim where the half shaft went right through it as well as through the tire itself. You can see that the rest of the wheel didn't crack or break. This alloy seems to be very ductile.