Actually, I have seen a couple of Colnagos whose top tubes seem to be in a diamond shape, corner up, and concavities on each side. That seemed intuitively to be a much stronger cross section that the large oval downtubes I see on many bikes.

Just to be sure, I did mean "unintended" incidents as I stated - like dropping a big wrench on the top tube, not everyday riding stresses. It seemed almost as though I could dent some of them by squeezing it in my hand.

After the "puns" thread earlier in the day, I am not taking any chances.

Cheers...Gary