Why are large tall vehicles such as tractor trailer trucks and large vans more likely to roll or tip over on sharp curves than smaller cars?

This is because of weight distribution and size. A large tall vehicle has a higher center of gravity and is therefore more unstable than a smaller car which would have a lower center of gravity.

Semi trucks sometimes tip because of the items in the trailer moving to one side. When that happens, the truck tips.

Vans are not as likely to tip at highway speeds. Vans would tip at an estimated 90-mph.