Why do cars have ridges in them?

I heard that it was for traction.Why do cars have ridges in them?
Hmm? Ridges. I thought you were talking about the ridges on the roof (which incidentally is for strength).





If you meant to ask why tires have ridges in them, yes, it is for traction. The proper term for them are sipes. The differing patterns allow a tire to do different things. Some are better for wet traction, some are better for mud, some are better for dry pavement only. No tire will be all things to all people, so you choose what's best for you. Anyway, I hope that I understood your question.Why do cars have ridges in them?
Do u mean to say ...on tyres.


ie., for ROAD grip.ie., on wet roads /smooth roads.
Traction, strength of hull, plus it makes the car look sleek and aerodynamic.
Pls. be more specific. If you mean ';stiffeners'; they tend to make metal stronger than a flat surface.