There is a certain area under the car where you shouldn't have a low point in the exhaust. My exhaust is 3 inch, and never bottoms out.

The cat converter must be as tight up to the body as possible.

Have someone stand perpendicular to a speed hump that frequently gives you trouble. Drive over it at a speed you normally would, and have them mentally (or digital photograph) the point where the car bottoms out on the speed hump. Once idenfied, make sure that part of the car has it's exhaust bits as snug to the body as possible.

Using more exhaust hangers stabilises the exhaust, and stops it from drooping when going over speed humps also. Hanging 3 inch on the standard hangers is a bad idea.

Getting stiffer front springs is also a good way to reduce the spring compression at slow speed.

Cheers,
Chris

twins is too heavy..unless it's titanium.