[Sirrotica]

The convertible chassis are actually stiffer when ordered in a hardtop car, there used to be an option to order them new that way.

Hardtops are C channel along the rocker panels, the convertible chassis is boxed in that area. They will still bend because of the loss of the roof to stiffen the body. The best option we used when building stock cars was get a convertible car, weld in the cage and then weld a hardtop roof on it. Fine if you're wanting a strictly race car, but not for a driver.

Putting a street type roll bar in a convertible will help immensely with stiffening the whole car, but many people won't want to cut the car up and put bars in it.

There are ways to stiffen the chassis underneath with X members and extra bars tying the front and rear together, but it will not work as well as roll bar with struts running front and rear to triangulate the chassis. Losing the roof panels also loses a lot of stiffening from front to rear. If you compare a street car to a car with a cage in it, it's apples to oranges. It all depends what you want to end up with, how much work and money you want to invest, and what you feel you want to compromise.

Convertibles that are drag raced many times end up with wrinkled quarter panels without some sort of bracing or cage to limit twisting. I've even seen sedans, and hardtops wrinkle the quarters too.