Because the roof is a critical part of a car's structure, convertibles need extra bracing to stiffen their bodies. As a result, they typically are hundreds of pounds heavier and a bit slower than their hardtop counterparts.

Is a convertible faster with the top up or down?

On the other hand, when Best Motoring did an all-convertible battle, they found that the cars were faster with the tops down (the exception was the Boxster S, which was nearly identical). Maybe it's because racing isn't time attack (i.e. there is drafting).

Why you shouldn't buy a convertible?

They're more expensive than other cars. Maintenance costs more, too. There's less passenger and cargo space. Convertible tops can leak.