Originally Posted by
Sy Reene
I believe it's more correct to say that external cam skewers require more force to close in order to achieve the same clamping power as an internal cam skewer, but if you're not strength limited, either type of skewer can provide adequate clamping force.
Internal cam skewers have greater mechanical advantage than external cam skewers, and since the length of the lever arm is pretty much the same on each, it's harder to clamp an external cam skewer effectively on a horizontal dropout.
As an aside question.. is there such a thing as using too much clamping force?
You can exceed the strength of the component parts; e.g. I've seem broken aluminum external cam levers from using a leverage-enhancer ("cheater pipe," wrench, etc.) on the lever to get it to clamp properly on a horizontal dropout.