Pia -

It's the rotors that are vented. The calipers for that type have to allow for the additional thickness of the rotor, the they won't swap to solid rotors.

Vented is better at dissipating heat. Means better stopping and, maybe, less liklihood of rotor warping. Even so, if you brake to a hard stop which heats up the rotors, try to get off the brake pedal ASAP.

Also, be off the brake pedal when you go over a hard bump. If the wheel get airborne, it will stop dead. Then, when it hits the ground again, the suspension get a big jerk as the wheel is re-started.

Most if not all Volvos with the front air dam got vented rotors.

You can check yours by looking at the edge of the rotor. The vents are very visible.

Good Luck,

Bob

:>)