We're talking "apples to oranges" here.

On a medium-duty, you have juice brakes, air over hydraulic, and pure air. Disk, drum, and combination. On these trucks and buses, 60-70% of the braking is on the drive axle, which is the opposite of a passenger car. They have a very large swept area, and the larger ones have relatively slow-turning wheels so the speed that the friction material sees is low (504revs/mile IIRC on a big-rig with 11Rx22.5 rubber).

Many have drums on the drive axle, just because they couldn't get the swept area on a disk. When drums heat up, they grow in size, and eventually the S-cam can't apply enough pressure or it is only at one end of the shoe, which is bad (BTDT). Disks don't run out of travel, which makes them inherently safer, but the temperature of the friction material if too high starts to reduce the coefficient of friction, meaning it needs more pressure to brake, and that too can eventually become a problem.

On a truck, the rule is that you never rely on brakes to hold speed, only engine braking/retarder. If your engine can't hold your speed you need to slow down and gear down until it does.

The brakes on a car, being 4 disks on most of our Mercedes, aren't as prone to fading as drum brakes and are usually the same ones that are supplied in Germany where it can legally be driven much harder/faster. I've not yet driven a Mercedes car that didn't originally have excellent brakes for its power and weight.

The cooling effect of air escaping from under the car through the wheels becomes important when driving on a mountain as mentioned, or hauling / carrying a load. Also if driving hard enough to brake hard and then accelerate to brake again (and again). If the OP is planning on any of these, I'd say that better cooling from removing these shields is a good idea as they almost certainly must reduce airflow significantly compared to the centrifugal air-pump design of the original 15-hole wheels. It also will decrease (however slightly) the heat transferred from the rotor/hub into the alloy wheel.

If normal driving, I'd not worry too much about brake cooling.

__________________

Gone to the dark side

- Jeff