Q: Why does my BMW make so much black dust on the wheels? I’ve seen this on other cars but it’s not usually as bad as what I’ve noticed on other BMWs and some Mercedes. The wheels are difficult to clean thoroughly and look unsightly when they’re full of the black dust. Is there anything that can be done? I was told I’m almost ready for new brakes.

A: Brake dust is an annoying byproduct of a disc brake system, and can certainly make a mess of attractive wheels. This dust consists of microscopic particles of friction material shed from your disc brake pads and the metal brake rotor. High performance vehicles often have the worst and darkest dust, as the vehicle’s brake design places a higher priority on stopping power than clean wheel appearance.

You have multiple choices when shopping for new brakes, each with pros and cons, if the service facility offers them. When comparing replacement brake pad attributes, these are the things to consider: stopping power, quietness, life span, dustiness and brake rotor life. Softer organic composition brake pads tend to stop the best, are quiet, but emit lots of dark dust, and wear out sooner. Harder semi-metallic pads last a long time, are tough on brake rotors and are more likely to be noisy. Ceramic brake pads have become quite popular as they offer the best compromise of desirable qualities and emit a lighter color dust that doesn’t seem to stick to the wheels as readily as the other brake pad compositions. If your repair facility doesn’t offer choices, or isn’t willing to explain them to you, find another!

Another option to limit brake dust is to install a set of Kleen Wheels Brake Dust Shields behind the wheels. These are aluminum discs that block dust from reaching the wheels, and for your car, run perhaps $50 per pair. They’re certified by TUV, a respected German safety evaluation company, so brake cooling shouldn’t be a concern with everyday driving. I personally like the looks of an exposed brake rotor and nicely painted brake caliper, as viewed through the wheels, so I’ll hang on to my wheel cleaning brush.

When cleaning alloy wheels, be sure to use a cleaning solution that’s appropriate for your wheel type. Painted or clear-coated wheels need one type of cleaner and polished or rough aluminum, billet, and anodized wheels need another. I like Mothers FX wheel and tire cleaner for typical original equipment manufacturer coated wheels. There are several clever wheel cleaning brushes available. Choose the one that works best for your wheel style.

On another note, John G. reminded me when defrosting that it is best to make sure your HVAC system is set to “fresh air” and not “recirculate” if these settings are allowed. On a vehicle that doesn’t employ a separate control for this, it will be drawing fresh air automatically for all modes except “MAX A/C” Switching to fresh air during the last few miles of summertime A/C use can help reduce fungus and odor issues in the evaporator and its housing.