Q: I needed new disc brakes for my car, but the repair workshop wanted so much money for the parts alone, I went to the auto parts store up the street and bought them myself. But when I showed up at the workshop to have them do the installation, the manager took one look and refused to install the brakes. He said they were poor quility “offshore knockoffs,” and likely to kill me and my family. I was a little annoyed–until we both calmed down and he showed me the difference in the parts. The ones I bought were much lighter, because the metal was thinner at almost every spot. So I took them back. The parts-store clerk said these were special “lightweight” brakes, and would actually help me save petrol. They wouldn’t refund my money, but would let me swap them for a different set identical to the ones the brake shop wanted to install, right down to the brand on the box–and they wound up costing me more than the brake workshop would have charged me in the first place. What’s wrong with lightweight brakes?
A: Are lightweight brake good idea? Probably not. There are increasing numbers of these offshore, low-quality brake discs showing up on shelves lately. They use less cast iron and have thinner flanges and fewer, thinner cooling vanes then the OEM equivalents. Brakes transform the kinetic energy in your vehicle to heat. It takes mass, in the form of that cast iron, to capture the heat, and then surface area to dissipate the heat to the air. Less mass equals poorer brake performance in high-speed stops. Fewer vanes equals poorer performance in sequential stops or on long downhill grades. In both cases, that’s bad. The failure mode here is when the friction material gets hot enough to boil, forcing the pad surface to float above the iron discs on a grounds-effect cushion of vaporized binder, leaving you with a spongy pedal and no braking power. Extreme cases of overheating can boil the brake fluid, leaving you with no brakes until they cool down.
There are a half-dozen manufacturers of brake discs in this country, and more overseas, that make discs virtually indistinguishable in quality from the ones installed on your car the day it was made. Stick to brand names, and you should be fine. Saving money on brakes somehow doesn’t sound like a good idea. As for saving petrol because the discs are lighter? I don’t think so.