Disc Brakes vs Drum Brakes – Why Do We Use Discs and Drums in Almost All Modern Vehicles?
In today’s automotive world, it’s not uncommon to find four-wheel disc brakes as standard equipment on medium-priced, non-performance-oriented models. The majority of new vehicles, however, continue to utilize a front-disc and rear-drum brake setup. What does this say about the current state of braking systems? Are these manufacturers sacrificing vehicle safety in order to save a few bucks by installing disc brakes on only the front wheels?
The truth is that today’s disc/drum setups are completely adequate for the majority of new cars. Remember that both disc and drum brake design has been vastly improved in the last 20 years. In fact, the current rear drum brake systems on today’s cars would provide better stopping performance then the front disc setups of the ’70s. And today’s front disc brakes are truly exceptional in terms of stopping power. Combined with the fact that between 60% – 90% of a vehicle’s stopping power comes from the front wheels, it’s clear that a well-designed, modern drum brake is all that’s required for most rear wheel brake duty.
High performance cars can justify a four-wheel disc brake system, especially if their owners participate in some form of sanctioned racing activity on the weekends. The rest of us get more of a benefit from the lower cost of drum brakes. Expecting every vehicle built today to come with four-wheel disc brakes would require an across-the-board increase in purchase price, and that could stop new car buyers much quicker than any brake system.
Disc brakes have a higher overall capacity, but drum brakes are cheaper and take less hydraulic force to activate. When you stop your car most of the braking is done by the front brakes because of weight transfer (how you feel pressed towards the front when you hit the brakes). These two facts are why you usually see a mixture of the two in this manner.
Drum brakes have less hardware since everything is included near the hub and there’s no caliper bracket. Drum brakes also let you have a bit smaller master cylinder (at the pedal) because they don’t take as much initial pressure to apply as disk brakes. However, they’re less capable of stopping overall and they are more susceptible to warping and brake fade due to high temperatures than disk brakes. They’re worse at cooling, and more likely to need cleaning and adjustment for optimal operation than disk brakes because a lot of the dust from brake shoes stays inside the drum. Also, the hand brake which is applied on the rear axle is easier to add to a drum brake than to the inside of the hub of a disc brake.
Disc brakes require more hardware and higher overall hydraulic pressure to apply. But they cool better, have better overall stopping power and are less susceptible to warping or brake fade with temperature. So they are better suited for the front axle.
So to summarise, the needs of modern cars have changed, and to save costs without compromising efficiency, safety and quality is the major reason we see this trend on the rise.
Cover Image Credit: Car From Japan