Mechanical Ramblings: High Performance Brakes
Disc brakes on bikes, particularly the newer generation of road bikes, cop a lot of flack for various reasons (some of it is justified…) but on the whole they are actually incredibly high performance products that punch well above their weight (literally)
But….like most things in life….complaining about problems is a lot easier than engineering solutions. For this example we have a high quality TRP rotor off a road bike, measuring 140mm in diameter – nestled snugly inside a fairly monstrous 380mm disc rotor off a car.
- The bike disc weighs 100g.
- The car disc weighs 11kg (my scale really struggled to settle on a number, let’s call it 11kg)
- Bikes have 2 rotors.
- Cars have 4.
This car disc is 110 times the mass of the bike disc. Multiply that by 2 (4 brakes vs 2) and you’ve got an automotive brake system equivalent to 220 TIMES the rotor mass of a high end road bike braking system.
- A carbon road bike with a rider aboard can weigh anywhere from 50-130kg
- An average sports car with fluids and a driver weighs about 1900kg.
Suddenly we can look at this in a different light: 200g of bike disc rotors capable of safely stopping up to 130kg of mass at any real world speed. The braking system on the bike is handling 650x its own mass – 0.2kg of rotor is stopping 130kg of bike and rider. The 44kg worth of discs on the car can likewise safely stop 1900kg….. But it’s only handling about 43x its own mass! All of a sudden, disc brakes on bikes really do look like they perform at an incredibly high level, right?