For those that dont want to click the link, the relevant section is below... I know its long, but its worth it:
Can you brake faster than cars?
Good question. During our emergency braking exercises I always ask this question, and I get two answers, both wrong. One is "Certainly not; motorcycle tires have two small contact patches, car tires have four larger contact patches, so motorcycles have less traction." You can read my page on traction and contact patch area to see why contact patch area is irrelevant, so this answer is wrong. The other answer is "Certainly; you can accelerate faster than cars because you're lighter. You can decelerate faster than cars, because you're lighter." I subscribed to the second view until one of my students, Eli Baldwin, said that the physics in the two situations is entirely different. He's right. Motorcycles can accelerate faster than (most) cars because the ratio of power to weight is greater for motorcycles; there may be less horsepower but it's pushing a lot less weight. But for braking, the horsepower of the engine is irrelevant. To find out whether motorcycles brake better than cars we have to look deeper into the physics of braking.
The force on a vehicle during a stop is just the vehicle's mass times the (negative) acceleration, F = ma. That force has to be applied at the tires via their traction. The friction equation is F = μW (where W is the weight of the vehicle and μ is the Greek letter mu, the coefficient of friction — again see laws of friction for details). The weight of the vehicle is the mass m times the gravitational force g, so F = μmg. The maximum stopping force that can be applied is the maximum frictional force that the tires can sustain, so ma = μmg; and we can cancel the mass which appears on both sides to get the maximum deceleration possible:
a = μg
Now before we go further, let's note some assumptions. One is that the downwards force in the friction equation is actually the weight of the vehicle. Race cars use airfoils to develop a downward force to improve their traction, so their stopping distances would be better than an unassisted vehicle (at speeds allowing the airfoil to work). If street cars ever begin to use this technology then the conclusions would have to change to take that into account.
Another assumption is that the limiting factor in stopping is traction, rather than the ability of the brakes to dissipate the energy. This is true of cars and motorcycles at normal speeds, as their brakes can overwhelm the traction of the tires, causing a slide. But it isn't true of large trucks. Their additional mass provides additional traction, as shown in F = μmg, but the additional energy is more than the brakes can deal with, resulting in longer stopping distances. And a reader, Garrett Underwood, pointed out to me that as speeds increase, even cars and motorcycles may become limited by the ability of the brakes to deal with the energy (which increases as the square of the speed). If this point is reached then motorcycles may have an advantage in stopping distance, as motorcycles generally weigh a quarter or less of a car's weight, so the kinetic energy which must be converted to heat is also a quarter or less. I don't know where the tipping point is between tire traction and braking energy as the limiting factor, but as Garrett mentioned, the difference in stopping distances between smaller passenger cars and larger SUVs and pickup trucks widens dramatically from 60mph to 80mph, suggesting that energy becomes a factor even at those speeds.
Brake design plays a role. Drum brakes don't deal with energy as well as modern disk brakes. Two large brake disks on a sportbike will move more energy than a single small disk on a cruiser. More pad area pushed by more pistons will reduce lever effort on the part of the rider, making it easier to achieve the maximum braking force. The same factors in auto brakes will affect which auto can outbrake which motorcycle.
The limiting factor in a stop of a motorcycle may also not be the traction, but the stability of the vehicle. We've all seen sportbikes with the rear tire in the air in a stop. The front tire isn't sliding, so there may be still more traction available to slow, but any additional braking will just result in the motorcycle going over the front tire.
But with the assumption that stopping distance is limited by the traction of the tires, a = μg shows that the mass of the vehicle is not relevant; it does not enter into the equation. The only difference might be in the value of μ for car and bike tires. I had speculated that motorcycle tires have stickier rubber than auto tires, because of the difference in tire life. Softer rubber being stickier than harder rubber, and having a shorter life, it might follow that motorcycle tires are stickier than auto tires. But a reader, Blane Baysinger, pointed me to a Society of Automotive Engineers article comparing motorcycle and auto tires. This article indicates that the coefficient of friction of both auto and motorcycle tires is about 1.2 on dry surfaces (declining to .7 to .9 when skidding). The difference in longevity appears to be due to the greater amount of rubber on the auto tires; and it appears that if you can stop faster than a car, it's because you're better at using the brakes, not because of any inherent superiority in the braking capability of a motorcycle.
And there is one final complication: Can you use all the traction of your motorcycle tires? If you get too hard on the brakes in your car, you slide, you let off the pedal to resume rolling, you get back on the brakes. When the same thing happens on your motorcycle, the slide generally results in a fall. Thus motorcyclists are reluctant to approach the limit of their braking, where the same isn't true of auto drivers.
So where does this leave us? Here's my rule: I figure the guy in front of me is able to outbrake me, so I leave enough room between us, and look well ahead of him, so that I won't hit him. And I figure I can outbrake the guy behind me, especially if he's too close or not paying attention, so I leave even more room in front (to reduce the probability that I'll have to brake hard), and keep a close eye on my mirrors, and stay in the proper gear so that after braking hard I can escape if needed.
No mention of the fact its on your channel 08ride, with no credit to RYANTCB I notice.
