Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Braking Distance - Bike vs Car

Discussion in 'General Motorcycling Discussion' started by Bravus, Feb 15, 2008.

  1. The conventional wisdom around here seems to be 'a car wil out-brake a bike because it has a much bigger contact patch'. Now, I definitely don't advocate tailgating, and the answer to this is not going to change how I ride in terms of leaving space, but just as a matter of physics...

    Sure, the car has a bigger contact patch, but it's also trying to decelerate a far bigger mass/dissipate far more energy. Do we have any empirical tests of braking, or experience, that would answer fairly conclusively whether, other things being equal (e.g. dry road with goad surface, good brake pads and tyres, etc), a car can get better stopping power than a bike?

  2. It depends on the tyre traction vs the ability of the suspension to keep the tyre in contact with the road. For bikes, and cars as well if there's enough traction, stoppies become a limiting factor.

    In general though, a car with ABS and a bikes will brake about as hard as each other. The ABS compensates pretty well for most car's less sticky tyres and crappier suspension, at least well enough such that bikes will be pulling stoppies by about that point.

    Weight and contact patch has little to do with it. Go read a physics text book for why that is. Won't get into the explanation here.

    The biggest problem with cars not stopping is time purely comes down to the fact that most drivers aren't driving around fully aware of their surroundings, and when a bike brakes, they're not really looking for the brake light, and so will react too slow.
  3. #4 K!rkinpuzel, Feb 15, 2008
    Last edited by a moderator: Jul 13, 2015
  4. Yes, if you hunt through back issues of magazines you'll see a bunch of these tests, I'm sure that one mag or another does car v. bike tests about every 6 months.

    The limit of braking on a modern bike is not traction/contact patch though... it's usually related to wheelbase length, and height of the
    centre of mass. In other words, a stoppie or nose-wheelie.
    Ever seen a car or a cruiser brake so hard that the rear wheel lifts
    off the ground? Me neither. That's because they're long and low.
    BIKE U.K. magazine tested and found the shortest-stopping bike
    in the world was the ... Honda Valkyrie!
  5. Hard to compare apples to apples because many sportsbikes wear street-legal racing rubber that wears out in 10,000km, while most road-going sportscars don't run around on similarly-aggressive compounds (I don't fancy spending $1000 a corner on my ancient 1986 MR2's tyres).

    I can't seem to find any braking tests/distances for sportsbikes.

    The most recent MR2, not exactly a supercar, can stop from 60mph in 119 ft or so:

    There's this comparison of three bikes with and without ABS brakes:
    About 150 feet on dry pavement... But those are not out-and-out sportsbikes. So it's not even remotely apples-to-apples.

    (Off-topic, the ABS article makes a pretty good argument for having ABS in the wet, on motorcycles).
  6. Bikes are getting much better, I remember riding years ago and bikes took forever to pull up. However, despite these improvements a car will almost always outbrake a bike - so don't tailgate as you will definetely come off second best.
  7. cars do have greater braking power, but a bike will still out brake a car, one of the reasons stay upright tells you to what your mirrors
  8. Can you explain as I thought mass would be directly relevant as to how fast it stops, F=MA and all that.
  9. The not-100%-accurate-but-nice-and-simple explanation is that while you do need a greater braking force to stop a heavier vehicle, the vehicle's extra weight increases its grip on the road at the same rate.

    So long as the brakes are powerful enough to lock up the wheels at any given speed, the actual weight of the vehicle means little to its stopping ability. Tyres, suspension, weight bias and braking bias are bigger factors.
  10. Yeah, I'd like to see that explanation too, Flux (I'm a physics teacher, as it happens).

    Have to admit I was thinking of it in terms of bike-behind-car, but car-behind-bike is very relevant as well. As noted above, it's not so much braking power/stopping distance as reaction time in many of these situations...

    The moral of the story is defend your space
  11. Ah ok, so the weight of the vehicle is directly proportional to the disc size for instance so therefor a honda civic with tiny brakes will pull up the same distance as a HSV with massive brakes.
  12. No, I'm sorry, you are incorrect. I don't know how else to put this ....
    Go out and try it, particularly at high speed, it's not hard to do. You will be very surprised at just how much quicker a car pulls up.

    You need to watch behind you because, as a bike, we're smaller and it's possible that the car behind did not see you stopping and could hit you from behind. .
  13. well you go tell the instructors that, wasn't something off the top of my, head, stay up right literally hammer it throughh peoples heads on both the L's and P's courses
  14. The other thing is that there is next to no skill required to stop a modern car with ABS in a distance close to its best braking distance.... and conversely, there is a considerable amount of skill required to stop a bike in a distance close to its best braking distance. Raw figures don't mean so much in the real world.
  15. What can I say mate, I don't know why instructors tell you that.

    Not only can a car pull up faster than a bike under perfect conditions with a good driver and a good rider, but if you consider that many cars have ABS even a poor driver can now pull up real quick, whereas on a bike you need to know how to set up, then squeeze just right etc, not lock up .... you don't stand a chance.
    Don't even mention a slippery road (wet, oily or simply poor quality).
  16. Go to a race track where both bikes and cars race (on differant days) and see how much deeper the cars brake!
  17. Hey speedfreak. I think this topic is more about the physics aspect with ideal conditions etc. The instructors are more talking about the retards on the road that take about ten years to react then just lock up the brakes.
  18. Not completely accurate -
    Plenty of lightweight sportscars (and sportsbikes) have disproportionately huge brake discs to help them stop repeatedly from high speeds without the brakes overheating, so brake size isn't necessarily related to vehicle weight.

    (In fact, I've always thought of the lower-end Commodores and Falcons having woefully undersized brake rotors - Try following one down Jamberoo Pass, and admire the smell of burned-out brakes barely halfway down the hill)

    But generally, yes, a car's weight is not the deciding factor for how fast it can stop. I don't think even the vehicle's weight bias and brake bias matter much these days, since "stability control" and "electronic brake distribution" can brake each wheel up to its limit of traction... So then it comes down to suspension design and tyres.

    (Actually, bikes with ABS - since the front and rear brakes aren't connected to each other - can automagically brake each wheel independently depending on the grip available, just like a car with fancy electronic-brake-distribution)

  19. Friction force (F) is proportional to the force applied to the normal of the friction surface (the road) (N), multiplied by the co-efficient of friction (u).


    N, of course, is proportional to the mass of the vehicle. Increase N, and you increase F correspondingly.

    All things being equal, a truck will stop in the same distance as a car.

    The main limiting factor for why trucks don't/can't stop as fast as cars has more to do with the heat dissipation ability of the brakes. The brakes cook due to the massive amounts of kinetic energy being converted into heat (primarily - but also light and noise) by the braking system.

    Fix that heat dissipation issue, and you could have a truck the size of a oil supertanker, and it'll still stop just as quick as a car, provided the road and tyres were up to dealing with the weight load.