« on: August 26, 2005, 08:59:25 PM »
It would seem that the weight distribution is only part of the reason the front end dips when the brakes are applied. Another obvious factor is that most modern, "everyday" cars have larger rotors and beefier pads on the front wheels than the rear, leading to an innate asymmetrical brake force distribution between the front and rear. More substantial front braking systems = greater stopping force in the rear = tendency of rear of car to raise slightly. When this is combined with the uneven weight ratio (which only enhances the effect), you get a pronounced dip on braking. But it's foolish to say that "well, the car has an imbalanced weight distribution, so the nose dips;" that simply isn't the whole story.
And just in case you want to challenge this line of thinking...think about it the next time you see a tricycle-geared small aircraft land. Even though the nose of the aircraft tends to be much heaver than the tail (engine in the nose cone, pilot seated near the firewall, fuel in the wings near the midline), it doesn't dip when the brakes are applied, since all the braking is on the two rear wheels. As a private pilot with over 300 landings, I can confirm this from actual experience.
Just curious there Kang, how much experience do you have, with anything? You seem to talk a lot without much to back it up.
Well we might as well take this thread totally off topic. You're actually wrong in your reasoning, here's why. The size of the rotors/calipers has nothing to do with how the car settles under braking. Most people are confused when it comes to braking and its principles, with many believing nonsense like larger brakes inherently means harder stopping.
As we know from Newton (and having our eyes open ), an object in motion will tend to stay in motion unless counteracted. When an object slows down, its weight is transferred to the front; likewise, acceleration sends weight to the rear (I won't get into why). Therefore, even if the car did not have front brakes, it would still dip in the front when its braking.
So why are the brakes different size if it doesn't matter? Well, it does matter, but not for the reasons cited. The limiting force in braking is the coefficent of rolling friction between your tires and the road and the weight on the tires. (Frictional Forcel=coefficent of friction*mass*gravity) When your ABS comes on, you have locked the tires up and CANNOT brake any harder. You could have F1 Brembo brakes, but unless your tires (coefficent) or weight and/or weight distribution (mass) change, you will stop in exactly the same manner. You can think of locking your brakes as the point in which your brakes are pushing harder against the tire than the tire and road can push back against the brakes to keep the wheel spinning. As discussed earlier, the tendency is for weight (mass) to move forward under deacceleration, so most (more) of the weight is over your front tires. Therefore, your front tires have the ability to do most of the braking.
If your front brakes couldn't apply enough force, you could never lock them and never your achieve maximum braking potential. However, that still doesn't mean that they have to be bigger. Afterall, we're simply talking about a hydraulic clamp-- if the clamp can apply enough force, regardless of physical size, maximum braking can be achieved.
Which brings us full circle as to why they're bigger. They are bigger *simply* for cooling. The larger area of contact, the less heat is generated and the larger area that the heat can dissipate from. Those huge cool Brembo brakes are that size for cooling.
So what does create a car's "nose diving" if its not the size of the brakes? Is it weight distribution? Well, that can have a lot to do with how much mass is where under braking, cornering, and acceleration, but I think this thread is caught up in the visual "dipping" more than anything. That visual dipping is *COMPLETELY* the result of the suspension.
Actually I think the reasoning is pretty good...it appears you misunderstood what was meant by "greater force." (And the fact that where I wrote "greater force in the rear" should have actually read "greater force in front" may have contributed to the confusion.) I didn't use the term "greater force" with respect to the force of the pad on the rotor, but rather with respect to the force exerted on the vehicle by the braking wheels. So no, the front brakes don't grab the rotors any harder, but their larger size makes them more effective (as per that equation you cited), and the increased effectiveness (along with inertia, suspension, weight distribution, tire condition, etc) will help the front-end bite noticeably in most vehicles.
I hate to break it to you, but the front wheels don't require appreciably more force to stop than the rear. The brakes on the rear wheels are more than adequate to stop those wheels from turning (after all, if they weren't, there would be no need or benefit to having ABS on the rear wheels). You might argue that more force is needed in vehicles where the front wheels are driven, but that falls apart when you note that even most rear-wheel drive vehicles have larger front-end brakes. Front brakes are larger for increased efficiency, and their ability to cool is entirely dependent on their surface area and not their overall size.