I'm sorry I didn't quite say it how I wanted to. My implication was not to be that a small car is "not properly configured," but rather that a large vehicle, when given brakes appropriate to its size (ones that will not experience fade over the duration of the single stop, and that can also "lock" the brakes at any speed) will be able to stop in quite nearly the same distance as a small vehicle.

I personally own a tiny little 1-ton CW Saturn Sky and it has a 70-0 MPH braking distance of 168ft.

I am not suggesting that there are not light cars which stop faster than heavy cars; I am simply saying that a light car does not mean that you WILL stop faster than a heavier car. The physics of the problem are really quite simple.

What can help a car stop faster is any aerodynamic design features with the intent of providing down force, of course at lower speeds these become less relevant (fluid friction being dependent on v^2), but at high speeds extra down force means a greater normal force, which means more force that the road can apply to your vehicle. Small cars are usually designed to employ some decent down force to help all forms of traction, braking being one of them. You'll probably not find a pickup truck designed with a front air dam and rear spoiler (a real one...) to give any benefit, so that may make up some of the difference.

If I stick a ton of bricks in my little car right at the center of mass, I should be able to bring it to a stop (if I'm not fade limited) in the same distance as I can without.

As for tire diameter, and nearly any other argument, I submit that you can look at the car as a whole system. Completely ignore the internals of the vehicle, when you brake, you are trying to get the road to push you in the opposite direction of your velocity. The contact point of your car to the road is the contact patch of the tires. If you apply the maximum amount of braking possible, you lock the tires. You are then dealing with the kinetic friction regime, with coefficients of friction usually much less than those for static friction.

If, however, you get the tires to apply infinitesimally less force to the road than the "breakaway" force, you are in the static friction regime. This is what an ABS system lets you do.

The frictional force between the tire and the road is described by F=N*u, where u is the coefficient of friction. The acceleration of a mass under the influence of a force is: F=ma. Our force is friction, the normal force is N=m*g, so our braking acceleration is given by m*a=m*g*u. That is, a=g*u. The mass of the stopped object never enters into it; nor does the tire size, rolling resistance, or any number of other features.

There is a qualification with this, of course, and that is that the coefficient (u) can change based on temperature, and myriad other parameters, but it does NOT depend (in the first order) on the contact patch.

Basically, if your car can lock up its brakes, it can stop in roughly the same distance as any other car.

As for the ABS vs. Human, it would be quite interesting. I'd wager it could be close as a human might not apply the maximum force that they could, but an ABS system pulls off the brakes a bit more than it needs in order to switch back from kinetic friction to static friction. Lock up the brakes just once in stopping though, and the ABS will win by a long shot; I figure, at least, due to human reaction times.

P.S. Sorry this is such a ruddy long comment! I can shuttup if desired.

That's just silly.

If you had've said "not necessarily" and left out your opinion that lighter cars are not "properly configured", I might have given you some credit.

I say a one tonne car with 6" tyres will stop quicker than a two tonne car with 7" tyres.

But I can see we're not going to come to any agreement, so it's braking at dawn!

Or... Maybe we could ask MythBusters? We could also ask them to test the difference between ABS and a driver trained in emergency braking! John Henry style.

Robot verses Human! I'd pay to see that!

It's fine aside from that, but I just want to take a rubber mallet to each of 'em until the odd lump goes away.

I only have a minor nit to pick with: "Lighter cars stop quicker."

Given adequate braking systems and appropriately scaled braking capabilities, the mass of an average consumer vehicle should have no significant effect on its ability to stop in a single, isolated, fast stop event.

All of the qualifications are there just to handle the fact that a larger vehicle will have more kinetic energy which the brakes need to dissipate leading to possible fading on larger vehicles.

All other things being equal though (tires, road surface, etc.), the extra mass will result in a larger momentum which must be arrested; but, it will also provide a greater normal force for the load bearing surface contact (the tires) and as dry frictional forces (static and kinetic) are proportional to the normal force, the increased load will increase the force which may be applied to the vehicle by the road.

Now, the normal force is linearly proportional to the mass, and the acceleration response to a force by an object is linearly proportional to the mass, therefor, all things being equal, the mass of the object does not have an effect on the time or the distance it will take to stop it.

Of course, when you're dealing with a big rig truck, and stopping one of them hard pulls the road along with it a bit, and the brakes turn to molten steel...well, then we're not talking about the same situation. So, sorry for the narrative, but; no, having a smaller car will not make you stop faster than a normal big car that is properly configured.

Fashion?

Lighter cars stop quicker.

I've had two crashes in 20 years. Both in the tonnes wagon. When some idjut gets in the way, half em vee squared.

You can still get pretty lightweight cars with modern safety features, though. If you're in the States it's arguably not a great idea to drive an MX-5, Fiat Panda, Nissan Micra or whatever, on account of all the cavemen zipping around in pickup trucks and SUVs who can barely even see you. But in countries where the top ten selling cars aren't more than half "commercial vehicles" with pollution-regulation exemptions, you really can still get reasonably light, nippy cars that won't try to kill you, or someone else, once a year.

(I think the Nissan Exa was quite well represented in the accident-death stakes, when it was popular. Front-wheel-drive, short wheelbase, turbo, no anti-lock brakes of course... what could possibly go wrong?)

Those wagonbacks are a strange mix of attractive and repulsive at the same time. Kinda like the taste of mushrooms, it's a whole different flavour.

Also, the EXA/Pulsar/NX of the '80s was brilliant - but then, anything with T-tops and an optional removable wagonback has to be.

From that, I went to a '83 Nissan EXA turbo. 1.5L, 930 kg, 77 kW. Uses 7.5L of Juice per 100km. I enjoy contrast. This was built only 6 years after my 1.7t, 20L/100km wagon, and went just as fast.

What gets my goat (and the point I'm trying to make), is that we've been able to build light, efficient cars with plenty of power for decades, now. I'd say the EXA was before its time, but since then we seem to have gone backwards! Cars are getting bigger, fatter, squarer, greedier! Just look at all the Toorak Tractors! Automatics, too! You don't put automatic transmissions in four wheel drives!! It's an abomination!!! AN ABOMINATION!!!!

*ahem* As I was saying... The 2000 Camry is a decent, utilitarian car (so? It's a dishwasher). The new ones look stupid. Some marketing genius is trying to hack 1920s (not aerodynamic) grilles on the front.

It's not working for me...

But, I'm different. Very choosy. And not easily lead by the "market forces" of marketing "geniuses".

I choose cars for their cost, utility, efficiency, and unique style. A kind of Venn diagram. At the centre of that I found a '94 Nissan NX Coupe, affectionately known as the "Pregnant Egg". The cousin of the EXA, it weighs 200 kg more, has 50% more power, uses the same amount of Juice... And the roof comes off! :D

BTW, Dan, I'm not grocking your Camry = Die thang. Care to elaborate?

The North American model is here. I see that yours is nearly identical.

You'd think people would at least buy a similarly-sized but slightly-more-interesting Accord, at least.