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Many Americans seem to have been told they need to drive a tank-like car to be safe. I point out that the tank is safer in a crash, but a smaller car may be abl

Many Americans seem to have been told they need to drive a tank-like car to be safe. I point out that the tank is safer in a crash, but a smaller car may be able to stop in half the distance and avoid the crash altogether. I am assuming that its safer to focus on avoiding a crash than surviving it, but maybe I am wrong. Certainly it would depend on the driver. If you want to text on your phone and not maintain distance with the car in front than the tank approach is probably safer for you (but dangerous for everyone else).

10000truths 2y ago
It also fails to take into consideration that once everyone else gets a larger vehicle, you're less safe because two large vehicles colliding does far more damage than two small vehicles colliding at the same speed.
AnthonyMouse 2y ago
> I point out that the tank is safer in a crash, but a smaller car may be able to stop in half the distance and avoid the crash altogether. The problem there is that they're not actually correlated. A BMW M5 has a shorter stopping distance than a Mazda Miata even though it weighs almost twice as much.
- gregwebs 2y ago
  Good point, when buying a car, one can try to buy good stopping distance. Still, all things being equal bigger classes of cars take longer to stop: https://www.consumerreports.org/cars/car-safety/best-and-worst-braking-distances-a2960086475/ https://www.consumerreports.org/cars/car-safety/best-and-wor... I also wonder what happens in real world non-ideal scenarios (including rain and snow) rather than on the perfect test tracks they test stopping distance on. Perhaps the fundamental advantage of a smaller car is increased maneuverability.
  - AnthonyMouse 2y ago
    There isn't really anything fundamental. A heavier car has more momentum but it can also be fitted with larger tires with more contact area and the force of gravity pressing it into the road provides increased traction in proportion to mass. Cars aren't built to meet the theoretical limits of physics, they're built with trade offs against cost and other factors, so in practice things like stopping distance are less related to weight and more related to how much you prioritize it over the competing trade offs. A heavier car with the same stopping distance might cost more, but then there are people willing to pay for that.
- FireBeyond 2y ago
  That's a little contrived, no? I don't compare my RS 5 with a Corolla, either. The Audi and BMW have brakes like that because they also are literally designed to spend some time on the track (mine has integrated laptimers and speed calculators for 0-60 times, etc., and shows me individual tire temperatures not just pressure, as well as component temperatures for drive train, transmission, differential).
  - AnthonyMouse 2y ago
    But that's the entire point. If you want to design a heavy vehicle that can stop quickly, there is no physical law preventing you from doing so. I mean just think about it. If a 3000 lb car can stop in 3 seconds then two 3000 lb cars can also stop in 3 seconds even though together they weigh 6000 lbs. It would be no different for a 6000 lb vehicle with eight tires and eight brake discs, and you can also get the same result using larger tires and brakes instead of more of them.
crazygringo 2y ago
But smaller cars tend to have weaker brakes, and less weight that means less friction against the road in braking. Brakes are "sized" for the car they're in. Bigger cars have more powerful brakes. It would be a major safety issue if heavier cars couldn't brake as quickly as safety required. So no, smaller cars don't have any general advantage in being able to stop earlier and therefore avoid accidents.
- peoplefromibiza 2y ago
  That's true but only in perfect conditions. A not perfect breaking system or imperfect road conditions in a lighter car will cause a much smaller mass to not break as quickly as safety requires.

10000truths 2y ago

It also fails to take into consideration that once everyone else gets a larger vehicle, you're less safe because two large vehicles colliding does far more damage than two small vehicles colliding at the same speed.

AnthonyMouse 2y ago

> I point out that the tank is safer in a crash, but a smaller car may be able to stop in half the distance and avoid the crash altogether. The problem there is that they're not actually correlated. A BMW M5 has a shorter stopping distance than a Mazda Miata even though it weighs almost twice as much.

gregwebs 2y ago
Good point, when buying a car, one can try to buy good stopping distance. Still, all things being equal bigger classes of cars take longer to stop: https://www.consumerreports.org/cars/car-safety/best-and-worst-braking-distances-a2960086475/ https://www.consumerreports.org/cars/car-safety/best-and-wor... I also wonder what happens in real world non-ideal scenarios (including rain and snow) rather than on the perfect test tracks they test stopping distance on. Perhaps the fundamental advantage of a smaller car is increased maneuverability.
- AnthonyMouse 2y ago
  There isn't really anything fundamental. A heavier car has more momentum but it can also be fitted with larger tires with more contact area and the force of gravity pressing it into the road provides increased traction in proportion to mass. Cars aren't built to meet the theoretical limits of physics, they're built with trade offs against cost and other factors, so in practice things like stopping distance are less related to weight and more related to how much you prioritize it over the competing trade offs. A heavier car with the same stopping distance might cost more, but then there are people willing to pay for that.
FireBeyond 2y ago
That's a little contrived, no? I don't compare my RS 5 with a Corolla, either. The Audi and BMW have brakes like that because they also are literally designed to spend some time on the track (mine has integrated laptimers and speed calculators for 0-60 times, etc., and shows me individual tire temperatures not just pressure, as well as component temperatures for drive train, transmission, differential).
- AnthonyMouse 2y ago
  But that's the entire point. If you want to design a heavy vehicle that can stop quickly, there is no physical law preventing you from doing so. I mean just think about it. If a 3000 lb car can stop in 3 seconds then two 3000 lb cars can also stop in 3 seconds even though together they weigh 6000 lbs. It would be no different for a 6000 lb vehicle with eight tires and eight brake discs, and you can also get the same result using larger tires and brakes instead of more of them.

crazygringo 2y ago

But smaller cars tend to have weaker brakes, and less weight that means less friction against the road in braking. Brakes are "sized" for the car they're in. Bigger cars have more powerful brakes. It would be a major safety issue if heavier cars couldn't brake as quickly as safety required. So no, smaller cars don't have any general advantage in being able to stop earlier and therefore avoid accidents.

peoplefromibiza 2y ago
That's true but only in perfect conditions. A not perfect breaking system or imperfect road conditions in a lighter car will cause a much smaller mass to not break as quickly as safety requires.