Anonymous wrote:Aren’t heavier vehicles going to have longer stopping distances based in part on weight of the vehicle? That said, some vehicles brake when crashes are anticipated.
Braking systems vary in their capabilities. The same braking system on a heavier vehicle will have longer stopping distances, assuming the same tires, but different vehicles usually have different brake systems, so vehicle mass is just one variable. High performance pad materials, bigger rotors which are ventilated to dissipate heat better, and other details make a big difference. So a heavy vehicle with a high performance brakiong system may stop in much shorter distances than a lighter vehicle with a more pdestrian braking system. Even within similar models, brakes can vary. The M-design brakes on BMW M class vehicles are practically racing brakes, and clamp down very hard, so a BMW X3M, for example, can stop in a much shorter distance than a non-M X3, despite both weighing relatively similar amounts.
Additionally, tires are an important contributor to braking distances. So-called touring-type all-season tires, designed to maximize wear and ride quality, are less adhesive than shorter-lived high-performance summer-only tires, which stick to the road much better but also wear out relativelly rapidly, and also usually provide a harsher ride. In the xample above of the BMWs, the X3M comes from the factory with summer-only high performance tires while other variants of the X3 come with all-season tires. The X3M can corner much harder, will accelerate faster due to less tire slip as well as a bigger engine, and will stop faster, all due to the high-performance nature of the tires it uses. But, those tire may only last 20K miles if the car is driven hard, and the X3M has a harsh ride by most standards, with the tires as well as the sport suspension both cointributing to that. If safety, rather than economy or plushness, is the priority, the X3M is a much better choice (price aside, of course).