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Re: I know it does: but how much does weight really affect Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 3 Jun 2003 13:45:22
In Reply to: I know it does: but how much does weight really affect, anthony, Mon, 2 Jun 2003 20:07:41 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Weight directly affects acceleration. It just plain takes more energy to accelerate more mass at the same rate. So to get the same performance, you're going to dip into the throttle more, using more gas.
Going up hills takes more power, and therefore uses more fuel. From a pure physics standpoint, a car on top of a hill has more potential energy than one at the bottom. To get from the bottom to the top, you need to add energy, which comes from using fuel. The potential energy is directly related to weight. Put it this way - do you work harder lifting 5 pounds or 100 pounds over your head?
OK, so you say you get that energy back going down hill. Well, not really. If you use the brakes to maintain your speed going downhill, you're throwing that energy away as heat. If you use engine braking, you're foot is off the gas either way, and again the energy ends up as heat.
So instead, don't slow down - after all, the heavier car will go faster down the hill, and you'll recover all the energy. Well, not quite. Wind resistance increases with the cube of speed, so the faster you go, the more energy you throw away in drag.
Oh yeah, the heavier car probably has wider tires, with more rolling resistance.
Of course, you're talking about SUV's so a couple of hundred pounds is a small percentage of the weight, as as Michael says aerodynamics is probably more important when you're comparing one large brick to another. On a car, it starts to add up.
But weight is important, and don't put your stock in performance figures. How were the vehicles equipped? You can easily have a couple of hundred pounds different in optional equipment. Performance figures are always suspect - from a car magazine, they only test one vehicle. Was that one representative of the breed, or a little slower or faster? Tester skill can easly add or subtract a half-second 0-60.
And last one about performance - very true for SUV's. Accelerating is easy. Stopping is what counts, especially when it comes to not hitting things. The heavier the vehicle, the harder it is to stop. You either need bigger brakes, or longer stopping distances.
There is a very good reason why Colin Chapman (Lotus) lived by his motto - "Add Lightness".
posted by 192.249....
, Tue, 3 Jun 2003 13:45:22 <-- Viewing This Message
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