This of course also applies to the test that magazines conduct. However we make the assumption that they employ the same methods (and therefore accuracy) in all their test.Nochmal said:93 ft for 60-0mph braking means that it pulled an average of about 1.3g.
If the speed measurement for 60mph was high by just 4mph, the force of braking was really 1.1g which would imply a real 60-0 braking distance of about 109ft.
As you can see, accuracy in the speed measurement is very important. The equation describing this is (remember to use consistent units):
x = v^2 / (2 * a)
where x is the braking distance, v is the starting velocity and a is the deceleration. Since the original velocity is squared, the accuracy of the measurement of the velocity is very important. As the tester said, they are still nailing down the initial velocity measurements so it is probably best not to make much of the results until the error on that measurement is very small.
The moral of the story is: Whenever someone quotes you a number you should ask what the error on that number is. If they can't answer this question well, their number is somewhat meaningless. Nothing is ever perfectly measured...so knowing the error on a number is key in understanding the number.
Actually, the fact that they use the same equipment doesn't take care of all the errors in a measurement. While it does is take out any systematic shifts in their measurements, it doesn't take into account random inaccuracies in the measurements. If their speed measurement apparatus is only good to +-4mph then their braking distance measurements are only good to that precision (an error of more than 10 feet on the braking distance measurements as you see in my first post) and any comparisons of the distances have to take that into account. They rarely quote errors on the measurement apparatus though, so we don't know if we can compare braking distances with a precision of less than 10 feet or not.Derek said:This of course also applies to the test that magazines conduct. However we make the assumption that they employ the same methods (and therefore accuracy) in all their test.
My question is why do I see official numbers for everything but braking distance?
Isn't stopping ultimately the most important thing