All the talk at Michigan about high speeds and the hoopla over passing the 200-mph barrier prompts me to offer this caveat: Take the speeds you hear with a grain of salt because the average lap speeds are estimates, not measurements.
The quantity being measured is time. The speeds you see in NASCAR timing and scoring are obtained from the classic equation:
The whole business of how tracks are measured is sort of murky. Some tracks measure the distance around the apron. Some tracks measure the distance along a line 15 feet from the apron and others measure the distance along a line 15 feet from the outside wall. For simplicity, approximate a track as a circle with radius r. The distance around the circle at the radius r is 2 πr. Let’s say that is 2.0 miles. If I change r by 15 feet, I change the distance I have to travel by 94.2 feet (0.01785 mile). Given that the lap time is the same (we’ve measured it), changing the distance changes the speed. Mark Martin ran a lap time of 35.805 seconds. At 2.0 miles distance, that translates to 201.0892 mph. If he actually ran a shorter path (1.98215 mile, which corresponds to a 15-foot difference), then his speed was actually only 199.2945 mph. That’s about 2 mph from a very small shift. Of course, if he ran a longer distance than the 2.0 miles, he would have been going even fast. We don’t know exactly how far the car goes on each lap.
If you assume that the distance traveled in the straights isn’t going to vary too much with your position, this is probably pretty accurate. Michigan is a pretty wide track, too.
The conclusion: it’s nice to deal with round numbers like 200 mph, but all of the hoopla about passing some magic mark is just silly. The number gets attention and sounds impressive, but it’s not real. Trust in the lap times.
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