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Quarter Mile Calculator (ET to MPH)

Let me give you an example of what I call my Corvette Rule. Maybe it’ll help you next time out. 

In my early 20s, I made some big mistakes when I raced a new Corvette that was in our Sportsman ET class. This thing would dial towards the fast end of the class, but would have a trap speed probably 10 MPH faster than anyone else.

So seeing the dial, I’d expect a certain look.

That car made the race look much different, and more than once I start whomping on him only to give it back. His painfully slow 60 and half-track made me think I had him when I hit 1000′.

Nope.

Well when I started racing a new class a while back, all of the dial-ins and speeds were different. I wanted to know what the finish line would look like. 

But my new Corvette Rule came into play. The dial in isn’t the whole story – especially if you fancy yourself a driver. 

I switched the way I looked at the numbers. I began seeing myself as stationary and saw them as +3 or -11 or whatever the difference in speed. It’s much easier to mentally picture someone on a tricycle cruising by at 3 mph to judge than psych myself out trying to judge this guy at 122. 

I can judge a tricycle. 

I began collecting the new data. I put a notebook in my car that I would write down the other racers’ ET and MPH from the boards in time trials. Not only did it help me learn where the people I raced should be dialing, it helped me see potential speed differences. 

So I began wondering about the relationship between ET and MPH. I’ve taken a sample of 4,000 time trial passes and put them on a chart.

Each dot is an ET and the corresponding MPH. It obviously has a trend to it, and after a bit of curve-fitting (R2=0.96) we get an equation:

     y = 1264.3x-0.97

Plug in x (the ET of some car) and get a general idea of what MPH they should do.

If you’re wanting to put it into Excel or Google Sheets, do this:

     =1264.3*(POWER(A1,-0.97))

…where “A1” is the cell of the ET.

Granted, some of the upper range of the y values would be like my Corvette buddy, cars with turbos, and so on.

It’s especially varied as you enter the 6 second quarter-mile range with all the various power-adder options. The lower values at each ET could be cars that lifted slightly at the end or cars geared for acceleration. But for most NA cars you might race, this should get you within +/- 3 MPH.

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