## Thursday, September 30, 2010

### Vehicle Dimensions

Back 275 blogs ago, I wrote "language is a system for encoding and decoding information so it can be shared ... a language of counting, measurement, shapes and calculation. A language with precise definitions and specialized terms."

When we talk about certain math-related items, it's helpful to use precise terms. Here's an example.

Sunday my wife and I were looking at a car in front of us. She said "Wow! It's fat". I asked if she meant the rear tires, or the body shape and size. She replied "It's got a wide wheelbase." That was an excellent try - wheelbase is a good automotive dimensional term - but in this case it was not the right word.

Here's a Mercedes factory diagram labeled using terms I learned in an earlier automotive career:

Wheelbase (length) is the distance between the centerlines of the vehicle's front and rear axles. Track (width) is the distance between the centerlines of the left and right tires. Notice the front and rear tracks differ on this car. The wheelbase sometime differs from side to side too, although that's rare.

With enough effort, you can describe vehicles precisely with words, but it's often better to provide a diagram which saves words (and translating).

If you are wondering Why all those measurements?, parking garages and ferries use this to decide where to assign a parking place, how steep a ramp you can negotiate, how much to charge, etc.

Here are two dimension diagrams from Mitchell International, where I worked for many years. These are used by collision repair shops to return your vehicle to the proper condition after a crash.
Without this, it's very hard to return a metal cube to its original size and shape. There are several kinds of dimension products, to suit the equipment a shop uses to straighten vehicles. This data comes right off the car - guys like me spent days carefully measuring all these places! If you need good dimensional data, you can buy it from Mitchell.

Now back to my wife's comment - the best way to express her observation in a mathematical, dimensional, automotive sense would be to say "that yellow car's got a wide track."

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