The first thing we need is a nice straight bit of wood. I used a tanalised roofing batten, which is about 1.5 x 4.0 cm and just wider than the car.
Next, we need to make up a pair of pointers which replace the nails in the "old geezer" approach. To do this, I used aluminium straight bar and some aluminium right angle bar. The straight bar is about 10mm across and the angle bar is about 3cm on each side. It's scrap I had lying around and it is easily bought from your local DIY store (mine came from B&Q in the UK).
Measure the distance between the centre of the front wheel hub and the ground. Cut a piece of straight bar so that it is the same length, then grind a point at one end. Now attach to the
outside of the angle bar using pop rivets so that the pointed end is away from the angle bar and the edge of the angle bar is aligned with the base of the straight bar. Drill and put one rivet in place, then - using a set square - move the bar so that it is perpendicular to the angle bar and carefully drill and put in a second rivet to hold it securely in place. The rivets should face outwards, that is we want to have the low profile rivet heads
inside the 90 degree angle bar. When complete, put in some more rivets the same way round as the first two rivets - these are to ensure we have a consistent point of contact when we attach the pointer to the wood.
Make a second one of these tools. When done, they should look like this:
- Right angled pointers
As you can see, mine are not the same width but that is unimportant. What is important is the length of the pointer and the 90 degree angle between the pointer and the right angled base.
I think you can see where this is going... next, prepare the wood. All you need to do is take one of the pointers and clamp it to the batten at one side. Mark up where the pointer bar is if (like me) you're not going to permanently attach the pointer to the batten. This means you can easily take it apart to put away, and reassemble later as needed.
- First pointer in situ with marks
At the other end of the batten, we need to create a reference point from where we will take measurements. Take a rough measurement of the distance between the tyres at the same point on each tyre using a tape measure and deduct 6 inches. Now measure from the point between the two marks at the end of the batten where the first pointer was clamped and drive a small nail into the batten on the same face that distance away from the measurement start point. This doesn't need to be terribly accurate.
- Little nail..
Now, we are ready to take a measurement.