There are many ways to do this, but they usually involve spending money. Of course, we all know the more money we can save the more new cars we can buy. My idea is to make a simple but effective test rig from a plastic car case. This test rig is something all of us can make on our own, and it really costs almost nothing, since it uses items we already have. All you need is a car case, a steel bolt with a nut and washers, and the use of a Dremel Moto-tool or similar hand-held grinder for cutting. I used a case from a Fly Corvette, but after I had finished the project I saw that a case for a GB Track truck would have been a better one to use, because it is bigger and would provide more room to reach into the case and place the weight under the cars. It would also accept a longer bolt, perhaps providing greater scope for testing.

On the top of the case's black plastic base I ground down anything that wasn't flush with the surface, making it completely flat. Then I turned the base over and ground the guide slot off, making the bottom of the base completely flat, also. (Fig. 1) Next I cut out the top and one side of the clear case, leaving about 1/8" to 3/16" around each edge so it would still be solid. Then I put the base and cover back together and turned the case upside down. I now had a platform to set the cars on and an opening in the side to reach in. By holding the case up I could also use the cutout in the bottom to reach in.

For my first test I used Fly / GB Track classic cars, since this is one of the more popular classes of cars in 1:32 scale home racing. I set the first car, a Porsche 917 Spyder, on the test rig and placed a 5/16" x 1 1/2" steel bolt with a nut threaded onto the end up under the car to see if the magnet was strong enough to hold it. The cutout in the case side made it easy to reach in and put the bolt in place. The magnet held the bolt up. So, I removed the bolt, unthreaded the nut, and added a washer to increase the weight. The car proved able to hold up the bolt and nut with 2 washers, but not with 3. Now I had an idea of this car's magnetic downforce and could compare other cars to it.

The next car was a Porsche 917 K. This car had always been faster than the Spyder, and when it was placed on the test base, I could see why. This car could hold the bolt, nut and 5 washers. The ability to hold up more weight meant it had more magnetic downforce. I tested another car, a Chevron, which had always been faster than either of the Porsches, and it held the bolt, nut, and 7 washers, showing it had the strongest magnet installation of the three cars.

The objective is to get each car in a group of comparable cars to hold up the same amount of weight. To adjust the magnetic downforce of each car, simply raise or lower the magnet in the chassis by using shims or install tires of larger or smaller diameter.

This test simply compares total magnetic downforce. It doesn't differentiate between the magnet's strength and the height above the track at which it's installed. You can compare the strength of magnets directly, independent of their installation in the cars. Just remove the magnets from their cars, and test them one at a time on the test rig. If the magnets differ significantly in strength you can then swap them among the cars to help achieve parity, placing the strongest magnet in the car with the highest magnet position.

Using an accurate scale to measure the weight of the bolt, nut and washers creates a set of standards for record keeping and comparison and allows the racer to quantify each car's downforce in ounces or grams. When selecting a bolt for this project try to find one light enough to be held by even a mild magnet but capable of accepting enough washers to test even the strongest magnets.

Of course, this test rig evaluates only one specific component of performance and does not take into consideration tire grip, weight distribution, and other factors that contribute to handling. One important factor this test does not address is magnet location. Two cars with equal magnetic downforce but with magnets located differently in the chassis will have different limits and driving character. However, when equalizing a group of cars with identical or very similar magnet installations and chassis arrangements, such as the Fly classics, it can be a valuable tool. With magnetic force equalized, all the other performance factors can be evaluated and adjusted more accurately and usefully.

A rig like this can serve as a tech inspection tool, also. You can control the amount of magnetic traction used in your races by requiring every car to be tested with a bolt / nut / washer combination of a specified weight. Any car that holds up the weight has too much magnetic downforce and will need the magnet height adjusted to make it legal.