Slot Car Illustrated, The Online Magazine for Slot Cars! - How To

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Published: March 15, 2003

In slotcars, few things can be taken for granted. Often the same exact cars will run differently due to slight differences in downforce magnets, manufacturing tolerances, or motor magnets. One other difference is often the tires. Some manufacturers have better quality control than others when it comes to tires, but one thing is for sure: cars run best if their tires are round. Another word for round, is "true". In just about any slot car review, or any discussion on preparing a slot car for racing, you will come across the term "truing the tires". This refers to the process of making the tires round, or true. Described below, in brief, is my personal method of truing tires. Like anything in life, there is more than one way to skin a cat. Likewise, there is more than one way to true a "skin", and I make no claims that this is the best way, just the way that seems to work the best for me.
Most slot cars that come straight off the shelves will require some degree of truing. One reason might be that the tires are simply out of round. Cars with out of round tires will tend to hop at speed, especially on no-magnet or light magnet cars. When the rear end starts hopping you will notice that your cornering suffers the most because the rear end is continuously becoming light, even airborne briefly on one or more tires, and this causes the car to lose traction.

Another problem new cars have is not necessarily being out of round, but just not flat against the track. Sometimes the radius of the centerline of the tire is less than the radius of the outer edge of the tire. This is referred to as crowning. Because of this condition, the tire isn't utilizing as much of the tire surface as it could be, and will suffer on take off, braking, and cornering. By truing this we can make this tire flat, and put more tire on the track.

As stated, there are several ways to get a tire true, even some mechanical devices available. This method is a cheap way to get results, and will work for most home racing applications.

I take some 150 grit sandpaper and hold it on the track with a couple free fingers on my controller hand. Then with my free hand, I hold the car backwards on the track with the rear wheels over the sandpaper. You could tape the sandpaper to the track, but I find I like to have the freedom of taking it off the track at will when I want. I then give the car full throttle, and allow the car to settle down onto the sandpaper, making sure that both wheels touch the

sandpaper evenly. I'll let the tires spin on the sandpaper for about 10 to 15 seconds, then I will lift the tires off the paper and let them spin for a few seconds to let them cool.

It's important to use a light touch, and not try to get the tires round as fast as possible. If you use too much pressure, you may just end up sanding down the tires, but not getting them round. You'll just have less tire. Another problem with using too much pressure is that you might damage the gears, or over-tax the motor. If things start to get hot, you're either doing to too hard, or it's time to stop for a minute.

I will repeat this several times, looking at the tires periodically to make sure that they are truing evenly. Once I am satisfied that the tires "look" round, I will clean the tires with masking tape and do a few laps. It's on these laps that you will determine if you've done a good enough job. Listen for excess noise, and experience will tell you right off it it's tire noise, or just normal sounds.

The picture to the left shows the "crowned" tire after a bit of truing. Some people even take this a bit further, removing all the tread off the tires leaving slicks. Since this reduces the diameter of the tire, it also brings the traction magnet closer to the track. Whether you go this far or not, you will find that by having rounder, truer tires, you will increase your lap times considerably, and you will have taken your first step to becoming a slot car expert! Have fun, and be true!

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