If you enjoy racing your slot car around the track, you'll want it to move smoothly and fast. In this guide, we'll take you through the basics of HO slot car tuning to help your car reach its optimal performance. From the tire tuning to smoothing the gears and oiling the motor, these slot car tuning tips will improve your car's grip and all-around mechanical performance.
Initial Inspection
Before you get started, get your supplies together. You'll need basic tools like sandpaper, a screwdriver, a nail file, glue, tape and oil to tune your slot car. From there, the first step to tuning slot cars is an inspection. Start by unscrewing the chassis from the body and remove the tires from the rims. Taking the car apart like this will give you a good view of the parts to see what needs tuning.
Gently rotate each rim in both directions to see if they're loose. If they are loose, glue will help keep them firm on the axle. Make sure to check for any defects like cracks, too. Gently move the axle up and down and then side to side to check how the bearings fit in their holders. If you notice a little movement, you can use glue to keep them in place.
Once you inspected your car and know what needs attention, you can get started with the tuning.
Tire Truing and Cleaning
At first glance, the tires on your slot car may look round, but they will have defects that affect their grip on the track. The profile of the tires when you first get your slot car is either raised on the edges or in the middle. The aim is to have a flat tire that increases the contact area between the rubber and the track and gives a better grip. The way to do this is through tire truing.
How to True Slot Car Tires
The rear tires are the ones that you will true. You will need an elastic band or sticky tape and a few sheets of sandpaper — one coarse 100 grit and a finer grit of 500 or more.
Use the sticky tape or elastic band to hold down the trigger on your controller to give power to one lane on your track.
You can tape or use your hand to hold a piece of sandpaper on a flat and level part of the track. Place your car into the slot keeping the rear tires off the track. As the rear wheels spin, slowly and gently lower them onto the sandpaper. All you should focus on doing is holding the chassis steady for a few seconds at a time. Don't push down on the wheels. Applying too much pressure can cause the motor and the tires to overheat.
Throughout the truing process, take the rear tires off the track, check how the sanding is going and then continue sanding for a few seconds. You'll notice the sanded parts will be a different color to untouched areas. Those unsanded parts are the high points that you also need to sand down. Once the whole tire is the same color, the profile will be flat and the tire round. Then use the finer grit sandpaper to give the tires a smooth finish.
If you notice the tires have sharp edges, round them off to stop the car from tipping on the track. Take a small piece of sandpaper in one hand and the car in your other. Place it in the slot with the rear tires off the track and gently sand the edges, changing angles until you get that rounded finish.
Once you've done with the rear tires, the rims they sit on will also need truing using the same process. Plastic rims usually need truing as opposed to metal rims. Note that rims often have a central rib, making working with their shape tricky. Using a nail file can help you work on them.
When you're happy with your tires and rims, glue the tires back on to keep them from slipping off. Slip your tires back onto the rim, pull out the tire to make a gap between the rim and the tire and apply a small amount of glue. Press the tire onto the rim. Do this evenly around the tire at least three times, and then repeat it on the other side of the wheel.
To clean your slot car's tires, all you need is a little water and a cloth, then rub the tires in both directions to remove any dirt or dust.
Adding Weight to Your Slot Car
In an ideal situation, a slot car runs smoothly with no added weight. How your car behaves on the track, especially at or above its cornering speed limit, will show you if it needs more weight. Extra weight can solve the problem if you notice your car doing these three things:
Tipping: To keep your car from tipping over, add weight onto the chassis at a low, central point to keep the center of gravity low.
Oversteering: If the rear of the car has a habit of sliding off the track, added weight near the rear axle can help increase the grip of the rear tires.
Understeering: This happens when the front wheels go off the track or the front end of the car lifts on acceleration. In this case, add weight to the front of the chassis.
When you add weight, it's usually best to add it to the middle of the car. The car's mechanical parts are often in the center, so you'll likely have to add two weights of equal size on either side of the motor.
As you add weight to your slot car, do it in stages. Start with lighter weights, test the car and, if necessary, add more weights until your slot car runs seamlessly on the track.
Smoothing Gear Mesh
If your slot car is noisy, it could mean that your gears need smoothing. There's a simple way to check if the noise comes from the gears — turn the rear wheels manually. Ideally, they should turn smoothly, making no sound. If you feel like the gears are clicking with each wheel turn, they'll need attention.
To smooth your gears, all you need is abrasive toothpaste. Smear a drop around the gears and run the motor for 5-10 minutes while applying the paste. Remove the body first so you don't get toothpaste all over the interior.
When you hear the gears starting to mesh without the noise, you know they are running smoothly. Clean the toothpaste off the gears thoroughly. If any gets left behind, it will dry up and jam the gears. After this cleaning, you'll have a slicker and faster-running slot car.
Misshapen Gears
In some rare cases, slot cars come with distorted gears. A quick way to check this is by again turning the rear wheels. If you feel immobility once in a rotation, it's likely that the tooth called the crown or spur on the large gear is the problem. Stiffness that happens more than once in a turn of the wheel means that the problem is the pinion, which is the smaller gear on the motor shaft.
Remove the body from the shaft and mark the point where you feel the stiffness as you rotate the rear wheels.
The defects can be hard to spot, so you'll need a magnifying glass for a better look. Depending on which gear is the problem, remove the rear axle or motor and use your magnifying glass to inspect the point you marked. The area may have excess material on it or be misshapen. Use a file or scalpel to make the tooth the same shape as the others.
Body Float
Instead of an inflexible body attached to the chassis, you want it to be able to float or rock when the car is in motion. Loosen the screws between the body and chassis to get this result. The car's weight moves to the outside wheel when cornering, so it needs to be able to keep the car from sliding. How does this apply to body float? When you loosen the screws, you achieve two things:
Reduce the body stress that can cause the chassis to flex and interfere with the tire grip.
Allow for more weight distribution on the outside wheel, creating better grip and even cornering.
Use a screwdriver to loosen the screws by one complete turn. It'll take a few test runs to get it right and have your car running on the track without deslotting around corners.
If you're wondering whether your slot car will benefit from loosening the screws, these factors and tips can help you make your decision:
It's best to loosen the screws on non-magnetic cars. In a magnet slot car, if the body is too loose, it could disturb its motion, causing the magnet to pull it downwards.
This process works best on cars with a low center of gravity. High-center-of-gravity cars with loose screws may tip over unless you add weight to the chassis too.
Cars with the chassis within the body gain more from added weight than cars where the body is on the chassis.
Some cars have bits inside that you'll need to trim down with a craft knife to stop them from interfering with the body float.
If your car has regular full-thread screws, replace them with screws with an unthreaded shoulder to prevent the body post from catching on it.
Once the screws are loose, put insulation tape over them or use tack to keep them in place.
Running the Motor
A slot car motor has a few parts, but the ones we're most interested in during the tuning process are the commutator and the two brushes around it. Brushes are mass-produced items, so the fit is not custom-made for the commutator. Slot car motor tuning will help minimize the friction between these parts.
To run the motor, you'll need a simple adjustable power supply. It's best to leave the motor in the car and run the gears at the same time so all the parts work together with these steps:
Remove the car's body and add oil to each point where the shaft comes out from the can.
Lift the rear wheels to allow them to spin freely.
Connect the motor to the power supply and run the motor forwards at three volts for 30 minutes.
Add more oil and repeat the running of the motor at six volts.
If you listen carefully, you'll pickup on the increase in the revs.
There is another method where some believe running the motor underwater gives better results. If you choose this process, you must take extra care to protect your motor. To tune your motor using the water method, you'll need deionized water, isopropyl alcohol and an air duster canister. Then, follow these steps:
Take the motor out of the car.
Add a few light drops of oil to the shaft and submerge the motor vertically in the deionized water.
Connect the motor to the supply, running it at three volts for 30 minutes. You'll notice the water color change and become murky as the carbon releases from the motor.
After 30 minutes, change the water to fresh deionized water.
Lightly oil the spindle again and repeat the submerging process at six volts.
Take the motor out of the water and place it in a container with the isopropyl alcohol running it for 15-20 seconds.
Remove the motor and dry it using the air duster canister.
Apply oil one last time, and the tuning is complete.
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