Posted by AFX Road Racing Handbook on

Driver experience and proficiency, as well as the quality of the work performed on a model car, are of prime importance in AFX racing. To go beyond these factors in creating further im­provements, the forces that act on the model car must be understood. These are the same forces that act on real cars, and their results are identical.

The laws of gravity and motion dictate how fast you can go, cor­ner, and stop in any size car. Geometry — How round, how square, at what angle, and how



1.               A car that understeers tends to lose traction at the front end, refusing to follow the curve and going straight oft the road. In slot racing, this usually means the car "deslots”. There are ways to minimize this condition.

2Oversteer is the opposite of un­dersteer. Here, the rear end loses traction and slides toward the outside of a turn. It oversteer is too great, real cars usually spin toward the inside of the turn. In slot cars, you lose forward speed.

Building and driving to win requires basic knowledge of how cars work. Here’s the information that will put you . . .


precisely everything works together — determines how effectively you can reduce friction and take ad­vantage of these laws. Acceleration and speed are dependent on torque and horsepower at the driven wheels; deceleration (braking) depends on the weight of the car and resistance of the motor.

For racing, the lower the center of gravity the better (this means that the greatest part of the car's weight should be down close to the track). A low center of gravity improves cornering; it also reduces weight transfer during acceleration and braking. The lower the chassis, the better, to minimize drag caused by air getting under it. Remember, too, that a lower body profile reduces frontal area and decreases air resistance so higher speeds can be obtained.

Lowering the chassis is relatively easy: just reduce the tire diameter. Lowering the center of gravity requires the use of a brass pan, lead weights, or similar devices. Some of these are articulated to cancel vibration and shock. Replacing the stock body with a light-weight, vacuum-formed one also lowers the center of gravity. These changes will improve cor­nering which, in turn, will improve your speeds on the straights since

you'll be cornering faster with more speed in hand when you start down the 'chute.

To further improve cornering speeds, chassis balance must be understood. Proper balance be­tween "oversteer" and "un­dersteer" is essential to fast cor­nering and the bonus it gives — faster speed on the straightaways.

These two terms, "oversteer" and "understeer", are much used in real racing to describe car han­dling into, around, and out of cor­ners. In real racing, engine and fuel placement; tire pressures, widths, and compounds; sway-bar set­tings; spring rates; and aerodynamic devices; all are used to balance oversteer and un­dersteer to optimize car handling.

To achieve proper balance of our model car, we must use other methods. Before you begin ex­perimenting, however, make sure your track is clean and the slot is clean, or your tests won't be con­clusive.

Understeer is unwillingness of a car to turn into and follow through a corner. Although, in theory, the guide pin should lead the AFX car's front end around the turn, chassis understeer may be so great as to cause deslotting: The car simply won't go around the corner at thedesired speed. Several things may cause this disturbing situation. When you accelerate the motor, it develops a torque reaction that causes the chassis to lift in front — sometimes enough to lift the pin right out of the slot. It also hap­pens when you go into a corner much too fast. Or, it may be caused by putting wider or stickier rear tires on the car to get a better 'bite', thus increasing torque lift of the chassis. In stock car terms, un­dersteer is known as “pushing” or "plowing”.

The solution to excess un­dersteer or deslotting is to add weight at the front of the chassis to keep the guide pin in the slot. Remember, tho', that adding weight reduces acceleration as the motor must do more work to push the car along the track.

For faster racing, the idea is to get your front end to stick well so you can corner faster and — as we've said above — exit from the turn with more speed available for the straightaway run, thus covering more distance per second than your competition. If too much weight is added to accomplish this, your acceleration will suffer, thus cancelling out the advantages of faster cornering.

Oversteer refers to the behavior of the car's rear end. If a car habitually slides toward the outside of a turn, it is oversteering. If this tendency can be overcome, the car will lap the track more rapidly since so much of the motor's per­formance is wasted by spinning the tires. Also, exiting from a turn with the car sideways isn't the fastest way to go down the 'chute'. Ask any drag racer or racing driver. It looksBas "hairy”, but it's not the win­ning way.

While there are a number of tricks you can use for correcting understeer, such as reshaping

guide pins and pickup shoes, only two things will reduce oversteer. The first is adding weight, the second is using a wider or stickier tire. If these are overdone, your front end will start plowing again and deslotting, so a delicate balance must be achieved for the greatest success.

The 'ground-hugging' charac­teristics of a car can be improved dramatically by installing separate magnets in the chassis or lowering the motor magnets as in the AFX 'Magna Traction' or G-Plus cars. In either case, the magnets are at­tracted to the steel conductor rails imbedded in the track, providing a strong down-force that improves traction and handling.

3.               Brass pans, articulated pans, and weights all lower the center ot gravity while adding weight front or rear to help balance oversteer and understeer. Some articulated and iso-fulcrum pans are mounted ‘loose’ to cancel out track bumps and vibration.

4.               Lightweight, vacuum-formed bodies decrease body weight and automatically lower the center of gravity. They are usually of lower profile, thus reducing wind resistance.

5.               Acceleration forces try to lift the car’s front end up and out of the slot, due to inertia, tire resistance, and axle gear ‘wind-up’ when you "get on if’. Remedy: Add weight to the front end. There's more, tho' — see text.

Increasing power will change the situation as more weight can be added front and rear to control balance without cutting ac­celeration drastically. Heavier cars will stop more quickly, although that may seem to be a paradox.

More power and heavier cars require larger powerpacks and controllers, which generally create more heat and require more ex­pensive components — and a higher cost of racing. In model car racing, just as in real car racing, the objective is to select a class that you want to race in because it's the one you can afford or like best. Im­prove your car until it's running with the fastest in the field. Balance it, because that makes it easier to drive. In a way, your car then becomes like a finely tuned musical instrument!

6.  Sedans and stock cars have a high center of gravity. This means that the weight is higher than that of a low-profile racing car, so acceleration, deceleration, and centrifugal forces (in cornering) produce more weight-transfer. This ‘rocking’ or shifting balance is hard to predict for out-and-out racing slot cars.

7.  A low center of gravity is typical ot racing cars, designed for all-out speed and cornering. In fact, the lower the cen­ter of gravity, the better. Racing bodies also have less frontal area, hence less air- resistance and higher top speed for a given amount ot horsepower.

8.  A high chassis has a high center of gravity and more air under the chassis when racing. Ground clearance is im­portant: Even stock cars or sedans should be kept as low as possible for best han­dling. 9.      A low chassis gives a low center of gravity, less air under the chassis, and a low profile. All these lead to better han­dling and higher speeds.

10. The Aurora AFX Magna Traction and G-Plus cars employ the motor magnets to create a strong down-force. The same steel rails imbedded in the track that supply power to the pickup shoes also provide magnetic action. The powerful motor magnets are lowered In the chassis to within thousandths of an inch above the rails; thus, magnetic attraction occurs. This also tends to act as a shock- absorber, keeping the car from bouncing on even a very bumpy track.

11. Tire profiles. You can lower chassis height by run-sanding the tires and profiling them at the same time. Every builder has his own favorite ‘tweak’, but here are the basics: (A) is a stock tire, out of shape, out of round, needing run-sanding. (B) edges have been sanded off to eliminate flips while cornering. (C) Hollow-center shape, preferred by some who use super-soft sponge tires. (D) an unstable design, since the taper causes oversteer and flips.

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