Basic Racing Facts
Understeer is straight off!
Building and driving to win requires basic knowledge of how cars work. Here’s the information that will put you right 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 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. The 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 the 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 the 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 the desired 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 life 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 canceling 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 looks “hairy”, but its 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.
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 its running with the fastest in the field. Balance in, because that makes it easier to drive. In a way, your car then becomes like a finely tuned musical instrument!
Please be aware this an experimental blog that we plan to create that will share more information about the slot car enthusiasts. There are no images but those will be added later. - Ryan