CHARACTERIZING A CAR form Tamiya guide book

CHARACTERIZING A CAR
There are a variety of car characters fast cars, cars with excellent acceleration, cars with good cornering capability, and so forth. Cars assembled from kits come out diversified in quality because they are built up through the assembler’s own techniques. Build your car in your own way. The most apparent characterizations are formed in the gear ratio and the steering characteristics.

1. GEAR RATIO SETTING
At a given output power of the motor or engine, the maximum speed and acceleration capabilities are determined by the gear ratio. The gear ratio means how many rotations of the pinion gear are required for one rotation of the drive wheel. This is generally adjusted by altering the pinion gear to one with a different teeth number.

RELATION BETWEEN THE GEAR RATIO AND SPEED/ACCELERATION
You will have a higher gear ratio with a smaller pinion gear (smaller number of teeth) and a larger gear on the rear axle. The opposite makes a low gear ratio. With a high gear ratio, the car has a better acceleration capability, but a limited maximum speed. A car with a low gear ratio has poor acceleration but a higher maximum speed.
A car with a low gear ratio has poor acceleration but a higher maximum speed.
A car with high gear ratio is suitable for a technical course which is built with hair pin curves demanding low speed driving, while a car with a low gear ratio is for a speed course consisting of longer straightaways and curves of larger radii.
*A too low of a gear ratio will overload the motor/engine, resulting in overheating and eventual burn-out.



GEAR RATIO AND RUNNING TIME
In general, the higher the gear ratio is, the longer the running time, and vice-versa. When entering a time race such as a 4-minute or 8-minute competition, a suitable gear ratio to complete the race must be chosen. In endurance competitions, the gear ratio influences times of battery change or refuelling.



GEAR RATIO SUITABLE TO THE MOTOR/ENGINE
A wide range of optional pinion gears are on the market for many variations in the gear ratio settings. You should always bear in mind that motors and engines have their own power output characteristics and effective power range. If the motor or engine is replaced with one with higher performance, replacement of the pinion gear will also be required to obtain a suitable gear ratio. The diagrams below indicates suitable pinion gear for Tamiya electric cars and motors.

GEAR RATIO SETTING PROCEDURE
Start from a large gear ratio (small pinion gear teeth number) and move to smaller gear ratios. Check lap times on a track or running time and select a suitable gear ratio for the track.

DRIVE WHEEL DIAMETER
The diameter of the drive wheels are also related to the speed and acceleration characteristics. The larger the diameter of the drive wheels is, the higher the speed of the car will develop within certain limitations.
*Attaching too large a diameter of wheels will overload the motor/engine and resulting in overheating and burn-out.

2. UNDER STEERING AND OVER STEERING (STEERING TENDENCY)
When the steering wheel is turned, the car will also turn in the same direction. However, most cars have the tendency to turn excessively or inadequately. These characteristics are called steering traits. Cars that turn excessively have over steering traits and the others have under steering traits. Cars that turn in close proportion to the control have neutral steering. This is hardly achieved except with cars that are running at a low speed.



A car with under steering is easy to drive. A car with over steering will spin when taking corners high speed. Even on a straight course, it An under steering car has difficulty making sharp turns, and at a high speed it may not be able to take corners and could leave the course. In either case, excessive steering makes a car difficult to control.


MOTOR/PINION GEAR CHART (ACCORDING TO CHASSIS)






FACTORS TO DETERMINE STEERING CHARACTERISTICS
The steering characteristics are affected by the difference between the traction of the front and rear tires. When the traction of the front tires is greater than that of the rear tires, the result is over steering. The opposite condition causes under steering. Therefore, adjust the traction of the rear tires so that it is a little greater. You will attain a slight degree of under steering.
The traction of a tire is determined by the following factors. By adjusting these, the steering tendency of a car can be altered.



3. CHOOSING TIRES
Motor/engine power is transmitted to the ground via tires, and a car’s stability during running is also greatly affected by the tire’s traction. Choosing suitable tires is a very important point in the car’s setting.
Two types of tires are used on cars; synthetic rubber semi-pneumatic tires and sponge tires. In addition, tires of various materials, widths, tread patterns etc. are available for broad range of settings.
*The diagram above indicates the grip of Tamiya optional tires. The tire grip may differ depending upon the track surface condition, temperature, etc.

ON-ROAD TIRES
Both sponge and semi-pneumatic tires are used for on-road track running. In case of sponge tires, sponges of different stiffness are used to obtain different traction. Special synthetic rubber caps are sometimes used to cover the surface of sponge tires (these are
called “capped tires”). Semi-pneumatic tires for on-road running are roughly divided into the treadless slicks or treaded tires. These are sometimes used in combination with inner sponges.



Reinforced tires are used on M-chassis, F-1, GT and oars. Furthermore two—types of reinforced tires, A-type and B type are prepared for F-1 and GT cars according to circuit temperature. A-type is resistant to changing temperature. Special material is used on B-type for high-grip under high-temperature conditions.

COMPARISON BETWEEN A-TYPE & B-TYPE


EFFECT OF INNER SPONGE
Inner sponge and insert provide even contact between the tire and ground relation, and are effective in increasing overall traction. Insert is ring-shaped synthetic rubber foam to fit the cavity between wheel and tire. Without the inner sponge, the car’s weight is carried by side walls of the tires. Therefore tire edges are liable to wear. Inner sponge helps these problems, by providing an even contact of the tire surface to the ground.
Belt-shaped inner sponge, inner foam and ring-shaped insert are prepared. We supply standard and hard types as inner sponge, standard and soft types as ring-shaped insert. We recommend to use foam and reinforced slicks type-A together for more efficiency.



SECURING TIRE
It’s important to secure semi-pneumatic rubber tires to the wheels. In that case, tire-c:ementing helper is useful. Just set tire into the inside of helper, then hold it down to make a gap between tire and wheel. Now, apply instant cement between them. We recommend to use TAMIYA CA cement (for rubber tires). TAMIYA CA cement (fot ruber tires).



OFF-ROAD TIRES
Semi-pneumatic tires are mainly used for offroad cars. Tires with various spikes and tread patterns are available. These spikes and patpatterns provide positive traction while running on rough terrain. Choose tires according to
the running surface. Semi-pneumatic off-road tires can be combined with inner sponges when necessary.



4. SUSPENSION SETTING
On full-sized vehicles, the suspension is important in providing a comfortable ride to passengers. On cars, its main objective is to keep the wheels on the ground and maintain constant traction to obtain the maximum maneuverability.

A GOOD SUSPENSION PROVIDES TRACK-HUGGING PERFORMANCE
In order to run a radio controlled model smoothly and swiftly over differing road conditions, the suspension system that joins the wheels to the chassis plays an important role. Various types of suspension systems are used for buggies and on road cars to obtain maximum traction from the tires on the running surface.


SPRING AND DAMPER STIFFNESS ARE IMPORTANT
Suspension systems such as double wishbone, and trailing arm type are used on model cars just as on full sized vehicles. These are basically composed of upper and lower arms, coil springs, and damper units that absorb the energy stored in the spring upon compression. A simple 3-point suspension system is often used on the Formulatype on-road cars. In this case, front wheels are independently damped by coil springs, while the rear wheels are damped by a single shock unit. When adjusting suspension systems to track conditions, first adjust the coil spring stiffness, then the damper.



COIL SPRING ADJUSTMENTS
Coil springs fitted to suspension units are there to assist the suspension in following the surface it’s running on. It is a mechanical device that stores and dissipates shock energy to keep the car running steadily on the track. A too stiff spring results in an uncontrolled suspension that will cause the car to hop around wildly. If it’s too soft, the car will bottom out on the ground at each bump on the track. Springs should be adjusted according to the overall weight that compresses them. The coil springs included in the kits are designed and matched to the car, and should provide standard performance. If the car is modified and trimmed for lighter weight, use a softer spring.
Springs should be stiffened using spacers, after installing higher output motors, in order to compensate for the extra power. Using stiffer springs on rough terrain and softer springs on flat tracks is the normal rule.

ADJUST DAMPER ACCORDING TO SPRING STIFFNESS
The dampers widely used in cars are of the oil filled type. The higher the viscosity of the damper oil, the stiffer the damper, on the other hand, the lower the viscosity, the softer the damper. When using hard springs use harder damper oil, and for soft springs use softer damper oil.

OIL FILLED SHOCK UNITS
From the economical and long-wear plastic cylinders to competition low-friction aluminum cylinders, Tamiya offers a wide range of high performance oil filled shocks to meet your car’s requirement. All shock units are designed to provide the smoothest shock action while providing optimum road hugging ability to the vehicle. Adjustments can be made at the coil springs and pistons to compensate for the different track conditions. Oil viscosity can be altered by using the Tamiya Silicone Damper Oil set, to obtain the best possible performance.
*Shock unit dimensions differ according to the vehicle. Refer to illustration and notes.

TAMIYA SILICONE DAMPER OIL
Tamiya’s quality Silicone Damper Oil is developed exclusively for oil filled shock units used on car * models. It is formulated to maintain constant viscosity throughout
a wide temperature range. 3 sets; soft, medium and hard, are available with each set consisting 2 bottles of different viscosity oil. Select oil according to your track requirements.

FRICTION DAMPERS
This damping system is used on some on road racing cars. Several discs and pads are overlaid and damping effect is obtained by their friction. By applying oil or grease to the pads, the damping effect can be adjusted. Oils and greases of different viscosities are on the market for this purpose.



STABILIZER
During high speed cornering, a car tends to roll or incline outward, resulting in less traction of the inner wheels and causing instability of the car. Stabilizers are used to reduce the roll, and it contributes in improving the car’s overall maneuverability.



HOW TO CHECK YOUR CAR'S SUSPENSION SETTING
Place your car on a flat surface, and if its damper springs are slightly compressed with the car’s weight, spring stiffness is set correctly. Press the car down to the ground and release. If the car rises smoothly (not instantly), an adequate damping is obtained. For off road cars, drop the car to the ground from a height of about 30cm. If the setting is acceptable, the car will not bump or its bottom does not hit the ground because the dampers absorb shock. Of course, the final adjustment must be done while test running the car.

5. WEIGHT DISTRIBUTION BETWEEN WHEELS
The heavier the load carried by a wheel, the more traction it has because more pressure to the ground is produced. Thus, the weight distribution between the front and rear wheels greatly influences the car’s handling characteristics. Generally, the distribution ratio between the front and rear is from 35:65 to 45:55. Adjust weight distribution by moving heavy components such as Ni-Cd battery to the desired direction. Front or rear wheel load can be roughly checked by the method described below.

6. WING & SPOILER
The wing attached on many racing cars is employed to gain stability at high speed running. With your radio controlled cars, the rear wing is used to press down the rear wheels for improving the traction on the road. In this way, the gripping power of the rear wheel becomes greater than that of the front wheels and the steering trait changes toward understeering. The faster the car goes, the more effective the wing becomes, that is, the greater the down thrust on the rear wheels. Depending upon the way you adjust the wing, the car can have an excellent cornering characteristics on a low speed curve, but still keep superb stability on the high speed straights.
Such a car, also, will show a good adhesion to the road at high speed running. The effect of the wing is lessened when the wing is flattened. The more it is lifted, the greater the down-force. However, it increases the air drag, too, and the velocity of the car is slowed. Therefore, the adjustment of the wing must be made carefully, and with the proper adjustment an ideal maneuverability will be attained.



A LARGE WING WILL INCREASE AIR DRAG
The larger and the more angled a wing is, the more downward force is produced during running by the air flow. However, a too large or too steep wing will produce more air drag than desired, resulting in reduced speed of the car. The position of a wing/spoiler also influences its effectiveness. If attached at front, it increases the traction of the front wheels, and vice-versa.

DOWNFORCE DIFFERS ACCORDING TO RUNNING SPEED
Wings and spoilers produce more downward force during running, as the car’s speed comes faster. If a car has an oversteer tendency, use a large, steep angled rear wing. During high speed running, it will produce more downforce and augment its rear wheel traction, thus understeering characteristics can be obtained. When the speed becomes low, the effect of the wing lessens, and the car recovers its original oversteer characteristics.

MOUNT THE WING FIRMLY
lf a wing is mounted to the chassis with a flexible stay, the downforce produced by the wing cannot be effectively utilized by the car. Some cars’ wings are mounted directly onto their polycarbonate body shell. In such cases, the body itself should be firmly secured to the chassis.

7. WHEEL ALIJGNMENT
This is the term for indicating under what condition the wheels are attached to the chassis. Typical factors are toe angles, caster angles and camber angles, which plays portant roles in car settings.

TOE ANGLE
This term indicates the wheels on the both sides are parallel or inclined when viewed from above. If they are inclined forward, it is called “toe-in”, and if inclined rearward, they are in a “toe-out” setting. lf they are parallel to each other, they are neutral. Toe angles on the front wheels can be adjusted by altering the length of the steering tie-rods. In addition to the standard adjustable tie-rods, turnbuckle tie-rods are available which allow quick and easy adjustment of the length without removal of the rod. Rear wheel toe-angle is adjustable on some cars, but in most cases, replacement of suspension arms etc. will be required. Take care not to set an excessive toe-in or toe-out, otherwise the resulting drag will hinder the handling of the car. Begin with a little toe-in and work from there.



CASTER ANGLE
This angle indicates how much the king pin on the front upright is inclined rearward from the vertical. Generally, a larger caster angle improves the car’s straight running stability. However, with a large caster angle, the front wheels become slanted when steered. This may result in reduced traction during cornering and an uneven wear to the tire tread.



CAMBER ANGLE
This is the angle of the right and left wheels when viewed from the front or rear. If the wheels incline inward to the top, it is in negative camber. lf inclined outward to the top,



they have a positive camber. The camber angie detemrines the area of contact on each tire during cornering, and therefore the traction of the tires can be made greater or lesser through its adjustments. To increase traction during cornering, adjust to negative, and for reducing traction, adjust to positive. The steering characteristics can be changed by altering the traction of the front and rear tires. The car can be made to oversteer with the front adjusted to negative camber and the rear to positive. To cause the car to understeer, adjust front to positive camber and rear to negative. Camber angle adjustment is done by altering the length of the suspension upper arms. Use of turnbuckle shafts on upper arms allows quick camber angle adjustments.



8. WHEELBASE AND TREAD (TRACK)
Wheelbase is the distance between the car’s front and rear axles. Tread or track means the distance between the left and right wheels. If the tread is the same, a car with longer wheelbase has better straight running stability and reduced cornering performance. If the wheelbase is the same, a wider tread provides quicker cornering. Cars which have adjustable wheelbase are not common, but in some cases, this can be done by adding spacers or replacing chassis members, etc. Tread can be altered by using wider or narrower wheels or of different offsets. When doing this, you should be careful so that the wheels do not contact the body shell, and also within the limits of race regulations in which you are participating.



9. DIFFERENTIAL GEARING
When the car is turning, the distance travelled by the inside wheels is less than that of the outside wheels. The differential gearing provides a smoother cornering performance by absorbing these differences by altering the rotating speed of each wheel. Without the differential, a car is apt to make big turns or take corners awkwardly.



BEVEL GEAR DIFFERENTIAL
This differential system is used on both the full-sized vehicles and R/C cars. During straight running and if both the left and right wheels contact with the ground, the differential does not work and the motor/engine power is transmitted to both wheels evenly. When cornering, the bevel gears in the differential unit rotate according to the travel of the left or right wheels, thus absorbing the difference of their rotation. One shortcoming of this system is that when the wheel of either side loses contact with the ground, the power is transmitted only to this wheel to rotate it, and the wheel keeping contact with the ground will not rotate, thus the car’s driving force will be totally lost.



BALL DIFFERENTIAL
This is a unique differential system used on cars. A ball differential consists of metal balls sandwiched between two pressure plates. The balls work like the small bevel gears in a gear differential, absorbing rotation differential between the right and left wheels during cornering. Even when a wheel leaves the ground, because of the friction caused by the pressure to the balls, power is transmitted to some extent to the wheel that is in contact with the ground, thus a total loss of the driving force is avoided. The pressure can be adjusted by tightening a screw, and adding spacers or washers etc. Too little pressure results in slipping of the balls, so the power is not transmitted to the wheels.



TORQUE SPLITTERS AND ONE-WAY DIFF UNITS
There is a slight difference of travel between the front and rear wheels. The rear wheels turn more inward than the front wheels, so the front wheels rotate more than the rear. In a shaft-driven four wheel drive cars, the front and rear wheels are connected with a propeller shaft, and the rotation difference causes stress to the propeller shaft. Torque splitter and one-way diff units are developed to solve this problem. Both systems use a oneway bearing which rotates freely only in one direction, allowing the front wheels to rotate faster than the propeller shaft rotation during cornering.

10. FINE-TUNING AN CAR’S PERFORMANCE
A car's performance characteristics are influenced by many factors. Unthought alteration of various components results in mere confusion. Observe and follow the points described below.

TRACTION OF THE DRIVING WHEELS IS IMPORTANT
The motor/engine power is transmitted to the car’s driving wheels and propels the car. To make the best use of the power, concentrate on obtaining the utmost traction at the driving wheels.

REAR WHEELS’ TRACTION MAKES A CAR STABLE
When a car turns its direction, the front wheels steer while the rear wheels act like a fulcrum. If these support points do not grip the ground properly, the car’s stability will be reduced. In rear wheel drive and four wheel drive cars, the rear wheel traction should be most valued. In front wheel drive cars, balance between the front driving wheels and rear wheels traction should also be carefully considered.

ALTER STEP BY STEP
Attempting to modify-it-all in one try should be avoided, because if any effect is obtained, you cannot figure out exactly which alteration led to the obtained result. Alter/adjust one point at a time and perform a test run each time. By repeating this procedure, you will know the individual effect of each adjustment, which greatly helps you in attaining a balanced setting on your car.

BALANCED ADJUSTMENT BETWEEN THE RIGHT AND LEFT
If a suspension setting is different between the left and right side of your car, it will have different tendencies when taking corners and turns. Settings must be equal on the right and left. tin oval track competitions as seen on the full-sized Indy Car events, cars have a different weight distribution on the right and left side, because these cars take corners only in one direction.

CONSIDER THE WEATHER AND TEMPERATURE
High temperatures cause oil and grease to become softer and thus their viscosities are lowered. Conversely, they become stiffer under low temperatures. Therefore, different greases and oils will be required to obtain the same setting condition during summer and winter. The setting should be also done according to the track surface conditions. When running on a wet or slippery surfaces, higher traction tires and/or larger spoilers to produce stronger down force, should be employed.


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