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Technical Information



Evolution of Wheels, the Key to “Driving Stability”

In order to enjoy driving safely in a sporty style, it is essential that a vehicle has basic performance capabilities; “run”, “turn” and “stop”. These
three key elements are evaluated for what is called, in generic terms, “driving stability”. Suspension and steering features directly concern the basic
performance capabilities of a vehicle and are closely tied to the sensitivity of the driver of the vehicle. Along with the history of the evolution of
suspension, wheels have also evolved. The history goes back a long way to the time when horses and carts were used and, much later, a vehicle equipped with
the very first independent suspension was launched. Meanwhile, wooden wheels were replaced with steel wheels; and, in 1924, the world’s first aluminium
wheels were fitted to a Grand Prix machine “Bugatti Type 35”. Since then, light alloy wheel technology has been improved continuously in the field of
motorsports in pursuit of “lighter weight and higher precision” and in response to harsh test-and-try feedbacks.



Transition to Light Alloy Wheels Brings Many Advantages



There are two types of discs, one is made of aluminium and the other is made of steel, and they both have a diameter of 50cm and a thickness of 1cm. When
the discs are rotated at the same speed, because the aluminium disc is lighter in weight than the steel disc, it can rotate with less driving force and
stop more easily. This effect is called “gyroscopic precession”. If, for example, the centre shaft of a wheel is an axle, the weight of the wheel affects
significantly the steering response and the attitude control when steering. A rotating object, such as a tyre, rotates at a high rate and generates a force
in the rotating direction. This force is called, in dynamics, “a moment of inertia”. The moment of inertia increases as a high load is applied to increase
the speed. Simply replacing steel wheels with aluminium wheels can reduce the wheel weight by 28%; the role of aluminium wheels is significant. For
instance, between two cars which have the same weight and the same power but one has steel wheels and the other has aluminium wheels, the one with
aluminium wheels having a smaller moment of inertia can manoeuvre better by quick steering in response to a road surface reaction force or when the
attitude of the car becomes unstable. The power in the car equipped with aluminium wheels also flows in a more linear fashion, thus enabling quick
responses to starting and braking the car. Wheel materials are required to be light in weight yet rigid; a material that is simply lightweight is not
suitable. When comparing the data that simultaneously indicate the strength and lightness of steel, aluminium and magnesium, the “strength-to-weight ratio”
(tensile strength ¸ specific gravity) of steel is 5, aluminium 9, and magnesium 15, showing the superiority of aluminium and magnesium over steel.



“Unsprung weight” refers to the total weight of components, including the tyre wheels and brakes of a vehicle, which are arranged below the suspension
springs. Meanwhile, “sprung weight” refers to the total weight of components, including the body and engine of the vehicle, which are arranged above the
suspension springs. An unsprung weight of 1kg corresponds to a sprung weight of 15kg. For example, reducing the weight of one wheel by 3kg has an
equivalent effect of reducing the weight of a vehicle body by 180kg (3 x 4 x 15 = 180). Imagine a weight which is suspended from a spring and moves along
with the expansion and contraction of the spring. The lighter the weight, the less expansion and contraction of the spring and the easier it is to stop the
movement, whereas if the weight becomes heavier, it creates the opposite effect altogether. That is to say, the steering follow-up time loss increases in
response to the input from the road surface to the wheels of a vehicle. When compared to a vehicle equipped with steel wheels, a vehicle equipped with
alloy wheels can facilitate smooth cornering and smooth load shift, thus ensuring stable driving while suppressing unsteady behaviour. Weight reduction
technology has also been evolving, which is observed in the use of carbon frames for racing machines, the use of monocoque frames for
commercially-available high-performance vehicles, and the use of new materials, such as high-tensile steel plates. Meanwhile, unsprung weight reduction has
grown in importance, and tuning up for light alloy wheels would be the best move in pursuit of further weight reduction.



The remarkable advancement of vehicle control technologies, such as 4-wheel steering and active suspension, involves the need for high-performance wheels;
the weight reduction of the functions that support suspensions. When a vehicle is driven on a rough road surface that causes a lot of pitching and bouncing
vibrations, light alloy wheels have a good grip to ensure a smooth ride, whereas steel wheels, when the vehicle is driven at the same speed, cannot trace
the profile of the uneven road surface very well, thus potentially causing unstable movements. Such a phenomenon becomes more apparent as the speed
increases and can cause what is called “judder”; a sharp vertical motion of the vehicle body. The phenomenon also becomes more obvious as the area of the
tyres which makes contact with the road surface increases, and it could not only cause an unnatural sensation in stroke steering but also put strain on the
suspension. Imagine that a tennis ball and a rubber baseball of the same size are dropped from the same height on to an iron plate on the floor. The light
tennis ball stops bouncing in a short while after it hit the iron plate, whereas the heavy baseball keeps bouncing on the iron plate for a much longer
time, i.e., the lighter an object, the better shock absorption. Similarly, in addition to better movement control by unsprung weight reduction, light alloy
wheels, typically aluminium wheels, play a role in ensuring driving performance that faithfully reflects the driver’s intention by becoming part of the
suspension of a vehicle which directly contributes to the manoeuvrability of the vehicle.

Wide Variety Derived from Racing Feedback

The setting of suspension geometry is essential for track racing. “RS Original Wheels” boasts a wide variety that takes care of both front-engine,
front-wheel drive (FF) vehicles and front-engine, rear-wheel drive (FR) vehicles. The extensive line-up will back up your sports driving performance.
Choose the offset model you like – it enables very accurate settings. “Offset” is the distance from the centre of the cross-section of a wheel (rim width)
to the disc face; it is a key factor for determining front and rear treads. By changing the offset value, tuning possibilities are infinite. For example,
increasing the offset, towards the positive side, increases understeer, and shifting the offset to increase the tread increases oversteer. You have
absolute control over how you want to drive your vehicle. By combining offset tuning with alignment tuning, you can enjoy the drive feel that you’ve never
experienced before. RS Watanabe wheel technology has been developed and sophisticated through races, including supporting domestic races such as Formula
Junior and Formula Nippon. In 1955, a Jaguar D-Type equipped with very first aluminium wheels won the Le Mans 24-hour race, during which the durability of
aluminium was demonstrated. It is right to say that in today’s motorsports, there is no machine that is not equipped with light alloy wheels. In the
background where light alloy wheels have become so widespread, the excellence of light alloys as materials must be mentioned in addition to realising
weight reduction. Compared to steel wheels, aluminium wheels are well known for high heat dissipation. They allow the heat of the tyres and brake of a
vehicle to escape, thereby preventing the deterioration of tyre performance and obtaining a steady braking force. Aluminium is also an excellent casting
material. It allows design variations, and designs, such as long selling “eight spoke” designs, are function oriented while being very popular as dress-up
items. “RS Original Wheels” unleash the potential of your beloved car to the maximum, with a promise that you will experience a new high-performance feel.


A “kingpin” is installed for supporting a wheel vertically. The point at which the kingpin axle and the wheel axle make contact with each other is normally
set lower than the ground plane. If the contact point is set above the ground plane, a vehicle will develop a wobble and possibly cause the vehicle to
overturn. The shift of the contact point (offset amount) is merely a matter of several millimetres, yet it is a key factor for ensuring directional
stability and manoeuvrability. For example, if wheels are fitted to a car with different offset amounts, by mistake of course, an angle error will be
caused to the kingpins and will affect directional stability. The kingpin angle is closely related to the offset amount and controls the toe-in angle, the
caster angle and the camber angle. The kingpin angle is therefore an absolutely essential factor in geometry.