A typical aluminum alloy has a density of about one-third that of steel.

Cast magnesium alloys are even

lighter, having a density of slightly less than one-quarter that of steel. The tensile strength is 40-50% of a
typical steel pressing, giving a great improvement in the specific strength (tensile strength per unit
density). A cast magnesium alloy wheel of 5.5-in rim width and 13 in nominal diameter, as used on a typical
works rally car weighs 4.2 kg in Minilite form. The weight of a steel wheel of this size can vary between 6.0
and 6.7 kg. Larger wheels yield a greater weight-saving. A 6JK x 15 steel wheel for a Jaguar weights 10.3 kg.
A Minilite magnesium replacement weighs only 6.7 kg.

The flange profile, indicated by letters K, JK, J

or -C in the specification, is designed to comply with the
tyre bead profile.

Whereas a rim thickness of 6.4 mm will be used on a rally magnesium wheel, a single-seater racing car wheel
is expected to survive with a rim thickness of no more than 2 mm.

On the inside of your wheel, you will find markings similar to this:

6 ½ J x 15 H2 5/112 ET39

Let’s see what each of these symbols mean.

6½
Inner width of wheel in inches (6 ½ x 25.4mm= 152.4mm).
J
Indicates the shape of the wheel on the place where the tyre bead sits
on the wheel.

x
Indicates that the construction of the wheel is one-piece.

15
Nominal wheel diameter in inches (15 x 25.4mm= 381mm).

H2
Type of wheels flange. Wheels flange is a bulge on the wheel in the
place where the tyre bead lies on the wheel. It prevents the tyre from
falling inside of the wheel.

5/112
First number is the number of bolts (in our case 5). The number 112
indicates the so-called PCD (Pitch Circle Diameter) which is the
diameter of an imaginary circle drawn through the center hole of the
screws on which the wheel is mounted.

ЕТ39
ET is the offset, that is the distance between the centerline of the wheel
and the plane of the hub-mounting surface of the wheel. The offset is
measured in millimetres and can be positive or negative. In our case it is
 positive: 39 mm.

The tire works as a wheel only after it is installed on the rim and is inflated. Therefore, the
tire and wheel assembly influences the function and the performance of the vehicle. The tire
is designed and manufactured to suit a standard rim and once installed on the correct rim
the tire will perform up to its desired level. It is needless to say that the life of the tire will be
shortened if it is installed on an unsuitable rim.
The rim is actually the name for the cylindrical part where the tire is installed. A wheel is the
name for the combination between the rim and disc plate. Once the disc plate is installed
inside the cylinder this assembly becomes a wheel.
Toyo Tire Talk at this time would like to introduce basic technical knowledge about
passenger vehicle rims.

1. History of Wheel/Rim
Several thousand years ago was the start of the history of wheel when the human race
began to use the log to transport heavy objects. The original of the wheel were the round
slices of a log and it was gradually re-inforced and used in this form for centuries on both
carts and wagons.
This solid disc changed to a design having several spokes radially arranged to support the
outer part of the wheel keeping it equidistant from the wheel centre. A wooden wheel which
used hard wood stakes as spokes was very popular as a wheel for many vehicles up to
 about 1920. Afterwards the disc wheel, in which the spokes were replaced with a disc made
of steel plate, was introduced and is still being used to this day.

2. Type of Wheel/Rim (Dimensional)

The rim used for vehicles is provided depending on each countries standard. This
international standard, similar to tires, provides for a basic dimension for the rim diameter,
width, and the flange shape, etc. and is common to every country in the world.
Recently the shape of the rim has settled to 5 degree Drop Center Rim to provide for
international harmony.
A. Shape of Rim
Typical rim shape vehicles are made up of the following three types.
(1) Drop Center Rim ( DC )
Drop Center Rim (DC Rim) is shaped so there is a well between the bead seat part which is
located on both sides of the rim. This well is to make the mounting and dismounting of the
tire easy. In most cases there is a taper of 5 degrees in the bead seat area. Furthermore, a
light alloy has come to be used currently as a wheel material for many types of vehicle.

(2) Wide Drop Center Rim ( WDC )

Wide Drop Center Rim (WDC Rim) is basically the same as DC Rim. To expand the width
of the rim, with a shallower well and a lower flange height, this rim is mainly applied to low
aspect ratio tires. This design is currently applied to rims for tires of most passenger
vehicles.

How is tire aspect ratio measured?

It is measured by taking the diameter of the tire, subtracting the diameter of the rim and then dividing by the
width. The actual ratio in this example is 0.65, but typically described as 65. To put it simply, the lower the aspect
ratio, the shorter the tire. At one time, most tires had ratios of about 70 and rim sizes of 13 to 15 inches
(3) Wide Drop Center Rim with hump ( WDC )
In addition, this design has a bump, which is called a hump, on the beginning of the bead
seat area. This hump is to prevent the bead slipping down and air leakage from the rim due
to the horizontal force applied to the tire when a vehicle tubeless tires turns at high speed.
B. Rim Size Designation
Rim size designation is as below;

C. Rim Nomenclature

(1) Wheel: Wheel is generally composed of rim and disc.

(2) Rim: This is a part where the tire is installed.
(3) Disc: This is a part of the rim where it is fixed to the axle hub.
(4) Offset: This is a distance between wheel mounting surface where it is bolted to hub and
the centerline of rim.
(5) Flange: The flange is a part of rim which holds the both beads of the tire.
(6) Bead Seat: Bead seat comes in contact with the bead face and is a part of rim which
holds the tire in a radial direction.
(7) Hump: It is bump what was put on the bead seat for the bead to prevent the tire from
sliding off the rim while the vehicle is moving.
(8) Well: This is a part of rim with depth and width to facilitate tire mounting and removal
from the rim.

D. Rim Width
The width of the rim is provided in TRA, ETRTO, and JIS, etc. according to the size of the
tire. Generally rim width difference of about plus/minus one inch is allowed to be used in
comparison to the design rim; you should confirm the most suitable rim size for the tire from
the tire dealer. The tire manufacturer designs the tire to become the best profile when the
tire is mounted on a design width rim. Generally, it is best to use the design width rim to
obtain the optimum performance from the tire.

When the car installed with Tubeless tires under greatly decreasing the air pressure turns
rapidly a large side force is applied to the tire. The bead sometimes drops into the well of
the rim, and the air comes out suddenly. This situation is made worse when an overly wide
rim is used.

If the tire is used on a narrow rim, the stress concentrates on the bead part where it touches
the rim and flange. The rubber in this part and the ply cord wear out, and becomes damage
which is called Rim Chafing. Moreover, if severe cornering is repeated with the air pressure
of the tire lowered, Rim Chafing might occured to the tire.
3. Type of Wheel/Rim (Material)
Steel and light alloy are the main materials used in a wheel however some composite
materials including glass-fiber are being used for special wheels.

A. Wire Spoke Wheel

Wire spoke wheel is a structural where the outside edge part of the wheel (rim) and the axle
mounting part are connected by numerous wires called spokes. Today's vehicles with their
high horsepower have made this type of wheel construction obsolete. This type of wheel is
still used on classic vehicles. Light alloy wheels have developped in recent years,a design
to emphasize this spoke effect to satisfy users fashion requirements.

B. Steel Disc Wheel

This is a rim which processes the steel-made rim and the wheel into one by welding, and it
is used mainly for passenger vehicle especially original equipment tires.

C. Light Alloy Wheel

These wheels based on the use of light metals such as aluminium and magnesium have
become popular in the market. This wheel rapidly become popular for the original
equipment vehicle in Europe in 1960's and for the replacement tire in United States in
1970's. The features of each light alloy wheel is explained as below;

(1) Aluminium Alloy Wheel

Aluminium is a metal with features of excellent lightness, thermal conductivity,  corrosion
resistance, characteristics of casting, low temperature, machine processing and recycling,
etc. This metals main advantage is reduced weight, high accuracy and design choices of
the wheel. This metal is usefull for energy conservation because it is possible to re-cyle
aluminum easily.
(2) Magnesium Alloy Wheel
Magnesium is about 30% lighter than aluminium, and also, excellent as for sizestability and
impact resistance. However, its use is mainly restricted to racing, which needs the features
of lightness and high strength at the expense of corrosion resistance and design choice,
etc. compared with aluminium. Recently, the technology for casting and forging is improved,
and the corrosion resistance of magnesium is also improving. This material is receiving
special attention due to the renewed interest in energy conservation.

(3) Titanium Alloy Wheel

Titanium is an excellent metal for corrosion resistance and strength (about 2.5 times)
compared with aluminum, but it is inferior due to machine processing, designing and high
cost. It is still in the development stage although there is some use in the field of racing.

(4) Composite Material Wheel

The composite materials wheel, is different from the light alloy wheel, and it (Generally, it is
thermoplastic resin which contains the glass fiber reinforcement material) is developed
mainly for low weight. However, this wheel has insufficient reliability against heat and for
strength. Development is continuing.

4. Manufacuturing Method of Wheel/Rim

The steel disk wheel and the light alloy wheel are the most typical installation. The method
of manufacturing the light alloy wheel, which has become popular in recent years, is
explained here. The manufacturing method for the light alloy wheel is classified into two.
They are cast metal or the forged manufacturing method.
The aluminum alloy wheel is manufactured both ways, and the casting manufacturing
method is used as for the magnesium alloy wheel. There are the following three methods of
manufacturing the aluminum alloy wheel.
One piece rim: This is a method of the casting or the forge at the same time by one as for
the rim and disc.
Two pieces rim: This is the methods which separately manufacture the rim and disc similar
to the manufacture of the steel wheel and these components are welded afterwards.
Three pieces rim: This is a method to manufacture each flange separately, and combining
later to the disc by welding.
Each method is shown in the figure from next page.
5. Test of wheel
Wheels are part of a vehicle and as such subjected to a high load. The durability of the
wheel is important for the safe operation of the vehicle. Therefore, it is necessary to
examine a wheel for both strength and fatigue resistance.
(1) Endurance test in direction of radius of rim
The tire on the test rim is rotated under high pressure condition on steel drum and the
durability of the rim is examined. Sometimes, test is done giving camber angle and adding a
side force.
(2) Test of disc
The rim flange is tested by applying a load from an arm mounted to the hub. A bending
moment is applied while the rim rotates.
(3) Impact Test
The case where the wheel collides with curb of the road or a large obstacle is assumed and
the fall impact examination is done.
(4) Others
The test for welding between rim and disc and the nut seat tightening etc. are provided in
the vehicle test standard. Moreover, nondestructive testings such as X ray and color check,
etc. are adopted to the light alloy wheel to detect the defects in the casting process. Bead
Unseating Test, provided in the tire safety standards, for a mounted tire and the rim is also
applied. In addition tests are carried out in the field with the assembly mounted on a vehicle
under various road surfaces.

6. Use limit of wheel

Though we think it is possible to permanently use a wheel until it rusts away there is a limit
to a wheels useful life. If a rim is used in severe operations such as racing or rallying hidden
damage is caused. This may result in a an accident or sudden rim failure whilst damage is
caused. This may result in a an accident or sudden rim failure whilst the vehicle is in
service. The life of a rim is varied according to using conditions.
A rim normally lasts longer than a tire so at time of a tire change a rim should be checked
for damage or sign of failure. If any are found the rim should be scrapped.
In the case of steel wheel, cracks and corrosions by rust at the joint parts of rim and disc,
nut seats, between decoration holes of the rim or the flange is bent, you should scrap the
rim.

WARNING
If you install a tire on a different size rim •••
you could be dead wrong !!
Although it is possible to pass a 16 inch tire over the lip or flange of a 16.5 inch rim, it can
not be positioned properly. Attempting to seat the rim by inflating will cause an explosive
force that could cause injury or death.

Rims of different diameters and tapers can not be interchanged.

The diagram below illustrates the difference between rims of two different tapers and
diameters.

Every rim include information on diameter and width. Always make sure the stamped rim
size matches the tire bead diameter. Most wheels include a warning label inside the rim to
protect employees who mount tires and wheels.
 What Is Tyre Aspect Ratio

When it comes to car tyre maintenance there are many things that go unnoticed, like the
alphanumeric codes inscribed on the side wall of your car’s tyre. Most of us don’t know what they
are meant for. The side wall of a tyre carries vital information with respect to the tyre size and helps
you get the aspect ratio of a tyre. The tyre ratio helps you find the right tyre for your car. By looking
at it, at first instance, the cryptogram appears no less than a riddle. Despite that fact, we Indians
have a legacy to solve the unsolved. So, come along, let’s crack down this mystery and unveil the
secret behind.

 Tyre aspect ratio explained

The side wall code lets you know the tyre specs such as width, load index, diameter, speed rating
and profile of a particular tyre. Aspect ratio of a tyre in layman’s term is denoted by a percentage
(nos.) which hints at the tyre height (or section height), from bead to the tread, with regards to the
tyre width (or section width).

 How does tyre aspect ratio matter?

If the aspect ratio of a tyre is higher, then the side wall will be clearly taller. You must have noticed
that the trucks, buses and even luxury cars possess high aspect ratios of about 95. Such tyres, at
one point may compromise on the handling part but will surely provide you with ultra comfort ride
due to more amount of air inside the tyre. So what about the tyres with low aspect ratio? Such tyres,
with shorter side walls, will play their role heroically while cornering and by providing better handling.
However, here you cannot expect cushioning comfort, as the suspension suffers from the vibrations
produced by tyres because the tyre here, holds less air.
Therefore, in order to provide a mix of decent handling quality and comfortable ride, an even balance
of high and low aspect ratio is witnessed in most of our regular tyres.
 

Decoding the tyre measurements and tyre sizes code-

 
Understand this trail of confusing alphanumeric figures in this way.
For instance, if the side wall of a tyre reads: 205 / 60 R16 92 H
This means,
1) 205 (section width in mm) – It’s the total width of the tyre in millimetres.
2) 60 (aspect ratio in percentage) – As explained above, it’s the ratio of section height to the section
width.
3) R (radial construction) – Denotes that the layers run radially across the tyre
4) 16 (rim diameter in inches) – The measurement of rim
5) 92 (load index) – The number states the maximum load carrying capacity.
6) H (speed symbol) – This symbol signifies the permissible speed.
 

Tyre aspect ratio calculator

Here, if we go by simple mathematics, the tyre aspect ratio percentage can be calculated as under:
H (Section Height of Tyre) / W (Section Width of Tyre) X 100 = Aspect Ratio (%)