Beads are shaped like hoops. It has a high tensile and high fatigue life steel wire
(coated with brass) as it backbone. The bead fits against the wheel rim. Strands of steel
are arranged sided by side in the form of a ribbon and are coated with rubber for good
adhesion. Special shapes like pentagonal beads are used which provide extra stability
under low inflation conditions and prevents the bead from slipping off the rim bead seat.
Bead wires come in different configurations like weft less, cable beads and single
strand. Similar to steel cords used in steel belts of radial tires, these are also transported
in hermetically sealed containers and appropriate precautions have to be taken to prevent
contamination by impurities like moisture and dust leading to corrosion and thus loss of
adherence to rubber while coating.
The main function of the bead loop is to support or anchor the body plies and to
prevent the wheel from slipping or rocking the rim.
The bead may look like a simple component but in reality it has many sub –
components in its purview. To start with it has the steel wire loop which gives it he
required structure and elasticity. Next comes the apex or “bead filler” which is from a
very hard rubber compound, extruded in the form of a wedge. The bead loop and bead
filler are assembled on the bead – apex assembly.
Then comes the “chafer”, which protects the wire bead components followed by
the “chipper”, which protects the lower sidewall. Finally, there is the “flipper” which
helps hold the bead in place.
The precision of the bead circumference is very important. If is too less, then the
tire mounting on the rim will be a problem and if it is too large, then the tire may come
off during loading or during cornering conditions.
During coating or “mini extrusion”, the insulating rubber is usually pressed into
and around the bead when it is drawn through an
extracting die.
(coated with brass) as it backbone. The bead fits against the wheel rim. Strands of steel
are arranged sided by side in the form of a ribbon and are coated with rubber for good
adhesion. Special shapes like pentagonal beads are used which provide extra stability
under low inflation conditions and prevents the bead from slipping off the rim bead seat.
Bead wires come in different configurations like weft less, cable beads and single
strand. Similar to steel cords used in steel belts of radial tires, these are also transported
in hermetically sealed containers and appropriate precautions have to be taken to prevent
contamination by impurities like moisture and dust leading to corrosion and thus loss of
adherence to rubber while coating.
The main function of the bead loop is to support or anchor the body plies and to
prevent the wheel from slipping or rocking the rim.
The bead may look like a simple component but in reality it has many sub –
components in its purview. To start with it has the steel wire loop which gives it he
required structure and elasticity. Next comes the apex or “bead filler” which is from a
very hard rubber compound, extruded in the form of a wedge. The bead loop and bead
filler are assembled on the bead – apex assembly.
Then comes the “chafer”, which protects the wire bead components followed by
the “chipper”, which protects the lower sidewall. Finally, there is the “flipper” which
helps hold the bead in place.
The precision of the bead circumference is very important. If is too less, then the
tire mounting on the rim will be a problem and if it is too large, then the tire may come
off during loading or during cornering conditions.
During coating or “mini extrusion”, the insulating rubber is usually pressed into
and around the bead when it is drawn through an
extracting die. Functional parts of a bead winding system
1. Spool – These spools give of the steel wires needed to make the bead.
2. “Mini extruder” – The screw extruder coats the steel wires with rubber. The
extruder comes with temperature and output pressure control systems.
3. Reserve “festoon”– Acts as the storage for the coated bead wires and cools it
also. A servo matches the speed to the winder speed.
4. Windup – Winds the coated wires into a bead “loop”
The finished bead may have a special tape wrapped around it prior to the apex or
“bead chafer” being bonded to it.
2. “Mini extruder” – The screw extruder coats the steel wires with rubber. The
extruder comes with temperature and output pressure control systems.
3. Reserve “festoon”– Acts as the storage for the coated bead wires and cools it
also. A servo matches the speed to the winder speed.
4. Windup – Winds the coated wires into a bead “loop”
The finished bead may have a special tape wrapped around it prior to the apex or
“bead chafer” being bonded to it.
FUNCTIONS OF BEAD
• Hold the tire tightly against the two rims
• Provide tight grip on the rim to avoid rotation
when tire rotates and brakes
• To hold air without leak in tubeless tires
• Provide adequate safety from slip inside
the rim especially during cornering
maneuvers
• Holding against over inflation
BEAD DESIGN
Basic design parameter is safety factor, which is
calculated from the following inputs;
• Bead wire strength
• Tire / Rim dimension
• Inflation pressure
• No. of turns and strands
Bead Safety Factor Calculation
( Breaking strength of the bead wire )
Bf = --------------------------------------------------
( Bead wire tension )
Bead wire tension = P.W.( 3Dr +D ) / 16N
P = Inflation pressure
W = Rim width
Dr = Rim diameter
D = Tire OD
N = Number of wires
• Hold the tire tightly against the two rims
• Provide tight grip on the rim to avoid rotation
when tire rotates and brakes
• To hold air without leak in tubeless tires
• Provide adequate safety from slip inside
the rim especially during cornering
maneuvers
• Holding against over inflation
BEAD DESIGN
Basic design parameter is safety factor, which is
calculated from the following inputs;
• Bead wire strength
• Tire / Rim dimension
• Inflation pressure
• No. of turns and strands
Bead Safety Factor Calculation
( Breaking strength of the bead wire )
Bf = --------------------------------------------------
( Bead wire tension )
Bead wire tension = P.W.( 3Dr +D ) / 16N
P = Inflation pressure
W = Rim width
Dr = Rim diameter
D = Tire OD
N = Number of wires
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