TIRE UNIFORMITY

Why Uniformity…..

· Vehicle manufacturers are far ahead of us in
development
· They find out vehicles misbehaves due to tire
abnormality
· Various kind of vibrations are created due to
abnormality in tire.
· Vehicle handling becomes difficult at high speed due to
tire abnormality

· Severe market competition in car market
.
· Customer wants value for money
· Uniform tires leads to satisfied customers and
enhanced business.

Dimensional Variations

This is basically the roundness of the tire or lateral and
radial run out of the tire.This is controlled by controlling the
run out of the tire mould in the mould manufacturing process.
Dimensional Uniformity

· ? Radial run out
· ? Lateral run out
· ? Bulge
· ? Depression

The different kinds of force variations are…..

Radial Force Variation
Lateral Force Variation
Harmonic
Conicity
Plysteer

The forces in a tire are relatively complex.The tire being an elastic
body analogous to an array of radial springs with a distributionof
mass. If the spring are of the same length and have the same spring
constants, then the displacement as the tire is put into motion , would
remain in a straight line. But that is not the real case. Each portion of
the tire is having a different spring constant or length.

The important force variations are…..

Radial force variation -which acts in the radial direction. Higher the radial
force variation, higher will be the vibrations experienced in the vehicle
especially on the steering at high speeds.

Lateral force variation -which acts in the lateral direction. . The side to side
force acting along the rotation axis between the tire and the road or the load
wheel. Higher the lateral force, the vehicle will move in a zig zagway.

Conicity -which acts in the circumferential direction or the direction of travel.
Conicity is the tendency of a tire to roll in the same manner as a cone and has
a strong influence on vehicle pull or steering pull.

Radial force variations

· This is the vertical force between the tire and the
road (or the road wheel)
· Force responses was based on the measurement
of a tire’s carcass stiffness or the resistance to
flexing while it revolves under a load on a vehicle.
· The variations in the force responses were
transmitted to the vehicle suspension system,
which is felt by the driver.


Radial force variations

There is variation in the spring rate throughout the periphery of the
tire. Or in other words there are hard and soft spots in a tire. The
difference between the hard and soft spots are measured as radial
force. The causes of varying spring rates can be attributed to minute
variations in theepi, fabric splices, tread splices, cord angles, cure
state etc,.
Higher the radial force variation, higher will be the vibrations
experienced in the vehicle especially on the steering at high speeds.


Lateral Force Variation

· The side to side force acting along
the rotation axis between the tire
and the road or the load wheel.
· This force varies around an average
point. The average point is called
lateral shift and the variations are
called lateral force variations.
· High lateral force can cause low
speed waddle and lateral shakes.
The vehicle will never move in a
straight line.

Conicity

Conicity is the tendency of a tire to roll in the same manner as a
cone and has a strong influence on vehicle pull or steering pull.

Vehicle pull is the condition where the driver must apply a
constant torque to the steering wheel in order to maintain a straight
line course with the vehicle.

An easy description can be everything that is different from one
side of the centerline to the other side has a significant effect on
conicity.

On a production basis this means all off centre component
application and all side to side gauge variations are causing
conicity

Ply steer


Ply steer is a design controllable variable and is related
to the direction of the cords in the outer most ply

When a tire is rotated it wants to travel along the
geometric centre of the tire in the direction of rotation.How
ever, because of ply steer, it may travel slightly off the
geometric centre in the direction forced by the twisting
action of the composite material.

This is usually such a small quantity and does not require
any correction in the steering of the vehicle and does not
cause any vehicle pull.

MASS UNIFORMITY

Commonly known as Unbalance in tire
Two different kind of unbalance are:
Static Unbalances
Dynamic Unbalances

Trouble shooting guidelines of Radial force/radial force harmonics.

· Uneven ply epi, pulled ply
· Stretched components
· Wrinkles in fabric liner
· Heavy component splices
· T-up height variations
· Loose T-up
· Tread length variations
· Drum width variations
· Bead ecentricity
· Angle variations in components
· Poor tread contour
· Spotting variations
· B&T/expander drum run out not ok
· Proper bead lock operation
· Excess tension on cap ply
· Improper tread stiching
· High stiching pressure
· Snaky side wall applications
· Uniform inner paint applications
· Off center loading at press
· Poor cured bead shape
· Out of round bladder
· Improper shaping pressure at press
· Open mould

Trouble shooting guidelines for Lateral force

· Uneven component stretch causing snaking effect
· Leading and trailing end of tread off center
· Cap ply wandering from side to side
· Excess tension on sheet cap ply
· Breaker with dog ear splice
· Loose t-up
· Bead off
· Breaker band tight or loose on B&T drum
· High lateral run out on second stage building m/c
· Breaker width variations
· Snaky belt-treadapllications
· Mould not concentric to press
· Mould step off/ off register
· Improper shaping

Trouble shooting guidelines for Conicity

· Breaker step off on both sides
· Tread hump gauge variations on both sides
· T-up ht variations
· Bead holders on expander drum loose
· Center light off
· T-ring off center
· Expander drum off center
· Off center belt and tread applications
· Scrapping of green tire against mould




Uniformity measurement…

To measure uniformity, tire is mounted on a steel rim, inflatedand
loaded against a load wheel.
A drive motor is connected to the axle of the load wheel and drives the
tire and drum at 60 rpm.
The non –uniformities of the tire create a wave form of force variations as
the tire rotates.
Force variations in the radial and lateral directions are then measured
using strain gauge transducers mounted on the axle supports.