Tyre Asia April/May 2018 83
substantial.So performance optimization
is a big challenge.Can you explain your
proposition that selection
of tyres for EVs depends
on real world usage profile
(RWUP)? Can you elaborate
this concept?
Because low-rolling-resistance tyres
are harder, they are also louder on the
road. They provide a slightly rougher
ride and that they even reduce handling
performance and increase braking
distances.The real world usage pattern
for different categories call for different
applications.
Design of tyres differs for various
weather conditions as well. There are
differences in winter and summer
application.The tuning needs to be
different for commercial and personal
segment.This is actually the primary
reason for tyre manufacturers to go for
different variants.
For example, at low speeds tyre rolling
resistance is the primary contributor
to increased vehicle resistance at
cold temperatures. Snow tyres have
both higher resistance and a stronger
dependence on temperature than low
rolling resistance tyres. Lowering tyre
pressure increases both resistance and
temperature but this also improves
traction and therefore may serve as a
temporary safety measure in winter
conditions.What are the methodologies
that you have followed
in determining rolling
resistance and its importance
in mobility particularly when
you expect more mileage out
of each watt?Rolling resistance is difficult to measure
.One approach would be to develop
individual factors for each and every
rolling resistance parameter by which
a tyre in question could differ with
respect to the reference tyre. Some
of the parameters that might require
evaluation could include: diameter (rim,
rolling), width (rim, tyre), number of
plies (carcass, tread), type of material
(carcass, rubber), tyre volume, tyre
surface area, and tyre surface roughness.
The total number of parameters
requiring evaluation could easily exceed
this list of 12 if this were the approach.
The second approach, which seeks to
develop a limited number of adjustment
factors (initially just 4), implicitlycombines the various parameters into
something more manageable. This
approach begins with the formula for the
tread contact area of a tyre under load.
Tyre manufacturers have also developed
test vehicles in standard test conditions
for measuring the same.
The EV tyres are manufactured using
a harder rubber compound. And since
harder tyres roll easier than softer ones,
this translates into fuel savings because
the vehicle’s engine (or electric motor)
has an easier time getting the car moving
and keeping it moving - the vehicle’s
rolling resistance is reduced.Do you expect major design
changes in EVs tyres in
coming years? What are the
major attributes of a perfect
tyre for EVs?
In order to reduce tyre rolling resistance,
EV tyres have reduced tread pattern
thickness, a lot of rather shallow grooves
and narrow sides and very good quality
rubber mix. Tyre sidewalls and tread
belt are very thin and flexible while tyre
aspect ratio is low. In order to achieve
low rolling resistance tyres for EV’s
and HV’s should have as big a diameter
as possible. Recent trends in tread
compounding have helped in achieving
tread life in competitive to the non-LRR
tyres (ie EV Tyres).Do you think that the role of
natural rubber in EV tyres
is likely to increase because
of its unique qualities in
comparison with SR?Performance requirements will dictate
the materials that can be used. First, it is
necessary to understand that almost all
tyres have at least some natural rubber
components. Synthetic rubber will
tend to noticeably impact major tyre
features like rolling resistance, quality,
and handling. So NRwill be for low-end
tyres rather than the higher performance
types, which need specialized
tread materials to remain relatively
unmodified.
Pradeep Chandrasekaran , a
post-graduate in Automobile
Engineering and an SAE
International Member says all the
Indian OEMs are working towards
electric mobility and making it
affordable by 2030.He is one of
the industrial experts working
towards increasing the India’s
electric mobility market share with
contributions on ‘Technology and
Frugal MindSet’B
ecause low-rolling-
resistance tyres areharder, they are also
louder on the road.
They provide a slightly
rougher ride and that
they even reduce
handling performance
and increase braking
distances. The real
world usage pattern
for different categories
call for different
applications