Low
profile and wide tyres certainly enhance the looks of a car and this is
the main reason why motorists go in for them. However, switching to different
sized tyres can have serious dynamic implications which need to be understood.
Lower profile tyres improve the steering response and overall handling
but dramatically reduce ride comfort. For our road conditions with speedbreakers
and broken patches, low profile tyres are not advisable and it's best
to stick to the original size, or something close.
What you could do if you are looking for better performance is to go in
for a tyre with a higher speed rating. As a general rule, tyres with a
higher speed rating also perform better.
However, if you do want to go in for a low-profile tyre you need to ensure
that the overall circumference of the tyre doesn't change dramatically
as this could affect the ground clearance, speedometer readings and gearing
of the car. This might mean changing over to a larger rim size to compensate
for the shorter sidewall height of the low-pro tyre.
This is where the 'Plus One/Plus Two concept comes in (see table alongside).
The whole objective of the 'Plus' concept is to arrive at the right wheel/tyre
size combination that maintains the vehicle's original tyre diameter.
If the diameter is too small, the ground clearance could become too low
and the car could ground. If the diameter is too big, the gearing could
become taller and affect the car's performance and there is a danger of
the tyre fouling with the wheel arch.
Another myth is that fitting fatter tyres gives a better road contact.
Car manufacturers do keep in mind that with replacement tyres owners may
go in for an 'upsize' and therefore most manufacturers advise upgrading
of a size or two (upto 20mm).
Fitting wider than what is recommended not only leads to instability and
poor performance but may also prove to be dangerous. It has often been
seen that too wide a tyre not only leads to aquaplaning but also cannot
produce the required traction needed for the car. This is because the
wider tyre results in a different camber and in effect reduces the actual
contact patch or footprint of the tyre.
June 2002
