The
super-fast Mumbai-Pune expressway has highlighted the importance of tyre
performance at high speeds. An alarming number of tyre blow-outs has led
to the general belief that Indian tyres are not suitable for the speeds
today's new-generation cars are capable of. The 'speed rating'
of a tyre (see box) denotes the highest speed a correctly inflated and
loaded tyre can be driven for one hour without deforming. However, for
all practical purposes, the safe speed limit is 30kph less than the tyre's
speed rating. Most cars in India come with 'S' rated tyres which have
a speed rating of 180kph (or 150kph for prolonged driving). Whilst the
'S' rated tyre is fine for most small cars, the same speed rating is used
on more powerful cars like the 1.6 Palio, Ikon, Accent, Corsa, Lancer
etc. These cars are capable of speeds well in excess of the safe limit
of 150kph and in the case of the Palio, beyond the ceiling of 180kph!
Ideally, the Palio should come with a tyre with a 'H' speed rating which
is good for 210kph.
The reason why car companies skimp on providing tyres with higher speed
ratings is to cut costs and to trade off high-speed performance for longer
life and better comfort.
The argument is that there are no roads in India where you can sustain
180kph for more than an hour, which is why the 'S' rated tyre is fine
for most models. However, as a matter of policy (and safety) car manufacturers
should only provide tyres that carry a speed rating well in excess of
that particular model's maximum speed.
For high speed driving, it is always advisable to increase your tyre's
inflation pressure by 2-5psi. This will hurt ride comfort at slow speeds
but reduce the chance of heat build up, punctures and tyre failures as
the increased pressure reduces the sidewall flexing of the tyres.
SPEED
RATING
Speed
Symbol |
Max Car Speed Capability |
Speed
Symbol |
Max
Car Speed Capability |
|
KPH |
MPH |
KPH |
MPH |
| L |
120 |
75 |
S |
180 |
113 |
| M |
130 |
81 |
T |
190 |
118 |
| N |
140 |
87 |
U |
200 |
125 |
| P |
150 |
95 |
H |
210 |
130 |
| Q |
160 |
100 |
V |
240 |
150 |
| R |
170 |
105 |
W |
270 |
168 |
| |
|
|
Z |
240+ |
150+ |
|
May 2002
