Understanding Your Tyres

Steer, Drive or Trailer Truck Tyres

The difference between Steer/All Position tyres, Drive tyres & Trailer tyres.

Steer/All Position

Steer tyres are the most important tyres on your truck, designed to perform their best in the front (steer) axle position. They influence handling and ride, offering ribbed tread designs to help channel water away from the tyre. All position tyres are also used on the steer axle, but steer tyres are often superior in handling.

 

Drive

Meet your truck's workhorses and traction gurus, designed exclusively for drive (or torque) axles. Lug-type or siped tread designs help drive tyres maximise traction levels on various surfaces.

 

Trailer

Trailer tyres must withstand strong lateral and braking forces and varying loads. They are designed to perform best in free-rolling, trailer axle positions. Reinforced sidewalls help protect casing from curbing damage.

 

Tyre Size

Tyre size can be found on the sidewall of a tyre and appears as a combination of numbers and letters. Knowing what each section of these numbers and letters mean will make it very easy to find your car's tyre size. 

To explain tyre size further we have broken each section down, explaining what each number and letter means.

Sidewall MarkingExplanation
205The width of the tyre in millimetres
55The height of the tyre sidewall as a percentage of the width of the tyre.
RThe tyre is of Radial construction
16The tyre's inner rim diameter in inches.
91The Load Rating of the tyre.
WThe Speed Rating. This indicates the tyre's maximum speed at full load.


Tyre Load Rating



The tyre load rating indicates the maximum weight each tyre is able to carry.

If a tyre with an incorrect load capacity is fitted to your car your insurance policy can become void in certain cases. It is therefore vital to check your car is fitted with a tyre with the correct load rating.

The load rating of a tyre is usually found after the diameter reading and before the speed rating on the sidewall marking.

The table below shows the weight capacity in kilograms of each load rating.

Load IndexLoad in kgLoad IndexLoad in kgLoad IndexLoad in kg
6226584500106950
6327285515107975
64280865301081000
65290875451091030
66300885601101060
67307895801111090
68315906001121120
69325916151131150
70335926301141180
71345936501151215
72355946701161250
73365956901171285
74375967101181320
75387977301191360
76400987501201400
77412997751211450
784251008001221500
794371018251231550
804501028501241600
814621038751251650
824751049001261700
83487105925  


Tyre Speed Rating



The speed rating of a tyre is indicated by a letter at the end of the tyre size on the sidewall of the tyre, and specifies the maximum speed your tyre is capable of maintaining.

For example a tyre with a speed rating of "W" can reach speeds of up to 168mph.

A tyre's speed rating is the result of specific tests ran by engineers. These involve running the tyre at 6.2mph steps in ten minute increments until the required speed has been met.

If your car is fitted with a tyre with a lower speed rating than is appropriate for your vehicle you could invalidate your insurance policy, therefore it is essential you check your car's speed rating before purchasing new tyres.

The table below shows the maximum speed in mph of each speed rating.

Sidewall MarkingExplanation
N87
P93
Q99
R106
S112
T118
U124
H130
V149
Z150+
W168
Y186



TYRE PRESSURE

Correct tyre pressure can help to extend the life of your tyre, improve vehicle safety and maintain fuel efficiency. Pressure is measured by calculating the amount of air that has been pumped into the inner lining of your tyre in pounds force (PSI) or BAR pressure. The manufacturer of your vehicle specifies the suitable pressure, and it is your responsibility to make sure that the pressure is checked and corrected on a regular basis, at least every couple of weeks.

Maintaining correct Tyre Pressures.

There are three main reasons why maintaining the right tyre pressure is important. The first is safety. Tyres that are under inflated can overheat; and over inflated tyres can lead to poor vehicle handling on the road. The second reason is economy. Over or under inflated tyres suffer more damage than those with the correct pressure and need to be replaced more regularly. Vehicles with under-inflated tyres have increased rolling resistance that require more fuel to maintain the same speed.

Device

TYRE TREAD DEPTH

The legal limit for car tyre tread depth is 1.6mm (across 75% of the tyre). However, the deeper the tread the more grip you have. At eWinda.com we recommend that you replace your tyres when the tread is less than 3mm as the performance of the tyre will begin to reduce significantly.

Device