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There are three basic tyre designations seen on 4x4s: metric sizes,
floatation tyres, and numeric tyres. They are all a little different,
but they all share performance and construction information that is
embossed on the sidewall near the bead.
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| Metric Tyres |
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The metrics generally have the most information. They have been in use
in Europe and consequently South Africa for many years and have seen
adoption in the States since the late 1970s and early 1980s. They have
all but taken over the passenger car realms and dominate the light truck
and 4x4 market.
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| Tubeless |
Most tyres today are tubeless, although putting a tube into a tubeless
tyre may be a quick way to fix a puncture in the bush. Note that tubeless
tyres with tubes in them run hotter.
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| Treadwear |
Many tyres have a readwear rating that is an indicator of their ability
to last. Rubber compounds, tread depth and general construction contribute
to this rating. Sixty is the lowest rating and the numbers climb in 20-point
increments to the highest number, 500. Generally, if you see a tyre with a
nice deep tread and a low treadwear number, it probably has a very sticky
rubber compound that offers good traction but poor wear characteristics.
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| Traction |
This is an indicator of the tyres wet pavement traction performance. The
ratings run from "A", the best, to "C", the worst.
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| M&S |
If this is on the tyre, it's been approved for Mud and Snow use. It's kind
of a given for a 4x4 tyre, but the rating will get you past a chain stop
where they only allow snow-chains or M&S rated tyres.
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| Temperature |
This shows the tyres ability to tolerate and disipate heat. The ratings run
from "A", the best, to "C", the worst.
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| Load Range |
This is a rather archaic system that is mostly seen on light truck rated
tyres. In the old days, tyres were rated by the number of plies built into
the tyre carcass, four-ply, six-ply, etc., and more plies meant more capacity.
Nowadays they can get more capacity twith fewer plies, so a true four-ply
tyre can be rated as a six-ply. You will see it expressed as a "6 ply rating",
or as load ranges running from A to E, which correspond to the ply rating.
Here is how it works out:
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| Load Range |
Ply Rating |
| A |
2-ply |
| B |
4-ply |
| C |
6-ply |
| D |
8-ply |
| E |
10-ply |
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| Max Load |
A more useful way of expressing "Load Range" because it provides the
maximum load capacity of the tyre in kilograms and pounds and the maximum
rated pressure. Buying a tyre that is rated for grossly more than your 4x4
can carry is a waste of good money. Also if each tyre is rated for 1360kg
(or 3000 pounds) at 35psi and your 4x4 weights 1.5 tons (or 3,300 pounds),
running at full pressure is needlessly tough on the tyres.
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| Speed Rating |
The ability of the tyre to endure the heat and force of continuous high
speed driving. Not usually an issue with 4x4s, but a good indicator of
general robustness. The speed ratings apply mostly to metric tyres. The
table below shows some speed ratings seen on 4x4 tyres:
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| Designation |
Speed Rating |
| Q |
160 kph (99mph) |
| S |
180 kph (112 mph) |
| T |
190 kph (118 mph) |
| U |
200 kph (124 mph) |
| H |
210 kph (130 mph) |
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| Metric Tyre Details |
Metric tyres are measured in millimeters (except for rim
diameter) and a typical 4x4 tyre might read LT235/75R-15.
Breaking it down:
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| Designation |
Description |
| LT |
The tyre type, in this case Light Truck (P = Passenger Car and ST = Trailer) |
| 235 |
Section width in millimeters. The distance between the sidewalls but not the tread width. |
| 75 |
The aspect ratio, or the height from the rim to the tread expressed as a percentage of the section width. In this example, 75 percent of the 235-millimeter section width would be a 223.25 millimeter section, or sidewall, height. |
| R |
Denotes a radial tyre. |
| 15 |
The rim diameter in inches, believe it or not. |
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| Floatation Tyres |
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Floatation tyres are built, regulated and sized to a different standard.
Unlike metric tyres, flotation tyres are meant solely for use with light
trucks and are by their nature a little more robust in their construction.
You will also find that the tread depth is a little more than a comparable
metric-sized tyre. Floatation tyres are usually rated for capacity by the
A-E method and/or the actual capacity in pounds at a given maximum psi.
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| Floatation Tyre Details |
Figuring out tyre designations is easy on floatation tyres. Take a
31/10.50R-15 tyre, for example:
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| Designation |
Description |
| 31 |
The designated mounted height in inches. This may not be its actual height, however. A Dunlop 33x12.50R15 Mud Rover tyre has a mounted height of 32.8 inches while a 35x12.50R15 version is 34.1 inches high. Go figure. Read the actual mounted specs from the tyre manufacturer. Very few specs are precise in their rated diameter. |
| 10.50 |
The designated section width (sidewall-to-sidewall) in inches. Not to be confused with tread width. A Dunlop 31x10.50R-15 has an actual section width of 10.6 inches (more than designated) and a tread width of 8.1 inches. |
| R |
Denotes a radial tyre. |
| 15 |
The rim diameter in inches. |
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| Numeric Tyres |
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You may still see some light truck tyres that use designations such as
7.50-16. This is the oldest style of tyre sizing and very unusual, although
it is still in use on such popular tyres as the General Super All Grip (SAG),
a tyre designed for Land Rovers.
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| Designation |
Description |
| 7.50 |
The tyre's section width, in inches. Not to be confused with tread width. |
| 16 |
The rim diameter in inches. |
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