most times when we need new tires for our cars we just pull over in a tire shop and buy what we assume to be the right tires for our cars not mindful that tires actually have specifications which we ought to look out for. These are in the form of those extra numbers usually on the sides of tire outer walls........

For passenger car tires there are two sizing systems currently in common use.
"Passenger Metric" (P-Metric for short) tires will have a description that reads like
this: P205/55R16 89H The "P" actually signifies that this tire follows P-Metric load and inflation tables. "205" is the "section width" (not the width of the tread) or the width of the tire at its
widest point measured in milimeters. "55" is the "section height" sometimes called the aspect ratio and measures the tire
from the bead to the top of the tread as a percentage of the section width - 55% of
205 mm. "R" means the tire is of radial construction "16" is the diameter of the wheel on which the tire can be mounted, not the
diameter of the tire but of the hole in the center. "89H" is the "service description" and tells us 2 things. The "89" is the "load index"
which tells us how much weight the tire can carry at specific inflation pressures. In
this case the 89 tells us this is a "standard load" tire and at 30 psi for example this
tire can carry a load of 1,176 lbs. Maximum load carrying capacity is achieved at 35
psi and is 1,257 lbs. In the past most P-Metric tires had maximum inflation
pressures listed on the sidewall of 35 psi but most manufacturers have increased that to a maximum of 44 psi. Max load is still achieved at 35 psi however. The "H" is the tires "speed rating" or the maximum speed capability the tire is rated
for under specific test conditions. H translates to 130mph. Other common speed
ratings for tires in this size would be T (118mph), V (149mph), W (168mph), and Y
(186mph). It is recommended when replacing tires that you chose replacements with the same
load index and the same or higher speed rating as the tires originally fitted to the
vehicle. The other system is the European Metric (Euro-Metric) system. The size description
on a Euro-Metric tire can read several ways. Most common in this size would be: 205/55R16 91H. This is the most common "standard load" sizing for a Euro-metric tire and is the
original equipment size on many Volkswagon's, BMW's, Volvo's, Saab's etc. Notice
there is no "P" at the beginning of the description and the load index is 91 not 89.
Standard load Euro-Metric tires in this size can have load index's of 89 or 90 but
these are very rare indeed. Dimensionally this Euro-metric tire is identical to the P-Metric tire example above.
Where it differs is in that service description. A standard load Euro-metric tire with a
load index of 89 is not the same as the P-metric tire with a load index of 89. For
example at 30 psi where the P-Metric tire carries a load of 1,176 lbs the Euro-metric
tire carries 1,113 lbs. That is why the more common standard load Euro-metric tire
has a load index of 91 (1,179 lbs at 30 psi) as it can be pretty much freely interchanged with P-Metric standard load tires at the same inflation pressures with
no problems. In other words a 205/55R16 91H is usually equivilant to P205/55R16
89H and vice-versa. On a Euro-metric standard load tire maximum load is achieved at 36 psi instead of
35 psi and with a 91 load index that maximum load is 1,356 lbs - slightly higher
than the P-metric tire can do. Euro-metric tires in this size are also available in 2 "Extra Load" sizings with a load
index of 94 or 97. The size will read like this: 205/55R16 XL 94H or 205/55R16 XL 97H Extra load tires have maximum inflation pressures of 51 psi where standard load
tires are typically 41 or 44 psi. Maximum load capacity is achieved at 51 psi and is
1,477 or 1,609 lbs respectively. Vehicles that specify an extra load tire should never
be fitted with standard load tires. There is another, older and somewhat dated method of describing the tire size
which is still sometimes encountered. It might read like this: 205/55HR16 This is an outdated way of expressing a standard load Euro-metric tire with an H
speed rating (205/55R16 91H) and was often used before the sudden proliferation
of multiple standard and extra load fitments in the last 15-20 years. To add to the
confusion some manufacturers combine the older and newer descriptions like this: 205/55HR16 91H You might also encounter a description like: 205/55ZR16 The "Z" is an old speed rating that has now been superceded by Y and W. The Z
simply means the tire has a speed capability above 149mph. Sometimes again
manufacturers will mix the new and old description styles and use something like
205/55ZR16 91Y which is bascially the same thing as saying 205/55R16 91Y.

Source: http://answers.yahoo.com/question/index?qid=20080115195811AA15A6F

additionally.......
"M+S", (Mud and Snow), indicates an
all-season tire. The snowflake and mountain symbol
on the side of a tire indicates that it meets or exceeds the new snow tire designation specifications, and will provide
you with optimum traction in severe snow conditions.

The maximum pressure number gives the maximum cold pressure required to carry
the maximum load for which the tire is rated. The maximum
pressure number is not the same as the recommended tire
pressure for your vehicle. Important: Never exceed the maximum pressure written on your tire's sidewall. Explosive failure may occur as a result, leading to serious injury
or death.

The tread wear rating measures how long the tread takes to wear down.
The higher this number, the longer the tread should last. For
example, a tire with a treadwear rating of 400 should last twice as long as one with a treadwear rating of 200. The actual rate of treadwear for your tires depends on your unique road
conditions, climate and tire maintenance.

The tracion rating describes the tire's ability to stop on wet pavement
and concrete. Traction rating tests are conducted on vehicles
driving straight ahead, and do not measure the tire's cornering
abilities. Traction ratings are written (from highest to lowest) as "AA", "A","B", and
"C".

Driving creates heat. Excessive heat for prolonged periods can
degenerate the materials in your tires, and, under extreme
conditions, can lead to explosive failure. A tire's temperature grading measures the tire's ability to withstand and dissipate heat under
controlled, indoor laboratory testing. A tire's temperature resistance is assigned the following grades (from
highest to lowest): "A", "B",and "C".

Thank you for this information. Please where can one buy really good tires in lagos? I just bought a 2006 jeep commander and i want to embark on a cross-country trip in her, do i need to change the tires? The previuos owner maintained er well and the tires are really good?