Tyres are a major part of cars as round as they are and as non-mechanical or metallic. There are several numbers on the side walls of your tyres and they have their various meanings which should not be overlooked when choosing tyres for various vehicles and uses. Some basic things to note about tyres are hereby laid out as simply as can possibly be.
The first thing to note is that tyres come in various sizes and as the sizes differ, so does their uses. They come with different load capacities as well as speed capacities. They have their various max speed capacities or ratings. They also have different applications from snow to winter and the all season tyres. All these information are just right there on your tyre except if you do not check it out. It could be dangerous running tyres rated for a maximum speed of say 130kph at higher speeds. It could fail which in other words mean that it could be under more pressure than it can take more heat and less air. That may make the tyre to fail – tear or burst. All you have to do is check the side walls of your tyres for the numbers, be rest assured that they are not just there for decoration. They have their meanings which we should understand to help us make good decisions in tyre choices and maintenance and also keep us safe.
Nigeria is a country of two weather conditions; dry season and rainy season. No autumn, no winter, no anything of such. Most fairly used cars imported into Nigeria come with winter tyres. Unfortunately, there is no such thing as winter in Nigeria. Some tyres made for snow may not perform well in areas that are hotter than those regions for which it was designed. This here gives you the basic information or knowledge you need to make your tyre choices right and be safe in your driving.
There is a group of numbers on the side wall of your tyres like this: P215/55R17 93V.
P – Stands for ‘Passenger’ in the American tyre Metric but it would be left blank if it is Euro Metric Tyre. You may see LT meaning light truck or ST meaning special truck. T means temporary tyre.
215 – This is the width of the tyre – how wide it is.
55 – This is the aspect ratio of the tyre which in actual sense is a percentage of the width of the tyre which turns out to be the height of the tyre from ground to the rim. This is the reason it is called a ratio. Low profile tyres are generally at 55% and below. Ultra low profile tyres can be as low as 30%. Performance vehicles normally come with low profile tyres.
R – Simply tells us the design of the tyre and ‘R’ here implies that the tyre is radial in design which is the most common. There is the ‘D’ which stands for diagonal. There is the ‘B’ which stands for bias ply design which is not so much in use because of its lesser smoothness in driving though it is still in application in some trucks. Radial means that the layers that make up the tyre are laid along the circle of the tyre while bias ply means the layers are laid across the tyre.
NB: R doesn’t stand for radius. Bias ply tyres don’t ride as smoothly as the radial ply tyres. They are still in use but very scarcely.
17 – The diameter of the inner circumference of your tyre or the outer circumference of your rim which if we consider the number here means 17 inches. Never fit a rim to a tyre with a different diameter.
93 – Load index tells the maximum load per tyre. If you overload your tyre, it could give way.
V – Speed rating. This tells how fast you can go with particular tyres. Tyres undergo a lot of pressure and heat while you drive and they can handle the pressure only to degree they have been designed to. At higher speeds, the tyre can get so hot that the tread can separate from the belt and the tyre is destroyed.
M + S: This means that the tyre was made to handle serious snow conditions. Nigeria has no snow so, if your car came with some of those, you should consider replacing them.
This tells you the maximum speed at which your tyre can perform optimally without failure. Tyre ratings range from A to Z even though some numbers aren’t directly in their alphabetic positions like H which stands in between U and V instead of in between G and I. Some letters also have inbetweeners like A with all sorts like A1, A2, A3 and some more. There are no I, X and O ratings as well. Tyres have their speed ratings matched to the car. A car with a top speed of 220kph cannot come with tyres with S rating (180kph).
NOTE: don’t replace your car tyres with those with lesser speed rating. It could be dangerous or worst still, fatal at speeds higher than those of the tyre’s rating.
SPEED RATINGS AND THEIR CORRESPONDING TOP SPEED
|SYMBOL||SPEED (MPH)||SPEED (KMPH)||APPLICATION|
|B||31||50||Industrial machine like fork lifts.|
|L||75||120||Off road and light truck tyres.|
|M||81||130||Temporary spare tyres.|
|R||106||170||HD Light truck tyres|
|S||112||180||Family saloon and Space buses.|
|T||118||190||Family Saloon and Space buses.|
|H||130||210||Sport Saloons and coupes|
|V||149||240||Sport Saloon, coupes and sport cars|
|Z or ZR||Above 186||Above 300||High performance Super cars and sport cars.|
INSIDE AND OUTSIDE WALLS: tyres are designed to have outer walls and inner walls. Whenever a tyre is found to be inside out, it is suspected that something must have been wrong.
MAXIMUM LOAD RATING: this indicates the maximum load the tyre is designed to support when inflated to the correct specification. It is also on the sidewalls of your tyres.
DATE OF PRODUCTION:
These are a group of 4 figures. The first 2 figures tell the week of the year in which the tyre was made (There are 52 weeks in a year). The latter 2 figures tell the year of production.
TYRE PLIES COMPOSITION AND MATERIAL USED: This tells you basic information about the makeup of your tyre surface and sidewalls. It turns out that your sidewalls should not roll on the road surface as they are not as strongly built as the surface for road contact.
DOT: United States Department of Transportation tyre identification or serial numbers.
MAXIMUM SAFE INFLATION PRESSURE:
This tell you the maximum amount of air pressure your tyre should take in. it is always measured in kilopascal (kPa) or Pounds per Square Inch (Psi). Inflating to a higher pressure than recommended may make the car bouncy and lower may get your tyre destroyed. When your tyre in under inflated, it makes your car drag the tyres which makes your car use more fuel than normal. One way to know that your tyre is under inflated is that the sidewall becomes dirty because it is rolling in contact with the road which it is not designed strongly enough to do.
THREADWEAR, TRACTION AND TEMPERATURE GRADES
Treadwear, traction and temperature are made with expected grades which are denoted with letters as well. Note that tread is the part of the tyre that gets in contact with the road surface. It is the part or surface with all those grooves. If your tyre side walls are getting dirty, your tyre is underinflated and your side walls were not designed to come in contact with the road. Your tyre may fail for this reason.
XL: Extra load. This implies that your tyre is way tougher than standard load tyres (SL). It was made to have more tolerance for weight and bear more heat. It could be designated EL, RF OR RHS which means REINFORCED which could as well be spelt out on the tyre sidewall.
NB: having tyres with high speed ratings is not a reason for over speeding.
LOAD INDEX AND THEIR CORRESPONDING LOAD IN KILOGRAMS.
|Load index||Load (kg)||Load Index||Load (kg)||Load Index||Load (kg)||Load Index||Load (kg)|
NOTE: If your car has four tyres and their load index is 94. The load index corresponds to 670kg on the table. You should note that the combined weight your tyre would carry without failing is 670 x 4 = 2680kg. Also note that the weight of the entire car is also considered.
It is worthy of note that tyres with higher speed ratings deliver better handling even though there are down sides to it. They also may deliver a little less comfort than those with lower speed rating because of stiffer construction. They will also wear faster due to the softer material used in making them. Don’t also get tyres that are rated lower than those that came with the car. It could be disastrous and even fatal.
You should watch your tyres for under inflation. Once your tyre is under inflated, the side walls will roll on the road. This makes the sidewall dirty. Note that the sidewall is not strong enough to handle the contact with the road and it could be destroyed.
If you drive hard into pot holes, your tyre could become pregnant or swollen. The tyre could eventually burst from the point of swelling.
NOTE: changing your tyre sizes can alter your speedometer readings. There are tyre and rim variations that will give you about the same reading. Going higher or lower may need you to talk to an expert.
Several people buy 2 new tyres and just put them in front and put tyres with lesser tread behind. It may not be the best thing to do. If your car is rear wheel drive, it is better to put the tyres with better grip at the rear – not everyone can handle a car that loses control at the rear. If your car is front wheel drive car which implies that most of the load is in front (engine, gear and drive shaft load).
If your tyre is badly installed, it could burst or explode at high speeds.