All Terrain tyres or AT are a compromise. All Terrains are an attempt to offer good performance both on road as well as offroad. The ALL TERRAIN TREAD is intended to perform well under a variety of conditions found offroad while still offering acceptable on-highway performance. This is accomplished by using a tread pattern design where the lugs are tighter together than a more aggressive mud tyre’s tread. The result is usually a quieter ride on the street than a mud tyre due to its lesser aggressive tread pattern. When compared to a street tyre, All Terrain tyres usually produce more noise. The payoff of an All Terrain Tyre is that they performs well on a variety of terrains: rocks, sand, somewhat in the mud while still offering decent traction on the paved road. One drawback of an all terrain is that the tread design tends to pack with mud however some of the AT designs perform surprisingly well in muddy conditions. The AT All Terrain is typically the tyre for the 4-wheeler who drives their 4×4 as a daily driver and will see minimal trail use and more on highway driving.
There are two basic types of tyre construction that mud, all terrain and street tyres use as their foundation. They are bias-ply and radial designs. Each type of tyre construction has its own unique set of characteristics that are the key to its performance, whether on road or off road and these characteristics can help to define the purpose of the tyre. The following information will explain what identifies the difference between a bias ply tyre and a radial type tyre.
The bias ply tyre construction utilizing rubber-coated layers known as plies composed of textile cords, usually nylon and sometimes Kevlar. The plies layered diagonal from one bead to the other bead at about a 30 degree angle. One ply is set on a bias in one direction as succeeding plies are set alternately in opposing directions as they cross each other and the ends are wrapped around the bead wires, anchoring them to the rim of the wheel. The layers of plies are them covered with more rubber to form the tread of the tyre. Bias ply tyres are sometimes called cross-ply tyres.
Bias ply tyres have a limited purpose in life and are only used for specific purposes or jobs. The reason for this is because of its performance characteristics. However for some jobs the bias ply tyre is an idea tyre for the purpose such as for the tyres of a towed trailer, farm equipment tyres, some purpose built tyres like extreme terrain tyres and some forms of racing still use bias ply tyres. The reasons for this limited use are:
1. The bias-ply tyre casing is constructed to form one working unit. When the sidewalls deflect or bend under load, the tread squeezes in and distorts. The distortion affects the tyres footprint and can decrease traction and increases wear depending on the terrain. The tread distortion also causes abrasion from the ground surface, which reduces the life of the tyre. These factors are why bias ply tyres are not idea for passenger car tyres or as tyres that my see highway use unless used as tyres for a towed trailer.
2. Bias Ply Strength – The way to increase the strength of bias-ply tyres is by increasing the number of plies and bead wires. More plies means more mass which, increasing heat retention and reducing tyre life.
3. Because of the bias ply inherent construction, sidewall strength is less than that of a radial tyre’s construction and cornering is significantly less effective. This is probably one of the main reasons bias ply tyres are not used for passenger cars and trucks.
However because of the bias ply construction and inherent strength of a properly inflated tyre, the bias ply is idea for straight line towing.
The radial is a type of tyre that is constructed with rubber coated, reinforcing steel cable belts that are assembled parallel and run from side to side, bead to bead at an angle of 90 degrees to the circumferential centerline of the tyre. (As opposed to the 30 degree alternating application lengthwise as in bias ply tyres). This makes the tyre more flexible which reduces rolling resistance to improve fuel economy. Then numerous rubber coated steel belts are then constructed into the “crown” of the tyre under the tread to form a strong stable two-stage unit.
Radial tyres are the preferred tyre of choice in most applications for several key reasons.
1. The combination of steel stabilizing belts in the single-layer radial casing allows the tread and sidewall to act independently. The sidewall flexes more easily under the weight of the vehicle and its cargo, while the tank-track type tread provides even contact with the ground. Greater vertical deflection is achieved with radial tyres. This is desirable because extreme flexing greatly increases resistance to punctures.
2. To increase a radial tyre’s strength, larger diameter steel cables are used. Larger steel cables can help reduce punctures, tears and flats. Larger steel cables also help distribute heat, resulting in a cooler running tyre and improving fuel economy. Unlike bias ply tyres larger steel cables have little negative affect on performance.
3. The parallel stabilizing steel belts of the radial minimize tread distortion. As the sidewalls flexes under load, the belts hold the tread firmly and evenly on the ground or object and thus minimizing tread scrub and greatly increasing tread life.
4. When cornering the independent action of the tread and sidewalls keeps the tread flat on the road. This allows the tyre to hold to its path.
When offroad, the radial tyre’s stabilizing steel belt design aids in greater traction by holding the tread evenly over obstacles allowing the tread of the tyre to have a better chance of finding traction.
Sipes are the small slots that are cut or molded into a tyre tread surface. These slots are meant to aid in increasing traction in snow, ice, mud, and wet road surfaces. The name of the concept of siping a tyre comes from a man named John Sipe, who received a patent in the 1920’s, after realizing that an array of small transverse cuts in the heels of his shoes gave him better traction. Later Goodyear received a US patent claiming that the “sipes” improved traction characteristics in tyres.
Tyre tread is a series of block shapes, groove configurations, and sipes, all of which have an affect on the tyres traction and noise level. Typically, wide, straight grooves running in the direction that the tyre travels will have a lower noise level and good water removal. More lateral grooves running from side to side will usually increase traction while increasing noise levels. Sipes are the small grooves or slits that are cut across larger tread elements. Up to a point, more sipes give more traction in snow and mud as well as over various terrains found offroad.
All tyres are required to have certain information molded into the side of the tyre in a location known as the sidewall. Some of the information is self explanatory while other information requires a little knowledge to decipher. The following will help you understand what this information means.
This Defines the intended proper use of the tyre. P indicates this is a passenger car tyre while LT indicates the tyre would be for a light truck with a heavier load rating.
This is the width of the tyre measured in millimeters from sidewall to sidewall. An example might be 215 representing 215 millimeters.
This is the ratio of the height of the tyre’s cross-section to its width. An example of this might be 65, which means that the height is equal to 65% of the tyre’s width. To calculate the aspect ratio, multiple the first number (e.g. 215) by the second number with a decimal before the number (e.g. .65). Using the example numbers the tyres aspect ratio would calculate as215x.65=139.75 where 139.75 is the tyre’s height in millimeters. This is the height of the rubber from rim to tread on one side of the tyre.
Convert the above calculated tyre height (aspect ratio) in millimeters to inches by multiplying the millimeters by .03937 (139.75 x .03937 = 5.5 inches). Then take the inches and multiply by two and add the rim size. Example: 5.5 x 2 + 15 (rim size in inches) = a 26 inch tall tyre.
This indicates how the how the tyre was put together and will say much about the tyres handling characteristics. R indicates the tyre is a radial type tyre. B indicates the tyre is a bias ply type tyre.
This is the width of the opening in the tyre where it would be mounted to a wheel. This is measured from one bead across the opening to the other side of the same bead. This measurement is in inches and an example would be 15 and indicates that this tyre is for a 15 inch rim, or wheel.
This is a number corresponds to the maximum load in pounds that a tyre can support when properly inflated. You will also find the maximum load in pounds and in kilograms molded elsewhere on the tyre sidewall.
| Tyre Load Ranges | Inflation Pressure As For” | |
| “Maximum Load” | ||
| P-metric | ||
| Standard Load | (SL) | 35 psi |
| Extra Load | (XL) | 41 psi |
| Light Truck | ||
| Load Range C | (LRC) | 50 psi |
| Load Range D | (LRD) | 65 psi |
| Load Range E | (LRE) | 80 psi |
This is a number that corresponds to the maximum service speed for a tyre. See Chart for ratings. Note: Speed ratings are specific for passenger car tyres and not light truck tyres. Light truck tyres (LT) are not speed rated.
| Rating | Maximum Speed |
| Q | 99 mph |
| T | 118 mph |
| H | 130 mph |
| W | 168 mph |
| Z | Above 149 mph |
| Disclaimer for the common sense challenged: Please note that this rating relates only to tyre speed capability based on tyres’ limits, and is NOT a recommendation to exceed legally posted speed limits; always drive within the legal speed limits. | |
Pounds per square inch – used to measure air pressure in a tyre. The PSI rating on tyres is typically the maximum recommended tyre pressure for that tyre. Tyre pressure should always be checked periodically and when the tyres are cold. Under normal operation, tyres can lose approximately 1 PSI of pressure every month. For every 10 degree change in ambient temperature, tyre pressure can change by approximately 1 PSI.
This means the tyre is compliant with all applicable safety standards established by the U.S. Department of Transportation (DOT). Adjacent to this is a tyre identification or serial number; a combination of numbers and letters with up to 12 digits.
This stands for Uniform Tyre Quality Grading, which is a quality rating system developed by the Department of Transportation (DOT). The DOT requires the manufacturers to grade passenger car tyres based on three performance factors: tread wear, traction, and temperature resistance. Note: snow tyres are exempt from the UTOG rating system.
| Greater than | 100 | Better |
| 100 | Baseline | |
| Less Than | 100 | Poorer |
The tread wear grade is a comparative rating based on the wear rate of the tyre when tested under controlled conditions on a specified government test track. A tyre graded 200 would wear twice as long on the government test track as one graded 100. Your actual tyre mileage depends upon the conditions on which they are used and will vary with driving habits, service practices (alignments, proper air pressure, etc), differences in road characteristics and climate. Note: Tread wear grades are valid only for comparisons within a manufacturer’s product line. They are not valid for comparisons between manufacturers.
| A | Best |
| B | Intermediate |
| C | Acceptable |
Traction grades represent the tyre’s ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. The Traction grade is based upon “straight ahead” braking tests; it does not indicate cornering ability
| A | Best |
| B | Intermediate |
| C | Acceptable |
The temperature grades represent the tyre’s resistance to the generation of heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperatures can cause the materials of the tyre to degenerate and thus reduce tyre life. Excessive temperatures can lead to tyre failure. Federal law requires that all tyres meet at least the minimal requirements of Grade C.
LT 255/85B16
- LT = Light truck tyre
- 255 = Approximate cross section width in millimeters
- 85 = Aspect ratio (height to width)
- B = Bias ply construction (R = Radial construction)
- 16 = Rim diameter in inches
33×12.50R15 LT
- 33 = Approximate diameter in inches
- 12.50 = Approximate cross section width in inches
- R = Radial construction (B = bias ply construction)
- 15 = Rim diameter in inches
- LT = Light truck tyre
One or more rubber-coated plies (layers) of steel, polyester, nylon, Kevlar or other material running circumferentially around the tyre under the tread. They are designed to reinforce body plies to hold the tread flat on the road. Belts reduce squirm to improve tread wear and resist damage from impacts and penetration.
The main body of the tyre consisting of wire beads and body plies. The carcass does not including the tread or sidewall rubber.
A layer of specially compounded rubber forming the inside of a tubeless tyre, designed to inhibit loss of air pressure.
Plus Sizing is among the simplest ways for you to dramatically improve both the look and performance of your vehicle. The concept is to alter the wheel diameter and the tyre aspect ratio. There are three common categories of Plus Sizing: Plus Zero, Plus One and Plus Two. One or two layers of heat and impact resistant, rubber-coated fabric used to form the body of the tyre. Automobile and light truck tyre plies are normally constructed of nylon or polyester cords.
The portion of the tyre which comes in contact with the road. Tread designs vary widely depending the the specific purpose of the tyre.
The space or area between two tread rows or blocks. The Pattern of Grooves and Tread Elements.
The tread pattern refers to the overall structure of the tread. The tread pattern is made up of tread lugs and tread voids. The lugs are the sections of rubber that make contact with the terrain. Voids are the spaces that are located between the lugs. The mud-terrain tyre pattern is characterized by large lugs in the tread pattern with large voids between these lugs. The large lugs provide plenty of bite in poor traction conditions while the large voids allow the tyre to clean itself by releasing and expelling the mud or other material while spinning. The all-terrain tyre pattern is characterized by smaller voids and lugs when compared to the mud terrain tyre. A denser pattern of lugs and smaller voids make all terrains quieter on the street than the mud terrain tyre. The downside to an all terrain is that the smaller voids cannot clean themselves as easily of mud, slush or material as would the larger voids on the mud tyre. When voids fill up with mud the tyre loses much of it’s bite and traction. However the all terrain is a good compromise to general highway driving and minimal off-road use.
Self Cleaning is the effect of a tyre’s tread pattern to allow the release of mud or material from the voids of tread, thereby providing a good bite on every rotation of the tyre. The better mud terrain tyres will allow the mud or material to easily be released from the tread voids.
The design of the tread pattern changes from one side of the tread face to the other, in order to have two or more different types of tread patterns on one tyre for better overall performance.
A tyre designed to rotate in only one direction for maximum performance, especially on wet roads or in mud.
Sidewall strength refers to the tyres resistance to punctures and tears in its sides. The strength is typically a result of the number plys extending into the sidewall and by the tread design and tread pattern that extends down onto the sidewalls. Typically the greater the sidewall strength, the more resistant the tyre is to flex even when aired down to lower pressures.
A tyre with a heavy bar or block tread element design to provide maximum traction in mud or snow conditions. The tyre will be marked M+S or MT on the sidewall.
A tyre designed to rotate in either direction without loss in performance.
A numerical term which expresses the relationship between the section height of the tyre and the cross section width. The lower the aspect ratio, the wider the tread and the shorter the sidewall.
Associated with driving on rain-slicked roads with worn or poorly treaded tyres. It is the lifting action on a tyre when water pressure forces the tyre upward, leaving a cushion of water between the tyre and road surface.
A term which is gradually replacing the term “Ply Rating” and which is indicated as Standard Load (SL) and Extra Load (XL) for auto tyres and Load Range C, D etc. for light truck tyres. (The carrying capacity of the tyre at specific air inflation pressures).
A marking consisting of the load index and speed symbol, ie. 87S. A mound of rubber in the tread measured in 32nds of an inch from the tread surface to the bottom of the tread grooves. The pattern of grooves and tread elements.
Narrow bars of rubber molded into the tread at a height of 2/32nds of an inch. When wear reaches the tread wear indicator, it is time to replace the tyre.
The measuring, analyzing, and setting of angles to predetermined manufacturer recommended specifications to ensure maximum tyre service life, vehicle handling, and safety. Proper wheel alignment is attained when each wheel’s position, relative to the vehicle and specification, is correct.
Four-wheel alignment is the setting of all four wheels to specifications and referenced to the vehicle centerline.
Two-wheel alignment is normally performed on solid axle rear wheel drive vehicles, and is the setting of the front wheels relative to one another.
Adding external weights to compensate for unequal distribution of tyre and wheel weight. Unbalanced tyre and wheel assembly is balanced by clamping appropriate metal weight to the rim.