Tire Terminology

All Terrains - All Terrain tires 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 tire's tread. The result is usually a quieter ride on the street than a mud tire due to its lesser aggressive tread pattern.  When compared to a street tire, All Terrain tires usually  produce more noise.  The payoff of an All Terrain Tires is that they perform 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 tire for the 4-wheeler who drives their 4x4 as a daily driver and will see minimal trail use and more on highway driving.

Mud Terrain Tires - MUD TIRES or MT (Mud Terrain) are as you might have gathered from the name, designed to perform most specifically in the mud.  But when you look at the tread design of many mud tires, they generally perform well in other conditions such as on the rocks, in deeper snow, as well as in loose gravel and in the softer, constantly changing terrain of wooded trails.  This is because mud tires are usually designed from a softer compound with wider gaps (voids) between the lugs, which grab onto anything it can hook one of its lug edges around, especially when aired down.  Tread designs typically are what make or break a mud tire and vary widely from manufacturer to manufacturer. Drawbacks of  MT Mud Terrain tires are they perform poorly on the highway especially in the rain where the wide lug pattern results in less of a tire footprint on the road.  Even worse, the MT can be downright dangerous in icy conditions. Mud tires also tend to wear quicker than an all terrain or a street tire and depending on your perspective, the on-highway noise level can be considerably higher especially after they wear down with highway use.   

Sipes are the small slots that are cut or molded into a tire 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 tire 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 tires.

Tire tread is a series of block shapes, groove configurations, and sipes, all of which have an affect on the tires traction and noise level.  Typically, wide, straight grooves running in the direction that the tire 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 tires are required to have certain information molded into the side of the tire 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.

 WIDTH - This is the width of the tire measured in millimeters from sidewall to sidewall.  An example might be 215 representing 215 millimeters.

 ASPECT RATIO - This is the the ratio of the height of the tire's cross-section to its width. An example of this might be 65, which means that the height is equal to 65% of the tire'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 tires aspect ratio would calculate as 215x.65=139.75 where 139.75 is the tires height in millimeters.  This is the height of the rubber from rim to tread on one side of the tire. 

To convert the aspect ratio to a full tire height in inches, do this:
Convert the above calculated tire 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 tire.

 CONSTRUCTION - This indicates how the how the tire was put together and will say much about the tires handling characteristics. R indicates the tire is a radial type tire.  For more information about what a radial is, click here.  B indicates the tire is a bias ply type tire.  For more information about bias ply type tires, click here.

 DIAMETER - This is the width of the opening in the tire 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 tire is for a 15 inch rim, or wheel.

 LOAD RANGE (NOT HI-LIGHTED) - This is a number corresponds to the maximum load in pounds that a tire can support when properly inflated. You will also find the maximum load in pounds and in kilograms molded elsewhere on the tire sidewall.

- This is a number that corresponds to the maximum service speed for a tire.  See Chart for ratings.  Note: Speed ratings are specific for passenger car tires and not light truck tires.  Light truck tires (LT) are not speed rated. 

 PSI - Pounds per square inch - used to measure air pressure in a tire.  The PSI rating on tires is typically the maximum recommended tire pressure for that tire.  Tire pressure should always be checked periodically and when the tires are cold. Under normal operation, tires can lose approximately 1 PSI of pressure every month. For every 10 degree change in ambient temperature, tire pressure can change by approximately 1 PSI.