Source: Tire Rack

A Mud & Snow (M+S or M/S) rating is a secondary designation and will appear in addition to other designations when a tire meets the RMA definition of a mud and snow tire.
This symbol designates a tire for severe snow conditions. (i.e. a snow tire)
See: NokianTires.com

For tires having a maximum speed capability above 240 km/h (149 mph), a "ZR" may appear in the size designation. For tires having a maximum speed capability above 300 km/h (186 mph), a "ZR" must appear in the size designation.

The Department of Transportation (DOT) requires each manufacturer to grade its tires under the Uniform Tire Quality Grade (UTQG) labeling system and establish ratings for treadwear, traction (The tire's ability to stop on wet pavement) and temperature resistance.

Treadware:
A tire graded 200 would wear twice as long as one graded 100.

LT Flotation (Light truck "flotation" tire, designed to deliver better traction on sand and soft soil found in watery off-road situations):
29X9.50R15LT [29 - Tire Diameter, 9.5 -tire's section width in inches]

LT Numeric (older sizing system is still used on older commercial vehicles):
8.00R16.5LT [8.00 = tire's section width in inches, 16.5 - rim diameter]

All-season	Performanced All-season	Ultra-High -Performance	Winter	All-terrain

Some other examples:
BF Goodrich Mud-Terrain T/A

Light Trucks, Jeeps and SUVs

Highway All-Season	Off-Road All-Terrain	Off-Road Maximum Traction (Mud-terrain)

See larger sizes at off-road tires.

Tire Size:

Tire Sizes for Light Trucks at TireRack.com

• Changing to a larger diameter tire will have the following effects:
  
  • Raised center of gravity for better clearance at the cost of being more top heavy and prone to rolling over.
  • Like having a lower axle ratio for less power but better mileage.
  • Speedometer reading will be low. (ay be speeding ticket time!).
• Larger tires will be more prone to hydroplaning and have less traction in snow, however the large gap between treads will compensate for some of this in all terrain tires. According to a Jan. 2004 ConsumerReports article, a 245/40ZR18 tire (with 9% more contact area) will be 25% more likley to hydroplane and have 20% less traction in snow than a 225/55ZR16 tire, but will have a 4% advantage in wet/dry cornering and a 5% advantage in ice braking.
• Extreme plus-size truck tires put an even greater strain on brakes, wheel bearings, and suspension parts.
• Larger, grippier tires could also make some SUVs and trucks tippier by sticking rather than sliding under hard cornering forces and also during emergency road maneuvers.
• A March, 2004 ConsumerReports article describes a test comparing All Wheel Drive (AWD) cars with Front Wheel Drive using factor all-season and "winter" tires.
  Ice braking was virtually the same for all configurations.
  AWD cars accelerated to 20 MPH in 1/2 the distance of a FWD car with factory tires.
  Winter tires accelerated to 20 MPH in 2/3 the distance of all-season tires on a FWD car.

See ratings at off-road tire page. (e.g. Hydroplaining, Handling, ...)

Air Pressure:

• Underinflation, by as little as 6 p.s.i., can cut gas mileage by 3%.
• OR EVERY 10 DEGREE FAHRENHEIT CHANGE In ambient temperature, your tire's inflation pressure will change by about 1 psi (up with higher temperatures and down with lower.)
• Use higher pressures for sustained high speed driving.
• THE TIRE PRESSURE RECOMMENDED in your vehicle's owner's manual or tire information sticker is a "cold" pressure, so it should be checked in the morning before you drive more than a few miles.
• Tires lose roughly 1 pound per square inch of pressure for every 10° F drop in outside temperature. You should check your pressures in Spring and Fall.
• A standard load tire with a normal inflation pressure of 35 psi may be branded with a maximum inflation of 44 or 51 psi, indicating the tire's ability to meet special vehicle performance requirements. It does NOT increase the tire's load capacity.
• If you have 1/2" in the description of your wheel (i.e. 16.5x8 -- found on many newer SUVs), DO NOT reduce your tire pressure when offroad! The bead found on the 1/2" variety wheels is not deep enough to keep the tire on during 4-wheeling excursions if the pressure is lowered.

• Tread is considered worn out when it reaches the industry norm of 2/32 inches deep. CR tests have shown that tires typically lose much of their wet-weather and snow grip long before that. Recommendations are:
  In wet conditions 4/32 inch or more
  In snow 6/32 or more (recommended by TireRack).
• The Ultra High Performance tire that grips the track with tread temperatures of 200° is incompetent as its tread compound becomes like "hard plastic" at below 32°.
• Siping - Cutting small slits perpendicular to the face of the tire, which in turn creates thousands of tiny edges that help with grip to improve traction and braking. Along with those two benefits, it improves tire life by 15 to 20 % and helps the tire run cooler. The National Safety Council performed tests on tires that have been siped, and found that there was a 22% increase in traction on snow and ice. See article af 4X4 review.

Dealers:
Less Schwab
Tire rack

Glossary:
DOT - Department of Transportation

LR - Load Rating

NHSTA - National Highway Traffic Saafety Administration

PR - Ply Rating

RMA - Rubber Manufacturers Association.

Sidewall Types:
  BLK - Black, RWL - Raised White Letter
  WSW - White, OWL - Outlined White Letter

UTQGS - Uniform Tire Quality Grading System - A government-mandated tire rating system based on a tire's performance in treadwear durability, traction, and temperature resistance. UTQG ratings are branded on the tire's sidewall.

Tire Terms

Air Pressure at:
Tire Rack
Tire Wear and Pressure

Manufacturers:
Bridgestone
Dunlop
Michelin
BFGoodrich
Goodyear
See specific type links at the off-road tire page.

See Also:
Off-road tires and ratings at off-road tire page in recreation. formulas at TireRack.com
Recommended rim width
Substitute Sizes for tires
Tire labeling proposal at the DOT
Winter Tire Tech at TireRack
Tires at the National Highway Traffic Safety Administration (NHTSA) at the DOT