What does "UTQG" stand for? Uniform Tire Quality Grade. It consists of a numeric treadwear rating, a letter traction rating and a letter temperature rating.
Should I use these ratings to decide what tire is best? Short answer: No. While they contain some useful information, UTQG ratings are generally not sufficient to judge the actual quality of a tire. This is especially true of the treadwear rating. The treadwear number is determined by the tire manufacturer. Each uses their own scale, and they have a surprising amount of leeway when setting the wear number.
If the treadwear number is lower, does that mean the tire has more grip? Not necessarily. Advances in compounding have allowed manufacturers to increase both treadwear and traction compared to older models. Assuming that a tire with a lower treadwear rating has better traction is like assuming that a car with worse fuel economy has more power. It is sometimes true, but not always the case.
What about the traction rating? The traction rating only determines traction under one specific condition (locked-wheel braking on wet pavement). UTQG traction tests do not evaluate dry braking, dry cornering, wet cornering or high speed hydroplaning resistance.
If I live in a hot climate, should I be looking for an "A" temperature rating? Only if you plan to drive at high speeds. The testing for this rating is designed to evaluate the tires ability to withstand heat buildup caused by high speed operation. It does not accurately assess how well or poorly a tire will fare with regards to high ambient temperature. Tires with an "A" rating can exceed 115 mph in the lab test. Tires with a "B" rating can attain speeds between 100 and 115 mph. And tires with a "C" rating can reach speeds between 85 and 100 mph without failure. These ratings are similar to the speed ratings given to tires, though the methodology isn't identical.
Where can I go for more details about the methodology and ratings involved in UTQG testing? For more details and tables about testing procedure and ratings, read "Uniform Tire Quality Grade (UTQG) Standards."