1. 100-700 - The first number is an indication of how long the tire will last based on how the tire wears during a predefined test. Each manufacturer assigns Treadwear Grades based on wear during a 7,200 mile test. The test includes a vehicle running a prescribed 400-mile loop for a total of 7,200 miles in which the tire's wear is measured during and at the conclusion of the test. Since most tires last longer than this, interpretation of the data can vary. It was intended to be used as a multiplication system, meaning a grade of 100 would indicate the tire tread would last as long as the test tire, a 200 would last twice as long, 300 would indicate three times as long, etc. With each manufacturer interpreting the data differently, this system is somewhat helpful while attempting to compare the grades within a single brand and not as helpful when comparing two or more brands.
2. C-AA are the Traction Grades and they measure how much force the tire generates in the wet at lock up. Most cars on the road today don't lock up as ABS is pushing almost 20 years as standard equipment. When ABS is working, the tire rotates, allowing the tread shape to help disperse water. Besides hydroplaning resistance, the test also doesn't take into account dry braking, dry cornering or wet cornering. It's only testing the rubber compound itself.
3. C-A are the tire's Temperature Grades. This is important if you live in a climate that is warm and drive at high speeds. Typically, the size of the tire and the speed rating are more appropriate for consideration, but this does play a backup role in indicating what types of temperatures your tire can disperse. Every tire sold in the United States must be capable of earning a "C" rating which indicates the tire's ability to withstand 85 mph speeds. While there are numerous detail differences, this laboratory test is similar in nature to those used to confirm a tire's speed rating.
While the UTQG was designed for most passenger car tires, it's not required for deep treaded light truck tires, winter / snow tires, temporary spare tires, trailer tires, tires under 12" in diameter and other select tires. The Uniform Tire Quality Grade Standards hasn't met its original goal of clearly informing customers about the capabilities of their tires. With tires being so complex and their uses being varied, the grades don't always reflect their actual performance in real world use. To better understand each category of the UTQG test, read "Uniform Tire Quality Grade (UTQG) Standards."