Treadwear Grades
UTQG Treadwear Grades are based on actual road use in which the test tire is run in a vehicle convoy along with standardized Course Monitoring Tires. The vehicle repeatedly runs a prescribed 400-mile test loop in West Texas for a total of 7,200 miles. The vehicle can have its alignment set, air pressure checked and tires rotated every 800 miles. The test tire's and the Monitoring Tire's wear are measured during and at the conclusion of the test. The tire manufacturers then assign a Treadwear Grade based on the observed wear rates. The Course Monitoring Tire is assigned a grade and the test tire receives a grade indicating its relative treadwear. A grade of 100 would indicate that the tire tread would last as long as the test tire, 200 would indicate the tread would last twice as long, 300 would indicate three times as long, etc.
In other words, with a rating of 420 those tires are hard as fuck and have shitty handling for a nice car like yours. You can typically find economy non-sports cars at this level......A typical high performance car has tires in the 100-200 range. For example, my car's OE tires had a rating of 180...sure they wore out but they were nice n' sticky. Your OE tires were probably in the 200 range.
I do hate that I only got 32000 miles out of my tires (and they are almost bald). My OE tires are 140A A. Maybe a balance of 200-300 would be a good tire.
The 420's I was looking at are Kuhmo Ecsta ASX or SPT (320)
Last edited by Draconius; Feb 22, 2009 at 08:10 PM.