Many local circle tracks are now and have been only allowing DOT tires with a minimum of 200 UTQG rating on their entry level or budget classes. I have about 10 years of experience on our local bullrings and still talk set-up with some of the competitors. Over the next few weeks I will be researching the best combination of Rim & Tires, shocks and springs and tricks starting with what I believe should be Step 1 -- shaving the tires -- and we work our way through the other over the next few weeks
One of the reasons radial racing slicks are so effective is because they feature shallow tread depths and their contact patch acts as a single unit. However, any tread design breaks up the contact patch into smaller elements and additional deep tread depth (required to enhance wet traction) allows tread block squirm which will reduce dry performance. This means that tires typically provide their worst wet traction...and their best dry performance just before they wear out. However, its also important to remember that the heat generated every time a tire is driven activates bonding agents in the rubber. As this process is repeated continually throughout the tire's life, its rubber compounds gradually harden and lose flexibility reducing the tire's grip. Therefore, a shaved "new" tire will provide more traction than a tire worn to the exact same tread depth after being driven for thousands of miles on the road or exposed to several laps at higher temps.
Tire shaving is an effective means of permitting more of a tire's performance capability to be realized early in its life. Tire shaving removes tread rubber and reduces the mileage a tire will realize if being used on the street. Tires that begin being run at full tread depth will provide more mileage and a softer ride.
So with all of these benefits, the next important question is: "How far should a tire be shaved?"
Hoosier radials, as well as KUMHO ECSTA V series tires are manufactured with 4/32" to 4.5/32" of molded tread depth and do not require tire shaving.
Most other DOT-legal Competition tires begin with about 6/32" of molded tread depth. The higher UTQG tires that are being used on the circle tracks such as the Sumitomo HTR 200 high performance summer tires (shown below) are going to come with 9/32" to 11/32" of tread depth that we can turn down to meet your application.