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TIRE TESTS W The MSP tests included 100 pursuit-hot laps around a one-mile road course. Some aftermarket tires were too worn after this stage to continue the testing. ❯ STAGE 1 - Record pertinent sidewall information and the measurement of new tire tread depth before testing began. ❯ STAGE 2 - Condition the tires and brakes prior to the start of test- ing. Each candidate tire and vehicle brakes were burnished during 10 60-0 mph full ABS stops. Each stop- ping distance is corrected to reflect 60 mph as the initial speed, thus pro- viding a more accurate comparison of each stop. The dry asphalt coefficient of friction 0.85 was used. ❯ STAGE 3 - Each vehicle and candi- date tire conducted five 60-0 mph full ABS stops. In an attempt to eliminate brake temperature as a performance factor, a one-mile cool down was conducted between stops. Speeds at trigger of the measurement were ad- justed to 60 mph. Stopping distances were adjusted to reflect changes in track conditions using the track index established by the control tire. The MSP developed a list of tires to test based on input from automotive engi- neers from Chrysler, Ford and General Motors, in addition to their own years of experience. Of the selected brands, only Goodyear, Firestone and Pirelli make tires used by these automakers as "Origi- nal Equipment" on their police package vehicles. Cooper, Nitto and Nokian in- dicated to the MSP that their tires were "suitable" for police applications. How- ever, these last three do not conduct po- lice-specific durability testing. 12-Stage Testing The tire testing program was a 12-stage process conducted at the MSP Precision Driving Facility in Lansing, Mich. The tire testing program was conducted using a series of vehicle tests to assess straight- line stopping distance, maximum lateral acceleration in a steady state turn, wet Jennite® stopping distance and braking ❯ STAGE 4 - Each vehicle performed 10 35-0 mph full ABS stops on a wet Jennite (non-abrasive asphalt seal- ant) having a coefficient of friction of 0.35. Water is applied to the Jen- nite surface using large commercial irrigation sprinklers. In an attempt to eliminate brake temperature as a performance factor, a one-mile cool down was conducted between stops. Speeds at trigger of the measurement were adjusted to 35 mph. ❯ STAGE 5 - Each vehicle and can- didate tire performed 10 40-0 mph stops in a turn on wet asphalt. Water was applied to the road surface by a large irrigation sprinkler. Five stops were conducted traveling clockwise and five stops were conducted travel- ing counterclockwise. In an attempt to eliminate brake temperature as a performance factor, a one-mile cool down was conducted between stops. Speeds at trigger of the measurement were adjusted to 40 mph. ❯ STAGE 6 - Each vehicle and candi- date tire performed a steady state turn around a 300-foot diameter circle both clockwise and counter clockwise. The vehicle was driven to the point where it was unable to maintain its turn radius. The dual- axis optical sensor measured speed and lateral acceleration in relation to the force of gravity noted as "G" at point of departure. Vehicles hav- ing Electronic Stability Control (ESC) were run with ESC on, ESC partial off, or ESC off depending on system func- tionality. Lateral acceleration figures adjusted to reflect track changes using the track index. ❯ STAGE 7 - To complete the tire en- durance and wear test, each vehicle and candidate tire was driven 100 laps on a one-mile road course: 50 laps clockwise and 50 laps coun- terclockwise. Each lap was driven in a manner to simulate emergency or pursuit driving. Every 10 laps the vehicle stopped in order to obtain temperatures of rotor and tires. ❯ STAGE 8 - Repeat Stage 3 (dry brak- ing) with worn tires. ❯ STAGE 9 - Repeat Stage 4 (wet brak- ing) with worn tires. ❯ STAGE 10 - Repeat Stage 5 (wet brake and turn) with worn tires. ❯ STAGE 11 - Repeat Stage 6 (constant circle) with worn tires. ❯ STAGE 12 - Each candidate tire tread depth was measured at the conclu- sion of Stage 11. Measurements were initiated at the valve stem (considered Top Dead Center) moving clockwise to the 90-de- gree, 180-degree and 270-degree loca- tions. Using the beginning and ending measurements, average percentage of tread consumed during the test was calculated. www.lawandordermag.com 23