S.C. Code Regs. 38-393.52. Brake performance

(a) Upon application of its service brakes, a motor vehicle or combination of motor vehicles must under any condition of loading in which it is found on a public highway, be capable of (1) Developing a braking force at least equal to the percentage of its gross weight specified in the table in paragraph (d); (2) Decelerating to a stop from 20 miles per hour at not less than the rate specified in the table in paragraph (d); and (3) Stopping from 20 miles per hour in a distance, measured from the point at which movement of the service brake pedal or control begins, that is not greater than the distance specified in the table in paragraph (d). (b) Upon application of its emergency brake system and with no other brake system applied, a motor vehicle or combination of motor vehicles must, under any condition of loading in which it is found on a public highway, be capable of stopping from 20 miles per hour in a distance, measured from the point at which movement of the emergency brake control begins, that is not greater than the distance specified in the table in paragraph (d). (c) Conformity to the stopping distance requirements of paragraphs (a) and (b) shall be determined under the following conditions: (1) Any test must be made with the vehicle on a hard surface that is substantially level, dry, smooth, and free of loose material. (2) The vehicle must be in the center of a 12 foot wide lane when the test begins and must not deviate from that lane during the test. (d) Vehicle brake performance table: Notes: (a) There is a definite mathematical relationship between the figures in columns 2 and 3. If the decelerations set forth in column 3 are divided by 32.2 feet per second per second, the figures in column 2 will be obtained. (For example, 21 divided by 32.2 equals 65.2 percent.) Column 2 is included in the tabulation because certain brake testing devices utilize this factor. (b) The decelerations specified in column 3 are an indication of the effectiveness of the basic brakes, and as measured in practical brake testing are the maximum decelerations attained at some time during the stop. These decelerations as measured in brake tests cannot be used to compute the values in column 4 because the deceleration is not sustained at the same rate over the entire period of the stop. The deceleration increases from zero to a maximum during a period of brake system application and brake force buildup. Also, other factors may cause the deceleration to decrease after reaching a maximum. The added distance which results because maximum deceleration is not sustained is included in the figures in column 4 but is not indicated by the usual brake testing devices for checking deceleration. (c) The distances in column 4 and the decelerations in column 3 are not directly related. "Brake system application and braking distance in feet" (column 4) is a definite measure of the overall effectiveness of the braking system, being the distance traveled between the point at which the driver starts to move the braking controls and the point at which the vehicle comes to rest. It includes distance traveled while the brakes are being applied and distance traveled while the brakes are retarding the vehicle. (d) The distance traveled during the period of brake system application and brake force buildup varies with vehicle type, being negligible for many passenger cars and greatest for combinations of commercial vehicles. This fact accounts for the variation from 20 to 40 feet in the values in column 4 for the various classes of vehicles. (e) The terms "GVWR" and "GVW" refer to the manufacturer's gross vehicle rating and the actual gross vehicle weight, respectively.