Issue link: http://read.dmtmag.com/i/34501
MEASURING TIRES IN DUAL ASSEMBLY If drive and trailer tires are of equal tread depth and have equal inflation pressure, the inner tire in the dual assembly is subjected to more deflection, as it is under a heavier load and is affected by the condition of the road on which it operates. This result of road slope (Interstate System and primary roads) or road crown (secondary roads) on the inner tire is more grip than the outer tire achieves. Thus, the inner tire dictates the revolutions per mile of the assembly, resulting in the outer tire having more rapid tread wear. Measuring the circumferences of the tires with an endless tape after they are on the rims and inflated, but before they are applied to a vehicle, is the most accurate method. The endless tape, as the name signifies, is a tape made of one half inch bending steel, one end of which passes through a slot at the other end of the tape and forms a loop. Measuring in this manner takes into account any irregularities in wear. (B) Measuring with Endless Tape Use of String Gauge (A) Use of a Square In checking tires already on a vehicle, the following may be used: (A) a square (similar to but larger than a carpenter’s square), (B) a string gauge, (C) a large pair of calipers, or (D) a wooden straight edge long enough to lie across the treads of all four tires. (C) Use of the Calipers (D) Use of a Wooden Straight Edge Section Two: Mounting the Tire 33