ENGINEERING DESIGN INFORMATION

Page Rev. Date 3-24 2 7/27/04 THE TIRE AND RIM ASSOCIATION, INC.

DESIGN GUIDE PAVEMENT CONTACT PRESSURE GUIDELINES FOR

HIGHWAY TRUCK-BUS TIRES These guidelines are established to encourage future highway truck-bus tire standards that result in contact pressure indices that do not exceed those for tires currently standardized and used in similar type operations. Tire average contact pressure (CP) is defined as follows: CP = _L_ Anc Where L = Maximum Load (lbs.) Anc = Net Contact Area (in.2) In the absence of actual data for a particular tire, the following equations can be used to approximate the CP for a standardized tire: Anc = Agc x NG Agc = 39.8 - (0.315 x P) + (.00887 x L) + (.000938 x Vt) Note: The above gross contact area formula is appropriate for highway speed loads and inflation pressures for truck-bus tires shown in the TRA tables. Where Agc = Gross Contact Area (in.2) NG = Tire Tread Footprint Net/Gross P = Tire cold inflation pressure (psi) used in the application under evaluation Vt = Tire volume (in.3) approximation using the following formula: Vt = 3.14 (H + Dr) (S x H) Where: H = TRA Design Section Height (in.) Dr = Rim Diameter Code (in.) S = TRA Design New Tire Section Width on Design Rim Width (in.) NOTE: See page 8-12 for definitions of symbols used in formulae.