Tread for a tire including five rib parts

Abstract

A new pneumatic radial ply truck tire 10 for use on steering axles has a tread 12 with four circumferential grooves 14 that divide the tread 12 into a pair of shoulder rows 24, a pair of riding rows 26 and a center row 28. Lateral grooves 20 divide the rows into block elements 22. The centerline grooves 14 and shoulder grooves 16 have top and bottom potions 30, 32. The top portions 30 have straight sides 42 that are angled at top angles A1. The middle portions 32 also have straight sides 44 that are angled at bottom angles A2. To provide the grooves 14 with a general V-shape, it is preferred that the bottom angles A2 be greater than their respective top angles A1. Stone penetration protectors 34 are positioned within the circumferential grooves 34 to protect the tread 12 and the belt-package 13 from stone damage. The lateral grooves 20 that extend across the two riding rows 26 and the center row 28 have top portions 50 and bottom portions 52. The top portions 50 have first widths W1 and first depths D1 and the bottom portions 52 have second widths W2 and second depths D2 that extend to at least 85% of the tread non-skid depth D. The center row 28 and the riding rows 26 are formed at a tread arc radius TAR. The center row 28 and the riding rows 26 have radiused tread surfaces 27 with a tread arc radius TAR. The shoulder rows 24 have flat linear tread surfaces 25 that are tangent to the tread arc radius TAR. This provides for outside edges 56 of the shoulder rows 24 that have a shoulder fall-off distance X2 that is less than the shoulder fall-off distance X1 that would occur if the tread was made fully with the tread arc radius TAR. This multi-radii shape reduces irregular wear.