Truck steer tire tread including circumferential grooves

A new pneumatic radial ply truck tire 10 for use on steering axles has a tread 12 with a pair of centerline grooves 14 and a pair of shoulder grooves 16 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, middle and bottom potions 30, 32, 34 and 36, 38, 40. The top portions 30, 36 have straight sides 42, 48 that are angled at top angles A1, A2 respectively. The middle portions 32, 38 also have straight sides 44, 50 that are angled at middle angles A3, A4 respectively. To provide the grooves 14, 16 with a general V-shape, it is preferred that the middle angles A3, A4 be greater than their respective top angles A1, A2 respectively. The bottom portions 34, 40 are U-shaped and have bottom widths X1 and bottom depths D1, D2 respectively. These U-shaped bottom portions 34, 40 are wide enough to permit a tread gauge to be inserted for measuring the non-skid depth yet, are narrow enough to prevent stones of significant size from entering. The lateral grooves 20 that extend across the two riding rows 26 and the center row 28 have top portions 58, 64 and bottom portions 60, 66. The bottom portions 60, 66 have second widths W2, W4 and second depths D4, D6 that extend to at least 50% 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 shoulder rows 24 have inside edges lowered a first distance D10 with respect to the tread arc radius TAR and outside edges that are raised a second distance D11 with respect to the tread arc radius TAR. This single radius plus mixed shoulder off-set design reduces irregular wear and helps in achieving equal pressure distribution across the surface of the tread 12.

BACKGROUND 
The present invention relates to truck tire treads and tires for steer 
axles. 
The use of treads specifically designed for the steer axle of truck tires 
is well known in the art. It is also known, however, that improvements 
were desired. 
One problem is related to stones. It is known in the art for stones to 
become trapped or held within the grooves of the tread. Such stones may 
damage the groove bottoms and the belt-package that lies beneath the 
tread. Such damage caused by stones is known as "stone drilling." 
Another problem relates to irregular wear in the shoulder ribs of steer 
tires. Such irregular shoulder wear is known to produce peaking on the 
inside edge of the shoulder rib and drop off on the outside edge of the 
shoulder rib. 
The applicants have also noticed that, even though the molds used to 
produce steer tires are typically made with an equal width for shoulder 
and centerline grooves, the tire when in use may produce a footprint 
having shoulder grooves that are opened-up or greater in width than the 
centerline grooves. This opening of the shoulder grooves relative to the 
centerline grooves results in a lower local net-to-gross ratio. Since the 
same load must be carried, the footprint length increases locally yielding 
peaking around the shoulder grooves. 
The present invention provides circumferential grooves that are wide enough 
to permit a tread gauge to be used to measure the full intended non-skid 
depth, yet are narrow enough to prevent any stones of significant size to 
enter the grooves. The present invention also minimizes irregular shoulder 
wear by using a single radius plus "mixed" shoulder off-set design. 
SUMMARY OF THE INVENTION 
A new pneumatic radial ply truck tire 10 for use on steering axles is 
described. The tire 10 has a tread 12 with a pair of centerline grooves 14 
and a pair of shoulder grooves 16 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 have top, middle and bottom potions 30, 32, 34. The shoulder grooves 16 
similarly have top, middle and bottom portions 36, 38, 40. The top 
portions 30, 36 have straight sides 42, 48 that are angled at top angles 
A1, A2 respectively. The middle portions 32, 38 also have straight sides 
44, 50 that are angled at middle angles A3, A4 respectively. To provide 
the grooves 14, 16 with a general V-shape, it is preferred that the middle 
angles A3, A4 be greater than their respective top angles A1, A2 
respectively. 
The bottom portions 34, 40 are U-shaped and have bottom widths X1 and 
bottom depths D1, D2 respectively. These U-shaped bottom portions 34, 40 
are wide enough to permit a tread gauge to be inserted for measuring the 
non-skid depth yet, are narrow enough to prevent stones of significant 
size from entering. Preferably, the U-shaped bottom portions 34, 40 have 
bottom widths X1 and bottom depths D1, D2 that are less than 2.0 mm. 
The sides 42, 48 of the top portions 30, 36 are linked to the respective 
sides 44, 50 of the middle portions 32, 38 with radii within the range of 
5.0 mm to 15.0 mm. The sides 44, 50 of the middle sections 32, 38 are 
linked to the respective sides 46, 52 of the bottom portions 34, 40 with 
S-shaped links having two radii each within the range of 3.0 mm to 6.0 mm. 
The lateral grooves 20 that extend across the two riding rows 26 and the 
center row 28 have top portions 58, 64 and bottom portions 60, 66. The top 
portions have first widths W1, W3 and first depths D3, D5 that extend to 
less than 20% of the tread non-skid depth D. The bottom portions 60, 66 
have second widths W2, W4 and second depths D4, D6 that extend to at least 
50% of the tread non-skid depth D. In this way the lateral grooves 20 help 
in providing the tire 10 with an even wear profile, high mileage and safe 
wet performance. 
The center row 28 and the riding rows 26 are formed at a tread arc radius 
TAR. The shoulder rows 24 have inside edges lowered a first distance D10 
with respect to the tread arc radius TAR and outside edges that are raised 
a second distance D11 with respect to the tread arc radius TAR. Preferably 
the first distance D10 is less than 1.0 mm and the second distance D11 is 
greater than 1.0 mm. This single radius plus mixed shoulder off-set design 
reduces irregular wear. The two shoulder rows 24 have a shoulder width SHW 
and the two riding rows 26 and the center row 28 each have a center width 
CW. A width ratio equal to SHW divided by CW is at least 1.35. This helps 
in achieving equal pressure distribution across the surface of the tread 
12. 
Thus, the tire 10 of this invention having the tread 12 can exhibit a high 
wear rate and an even wear profile. It also protects the groove bottoms 
34, 40 and belt-package 13 from damage due to stones.

DEFINITIONS 
"Axial" and "axially" means lines or directions that are parallel to the 
axis of rotation of the tire. 
"Block Element" means a tread element defined by a circumferential groove 
or shoulder and a pair of lateral extending grooves. 
"Circumferential" means lines or directions extending along the perimeter 
of the surface of the annular tread perpendicular to the axial direction. 
"Equatorial Plane (EP)" means the plane perpendicular to the tire's axis of 
rotation and passing through the center of its tread. 
"Groove" means an elongated void area in a tread that may extend 
circumferentially or laterally about the tread in a straight, curved, or 
zigzag manner. Circumferentially and laterally extending grooves sometimes 
have common portions. The "groove width" is equal to the tread surface 
area occupied by a groove or groove portion, the width of which is in 
question, divided by the length of such groove or groove portion; thus, 
the groove width is it average width over its length. Grooves may be of 
varying depths in a tire. The depth of a groove may vary around the 
circumference of the tread, or the depth of one groove may be constant but 
vary from the depth of another groove in the tire. If such narrow or wide 
grooves are of substantially reduced depth as compared to wide 
circumferential grooves which they interconnect, they are regarded as 
forming "tire bars" tending to maintain a rib-like character in the tread 
region involved. 
"Lateral" means an axial direction. 
"Net-to-gross ratio" means the total area of ground contracting tread 
elements between the lateral edges around the entire circumference of the 
tread divided by the gross area of the entire tread between the lateral 
edges. 
"Radially" and "radially" means directions radially toward or away from the 
axis of rotation of the tire. 
"Radial Ply Tire" means a belted or circumferentially-restricted pneumatic 
tire in which the ply cords which extend from bead to bead are laid at 
cord angles between 65.degree. and 90.degree. with respect to the 
equatorial plane of the tire. 
"Rib" means a circumferentially extending strip of rubber of the tread 
which is defined by at least one circumferential groove and either a 
second such groove or a lateral edge, the strip being laterally undivided 
by full-depth grooves. 
"Shoulder" means the upper portion of sidewall just below the tread edge; 
tread shoulder or shoulder rib means that portion of the tread near the 
shoulder. 
"Sipe" means small slots molded into the tread elements of the tire that 
subdivide the tread surface and improve traction. 
"Tread" means a rubber or elastomeric component including that portion of 
the tire that comes into contact with the road under normal inflation and 
load. 
"Tread element" or "traction element" means a rib or a block element. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings wherein the showings are for purposes of 
illustrating a preferred embodiment of the invention only and not for 
purposes of limiting the same, FIGS. 1-6 show a pneumatic radial ply truck 
tire 10 for use on the steering axles that has a tread 12 with a non-skid 
depth D. The tread 12 provides a high wear rate and an even wear profile 
as will be discussed further below. The tread 12 includes four 
circumferential grooves including two centerline grooves 14 and two 
shoulder grooves 16 that divide the tread 12 into five rib parts 18. 
Lateral grooves 20 extend across the five rib parts 18 of the tread 12 to 
form five rows of circumferentially separated block elements 22 including 
two shoulder rows 24, two riding rows 26 and a center row 28. 
With reference now to FIGS. 1-8, in order to minimize possible stone damage 
to the grooves or the belt-package 13 caused by stones being trapped or 
held within the grooves, the two centerline grooves 14 and the two 
shoulder grooves 16 each have top 30, 36, middle 32, 38 and bottom 
portions 34, 40 respectively. The top portions 30, 36 have straight sides 
42, 48 angled at top angles A1, A2 relative to radial lines extending from 
the edges of the grooves at the maximum groove width as shown in FIGS. 
7-8. The middle portions 32, 38 also have straight sides 44, 50 that are 
angled at middle angles A3, A4 with respect to the radial lines extending 
from the edges of the grooves at the maximum groove width. To provide the 
grooves 14, 16 with a general V-shape, it is preferred that the middle 
angles A3, A4 be greater than their respective top angles A1, A2 
respectively. This provide for increased groove wall taper angles 
positioned where they are the most useful for stone ejection, in the lower 
portion of the grooves 14, 16. It is most preferred that the top angles 
A1, A2 be within the range of greater than 0.degree. to 10.degree. and 
that the middle angles A3, A4 be within the range of 10.degree. to 
20.degree.. 
With reference now to FIGS. 7-8, the bottom portions 34, 40 are U-shaped 
with bottom widths X1, bottom depths D1, D2 and radii R7. The bottom 
depths D1, D2 are preferably less than 15% of the tread non-skid depth D. 
The fact that the grooves 14, 16 will close significantly as the tread 
wears to the point of the bottom portions 34, 40 resulting in a worn-out 
looking tread pattern, is irrelevant because at that stage truck tires 
have reached the top of the legally require tread-wear indicators. It is 
also preferred that the bottom widths X1 and the bottom depths D1, D2 each 
be less than 2.0 mm. In this way the U-shaped bottom portions 34, 40 are 
wide enough to allow a tread gauge to be used to measure the full intended 
non-skid depth and yet narrow enough to prevent any stones of significant 
size from entering. 
Still referring to FIGS. 7-8, the sides 42, 48 of the top portions 30, 36 
are linked to the sides 44, 50 of the middle portions 32, 38 by radii R1, 
R2 respectively. It is most preferred that the radii R1, R2 each be within 
the range of 5.0 mm to 15.0 mm to provide a smooth transition from the top 
portions 30, 36 to the middle portions 32, 38. The sides 44, 50 of the 
middle portions 32, 38 are linked to respective sides 46, 52 of the bottom 
portions 34, 40 by S-shaped links 54, 56. The links 54, 56 provide a short 
yet corner-less transition to the narrow bottom portions 34, 40. The 
S-shaped links 54, 56 are formed using two first radii R3, R5 and two 
second radii R4, R6. The radii R3, R4, R5, R6 each are preferably within 
the range of 3.0 mm to 6.0 mm. These relatively large radii ensure that 
the U-shaped bottom portions 34, 40 are narrow enough to prevent stones 
yet the middle portions 32, 38 are wide enough to provide appropriate 
traction. 
With reference now to FIGS. 5-8, as noted above, the applicants have 
noticed that steer tires may demonstrate a footprint having shoulder 
grooves that are opened-up or greater in width than the centerline grooves 
even when molded to be the same size. This is believed to increase the 
footprint length locally and thereby cause peaking around the shoulder 
grooves. Thus, the preferred tread 12 has centerline grooves 14 with first 
groove widths GW1 and shoulder grooves 16 with first groove widths GW2 
where a groove width ratio equal to GW2 divided by GW1 is less than 0.90. 
With reference now to FIGS. 1-6 and 9, the lateral grooves 20 that extend 
across the two riding rows 26 and the center row 28 have top portions 58 
and bottom portions 60 respectively. The top portions have first widths W1 
and first depths D3 that extend to less than 20% of the tread non-skid 
depth D. The bottom portions 60 have second widths W2 and second depths D4 
that extend to at least 50% of tread non-skid depth D. This design 
provides block elements 22 that will provide even wear, high mileage and 
safe wet performance. It is most preferred that the second depths D4 
extend to at least 75% of tread non-skid depth D. The bottom portions 60 
are formed by blades (not shown) inserted into the truck tire molds (not 
shown). These blades provide for bottom portions 60 that extend to a 
constant depth level. 
With reference now to FIGS. 5 and 10, it can be seen that the lateral 
grooves 20 that extend across the two shoulder rows 24 have inside ends 62 
comprising top portions 64 and bottom portions 66. The top portions 64 
have first widths W3 and first depths D5 that preferably extend to less 
than 20% of the tread non-skid depth D. The bottom portions 66 have a 
second width W4 and a second depth D6 that preferably extends to at least 
50% of the tread non-skid depth D. The bottom portions 66 are formed with 
blades as discussed above. The remaining parts of the lateral grooves 20 
that extend across the two shoulder rows 24 do not have bottom portions 
but maintain the first width W3 and the first depth D5 across the shoulder 
rows 24. 
With reference to FIGS. 1-5 some skilled in the art have determined that 
lateral grooves angled at approximately 45.degree. relative to the tire 
centerline produce the lowest noise level. For this reason the lateral 
grooves 20 extending across the center row 28 are angled at approximately 
45.degree.. Also to minimize noise, the major parts (meaning more than 50% 
of the length of the groove) of the lateral grooves 20 extending across 
the riding rows 26 and the shoulder rows 24 are also angled at 
approximately 45.degree.. 
With reference now to FIGS. 1-6, the applicants believe that irregular 
shoulder wear can be initiated where groove edge amplitudes create 
variations in lateral stiffness. These variations may be caused by rib 
width variations, groove taper angle changes, notches, blades, and other 
design modifications as well. The effect of these amplitudes are believed 
to decrease with the tread non-skid depth level. In other words, the 
effects of the amplitudes are at their greatest in the new, unworn tire 
and are the greatest for deep tread non-skid depth D steer tires on 
trucks. Therefore to minimize the potential for irregular shoulder wear 
and to minimize the noise levels, the shoulder rows 24 have inside edges 
68 that are straight in the circumferential direction. It should be noted 
that the inside edges 68 are straight in the circumferential direction 
regardless of the tread non-skid depth. 
with reference now to FIG. 5-6, irregular shoulder wear creates shoulder 
peaking and shoulder drop-off. Peaking refers to areas of the tread 
surface that are radially higher than the rest of the tread surface and 
drop-off refers to the areas of the tread surface that are worn more 
(radially lower) than the rest of the tread surface. To combat shoulder 
peaking and shoulder drop-off, the tread 12 of this invention is formed by 
what is termed a mixed shoulder off-set. As shown in FIG. 6 the center row 
28 and the riding rows 26 have a tread arc radius TAR. The shoulder rows 
24 however are not radiused. FIG. 6 shows in a dashed line the tread arc 
radius TAR for the shoulder row area. As can be seen, the inside edges 68 
of the shoulder rows 24 are lower by a first distance D10 with respect to 
the tread arc radius TAR. The outside edges 70, on the other hand, are 
raised a second distance D11 with respect to the tread arc radius TAR. In 
this way, the tread surface of the shoulder rows 24 is not radiused but 
rather is flat. In the preferred embodiment, the first distance D10 is 
less than 1.0 mm and the second distance D11 is greater than 1.0 mm. This 
mixed shoulder off-set design is expected to shift pressure from the 
inside edge 68 of the shoulder rows 24 where peaking is known to occur to 
the outside edges 70 where drop-off occurs. Therefore, a more even 
pressure distribution will be obtained. To further combat shoulder peaking 
and shoulder drop-off, the two shoulder rows 24 have larger widths than 
the two riding rows 26 and the center row 28. In particular, the shoulder 
rows 24 each have a shoulder width SHW and the two riding rows 26 and the 
center row 28 each have a center width CW. A width ratio equal to SHW 
divided by CW is preferably at least 1.35. 
with reference now to FIGS. 1-6, the tread 12 also includes 
circumferentially extending circumferential grooves 72 within the riding 
rows 26. It also includes nearly circumferential grooves 74 in the center 
row 28 that link the lateral grooves 20 in the center row 28. These 
grooves 74, 76, are relatively shallow having a depth preferably equal to 
the first depth D3 and have a width less than 3.0 mm. To maintain a high 
wear rate, it is also preferred that the tread 12 has a relatively high 
net-to-gross ratio. Most preferably the net-to-gross ratio is over 80%. 
The invention has been described with reference to preferred embodiments. 
Obviously, modifications and alterations will occur to others upon a 
reading and understanding of the specification. It is intended to include 
all such modifications and alterations in so far as they come within the 
scope of the appended claims or the equivalence thereof.