COMBINATION OF HEAVY DUTY PNEUMATIC RADIAL TIRES FOR USE IN WINTER SEASON

COMBINAISON DE PNEUS RADIAUX HAUTE RESISTANCE A UTILISER EN HIVER

English Abstract

A COMBINATION OF HEAVY DUTY PNEUMATIC
RADIAL TIRES FOR USE IN WINTER SEASON
Abstract of the Disclosure
A combination of heavy duty pneumatic radial
tires for use in winter season is a tire to be mounted
on a non driven steering shaft of a vehicle and a tire
to be mounted on a driving shaft thereof, in which a
negative ratio of the former tire is made smaller than a
negative ratio of the latter tire.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A combination of heavy duty pneumatic radial
tires for use in winter season to be mounted on a non-
driven steering shaft and a driving shaft of a vehicle,
each tire comprising plural block rows located on a
surface of a tread portion and separated from each other
in a widthwise direction of the tread, in which each
block constituting each block row is provided with at
least one sipe, characterized in that a negative ratio
NF of the tire mounted on the non-driven steering shaft
is made smaller than a negative ratio ND of the tire
mounted on the driving shaft, and the negative ratio ND
is within a range of 0.32?ND?0.38 and the negative
ratio NF is within a range of 0.18?NF?(0.88-1.8ND).
2. A combination of heavy duty pneumatic radial
tire according to claim 1, wherein said sipe formed in
said block extends substantially in the widthwise
direction of the tread.
3. A combination of heavy duty pneumatic radial
tires according to claim 1, wherein said blocks in one
of said block rows are arranged at a given shifting
amount with respect to blocks in another adjoining block
row in the circumferential direction.
4. A combination of heavy duty pneumatic radial
tires according to claim 1, wherein each block
constituting a block row located at an outermost side of

the tread is provided with two sipes extending
substantially in the widthwise direction.
5. A combination of heavy duty pneumatic radial
tires according to claim 1, wherein each of said tires
comprises at least five block rows.
6. A combination of heavy duty pneumatic radial
tires according to claim 1, wherein said plural block
rows are defined by plural circumferential main grooves
each extending zigzag in the circumferential direction
and plural circumferential narrow grooves having width
narrower than that of the circumferential main groove
and extending zigzag in the circumferential direction.
7. A combination of heavy duty pneumatic radial
tires according to claim 6, wherein a pair of said
circumferential narrow grooves are arranged between a
pair of said circumferential main grooves in a central
portion of the tread and a pair of said circumferential
narrow grooves are arranged outside said pair of the
circumferential main grooves toward the tread ends.

Description

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A COMBINATION OF ~EAVY DUTY PNEUMATIC
RADIAL TIRES FOR USE IN WINTER SEASON
This invention relates to a combination of heavy
duty pneumatic radial tires for use in winter season,
and more particularly to a radial tire combination
effectively improving performances on ice while
05 sufficiently maintaining high performances on snow.
For example, when a vehicle~under a heavy duty
is provided with a non-driven steering shaft and one or
two driving shafts and two tires are mounted on the non-
driven steering shaft and four tires are mounted on each
10 of the driving shafts, it has been attempted to improve
performances on snow and ice road surfaces in winter
season by rendering all tires into studless tires having
a wider ground contactin~ width as far as possible. In
this case, the tire mounted on the non driven steering
; 15 shaft and the tire mounted on the driving shaft are
;~ equal to each other ln the ground contacting width and
negative ratio.
In order to bring about the improvement of
performances on ice road by such a conventional
20~technique, however, it is necessary to control the
occurrence of water film on the the surface of ice road
by decreasing the contact pressure of the tire against~
road surface.~ For this purpose, it is obliged to
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increase the actual ground contacting area of the tire
by decreasing the negative ratio of the tread portion
under a constant ground contacting width of the tire.
Therefore r there is caused a problem that the amount of
o~ blocks in the tread portion bitten into snow is lacking
and hence the traction performance on snow rather
lowers.
In this conventional technique, therefore, the
improvement of the performances on ice are naturally
restricted when the ground contacting width and negative
ratio are equal in the tire mounted on the non-driven
steering sha~t and the tire mounted on the driving
shaft.
It is an object of the invention to advantage-
ously solve the above problems of the conventional
techni~ue and to provide a combination of heavy duty
pneumatic radial tires for use in winter season which
can effectively improve performances on ice while
~: sufficiently maintainin~ high performances on snow by
differing the negative ratlo of the tire mounted on the
non-driven steering shaft and the negative ratio of the
tire mounted on the driving shaft so that the former
: : negative ratio tends to be made smaller than that of the
~conventional similar tire and ~the latter negative ratio
P6 tends to be made larger than that of the conventional
similar tire.
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In the combination of tires according to the
invention, the negative ratio NF of the tire to be
mounted on the non-driven steering shaft of the vehicle
is smaller than the negative ratio ND of the tire to be
o~ mounted on the driving shaft, and also the negative ratio
ND is within a range of 0. 32~ND~ O . 38 and the latter
negative ratio NF is within a range of
0.18~NF~(0.88-0-18ND)-
According to such a combination, at least one
sipe is formed in each block of the respective blockrow, whereby the improved performances on ice can be
developed based on the digging of sipe edges as well as
block edges into ice.
When the negative ratio ND is less than 0.32,
1~ the expected performances on snow can not be developed,
while when it exceeds 0. 38, the performances on snow
becomes saturated and also the performances on ice and
wear resistance are largely deteriorated.
On the other hand, when the negative ratio NF is
less than 0.18, the performances on snow and the
drainage property on wet road are largely deteriorated,
while when it exceeds ~0.88-1. 8ND), the sufficient
ground contacting area required for ensuring the
performances on ice can not be obtained.
Thus, according to the invention, the
performances on ice can effectively be improved while
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sufficiently maintaining the high performances on snow.
The invention can be applied to a vehicle
successively provided from forward side with one non-
driven steering shaft, one driving shaft and one non-
o~ driven shaft in addition to the vehicle provided withone non-driven steering shaft and one or two driving
shafts. In the former vehicle, the negative ratio may
properly be selected in two or four tires mounted on the
last non-driven shaft irrespectively of the invention.
The lnvention will be described with reference
; to the accompanying drawing, wherein;
Fig. 1 is a diagrammatically plan view of a
tread pattern used in the tire according to the
invention.
1~ The tread pattern shown in Fig. 1 is common in
the tire mounted on the non~driven steering shaft and
:
the tire mounted on the driving shaft.
The tire having~a ground contactlng width TW
~; ~ comprises a center block row 1, a pair of shoulder block
rows 2 and two pairs of block rows 3, 4 located between
the center block row and the shoulder block row at its
tread portion. Each of blocks la, 3a, 4a ln the respec-
tive block rows 1, 3, 4 other than the shoulder block
::
row 2 is provided with a sipe S, 6, 7 substantially
extending in the widthwise direction of the tread
portion, while each of the blocks 2a in the shoulder
,, `
,' ~

block row 2 is provided with two sipes 8 substantially
extending in the widthwise direction of the tread
portion.
In the illustrated tlre having such a tread
o~ pattern, the tire maximum width SW is 271 mm and the
ground contacting width of the tread portion TW is
224 mm irrespectively of the non-driven steering shaft
and the driving shaft.
Moreover, the negative ratio NF of the tire to
1~ be mounted on the non-driven steering shaft is 0.3 and
the negative ratio N~ of the tire to be mounted on the
driving shaft is 0.32. That is, the above value of the
negative ratio ND is a lower limit within the range
defined in the invention, while the value of the
1~ negative ratio NF is an approximately upper limit within
the range defined in the invention.
According to the combination of the tires having
the above structure, the performances on ice can
effectively be improved while sufficiently maintaining
high performances on snow.
A comparative test on the performances on ice
and performances on snow will be described with respect
to the tire combinations according to the invention,
conventional tire combinations and comparative tire
combination below.
In this test, two tires having a tire size of

9 ~ ~
10.00 R20 and a ground contacting width of 224 mm were
mounted on a non-driven steering shaft of a heavy duty
vehicle, and four tires having the same size and width
as described above were mounted on a driving shaft of
0~ the vehicle, and thereafter the vehicle was actually run
on snow and ice roads. The performances on ice were
evaluated by braking the vehicle from an initial speed
of 20 km/hr on ice road to measure a braking distance
(i.e. distance from the braking start to complete stop)
and indicating a reciprocal number of the measured
distance as an index value. Moreover, the test was
conducted 5 times ever~ the tire to be tested, and an
average of the measured values was the braking distance.
The measuring conditions were an ice temperature of
1~ -3C, an atmospheric temperature of -5C and a weather
of cloud.
On the other hand, the performances on snow were
evaluated by measuring a climbing limit angle on snow
road slope.
2~ The test results of each tire combination are
shown in Table 1. In Table 1, the larger the index
value, the better the result.
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As seen from Table 1, the performances on snow
and the performances Oll ice can simultaneously be
established in a sufficiently high level in the tire
combinations according to the invention.
o~ As mentioned above~ according to the invention,
the negative ratios NF and ND of the tires mounted on
the non~driven steering shaft and the driving shaft are
specified to certain values, whereby the performances on
ice can effectively be improved while sufficiently
1~ maintaining the performances on snow.
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2~ :

Representative Drawing