Tire Traction
There are a lot of different terms used
today in the tire industry. Some of them
actually mean something and some do not. In
this section, we'll try to explain what some
of the terms mean.
All-Season Tires with Mud and Snow
Designation
If a tire has MS, M+S,
M/S or M&S
on it, then it meets the Rubber
Manufacturers Association (RMA) guidelines
for a mud and snow tire. For a tire to receive
the Mud and Snow designation, it must meet
these geometric requirements (taken from the
bulletin "RMA Snow Tire Definitions for
Passenger and Light Truck (LT) Tires"):
1. New tire treads shall have multiple
pockets or slots in at least one tread edge
that meet the following dimensional
requirements based on mold dimensions:
-
Extend toward the tread center at least
1/2 inch from the footprint edge, measured
perpendicularly to the tread centerline.
-
A minimum cross-sectional width of 1/16
inch.
-
Edges of pockets or slots at angles
between 35 and 90 degrees from the
direction of travel.
2. The new tire tread contact surface void
area will be a minimum of 25 percent based on
mold dimensions.
The rough translation of this specification
is that the tire must have a row of fairly big
grooves that start at the edge of the tread
and extend toward the center of the tire.
Also, at least 25 percent of the surface area
must be grooves.
Severe winter
traction icon
|
The idea is to give the tread pattern
enough void space so that it can bite through
the snow and get traction.
However, as you can see from the
specification, there is no testing involved.
To address this shortcoming, the Rubber
Manufacturers Association and the tire
industry have agreed on a standard that does
involve testing. The designation is called Severe
Snow Use and has a specific icon
(see image at right), which goes next to the
M/S designation.
In order to meet this standard, tires must
be tested using an American
Society for Testing and Materials (ASTM)
testing procedure described in "RMA
Definition for Passenger and Light Truck Tires
for use in Severe Snow Conditions":
Tires designed for use in severe snow
conditions are recognized by manufacturers
to attain a traction index equal to or
greater than 110 compared to the ASTM E-1136
Standard Reference Test Tire when using the
ASTM F-1805 snow traction test with
equivalent percentage loads.
These tires, in addition to meeting the
geometrical requirements for an M/S
designation, are tested on snow using a
standardized test procedure.They have to do
better than the standard reference tire in
order to meet the requirements for Severe Snow
Use.
Photo courtesy Goodyear
A tire
designed to help prevent hydroplaning. |
