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Tire Pressure And Wet Tire Traction
What You Need To Know For
Safe Driving In Wet Conditions
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Most drivers realize that tire load capacity is determined
by tire size and inflation pressure. Larger tires and higher
inflation pressures provide more load capacity, while smaller
tires and lower tire pressures provide less.
An underinflated tire will tend to wear the shoulder areas
of the tread faster than the center. This is because there is
insufficient air pressure to allow the center of the tread to
carry its fair share of the weight. A correctly inflated tire
receives appropriate support from the contained air pressure
to provide an even distribution of load across the footprint.
And while most drivers recognize that this has a significant
impact on tire wear, rolling resistance and durability, only a
few realize it also has a noticeable influence on how
effectively the tires can resist hydroplaning to maintain wet
traction.
As they taught us in physics class, you can compress and
move a gas quite easily, but you cannot compress liquids and
it requires significant energy to move them. Our tires easily
push air around and through their tread designs as they roll.
However, when water pools in highway ruts and builds up on the
road surface during rainstorms, the vehicle's speed and
weight, as well as the tires' tread designs, tread depths and
evenness of their footprint pressures determines if and when
the tires will be forced to hydroplane.
One of the ways tire manufacturers evaluate their products'
hydroplaning and wet traction effectiveness is by driving them
over a glass plate covered with a specific depth of water. The
water is dyed for better visibility and to allow high-speed
cameras in underground rooms to photograph the tires from
below. Michelin has provided several photographs of its
HydroEdge premium All-Season tire to help illustrate this tech
feature.
The first photograph shows a tire properly
inflated to 35 psi sitting still in the water on the glass
plate. This provides an accurate idea of the tire's footprint
size and shape.
The black area is where the tire's rubber compound is
pressed on the glass, and the green areas identify water in
the tire's circumferential and high-angle lateral grooves, and
on the remainder of the glass plate.
A properly inflated tire will have enough pressure in the
center of its tread to resist collapsing
The second picture is of a tire properly inflated to 35 psi,
driving across the glass at 60 miles per hour. If the glass
plate were dry, the footprint size would be virtually
identical to the first picture because air does not prevent
the tread from contacting the plate. However with standing
water on the plate, the tire's tread depth and tread design
must evacuate the water as the tire rolls across the plate at
88 feet per second. You will notice that the footprint still
shows good contact with the plate, but is slightly smaller
than the static tire's footprint.
A tire that is slightly underinflated will apply less
pressure to the center of the tread and it will become
slightly concave.
The third picture is of a tire inflated to only 30 psi, again
driving across the glass at 60 miles per hour. With the same
amount of standing water on the plate, the center of the
tire's tread is lifted as the tread design unsuccessfully
attempts to evacuate water as the tire rolls across the plate.
You will notice that the actual footprint shows poor contact
with the plate and is significantly smaller than the footprint
in the photograph of the properly inflated tire.
A tire that is significantly underinflated will allow the
center of the tread to collapse and become very concave,
trapping water rather than flowing it through the tread
design.
The final picture is of a tire inflated to only 25 psi,
driving across the glass plate at 60 miles per hour. With the
same amount of standing water, the water lifts the center of
the tire's tread as its footprint rolls across the plate. You
will notice that the actual footprint shows little contact
with the plate and has been virtually reduced to the shoulder
areas.
Members of The Tire Rack team had the chance to experience
the affects of air pressure on wet performance at Michelin's
Laurens Proving Grounds. Drivers were given the opportunity to
compare identical cars on a wet-handling course with the
exception of one car having four properly inflated tires (35
psi) and the other car having significantly underinflated
tires on the rear axle (25 psi).
While driving at the edge of a tire's ability in wet
conditions is challenging, the car with the properly inflated
tires provide handling that was predictable. Driving the car
with the underinflated rear tires proved to be much more
difficult to drive and forced the driver to slow down to
retain control, producing lap times that were several seconds
slower than the properly inflated car.
While tire manufacturers can develop tires with great
hydroplaning resistance and wet traction, poor maintenance of
tire inflation pressures can make a great tire awful.
Adjust your tire pressures as indicated on the vehicle tire
placard or in the owner's manual. Check you inflation
pressures at least once a month and before highway trips.
article descriptions and images courteousy
The Tire Rack
Related Topics:
Consumer Tire
Ratings
Tire
Safety
Tire
Tips
Tire
Construction
Tire
Care
How
To Buy Tires
Don't
Be Oversold For Tires
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