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volume 14 issue 1 . technically speaking

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sperry boat shoes

Do shoes and tires share
anything in common?

You’re right if you said, “footprints,” but there’s more.

As the story goes, slaughterhouse employee John Sipe
was tired of slipping on slick floors, so he cut slits into
the bottom of his shoes. Impressed with the grip, he
patented his invention in the 1920s.

Tire manufacturers embraced his invention and
the idea spread to other products. In fact, in 1935,
avid boater Paul Sperry, who was tired of slipping on
slick boat decks, heard of Mr. Sipe’s invention and
cut grooves in the soles of his shoes. The pattern
resembled the pads of his surefooted dog’s feet.

If you own a pair of the Sperry^® Top-Sider
“boat shoes,” still tremendously popular today,
you can thank Mr. Sipe for the superior traction.

Sipes are still rather popular on tires, too.
Let’s find out why.

r195f sipes

Bridgestone’s R195F trailer tire uses
cross-rib sipes to evacuate the water into the grooves for a solid grip on wet roads.

Sipes are slits that open as the tire rolls through its footprint, drawing water and road films up and away from the road surface.

What is a sipe?

Sipes are simply thin slits across tread elements. Bridgestone builds its sipes into the tire mold, just the same as Equalizer Rib™ and Side Groove™ structures.

As the tire rolls through its footprint, the pressure opens the sipes, “vacuuming” or drawing the water up and away from the road surface.

Essentially the sipe acts as a channel into the tread grooves, giving the liquid a place to go.

bridgestone race car

Racing slicks have no sipes, no grooves, no biting edges and no tread blocks. They have tremendous grip on dry pavement but perform poorly on even the slightest wet surface.

Are sipes found on all tires?

Some applications need super smooth-surface traction while others don’t.

On/off-highway tires spend a majority of their time in rugged jobsites. The new Bridgestone M775 on/off-highway tire, for example, is built with thick, knobby tread blocks to chew through treacherous mud.

Yet the road from the terminal to the jobsite is likely asphalt or concrete. So each tread block uses a large sipe to “squeegee” road film and water away from the road surface.

Those tread blocks we just spoke about have numerous edges to slice through water. That’s why a partially worn drive tire will typically maintain great traction. In a sense, you could say, when you make a sipe, you’ve created two edges.

The most extensive siping designs can be found on tires that haul on smooth interstates and highways during all kinds of weather – especially snow.

R287 steer radial

Many sipes like this R287 steer radial are built with club shaped ends to help combat tearing by small stones and gravel.

What’s different about snow?

Snow on snow provides superior traction as opposed to rubber on snow.

That doesn’t sound right.

Conventional wisdom has changed about winter traction. The long-held belief was a self-cleaning tread offered the best traction.

But after participating in a few good snowball fights, we learned snow can be sticky. And the sipes help snow stick to snow for better traction.

How so?

As the tire moves out of the footprint, the sipes grab a little snow so when the tire rolls into its next footprint, there isn ’t a bare tread surface to meet the snow-covered road surface.

This snow-on-snow traction is an advantage for fleets who still have to make deliveries on highways, secondary roads, and alleys that haven’t yet been plowed.

Besides traction, some sipes also fight irregular wear. Bridgestone builds many of its rib tires using stress-relief sipes, those small notches in the main rib, to fight irregular wear in the footprint.

ball wrinkles

How does that help?

Remember playing with a small rubber ball as a child? When you smashed the rubber ball against a hard surface, like a glass coffee table, you could see wrinkles where the rubber had compressed. Why were there wrinkles?

Stress?

Yes, the compressed rubber has nowhere to go. If you continued to smash your little rubber ball flat, day after day, month after month, the wrinkles would deepen and wouldn’t look so new anymore.

Like the ball, the rubber at the very outside of the rib is compressed into itself each time the tread rolls into the footprint, revolution after revolution, mile after mile. The constant squeezing and expanding causes stress.

Notch-like sipes give the ribs small spaces to compress into, helping relieve stress at the rib edges. This fights irregular wear and promotes long, even rib wear.

Anything else?

If it’s raining outside, check the bottom of your shoes for sipes. You’ll have better traction in the wet weather.

sipe action
Sandwich electrical tape between two glass plates to simulate a “transparent” sipe.
Dip the sandwich into colored water, and the water climbs far above its own level by what is
called “capillary action.” It’s another way sipes may help to improve traction – by removing water
from the road. The captured water is expelled from the sipes by centrifugal force as the tire turns.

Try it for yourself: Tear a slit in the middle of a piece of paper and see how easily it rips when weight is hung from the end. Tear a second piece of paper and at the end of the tear, use a hole-punch to create a round keyhole. You’ll find much more weight can be added to this club-shaped slit before it tears.

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