FUEL FAQS
WHAT IS
ROLLING RESISTANCE? R OLLING OLLING
RESISTANCE, SIMPLY PUT, IS THE FORCE YOU MUST EXERT TO ROLL A
TIRE DOWN THE ROAD.
MOST OF IT COMES FROM THE ENERGY LOST WHEN THE TIRE IS DEFORMED UNDER THE TRUCK AS IT MOVES. °°°°°°
I
f you think about rolling a tire across the shop floor,
Some of the energy that deforms the tire turns into heat.
it will take effort to move it and even more effort if it’s
Tires and treads heat up as a result of rolling under load,
carrying a heavier load. That’s rolling resistance.
sometimes quite a lot. This heat is lost. It does nothing to help move the truck down the road. It is the source of what
Where does rolling resistance come from?
we call rolling resistance.
As a tire rolls under a load, it deforms. It has to. The load presses down on the tire and squashes it against the
How can we reduce rolling resistance?
road. As the tire turns, the squashed part comes off the
Anything that reduces the deformation of the tire
road and returns to its original shape while another part of
will reduce heat loss and therefore, rolling resistance. A
the tire gets squashed.
solid iron tire would deform less, and have lower rolling
The sidewalls of the tire flex over and over again, close
resistance. But even solid steel railroad wheels deform
to 500 times per minute at highway speeds. And, the tread
somewhat – and get quite warm. Besides, iron tires on
goes from a circular to a flat shape and back to circular
trucks wouldn’t be very good for either our roads or the
again.
cargoes we carry carry.. If we could figure out a way to avoid producing heat when a tire is deformed, that would help reduce rolling resistance.
SIDEWALLS FLEX
Tires deform as they roll. Sidewalls ex, and treads go from circular to fl at at fl ex, as they enter and leave the footprint. All of these deformations create heat loss that contribute to rolling resistance.
CIRCULAR TO FLAT FOOTPRINT
Visit us online at BridgestoneTruckTires.com BridgestoneTruckTires.com.. © 2012, Bridgestone Americas Tire Operations, LLC. All rights reserved.
Fuel FAQs/1 FAQs /1st Quarter 2012
1
There are some practical things that can reduce
rolling resistance may provide the same rolling resistance
deformation and heat. In flation pressure has an effect.
as wide base tires. With duals, you do not have to change
Underinflated tires deform much more, get much hotter,
wheels or maintenance practices to get best-in-class fuel
and cut fuel economy. So properly in flated tires save fuel
economy.
by reducing rolling resistance.
What role can the tire itself play? Tread design, casing design and rubber compounding can all reduce rolling resistance.
Effect of Speed on Tire Fuel Efficiency
RIB TREADS tend to deform less as they roll than do block or lug designs. If you don’t need aggressive
11.8% DIFFERENCE
8.6% DIFFERENCE
AT 55 MPH
AT 75 MPH
MPG
tread patterns, a switch to rib-style treads can cut fuel
6.12
6
consumption.
5.5
DEEP TREADS tend to deform more and generate
5
more heat than shallow treads. So a rib-type shallow tread
4.5
tire, like a trailer tire, often has lower rolling resistance than
4
a deep drive design.
ADVANTAGE CUT 27%
5.30
5.47 4.86
4.21 3.88
3.5
Likewise, worn tires usually have lower rolling 50
resistance than new tires of the same tread pattern.
55
60
65
70
75
80
SPEED (MPH)
CASING DESIGN can have significant effects on rolling resistance. Since the casing must deform as a tire
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rolls, anything that reduces that deformation, or the heat associated with it, will save fuel. Radial tires were a giant
Each of these factors can work individually, or together.
leap forward over bias tires in this respect. Casing design
For example, because aerodynamic resistance increases
and shape can often be optimized to reduce heat generation
much more rapidly with higher speeds than does tire rolling
and fuel consumption.
resistance, a fuel ef ficiency advantage resulting from low
RUBBER COMPOUNDS can reduce heat loss and rolling resistance too. Modern engineered synthetic rubber
rolling resistance tires might be canceled by losses resulting from aerodynamic factors.
and natural rubber blends can work together to minimize rolling resistance in both tread and sidewalls. TIRE TYPES can cut rolling resistance. Some wide base single radial tires can carry the same loads as dual pairs, but because there’s just one tire, have half as many sidewalls flexing as with a dual pair. That can reduce the rolling resistance of the wheel end. Nevertheless, dual tires speci fically designed for low
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For more information on truck tires and fuel economy, visit us online at BridgestoneTruckTires.com.
About our sources: The information in this article was provided by Sales Engineering & Product Marketing, Bridgestone Commercial Solutions, Bridgestone Americas Tire Operations, LLC. To download a copy of this article, please visit: www.bridgestonetrucktires.com
2 Fuel FAQs/1st Quarter 2012 © 2012, Bridgestone Americas Tire Operations, LLC. All rights reserved.
