We’ve had tires on the mind lately. Whether we’ve been pondering the unfortunate and undervalued retread or discussing the vices and virtues of low-rolling-resistance tires, we write about rubber.
Now the discussion moves on from individual types of tires to the tire as a whole. Fuel mileage is a hot topic on everyone’s mind, and although there are a number of factors that affect it, tires play a role.
Almost one-third of the fuel consumed by an average truck is spent overcoming rolling resistance in the tires. That’s no small number. So the type of tire being used makes quite difference to the bottom line.
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In the beginning, “tall rubber” 11R24.5 tires were the norm. Common wisdom said that a taller tire went through fewer revolutions per mile, and thus lasted longer. Oh, how times have changed.
Today, the most widely-used truck tires are the low-profile 22.5s varieties. Wide base singles are becoming the norm. Let’s take a look at how the components of a modern truck tire have shaped their use over the years.
It’s All About Air
It’s easy to get lost in all this talk of rubber and forget about what’s really doing the heavy lifting: the air. A tire’s primary purpose is to provide a secure casing in which the air will reside. Modern tires need to be strong enough to support the truck while also managing the truck’s relative motion.
A tire may look simple, but the fact is these are highly engineered, complex pieces of equipment. They have several layers and are often built with multiple materials in one tire.
At the edge of the tire, the bead clutches the rim. The cords running from one side to the other provide a basic cross section for the tire. This both contains the air and supports the tread.
The tire’s radial ply transmits steering forces, braking, and acceleration to the tread. Steel belts manage forces while stabilizing the tread, and are meant to protect the air chamber from punctures.
Talking About Tread
The tread is another complex component. It is generally composed of various blends of natural and synthetic rubber. It may also contain polymer compounds, silica, or carbon. Manufacturers typically have proprietary blends that they use in constructing tires.
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As you can see from looking at any tire, there are patterns and textures on tread. These designs are not random. They are meant to provide traction while minimizing wear.
Lug patterns are used on tires that are meant for off-road driving, or other applications where maximum grip is required. Rib patterns are used for on-highway applications. They are meant to provide a smooth ride and better fuel economy.
Lugs, Grooves and Ribs, Oh My
While it would be nice if we lived in a world where all roads were smooth and dry, sadly that’s not the reality. As politicians wrangle over the most basic aspects of highway funding, our roads and highways deteriorate. This fact makes tires that much more important.
Because we aren’t driving on NASCAR tracks, tires are designed with grooves to channel rainwater and snow. Lugs are meant to provide additional traction in dirt, mud and snow.
A fuel savings of anywhere from 2 to 4 percent can be realized simply by switching from lug to rib treads. Rib treads generate the most savings under 50 mph – up to 6 percent.
Under Pressure
We’ve covered a lot of the tire basics, but there is still one small aspect that makes a big difference: tire pressure. Tire pressure can make or break fuel economy numbers that already fluctuate in the single digits.
In a 2002 study done by the Federal Motor Carrier Safety Administration (FMCSA), out of 90,000 tires evaluated, less than half were found to be within 5 psi of their target pressure.
Fortunately, new tire pressure maintenance systems coming online have helped the situation. Some devices draw air from a compressor while others use a hub-mounted pump to maintain air pressure. More technologies are in the works to help truck drivers keep their tires at optimal pressure.
While we spend a lot of time talking about highway funding and the employment squeeze, it’s important not to forget about what’s really making all of this possible. The tires; our lowly rubber road warriors that keep on truckin’.