With the price of fuel as high and as volatile as we’ve ever seen, many truck operators are reviewing ways to conserve that precious commodity that can so severely impact the bottom line of any trucking operation.
You might wonder how this is related to tires. The answer comes in a number of ways, several of which may be turned into timely opportunities for knowledgeable commercial tire servicing dealers.
First, recognize that, since truck tires are manufactured primarily from petroleum products, merely extending the service life of tires through good maintenance practices and using effective retread programs can have a significant effect on our national petroleum stock requirements, and, ultimately, on the price of replacement tires required to keep your customers’ trucks rolling.
It takes some 22 gallons of oil to make the typical new 22.5 truck tire. Retreading that same casing uses about seven gallons, or one-third of the amount of a new tire. Fleets may be looking at a variety of ways to extend tire life or at least postpone new tire purchases, and this can often be translated into additional retread business.
More details of this fuel conservation approach can be obtained from the Tire Retread Information Bureau (www.retread.org or 888-473-8732).
Secondly, several basic service issues namely, inflation pressure maintenance and proper truck/trailer alignment are directly related to fuel consumption.
Industry testing has consistently shown that 15% underinflation (for example, 85 psi vs. a spec of 100 psi) results in a 2.5% reduction in fuel economy. Perhaps a better way to say this is that it equals a 2.5% waste of fuel!
Keep in mind that recommended pressures are nearly always stated as cold inflations and that overinflation can cost truck operators dearly in terms of increased irregular wear, harsh-ride complaints and lower miles to removal. Bottom line: Make sure your customers have the right spec and help them maintain it.
Contracted inflation maintenance checks and/or fleet surveys can be good methods of demonstrating your value to fleet customers. Most tire company field engineers can provide calculations and report formats that you can use to illustrate the impact that inflation pressures have on fuel economy and casing longevity.
Total Vehicle Alignment
A major goal of proper alignment is to reduce tire side scrub in normal vehicle travel. While improper steer tire toe settings reduce tire life and create fast shoulder wear, they have a relatively small effect on fuel economy. Drive axle alignment problems will also cause added steer tire side scrub and premature wear, which can detract from fuel economy.
Anytime the truck is traveling forward with a yaw angle caused by a chassis side thrust, rolling resistance is added and aerodynamics suffer, similar to operating in a constant crosswind. Maintaining axle parallelism within a tolerance of +/- 1/8-inch side to side (measured at the hub-end centers) will help make side thrust from this variable negligible. Granted, this spec is tighter than normally found in many alignment shops, but tire engineers have long maintained the payback is in longer tire life and reduced steer tire irregular wear.
Additionally, both axles must be square to the chassis centerline. This is sometimes difficult to measure, especially on newer trucks with lighter weight frame rails that are sometimes bowed in areas adjacent to cross members or suspension mounting points. Modern alignment machines that reference a calculated or theoretical chassis centerline can be helpful in obtaining a minimum thrust angle from this variable.
Finally, remember that drive axles are restrained by torque arms, trailing links, shackles or similar devices that are insulated by bushings or other damping materials. These wear items must be maintained to ensure there is no significant change from static (non-torqued) to dynamic (torque-applied) alignment.
The same basic concerns apply to trailer axles, but trailer yaw due to misaligned axles causes even greater fuel economy concerns due to the larger exposed sail area, especially of high-cube vans. That is not to mention the obvious side scrub problem and the added strain on the engine, which has to drag a misaligned trailer. There is a tiremaker test showing that drive and trailer axle misalignment can result in fuel economy reductions of 2.2%.
Now, let’s review other maintenance and operating variables some controllable at vehicle spec’ing that affect fuel consumption. Just knowing some of these factors and relating them to the needs of your fleet customers can enhance the credibility and effectiveness of your commercial salespeople.
While vehicle aerodynamics is a complex subject, the general idea is to maintain smooth (laminar) airflow over and around exposed surfaces. Turbulence, swirling air patterns and areas of low pressure immediately below or behind the vehicle may be of benefit to racecars, but these detract from a large truck’s fuel efficiency.
Aerodynamic fine tuning, including the addition of properly shaped mirrors; flush-mounted turn signals and clearance lights; and properly integrated cab side extensions, fuel tanks and battery box fairings all generally help.
There are, however, three primary turbulence-prone areas, two of which truck buyers might have control over when spec’ing new vehicles and while trucks are in normal operations.
First is the open area from the back of the truck cab to the front of the trailer. Keeping these points closer is better; avoiding gaps greater than about 30 inches is always advised, as larger gaps invite downward airflow and turbulence in this open area.
Smaller distances allow air to flow over the cab and continue rearward without diving downward in front of the trailer.
One trick is to observe trucks at speed in moderate or heavy rain. Trucks with less splash/spray exiting laterally around the drive tires tend to have better aerodynamics in this area, with resulting improved fuel efficiency. Of course, wheelbase selection, fifth wheel setting and trailer kingpin locations are important to maintain proper drive axle loading consistent with this small gap objective.
The second turbulence prone area is under the truck chassis and trailer. With a consistent road-speed-to-engine-rpm relationship, trucks with lesser ground clearances will deliver better fuel efficiency. Smaller tire diameters can be considered for this purpose.
Front air dams and trailer side skirts help maintain smooth airflow under the truck but must be balanced with the need to negotiate crossings and other elevation changes in route.
The third major area of turbulence is behind the truck, especially with regard to large van trailers. Numerous devices that help displaced air return to a neutral pressure without excessive turbulence/swirling (and resulting low pressure) behind the vehicle have been shown to benefit fuel efficiency.
However, to date, all of these devises are cumbersome, and no practical solution to this problem seems to be around the corner.
Tire Effect on Tires
Lastly, when helping your customers select new tires, keep in mind that deep-tread tires typically marketed as high-mileage drives are generally less fuel efficient than shallower treads. Also, continuous rib tires tend to have lower rolling resistance than laterally grooved designs.
Since all tires become more fuel efficient as they wear, it may also make sense for some fleets to use lower tread depth pull points (within the legal limits, of course) in spring and summer months than in the colder months (when added soft surface traction may be needed).
Experienced tire, alignment and truck service engineers can all be good sources of information for fuel efficiency enhancement. It’s time to take advantage of them all in these days of high fuel costs, for your benefit as well as that of your fleet customers.