ROCHESTER HILLS, Mich. (July 18, 2005) - Oh no! Not again! Yes, once again for the umpteenth time this year, the national average price for a gallon of diesel fuel hit a new record high in July at $2.348, according to the Energy Information Administration (EIA).
All regions of the country posted an increase, but California remains the most expensive region to fill up in as prices shot up to $2.554. (Just another reason to let California fall into the ocean!) An EIA economist indicated that the recent trend for high prices could pave the way for more record-setting prices in the winter.
Great. Just great. More agony for fleets whose largest cost after salaries and wages is fuel. Most large, for-hire carriers have gotten much better at imposing fuel surcharges than they were a few years ago when a sharp upturn in diesel prices put thousands of trucking companies out of business. But recouping the entire cost of fuel increases never happens.
Hurt the most by high fuel prices are owner-operators, small carriers and private carriers in competitive industries, where it's tough to raise prices.
Affecting the bottom line
In case you haven't already told your fleet customers at least a thousand times, now's a great time to reiterate the message: Tires play a significant role in affecting fuel economy and can directly impact a fleet's bottom line.
About 30-40 percent of the fuel required to move a vehicle down the highway is spent overcoming tire rolling resistance, which is the amount of drag created by the tires as the vehicle rolls down the road.
The greater the rolling resistance, the less fuel-efficient the tire is.
Tire manufacturers have worked hard over the years and continue to work hard to produce fuel-efficient tires. There are three areas in tire design in which they have been able to directly impact rolling resistance. These are tread design, tread compounding and casing construction. Most efforts have been focused on the tire tread. That's because two thirds or more of a tire's rolling resistance comes from the tread, and it's also relatively easy to change tire tread depth, pattern or compounding without affecting the tire's casing durability or retreadability.
Tread compounding is a critical factor in reducing tire rolling resistance. Today's fuel-efficient tires feature a “cap and base” design. The “cap” layer is the part of the tread nearest to the road.
A compound can be chosen with high resistance to abrasion, long tread life and good traction. Since a compound with these features tends to run hot, manufacturers place a “base layer” below the “cap.” That base is a compound that is cooler running and protects the casing from heat buildup.
The result is lower overall tire temperature that produces better fuel economy since less fuel energy is wasted as heat. The tread mileage, however, may be less than non-fuel efficient tires.
While the tire casing is a major contributor to fuel economy, changes in this area are more difficult to make without negatively affecting overall tire life and durability. Casing components like belts, beads and tire ply cords account for 30-40 percent of a tire's rolling resistance. Some methods for reducing rolling resistance are:
* Increasing the tire's air volume;
* Decreasing the bead filler;
* Reducing sidewall gauge; and
* Flattening the tread radius.
All of these can have negative impacts on casing durability and traction if care is not taken during the tire development process.
What fleets can do
While tire companies are doing their best to help fleets save fuel, what can truckers do to reduce tire rolling resistance and optimize fuel economy?
Fleets can start by lowering their running speeds. Speed is the largest single variable that affects fuel economy since rolling resistance increases with speed. In fact for every mile per hour increase above 55, miles per gallon will be cut by about 2 percent. A change from 65 mph to 55 mph results in a 22-percent improvement in miles per gallon with a cost of about 18 percent in extra travel time.
This is a good time for fleets to consider reducing the speeds their trucks will run, but it's tough to do that and retain drivers at the same time.
Maintaining the correct air pressure in all the tires on a fleet's trucks, tractors, trailers and dollies (if they've got them) is one of the things a fleet can do to positively affect fuel economy.
According to a study conducted in 2001 by the Technology and Maintenance Council (TMC), of the air pressures in more than 35,000 commercial truck tires, only 44 percent of all tires were inflated within +/- 5 psi of their target air pressure. Seven percent were underinflated by 20 psi or more and 4 percent were flat.
Increased flexing and the irregular footprint caused by underinflation results in increased rolling resistance, which leads to increased fuel consumption as more power is required to move the vehicle. In fact, for every 10 psi of underinflation there is a 0.5-percent reduction in fuel economy.
As a result, according to the data in TMC's tire pressure study, fuel economy loss due to improper tire inflation is about 0.6 percent for typical truckload (TL) and less-than-truckload (LTL) operations.
While it's important to encourage fleets to maintain the proper air pressure in their tires, over inflating tires is not an effective way to save fuel since irregular wear can develop and traction can be negatively affected, negating any savings in fuel economy. Instead, many fleets are now spec'ing tire inflation systems on their new trailers to ensure their trailer tires are properly inflated.
Talk about drag, vehicle alignment has a big impact on fuel economy too. When a vehicle is out of alignment, the tires are quite literally dragged down the road—which of course increases tire rolling resistance and consumes more fuel. A vehicle that is out-of-alignment by as little as one degree at each tire position can lose over 2 percent in fuel economy.
Naturally, the greater the load, the lower the fuel economy. However, maximum payload is usually a fleet's primary goal so it is unlikely that payload would be cut just to save fuel. Still, vehicles can be made more fuel-efficient by spec'ing lighter weight components and accessories such as low profile or wide-base tires, aluminum wheels, etc.
Wide-base tires are without a doubt the most fuel-efficient tires. Since a vehicle equipped with wide-base tires has only two sidewalls flexing and generating heat on an axle end instead of four, friction and rolling resistance is reduced. Further, since wide-base tire and aluminum wheel assemblies are much lighter than standard tire and steel wheel assemblies, the vehicle's weight is reduced by as much as 1,000 to 1,200 pounds on a tractor-trailer combination, further reducing the vehicle's total rolling resistance.
If fleets are considering changing tire types to reduce fuel consumption, it's important to know that each tire position accounts for only a portion of the fuel consumed in overcoming the vehicle's total rolling resistance.
On tractors pulling a single trailer, the steer tires contribute 15-20 percent to fuel economy, the drive tires provide 30-42 percent and the trailer tires account for 42-52 percent. On tractors pulling doubles, steers contribute 10-15 percent to fuel economy, drive tires provide 15-21 percent and trailer tires have a 64-75 percent effect on fuel economy.
Since most of the fuel economy produced by tires comes from the trailer tires, changing trailer axles to fuel-efficient tires would produce more benefit for less cost than replacing all the tires. Also, trailer-type tires are generally less expensive than steers and drives, which makes changing trailer tires an even more attractive purchase option. However, in most fleet operations, steer and drive tires are changed more frequently than trailer tires, so changing tractor tires to more fuel-efficient types may improve fuel economy quicker.
Obviously, once the treads of fuel-efficient tires are worn they should be retreaded with low rolling resistant tread compounds and tread patterns to ensure the tires remain as fuel-efficient as possible.
Fleets considering changing tires should be aware that there is usually a reduction in tread mileage, traction and/or retreadability when a switch to fuel-efficient tires is made. That could have a considerable effect on the fleet's bottom line and should be considered when making a decision like this. They may be swapping a headache for an upset stomach.
Encourage your fleet accounts to conduct tire tests before wholesale changeovers are made.