Measuring Hours vs. Miles in Medium-Duty Truck Performance

Measuring medium-duty truck performance helps fleets effectively manage vehicle replacement strategies, establish optimal preventive maintenance schedules, identify vehicle utilization, and calculate a fleet’s total cost of ownership. However, many (rightly) contend that mileage is not a true indicator of actual vehicle wear-and-tear.

“There are several ways to measure performance. Mileage continues to be popular, but, because of the variety of ways trucks are used, fleets and owners may want to consider other effective means of performance measurement, such as hours of engine operation or the gallons of fuel consumed,” said Joe Korn, senior analyst for ARI.

Tracking engine hours vs. miles driven is not a new concept. We all know the benefit of using mileage as a performance metric. Many fleets operate under a specific year or mileage replacement policy. So, are hours an important metric for measuring medium-duty truck performance?

Measuring Performance

“As an engine idles, the wear to consume one gallon of fuel is equal to driving up to 30 miles. In these situations, it is more effective to schedule future vehicle replacements or measure lifecycle costs based on the hours of engine operation or the amount of fuel burned over a period of time,” Korn said.

The main benefit of measuring certain factors by hour is using an alternative method to analyze the fleet. “Even for delivery fleets, the miles will vary greatly across different regions, and, in many cases, the highest cents-per-mile (CPM) locations are often New York City,” explained Collin Reid, truck strategic consultant for GE Capital Fleet Services. “Cost per hour gives fleet analysts an understanding of the locations and trucks that are costing more than the benchmark.”

Rob Kooken, director of business development and an account executive for PHH Arval, agreed. “Measuring certain factors by hours versus miles enables a fleet manager to get a more accurate insight into the wear-and-tear on a vehicle and plan PM accordingly,” he said. “For example, certain medium-duty trucks have special applications that may require the vehicle to be running — such as those equipped with PTO. These require constant charging of the battery to operate and accrue more time idling that won’t show up as mileage or utilization.”

The installation of telematics devices on company vehicles began tracking hours vs. actual miles driven. This was a key turning point in the hours versus miles debate, as it provided fleets an easier way to track hours, rather than simply trusting a driver’s log.

Idling — which came to the forefront thanks to telematics — is one of the main factors that can be analyzed by hours vs. miles.

“Many medium-duty truck applications perform a larger amount of their work at idle, or lower speeds, than either passenger vehicles or over-the-road trucks, and therefore will typically have low miles, but higher-than-normal hours-per-mile,” explained Brian Tabel, director of marketing for Isuzu Commercial Truck of America, Inc. (ICTA).

Idling in a medium-duty fleet vehicle can use up to a half-gallon of fuel, per hour, according to www.fueleconomy.gov.

“Idling is one of the main reasons a fleet manager would want to track hours instead of mileage,” said Kooken of PHH Arval. “Take an electric company truck, for example. That vehicle idles for hours each day while the crane is up. Mileage isn’t being recorded during this time, but one hour of idling is equal to 25-30 miles of driving. That usage needs to be properly accounted.”

Idling and PTO operation are not ideal conditions for some vehicle systems. “The diesel oxidation catalyst is less likely to achieve temperatures high enough to perform optimal regenerations. More manual regeneration is required when the operating temperature is lower than a typical duty cycle,” Tabel explained.

Engine hour usage creates wear-and-tear on the engine, and the usage by hour takes this into account, according to Reid. “Also, in many cases, the PM schedule would be better set with an hour guideline vs. miles, as PM ensures the engine and fuel system function,” he said.

Hours or Miles?

So, what should fleet managers be measuring, and when? When determining wear in medium-duty trucks, mileage calculations can be very effective, especially for trucks driven primarily over the road.

“Mileage over time can help determine a standardized replacement schedule, which can accurately layout the overall life-of-vehicle performance and pinpoint the ideal replacement time,” said Korn of ARI.

Currently, ICTA does not have a policy to directly equate engine hours to miles for service purposes, but did refer to the diesel particulate filter (DPF)-recommended service interval or 3,000 hours or 100,000 miles.

“Both hours and miles are important criteria when determining service timing for a fleet,” said Tabel of ICTA. “Any systems that directly interface with the engine (fuel, cooling, exhaust, etc.) would be strongly impacted by the engine hours.”

Most of the experts agreed that the main factor of whether to measure by hours or miles is the truck’s application.

“The more the truck is used with idle time versus drive time, the more important using cost per hour is to the fleet,” said Reid of GE Capital Fleet Services. “For some fleets, you find the lower mileage units (but with higher hour usage) have more maintenance costs than the lower mileage trucks. That is because the engine wear and tear of vocational equipment is more than a truck driving on a highway.”

Kooken of PHH Arval noted the determination of tracking by hours vs. miles should be strictly based on the application of the vehicle and that specific fleet.

“If you have a vehicle that has high frequency of idling — those trucks will accrue mileage that won’t show up on the speedometer. For example, I once had a client whose fleet was experiencing engine failures. The vehicles in the fleet did a lot of idling, and once we estimated the idle time, it was determined the vehicles should have had three preventive maintenance visits when, in fact, the vehicle had only one,” he said.

One example would be aerial bucket trucks. “These trucks may only need to travel a few short miles from their depot to an area where overhead work needs to be performed,” said Jerry Renauer, product order support specialist for Ford Commercial Truck. “Once they arrive at their destination the mileage stops but the engine continues to run another six to eight hours, after several weeks only a few miles may have accumulated but the hour meter tells the truth about the utilization and may be calling for an oil and filter change. Without an hour meter you start guessing when to perform this service if at all.”

According to Troy Davis of Ram Truck Engineering for Chrysler, one benefit for measuring hours is for oil-change monitoring.

“Hours are intended to monitor engine maintenance scheduling (oil change, fuel filter change, air filter change, etc.) for vehicles used frequently in stationary and/or idle condition,” he noted. “The benefit of measuring hours is for oil-change monitoring on vehicles that accumulate engine run time, but not many miles. Miles are typically best for measuring other factors such as chassis, suspension, and driveline components,” he noted.

Measuring a vehicle’s performance can also help determine if it is being fully utilized.

“While the required level of use and need will vary among companies and industries, for the most part, mileage accumulated during a given time period can help identify vehicles that are underutilized, as well as driving patterns that might be contributing to maintenance or other issues,” explained Korn of ARI. “In other cases, measuring the amount of fuel consumed or the number of engine hours can help identify more accurately the actual use of the vehicle. Regardless, measuring performance can give a fleet manager a better understanding of vehicle use, which in turn can offer insight into whether changes may or may not need to be made.”

Both hours and miles are valuable metrics for medium-duty fleets to track. While miles may be best for measuring many fleet analytics, hours is an important component to ensure total visibility into all aspects of fleet maintenance and measurements.