As passionate as you may be about your trucking business, it must remain first and foremost a business. Profitability makes for an enjoyable living for you and your employees.

With the freight market now softening and capacity getting back to higher levels, profitability can best be achieved by working on the expenses front.

And as fuel remains a fleet’s most important expense item after wages, lowering the speed – or revolutions per minute (rpm) – at which your trucks’ engines run is a great way to burn less diesel while achieving the same tasks.

Volvo, Cummins and many other engine makers now offer diesel power for which the sweet spot – the range where it performs the best with the greatest fuel economy level – has dropped almost 300 rpm while the peak torque level now flirts with the 1,000 and even 900 rpm mark.

Each downward increment of 100 rpm at cruising speed represents 1% to 1.5% in fuel economy improvement, according to Volvo Trucks USA’s Driver’s Digest, based on an interview with Johan Agebrand – Director of Product Marketing at Volvo Trucks.

That’s at least 3% fuel savings with newer engines.

Seeing an automated transmission shifting gears on a modern engine at a much lower point than expected can be surprising at first for experienced drivers, such as Marcel Pouliot, vice president, Industry & Regulatory Affairs for Trimac, a Calgary, Alberta, based carrier with a fleet of over 1,000 power units.

In a SmartWay partner profile published by Natural Resources Canada, Pouliot recalls how odd it felt seeing the rpm going below the 1,000 line while climbing a hill. “For someone like me who learned to drive a long time ago, that is so unnatural,” he said.

The whole drivetrain can also find it disturbing, as low-revving engines tend to cause vibrations in them, potentially leading to more driver fatigue or premature component wear. Engineers studied the issue and enhanced drivetrain components accordingly. For instance, Spicer enhanced its Dura-Tune self-aligning center bearings to provide better vibration isolation and dampening, ensuring a longer life for components along the way.

In gear

The new, low rpm engines provide their best fuel economy when mated to an automated, electronic manual transmission (AMT) programmed accordingly. AMTs now equip the majority of Class 8 trucks on the road but there are still applications out there where manual transmissions are preferred.

The same rules apply to keep a low rpm and good fuel economy with a manual; it’s called progressive shifting. The driver needs to upshift as soon as possible when accelerating and to downshift as late as possible when decelerating. Keeping the highest possible gear engaged at all times helps keep the rpm and diesel consumption low.

Fully automatic transmissions with a torque converter often used in urban settings can also help with fuel economy. Allison’s 1000 HS model has a feature that allows it to put itself in neutral when the truck is stationary, at a stop light for example. This eliminates the load on the engine when the vehicle is stopped, which trims fuel consumption and lowers emissions – both by 6% says Claire Gregory, Director of Communications at Allison Transmission.

Regardless of the transmission type, low engine rpm will provide additional benefits in the form of longer oil life – and less downtime required for drain intervals – thanks to reduced friction and lower heat transfer. The coolant system will also benefit from the latter. And a coolant system in good condition is less likely to leak fluid in engine oil, contaminating it and harming fuel economy.

That’s a great example of holistic fleet management, where a maintenance manager takes into account the interactions between a truck’s components and systems to maximize productivity.

Low rpm fuel savings can also be achieved by making sure that the idle speed is set according to the manufacturer’s recommendation.

But as a general rule of thumb, the best idle speed is… 0 rpm. Shutting down the engine when it’s not used to pull payload should become second nature to any driver and most successful fleets have put in place programs that monitor idle time and reward those who keep it the lowest. Idling doesn’t only waste fuel that was so hard to save in the first place; it also contaminates the oil quicker and generates more wear and tear on the engine.

Most truck engines can now be programmed to automatically shut down after a given period, usually in the 5-10 minute range that allows for a quick delivery.

Auxiliary power units (APUs) can be used to cut down on idle time while ensuring driver comfort by providing heating or air conditioning in addition to electrical power. Those small onboard generators do all that with a fraction of the diesel fuel compared to the truck engine idling. Though it may vary from one model to another, a truck engine idling will generally burn about a gallon (3.78 litres) of diesel per hour while an APU will keep the cab warm (or cool) for an eight-hour night with just two gallons of fuel. As a bonus, the driver will sleep better with the noise and vibration reduction.

Better yet, more and more truck makers now offer battery-based electric APUs.

Route planning, tires and aerodynamics

Another interesting fact about diesel fuel is that it weighs about seven pounds per gallon. So whether your trucks are often grossed out or maxed out, keeping a full tank when it’s not necessary cuts either payload or fuel economy, harming your bottom line in each case. Make sure your dispatch department makes that calculation when planning routes and identifying refueling points.

Route optimization will also help cut idling due to trucks being stuck in heavy traffic or waiting in line at customs during peak periods.

Tire selection is another area that can keep your fuel costs down. Low rolling resistance models will improve fuel economy while wide base tires also help save weight by reducing the number of wheels. Tire pressure needs to be checked on a regular basis to keep them safe, extend their life as well as their casing retreadability.

An automatic tire pressure regulation system can be used for more peace of mind or tires can be inflated with nitrogen instead of air to avoid leaks. That’s exactly what Andy Keith, vice president of Seafood Express in Charlottetown, Prince Edward Island, does. “It improves rolling resistance, it improves tire wear and it improves our fuel bill, too,” Keith says.

Last but not least, the way your trucks and trailers penetrate the air is a crucial fuel economy factor. Side skirts on trailers, sloped hoods, fairings on the truck roof that guide the air over the trailer and close the gap between the tractor and trailer where turbulence forms will all help cut drag – or air resistance – and less power will be required to pull your loads.

Generally speaking, each increment of 3% in aerodynamics improvement translates into 1% additional fuel savings at highway speed.

Yet, a trucking company’s profitability goes well beyond fuel economy alone. Mobil Delvac^TM has prepared a free guide for you to download by clicking here. Learn more about how properly spec’ed components, remote diagnostic technologies, the use of extended life coolants and oil analyses can all contribute to your business vitality and longevity.

Fuel savings are only the beginning.