Selecting buses and trucks
The importance of buying or leasing the right vehicle for the task cannot be overstated. Vehicle selection affects your business’ productivity, fuel efficiency, safety, maintenance and other operating costs.
Most costs are locked in place once you’ve bought or leased a vehicle. With typical profit margins of less than 5%, selecting the wrong vehicle can seriously damage your fleet viability.
- When buying a vehicle - the potential resale value needs to take into account the cost of finance, as your capital will be tied up until the vehicle is sold.
- When hiring or leasing a vehicle - you may be offered a larger, more highly specified truck at a good price. It pays to do the sums before accepting a deal, as higher running costs such as fuel and maintenance may cancel out any savings. Some truck leasing companies supply vehicles fitted with telematics systems and provide advice on fuel efficiency initiatives in line with the EECA fuel efficiency programme.
The New Zealand Transport Agency's Heavy Vehicle Selection Guide provides useful information on choosing a vehicle.
When you start to look at fuel efficiency, it's important to understand how heavy vehicle engines work.
Heavy vehicle engines burn fuel to produce the power needed to:
- overcome rolling resistance
- push the vehicle through the air (aerodynamics)
- run accessories (cooling fan, air-compressor, alternator, lights)
- overcome engine and drive train losses
- climb hills
- Gearbox and differential ratios - should be selected so that the engine runs at its most efficient speed when travelling at normal road speeds.
- Select the highest gear possible - and adjust speed when you’re climbing hills to make sure they stay within the green band.
- Select an engine power that is enough to climb the hills - without having a major impact on productivity.
- Speed is a big factor in fuel efficiency - check out the numbers in this example.
|70 km/h||27 litres/100 km|
|80 km/h||30 litres/100 km|
|90 km/h||34 litres/100 km|
Power and torque
- Torque is a measure of the turning force, for example, at the flywheel.
- Power is the amount of mechanical work done (force x distance) per unit of time. Put more simply - power is a measure of the effort needed, for example to push a 1 tonne car 100 metres up the road in 3 minutes.
- Power and torque are related: power = torque x rotational speed.
- For the same amount of power you can have high torque and low engine speed (revs) or low torque and high revs. For example, when climbing a hill you can keep the revs high but the torque at the flywheel will be relatively low.
- Modern engines are most fuel efficient in the high torque zone - at about 65% to 70% of maximum power. The improvement in fuel efficiency can be 7.5% or more when you operate the engine at 1400 rpm compared to 2000 rpm. You’ll also reduce engine wear by running the engine at lower speeds.