Jul 15, 12 | by: Bruce Smith
Fuel economy is all about priorities and physics; there’re no magic bullets to make it better– but there are a lot of ways to make it worse.
Fuel economy weighs heavy on the minds of every contractor who drives a pickup and fleet managers whose performance reviews are based on meeting ever-tightening budgets.
The topic extends well beyond the office or board room. Sit in on any jobsite conversation in the country where pickups and performance are the topic and once the my-truck-will-out-pull-yours bravado settles down the conversation inevitably turns to fuel economy.
Despite many pickup owners’ bragging their trucks get 20mpg-plus on the road and mid-teens in city driving, the reality is stock 4×4 pickups, gas or diesel, are probably seeing city mileage in the low teens and mid- to upper teens on the open road.
If the pickup is upgraded with bigger tires, a lift kit, or loaded down with tools and accessories, you can bet fuel economy is even lower. Slap an equipment trailer on the hitch and fuel mileage drops another 30 to 50 percent.
AERODYNAMICS & WEIGHT
The harsh truth is simply this: Most of the upgrades we make to our pickups to improve their efficiency and performance in the work place hurt fuel economy.
Make changes that add weight, increase rolling resistance, degrade aerodynamics or cause more throttle to be used to get up to and maintain a certain speed, fuel economy takes a big hit.
For instance, you upgrade to taller, wider tires to get better ground clearance and traction. Those four new tires are heavier than the stock ones, thus they increase rolling mass and rolling resistance.
More rolling mass and resistance requires more energy to accelerate and maintain a certain speed. Energy comes from fuel.
The taller tires also drop the overall gearing, so now it takes even more throttle to get moving – and to maintain speed.
For example, changing from 32-inch-tall tires to 35s is the same as changing your truck’s axle gearing from 3.55s to 3.24:1. The formulae: (Original Tire Diameter / New Tire Diameter] x Original Axle Ratio = Effective Axle Ratio)
That’s why pickups regularly lose 2-3mpg in highway fuel economy, and 1-2mpg in city driving going up in tire size.
Add a lift or leveling kit so you can get even taller tires under your truck and the hit to fuel economy is even larger.
That’s because those two changes compound the hit on fuel economy. Not only does the taller, heavier tires affect mileage, the body now sits higher, which creates more wind resistance over and under the truck as you drive down the road.