Whenever I'm checking out new pickups and SUVs in a dealer's showroom, I always hear other tire kickers ask about the fuel economy. It's a significant topic, and it can make or break a sale in some instances. It's ironic, though, that after the purchase, fuel economy takes a back seat to overall performance and is seldom mentioned again—unless it's to brag about the rig's good mileage.
So, while fuel economy is certainly important, there are more critical questions a potential truck buyer should ask, like, "What's its axle ratio?"
This plays a huge role in overall performance, yet all too often, a buyer of a pickup or SUV will not even think about it. Instead they buy a vehicle with the "standard" or base axle ratio, which is typically 3.42:1 or 3.55:1, thinking, "if it comes standard, it must be the best setup."
If they do inquire about a "lower" (numerically higher) axle ratio, the salesman likely tells them that the other ratios offered will drastically reduce the vehicle's fuel economy numbers.
Both of these trains of thought are more likely to lead to dissatisfaction with the truck's towing performance than doing much to hurt its fuel economy.
The truth is, vehicle manufacturers offer optional axle ratios for one reason: to improve the vehicle's acceleration and towing performance. What's more, they don't have as much adverse impact on fuel consumption as one might think.
Facts On Figures
A lower gear ratio, such as 3.73:1, 3.92:1 or 4.10:1, provides more lowspeed wheel torque, which means it takes less throttle to get the vehicle moving. This is a welcome help when the boatandtrailer rig is heavy, the launch ramp steep, or the pickup is under load in addition to a boat in tow.
With a lower axle ratio you can ease into the throttle and the tow vehicle will respond a lot quicker than it would with the standard "highway" gears. A lower axle ratio also means your vehicle will accelerate faster when pulling a heavy load.
It's for those reasons I make sure each new truck I buy is equipped with an optional axle ratio, typically a 3.73 or 3.92 when the primary boat being towed is less than 21 feet long. This is especially true if the vehicle has a V6 or small V8 engine.
If I were towing a bigger boat, say a 24to 28foot centerconsole, I'd choose the 4.10 axle. When tow weights get above 5,000 pounds, gaspowered V8s need all the pulling help they can get, and the 4.10s are just the ticket. Diesel engines can get by with a 3.73:1 ratio. And I wouldn't be concerned about fuel economy being hammered.
According to Roger Clark, senior manager for General Motors Energy Integration and Fuel Economy Learning Vehicles Program (ELVP), which handles fuel economy development of all GM trucks and SUVs, fuel economy will not change much by going to an optional axle ratio.
"The typical combined fuel economy impact, based on EPA lab test conditions, is about 0.4 mpg to 0.6 mpg between the base gear ratio and the lowest (4.10) offered," he says.
"That change is linear; equipping a truck or SUV with a 3.73 gear ratio, for instance, would affect combined fuel economy by less than a 1/4 mpg in highway fuel economy. The average truck owner wouldn't even notice that slight of a fuel mileage drop at the gas pump."
In the real world, Clark says, choosing a lower axle ratio may not even show up in city driving; it has the most impact on longdistance freeway trips.
"The reason we (truck manufacturers) offer the 3.42 and 3.55 ratios is that they offer the best fuel economy with today's automatic transmissions.
"If you want a truck that responds well with a heavy load or while towing a trailer, the 3.73, 3.92 or 4.10 ratios will provide the best pulling power and performance at the lower engine speeds."
As for general fuel economy, he says, "Sure, driving a truck with a lower axle ratio is going to have a cumulative effect in fuel economy. But it's going to be very hard to notice any difference when the vehicle is being driven in a mix of city and highway conditions."
The reason fuel economy doesn't take a big hit is that many other factors, like aerodynamic drag, weather conditions and your driving habits—not the gear ratio—are the major contributing factors in a vehicle's fuel economy.
According to the EPA, during the current highway test cycle where the average speed is 48 mph, 54 percent of an engine's power is used to overcome aerodynamic drag. At faster speeds it has to consume even more fuel, to push through the air.
By the way, expect EPA fuel numbers to drop about 10 to 15 percent across the board on new vehicles in 2008 because the agency will raise city and highway test speeds to better duplicate realworld driving.
"A good example of how drag affects fuel economy," explains Clark, "is a truck that has a 21 mpg highway EPA number. Drive at a 10 percent higher average speed than what the EPA test cycle averages and drag causes fuel economy to fall about 1.5 mpg."
Bump that to 10 mph faster and mileage can drop another 1 mpg. And if you run 75 mph, fuel economy in a bigger vehicle can fall 4 to 5 mpg.
Now, put a boat in tow, drive a conservative 65 mph, and fuel mileage will be cut by 30 to 40 percent because your tow vehicle is fighting its own wind drag, the boat's wind resistance and the extra weight of the boat/trailer combo.
The saving grace is that, when your truck has an axle ratio designed for towing performance, you don't have to get as deep into the throttle to get moving or maintain speed. So, when you buy your next new truck, put a check mark next to the box that lists the optional 3.92:1 or 4.10:1 axle.
You'll find you're a lot more pleased with its performance when those lower gears work their magic.