Should you care about this? If it’s a nice 70Fº morning with relatively low humidity and you are at sea level, then no. However, a hot summer day and high humidity will have a noticeable effect on acceleration and grade climbing ability, especially when your air conditioning is set on full blast.
The SAE provides standards by which trucks, and all vehicles in general, are measured against. The SAE J1349 standard (revision June 1990) provides a formula to calculate relative horsepower for naturally aspirated engines.
Turbocharged and supercharged engines, especially those with intercoolers, help alleviate negative effects of your surrounding environment. However, all turbochargers and superchargers are not created equal. Some are more efficient than others, but none are able to give you all 100 percent of power in heat or at high altitude. Thus, this formula only applies to naturally aspirated engines.
You can easily find relative horsepower calculators on the Internet. Just get the relative barometric pressure (measured in inches Hg/Mercury) and relative humidity percentage (percent) using your favorite weather information provider. You also need the current ambient temperature (degrees Fahrenheit) and the elevation (feet). Get these four numbers plugged into a calculator, and you get the percent of horsepower you are currently producing.
For example, our test track is located at 5,200 feet above sea level. Consider a barometric pressure of 30.08 in Hg, relative humidity of 25 percent, and temperature of 72Fº – the truck being tested produces only 82.4 percent of its rated horsepower. The big bad 6.2-liter EcoTec3 V8 in your GM pickup truck that is rated at 420 horsepower and 460 pound-foot of torque is making about 346 horses and 379 pound-foot of twist at our test track.
Okay, so you don’t live north of Denver, Colorado. How about Dallas, Texas? Elevation near downtown is 430 feet. A typical June day could bring a temperature of 95Fº, relative humidity of 89 percent, and barometric pressure of 29.96 in Hg. Your truck is making 93.4 percent of its power on that day. That same 6.2-liter V8 is now at 392 horsepower and 430 pound-foot of torque.
Naturally aspirated engines at the top of the Ike Gauntlet are losing about a third of their standard power rating. That big GM V8 is making 279 horsepower and 305 pound-foot of torque up there.
TOWING HIGHWAY MPG:
THE DAILY GRIND
The extreme Ike Gauntlet test is all well and good, but what about a more real-life example of how a truck performs? How does the truck do at the daily grind? Enter the towing highway MPG test! Why perform a towing MPG test on the highway?
Many truck owners spend time towing a trailer on a highway. They might be pulling a U-Haul trailer across country, hauling an equipment/supplies trailer to a job site, taking a camping trailer to the next adventure, or towing a boat for a relaxing day on the lake. People like Mr. Truck tow horses or livestock! Towing on a highway is something most of us can relate to.
Any meaningful test requires control of the environment. We picked a highway loop that measures precisely 98 miles on the Interstate I-76 northeast of Denver, Colorado. This stretch is not heavily traveled and the highway itself is relatively flat. It’s about as flat as an Interstate can get in Colorado.
2016 Toyota Tundra TRD Pro
We leave the truck stop and go forty-nine miles in one direction, and then return the forty-nine miles back to the same fueling station. We use cruise control set at 70 MPH for all runs. Although this stretch of the highway has a 75 MPH speed limit, we run all highway MPG tests at 70 MPH. This allows us a better margin of safety, as this stretch of highway can get windy.
The EPA rates midsize and light-duty (aka half-ton) trucks for city, highway, and combined MPGs, but they do not give a rating for trucks when towing a trailer or for heavy-duty pickups. This is where we come in.
We use a “double-click” method to top off the fuel tank before each run. We let the pump click the first time, we wait thirty seconds, and then manually add fuel until the pump clicks and stops for the second time. We use the same fill-up method when we return to the same pump after ninety-eight miles on the highway. We calculate the real-world MPG and also compare the results with the reading from the truck’s trip computer. The two results almost never match exactly. The number we finally report is the calculated number, based on the gallons filled at the pump.
When towing, we always use the truck’s Tow/Haul mode, although this does not significantly affect the results. Tow/Haul mode transmission shift logic does not really kick in at 70 MPH. We always use manufacturer recommended fuel and/or octane specification. We run all tests in 2WD mode. We do not perform tests during high winds, rain, or snow.
GOLD MINE HILL AND
CLIFFHANGER:
HIGH MOUNTAIN OFF-ROADING
Your truck is a symbol of freedom, and off-road capability is a big part of the equation. This is why we use two challenging trails in the Rocky Mountains near Boulder, Colorado to evaluate a truck’s off-road worthiness.
2016 Nissan Titan XD PRO-4X
The Gold Mine Hill is a moderately challenging trail. It is accessible year-round, but it may become impassable in the winter when the snow gets too deep. The trail is so called because it leads up to a defunct gold mine that was active in the nineteenth and the early twentieth centuries. This off-road challenge consists of three stages. First is a steep and rocky incline that is closely lined by trees. This is just a warm-up. The second is a 90-degree left turn that is part of the incline. We always come to a complete stop before the turn to kill the momentum and make it more difficult. This is a place where the truck’s 4x4 or AWD system is really put to the test as weight is shifted while navigating this tight turn. This is where tire choice becomes paramount. Finally, a steeper and washed-out section with large dips is there to test every aspect of the truck’s off-road performance, including: ground clearance, approach/departure/breakover angles, suspension articulation, and tire grip. The passenger front tire lits off the ground on most trucks that attempt the final stage. Trucks that don’t have off-road oriented or specialized tires or a locking differential are not likely to make it to the top of Gold Mine Hill.
We use five criteria to evaluate each truck’s off-road worthiness:
•Tires
•Ground clearance, approach/departure/breakover angles
•AWD / 4x4 system traction management
•Suspension articulation and comfort
•Power delivery
Some trucks make the Gold Mine Hill look easy. These are the trucks that are eligible for TFLtruck’s Gold Hitch: Off-Road Truck of the Year Award. These trucks also graduate to the Cliffhanger trail test.
The Cliffhanger 2.0 is a new trail that we certified in 2016 for testing the most capable 4x4 trucks. The likes of the Ram Power Wagon, Toyota TRD Pro, and the Ford Raptor are the trucks eligible to tackle this trail.
The Cliffhanger is longer than the Gold Mine Hill and it goes above the tree line. The payoff is a special 360 degree view that features the Continental Divide to the west and the Front Range to the east. The way to get there is a steep and rock layden trail that requires maximum traction. There is not much warm-up time. Rocks the size of basketballs, and often larger, can quickly stop your progress. There is a medium-sized ledge halfway through the trail that requires maximum ground clearance