Towing on extreme grades
September 24, 2012
The Sterling above is parked outside the Eisenhower Tunnel at 11,013 feet with a 7 percent grade coming East from Dillon, Colo. This is a favorite run for truck manufactures and journalists testing trucks.
I hear from folks that drive on 14 percent grades to get to their mountain ranches that up and down steep grades are stressful on brakes, transmissions and nerves. All new diesel pickup trucks have grade shifting automatic transmissions and exhaust brakes. Grade shifting transmissions while in "tow haul" mode will automatically downshift if you are going down hill, when you apply the trucks brakes. Downshifting going down hill is what we do with manual transmissions. The goal is to save your truck and trailer brakes. Diesel powered trucks with auto transmissions are built to grade shift better than most gas powered trucks. And diesels with exhaust brakes (closes off the exhaust pipe creating back pressure) can slow your rig down without using the brakes as much.
When I sold trucks in the 90s, you couldn't sell an automatic transmission to someone that lived in the mountains. They wanted to control the truck by down shifting the manual transmissions coming down hill. The newer automatic transmissions can be operated manually also to slow you down, the torque converter can lock up in all six gears.
Going up the mountain, down shift to keep your trucks engine running at the best RPM for power. Diesels need to run 1800-2500 RPM for their power band and gas engines, 5000-6000 RPM for power. Another reason for using automatic transmissions, is they will find the power band automatically. And going down hill, automatic transmissions won't downshift, it could over rap the engine (higher RPM than the engine should run at.) RPM is revolution per minute as seen on your tachometer gauge. Generally the trucks computer won't let the transmission down shift if it will over rap the engine RPM's. But it's good to know what the maximum RPM of your truck is encase the computer forgets. That can happen and it will cost you an engine. Most diesels top out at 3400 RPM and gas engines 6500 RPM.
I've taken a three horse trailer up Pikes Peak (14,110 feet) with a half ton Quadrasteer GMC and many times I go over Trail Ridge (12,000 feet) towing a trailer. These roads have 12 percent and higher grades. You need to watch your trucks gauges, not letting the engine or transmission temperature go into the red. Using your transmission to control speed will save your truck and trailer brakes for when you have to use them.
Constantly using your brakes can overheat them; wear out the brake shoes and drums, leaving you looking for a "truck runaway ramp." When I tow trailers through the Rockies in the winter and there is some ice or snow on the road, I use my trailer brake controller separately. I use the trailer brakes to slow me down on the curves to not start a skid, but I don't use the brakes hard or long (3 to 4 seconds). Learning to manually use your trailer brake controller is important on grades. It's wise to practice using your trailer brake controller to operate just the trailer brakes to control sway and for slick roads.
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PickupTrucks.com and I did a heavy duty shoot out a few summers ago at the GM proving grounds near Detroit. We towed 10,000 pound trailers with 3/4-ton gas and diesel trucks and 12,000 pound trailers with the one ton diesels. We did this on 7 percent and 16 percent grades. On the 7 percent grades, most of the gas powered trucks could get to third gear, the diesels made it to fourth gear. The grades where less than a mile long. The 16 percent grades, left most trucks in first gear. This tells you how hard a 16 percent grade is on a truck towing a trailer. At this rate it would take 2 miles of road to get to second gear. One of the diesel one tons, on the third run up the 16 percent grade overheated the automatic transmission.
Most Interstates don't go over 6 percent grade, but in Colorado we have 7 percent on Interstate 70 from Dillon to the Eisenhower tunnel and up Vail Pass.
On these high grades, running the engines at higher RPM's also uses more fuel. But if high grade roads are what you have to deal with, and you own a diesel truck, I'd recommend getting an aftermarket exhaust brake if your truck didn't come with one. With a gas engine, learn how to manually shift your transmission for engine braking whether you have a manual or automatic transmission. Having hydraulic disc brakes on your trailer is a worth while investment for mountain driving or any roads where cars headgate you (opposite of tailgate.)
Kent Sundling (alias "Mr. Truck") spent 20 years wearing out pickup trucks as only a farmer could. With over 1 million miles pulling trailers, Mr. Truck has a unique collection of truck and farm stories that will educate and entertain. Mr.Truck gave up his bib overalls and John Deeres in his quest to save the farm and moved to the big city to sell trucks. After selling trucks for 10 years, this farmer now writes for eight magazines and owns over two dozen Web sites, helping folks find the "Right Truck." If you have a question for Mr. Truck, you may contact him at his Web site, http://www.MrTruck.net. ❖
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