Monday, October 3, 2022


RV driving: Understanding grade signs

By Russ and Tiña De Maris

Photo: Near Alta Lake, Kern County, California by David~O on

If you’re new to RVing, or have spent your time in the Midwest flatlands, first hitting mountain country can be a bit of an eye-opener. Those yellow warning signs that talk about a “steep grade,” often accompanied by a percentage number, can be confusing. Road grades seem mysterious at first, but really are simple. Let’s work through the mysterious math of road grades.

Simply put, road grade is the amount of rise or drop over a given distance. A 5% grade means over 100 feet, the road will rise or fall five feet. In real life terms, a sign reading, “5% downgrade next 4 miles” indicates that you’ll lose 1,056 feet in altitude over the four miles of run. Here’s the math: 5,280 feet (per mile) times four miles = 21,120 feet x .05 (five-percent grade) = 1,056.

In practice, this is something you really should know about. Going up a long, steep grade can lead to overheating your engine and transmission. Heading down a long, steep grade requires preparation: An RV, heavier than most automobiles and trucks, must be kept in control. “Brake fade” resulting from overuse of brakes can lead to an out-of-control situation. Being aware of your rig’s handling on a grade is an important part of safe RVing.

So what’s a steep grade? Grades are typically marked when they reach 5% or more. On the U.S. Interstate Highway system grades are not allowed to be over 6%; On other roads and highways there is no limit. RVers generally agree that the longer the grade the greater the concern. We’ve been over short-length double-digit grades that gave us no trouble, but even a 5% grade can be worrisome if it goes on for miles and you or your vehicle are not prepared for it.

How do get ready for a steep grade? Going uphill keep an eye on your engine comfort. If you’re dealing with a long grade you may need to switch off your air conditioner to keep your engine cool. Watch your temperature gauge and — if you have one — your transmission temperature gauge. If things start heating up, back off the throttle and downshift. The same is true if your engine begins to lug — drop down a gear.

Going down a steep grade means keeping your rig under control. The old trucker’s adage, “You can come down the hill too slow many times, but you can come down the hill too fast only once,” applies well to RVing. It’s much easier to start out at the top of the grade slower than you “think” you should — once you build up downhill momentum things can get out of hand very fast. The rule of thumb says whatever gear you required to come up the pass is the one (or one gear lower) you’ll need to head back down. Beware, diesel engines don’t have nearly the compression braking of a gas engine.

Ideally the gear you choose for the downhill run should “hold” your rig at a comfortable speed, not allowing it to gallop away. Some truck drivers advise the use of aggressive braking: Keep the vehicle under control with the proper gear and figure a “safe” speed. When the rig hits the safe speed, bear down hard on the brake pedal and reduce speed by five miles per hour. Get off the brakes and hit them again when the safe speed is reached. NEVER ride your brakes — it’s a sure way to overheat them and lose braking power.

Don’t let those yellow grade signs throw you into a tizzy. Recognize what they mean, prepare yourself to drive them appropriately and enjoy the scenery!

##FT12-17 ##RVDT1839


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Rory R
2 years ago

There was one statement that jumped out at me. “Beware, diesel engines don’t have nearly the compression braking of a gas engine.” I have never heard that before. Is this article stating that even with an engine braking system, gas engines are more effective at braking than a diesel?

Richard Hubert
2 years ago

Good advice for tackling downhill grades. As for uphill – I learned (in towing a TOAD on our 2005 Winnebago Workhorse chassis) that your approach speed to the uphill is important too. The first time we were pulling our TOAD and came to a long grade up (rte 241 south from I-91 in southern CA) I let our speed drop to <50mph. The further we went up hill the slower we went, barely making the top at 20mph. With subsequent tows on other uphill grades I learned to approach the up hill at a higher speed. So once again coming to this same long grade I approached it @ 65mph and downshifted early in order to keep engine rpm up and more in its power band. This time was able to reach the top still going 50+mph. Just a matter of learning the rig's power train. However – for other grades – even steeper and longer (such as rte 154 heading north from Santa Barbara) we also learned it was just best to pull over and dis-connect the TOAD and drive it up separately.

Roy Christensen
2 years ago

On a steep grade going downhill, I use the Tow/Haul function on my 2016 Ford E450. Once I engage the Tow/Haul and slow down to the desired speed, I can take my foot off the brake and safely descend. I am sure other gas motorhomes have similar features to control the speed while going downhill.

2 years ago

The old trucker’s rule of thumb, “go down the hill in the same gear as you came up in,” may not work as well as it once did. These newer diesel engines have so mach more power than the older one. You may need to go down in a lower gear than you came up in. All I know is, trailering in the mountains with my ’16 Dodge with a 6-speed manual transmission and engine brake, is a lot more fun than it was when I had my ’99 with no engine brake!

Montgomery Bonner
2 years ago

Rule of thumb, never go down any faster than you came up. Put on engine brake if equipped. I try never to reach speeds over 45-50 mph going down long grade. BH says, that truck is going faster, keep up with him. NOPE I say, we are going to get to the bottom safely even if it takes all day. We have never had hot brakes, or any issues, going slower is safer. If you don’t know how, talk to a truck outfit, they can show you. Or better yet, take a hands on driving class/course and learn how to do it. Now you have the time. Going up, keep transmission in a gear which keeps engine at peak torque RPM, which will allow HYD pump (if equipped) motor to keep cooling fans speed on high. Turn of AC if necessary. Around 2100-2200 should do it for diesel equipped coaches. Pickup read the manual.

2 years ago

Pay attention sheep! I didn’t once coming out of Jackson WY, and dam near lost it all. At one point I thought about the parts the cleanup guys would be finding all along the river below, if they found us at all.
After all these years…… – well full confession – it’s what you learn after you thought you had it all down pat that really matters – that is if you get that second chance.
Thanks Russ and Tina – super article, one of the most important in memory.

2 years ago
Reply to  Alvin

You must have been coming out of Yellowstone toward the Cody, WY area on Hwy 14….

That has to be one of the longest (about 20-25 miles? I don’t recall exactly) and steepest declines in the US. (I did say one of…). Not to mention just going up before you even start down…

2nd gear, the engine brake on, and a howling engine that obviously did not like it. I had to keep the speed down to 35-40 mph due to some sharper turns in that run. Talk about white knuckles.

If you haven’t driven a road like this, find some 8% grades first.

2 years ago

The steepest grade I’ve hit is 18% going up from Red Rock Pa to Ricketts Glen State Park. They advise against it on their website but we were running late due to a trailer blowout. Not something I’d do again. Tacoma pulling 5500 lb trailer.

Rory Roberts
5 years ago

I don’t understand your reasoning when you say diesel engines don’t have compression braking. Diesels are designed with engine braking and or compression braking designed in. My rig has a 3 position switch for engine braking and has the total amount of HP available (500hp) for braking. In addition to that the cruise control works in conjunction with engine braking and downshifts the transmission to hold my downhill speed to within + or -1 mph of the speed I set it to.

2 years ago

Ram has had this for years. I have a 3500 now. Plan to purchase a 5500. They both have them. I thought Ford did as well?

Gene Bjerke
5 years ago

I’m not sure what you mean by “diesel engines don’t have nearly the compression braking of a gas engine.” Diesel engines have much more compression than gasoline engines; it is the heat of very high compression that fires the fuel. In practice, our diesel Sprinter motorhome will hold the rig back on hills quite well, while gearing down our Dodge SUV does nothing.

Bob p
2 years ago

On gas engines there is a throttle plate that opens and closes regulating air flow into the engine, when closed as when your foot is off the accelerator very little air is allowed in creating a vacuum inside the cylinders. A diesel doesn’t have a throttle plate meaning the engine “free wheels” under decelerations, without a “jake brake” or exhaust brake this free wheeling can create a runaway vehicle. You gave a good answer I just elaborated a little to explain what happens for the total newbie.

5 years ago

If the engine temperature is climbing, sure, turn off the a/c. But, if it is still climbing, turn on the heater. It acts as a second radiator.

Bob p
2 years ago
Reply to  RVBloggins

In our motorhome the heater hoses are shut off in hot weather with manual valves on the HVAC box to increase the AC performance. So I would have to stop and open the valves to operate the heater.

Daniel Jandon
2 years ago
Reply to  RVBloggins

in the late 80’s , in the summer time , was stuck in traffic in Dover , Del. (during the races ) in a 1986 ford Tempo , engine getting hot , turned off AC ,opened windows , turned heat on , 3 ladies didn’t like it , so I save the car , kept it for 16 years and other than a oil leak still ran good when traded it .

2 years ago
Reply to  RVBloggins

And when you complete that journey down the hill, don’t just pull over and shut off the engine. There is a cool-down period required. Read the Owner’s Manual on your brand to make sure. I know in the Ram there is…