The ups and downs of towing on steep grades

Since we tow a 23-foot Airstream Globetrotter with a compact Ford Ranger pickup, the question we get asked most often is "Can that truck tow your Airstream?"

When we answer in the affirmative, the next question is usually "But how does it do in the mountains?"

It does pretty well. In fact, we've been quite impressed with the Ranger's capability to tow up steep grades. Most modern trucks will do very well, so these days that's not the real issue.

The real issue is "How do YOU do in the mountains?"

Yes, it's really all about you. You need good skills at handling a trailer when you're in mountainous conditions—and those situations arise frequently, especially if you travel out west.

Let's start by getting an idea about road grades, first. Grades of 4-5% are pretty common and not usually much to get excited about. At 4-5% the grade is considered steep enough that you might see a sign warning about it, especially if it's a long stretch, and 6% grades are almost always marked.

At 8% you're talking about a very steep grade that presents much more risk of overheating or fading brakes, and at 10% and above you should be taking every inch very cautiously.

UPHILL

Going up a mountain grade is relatively easy, compared to going down. Your major concern is usually overheating, either the engine or the transmission—or both.

Slow down

The best way to avoid overheating is to slow down. Some combinations of truck and trailer can rocket up an 8% grade at 65 MPH but that doesn't mean it's a good idea. The longer or steeper the grade, the more likely that the engine or transmission will start to heat up, and you'll see that on the temperature gauge.

If this happens you'll need to slow down even more, get to the rightmost lane, and be prepared to come to a complete stop in the breakdown lane and wait until everything cools down again. Once an engine or transmission gets hot, it takes quite a while to cool down—easily 15 minutes or more before you can resume driving. 

It's far better to avoid letting things get hot in the first place, by setting a reasonable pace while climbing. Keep in mind that a "reasonable" pace is always going to be slower than the cars you see zooming past you. Don't compare your rig to other traffic. Your truck is hauling anywhere from 10,000 to 14,000 pounds (counting truck, trailer, and cargo) up the hill and it's a big effort.

Even if your truck can do a steep grade at highway speed, there's another reason to slow down. Once the commercial truck traffic starts to slow down and cluster in the right lane there's often a scramble among other drivers to get away from them. That means lots of cars changing lanes, sudden slow-downs, and occasionally a few "stupid driver tricks."

Your tow combination is not as nimble, so you'll want to have plenty of room for braking and never put yourself in a situation where you need to do a rapid lane change to avoid crunching a slow truck in front of you.

Keep an eye on the temperature gauges

Watch the temperature gauge as you climb. If it starts moving even a little bit out of the normal range, slow down as much as needed until the temperature starts to decline again.

If you are forced to make a short stop for cooling, you'll probably find that even after the temperature gauge returns to normal the engine is prone to overheating again much more quickly on the same hill climb. This is because the engine block is still hot. The temperature gauge tells you only that the coolant has returned to normal. You should go even more slowly than before, or you'll be stopping again soon.

Many tow vehicles don't have separate transmission temperature gauges, so you won't know the transmission is overheating until a warning light comes on. This is another good reason to keep your climbing speed moderate.

Overheating the transmission fluid greatly shortens its life, so it's a common practice to do transmission fluid changes more frequently on vehicles that are used for towing. Your vehicle owners manual will have details.

Chill out

It's pretty common advice to turn off the air conditioning, and even put on the heat, when you are climbing a steep grade. Turning off the air conditioning definitely can help. But it's not highly practical advice when you're climbing I-17 north of Phoenix and the outside temperature is already 106°.

You can try turning off the air conditioning for a few minutes until the car interior becomes unbearable, then cycling it back on as needed, but this is extra workload for the driver at a time when you probably are already feeling stressed.

Instead of drastic measures, try patience. Get in the right lane with the big 18-wheelers that are slowly grinding their way up the hill, put on your flashers, and enjoy the scenery. You might end up climbing a 10% grade at 25 MPH but it's still probably quicker overall than having to stop halfway to cool the engine for 15 minutes.

DOWNHILL

Going downhill on a steep grade is mostly a challenge because of the brakes. The rig will naturally want to gain speed and you'll need to keep it down, but if you use the brakes too much they'll overheat (and stop working).

The photo above shows one of the worst-case scenarios: a long, curving, 12% downhill grade that ends at a stop sign—partially in fog. (Add in some rain or snow and it would be a nightmare.) But I got down it without incident using a simple 3-point strategy:

1. Find your safe speed

Obviously you don't want to go too fast. Your max speed in a situation like this should be something less than the posted speed limit. Find a speed that you feel comfortable going, even through curves, and make a note of that.

Then, pick a slower speed that's reasonable for the traffic situation. It should be at least 10-15 MPH less than your max speed.  

For example, there's a stretch of highway in Arizona I often travel that has a 2 mile downhill grade at 6-8%, and there are a couple of sweeping curves in it. The speed limit is 65 MPH, but when towing I'm only OK going about 55 MPH maximum, and I'll go as slow as 40-45 MPH, in the right lane. 

2. Use the brakes only as needed

Riding the brakes as you go downhill is a nearly-guaranteed way to overheat the brakes. Never do this when towing.

Instead use the brakes periodically. When the rig gets up to your max speed, apply the brakes and slow down to your minimum speed. For me, that meant letting speed build up to 55, then braking firmly to get back down to 40.

Then you can coast and let the brakes cool, until the speed climbs back up to your max. Repeat braking down to the minimum as often as needed. 

If you find the rig is reaching your max speed too quickly, revise both your max and minimum speeds downward. On the 12% grade I was often cycling between 25 and 35 MPH. It took only a few seconds on that steep hill, so I revised my speeds to 20/30 MPH, and felt much more comfortable.

3. Be careful braking in curves

Depending on how your brake controller is adjusted, you may notice a significant lag between the time you apply the brakes on the truck and when the trailer brakes engage. 

On a straight downhill road this is less noticeable, but in a curve you may experience a very disconcerting off-center "push" from the trailer for a split-second. This can be alarming, or even enough to push the truck out of control.

To avoid this, try to do most of your braking on the straightaways. If that's not possible, lower your target speeds and try to apply the brakes slowly. Applying the brakes more slowly gives the trailer brakes a chance to "catch up" with the truck brakes so you don't get that scary feeling of being shoved around by the trailer.

If it's still a problem, you should revisit the brake controller settings. It may be that you need to increase the "boost" or "gain" setting. Check the owners manual for your brake controller for specific advice.

Use the tow mode for engine braking

As numerous commenters point out below, in the first version of this blog I didn't mention "engine braking"—which simply means putting the truck in a lower gear and letting the drag of the engine do some of the work of slowing down the rig.

This is an important and useful strategy. Most tow vehicles will have a "tow mode" and it may automatically downshift the transmission when the computer senses you need it. If not, you can always manually set the transmission in to a lower gear. 

When you use this technique, keep in mind that the engine will rev up quite a lot. It can be disconcerting if you're not used to it: loud and a little intimidating as the tachometer climbs toward the red line. But it's OK.

On most steep downhills you'll find that engine braking isn't enough by itself. You'll still need to use the brakes. Running in a low gear helps slow the rig, which means you're less likely to overheat the brakes on a long grade.

Even with the best strategy you might find your trailer brakes overheating. This happened to me once in Yosemite. If you see any smoke coming from the brakes, or are just suspicious because you've been on a long grade, pull over safely and do a quick inspection.

If you can smell the brakes from a few feet away, it's time to stop for a while. Take a walk, have lunch in the rest area, or some other form of long break, and let everything cool down. You'll still get where you're going—safely!

16 comments

steve benson

steve benson

Thanks great help looking forward to trip out west any advice is wonderful even for people experienced

David J

David J

I’m surprised that you did not mention downshifting then going downhill. By manually selecting 3rd or 2nd gear, you can use your engine for braking and avoid overheating your brakes. Of course, this means that the trailer brakes are not engaged. So, downshifting is generally safer on 3-6% downhill grades.

Bill Yanke

Bill Yanke

Rich;
For what it is worth my 2019 F150 Lariat has a tow mode that allows me to set a speed using cruise control that then automatically does a combination of downshifting and braking to keep me at the desired speed. Most trucks also allow for downshifting manually. What role does that play and to what extent does it promote transmission overheating as opposed to overheating the brakes. Great topic. Thanks for posting your blog.
Bill

Randy Godfrey

Randy Godfrey

You didn’t mention downshifting the transmission to take advantage of engine braking on the way downhill. I have descended grades where I had to be in 1st gear to maintain the 20/30 (actually 10/20) mph decent speed.

Jim MacDonald

Jim MacDonald

Great article! I thought I was an experienced and cautious Airstreamer and “knew it all” until I dropped down Teton Pass into Jackson Hole Wyoming this summer. I started down at 40-45 mph, as my max speed, pulsed braked as you recommended, and halfway down smelled hot brakes, and then they began to fade out! First time this ever happened to me. After pulling over and letting things cool down, I dropped my max speed to 25 mph with the four-way flashers on and finished the descent. Lesson learned.

Jeffery Hammonds

Jeffery Hammonds

Rich, as to going downhill, what about downshifting so as to let the engine compression keep the RPMs lower, and thus to slower?

Hervey

Hervey

Thanks for the article.
Great advise but once you see smoke coming from trailer brakes the damage is done. You just glazed the shoes and pretty much need a brake shoe and drum inspection asap.

Bill Smith

Bill Smith

If your tow vehicle (truck) has an “engine brake” it helps a lot (especially if towing something like a Classic @ 33 feet).

Bill Smith

Bill Smith

A “load leveling and anti tail wagging” hitch like the Hensley make both uphill & downhill less “white knuckle driving.

David Hueter

David Hueter

?Engine braking?

Jiminy Cricket

Jiminy Cricket

Also worth mentioning is the use of engine braking to moderate downhill braking. Most trucks have it or downshifting can be manually introduced.

Dan & Sherri Johnson

Dan & Sherri Johnson

What about using lower gears for going downhill?

Monique

Monique

What a great post. So much thoughtful advice. It’s good to know that you have navigated through these hurdles (and lived to tell) and are generous enough to pass on your knowledge to fellow Airstreamers. I really appreciate it.

sid T

sid T

Going down hill You might want to use a lower gear so you can maintain your safe speed longer and in return less brake heat. Todays engines will handle up to 4500 or a little more RPM for an extended time.

Gary S Griffin

Gary S Griffin

You never mention using the transmission. My 2020 GMC Sierra (6.6 gas motor) has the GM automatic transmission with tow/haul mode. When in tow/haul mode while braking braking, the transmission will downshift and holds that lower gear until the driver applies the accelerator causing the transmission to upshift. It’s a sweet set-up. The transmission and engine will hold your speed on steep grades with light braking assist.

Rich Luhr

Rich Luhr

To all of you who pointed out that I didn’t mention engine braking: thanks for pointing that out. I’ve revised the blog to cover that topic.

Bill Yanke: Your suspicions about transmission wear and heat have merit. Using the transmission to slow the truck is just shifting the heat energy that would have been generated at the wheel brakes, to the engine and transmission. There ain’t no such thing as a free lunch. But those components are designed for such loads (occasionally) and it should be OK.

Bill Smith: I also tow with a Hensley hitch. The nudging sensation when braking on curves that I described will occur even with a Hensley. It is caused by brake lag, not any part of the hitch setup. Although the Hensley completely eliminates sway, it will still articulate a little on a downhill if the truck brakes are more aggressive than the trailer brakes, and that can cause a very startling “Hensley bump”.

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