Getting your rig safely to the bottom of that long grade

12

By Russ and Tiña De Maris

Old trucker’s maxim: “You can go down the hill too slow many times. You can go down the hill too fast only once.”

Getting the RV down a steep grade safely is an art, one that all of us need to perfect. If you’ve hit the bottom of a long, steep grade and seen an RV beside the road, smoke pouring out from the wheels, you may have muttered something about the “Grace of God.” So just how do you make the grade on the downhill side?

A quick review of physics will help. Brakes work by causing friction (between the brake pads and the rotors or drums) to create heat. That brake action converts kinetic energy (movement) into heat energy. How much heat is produced is a factor of how heavy your rig is and how much speed you want to scrub off with your brakes.

Here’s the rub: If you convert too much kinetic energy into heat energy too fast, you’ll encounter brake fade. There are actually two causes of brake fade – one is when the brake linings reach such a high point that gas builds up between the brake lining and the rotor or drum. The brakes “feel” like they ought to be working, but the ability to scrub off speed is reduced. The other cause of brake fade, again heat related, is when the brake fluid in the system reaches such a high point that the fluid begins to boil, causing a loss of pressure between the brake pad and the drum or rotor. In this case, the brakes will feel “spongy,” and typically your heart feels a bit heavy in your chest.

To keep your rig under control, how you shake off heat from your brakes can make a big difference between making a slow, controlled descent, or one that could be your last. Back when we were kids in driver education (a few ages ago) we were taught, “When you go downhill, step on the brakes lightly, and keep the pressure on until you get to the bottom of the hill.” This is the so-called “controlled braking” method. The theory behind controlled braking is that brake heat is never built up suddenly, but in a gradual fashion.

Photo: Percita on flickr.com

Here’s the problem with controlled braking. Heat does indeed build up and, yes, perhaps gradually. But on a long grade, the brake materials are constantly producing heat, and never allowed an opportunity to cool down. What can result is damage to the brake system and, ultimately, failure. And if one brake in the system isn’t doing its fair share of the work, the rest of the brakes in the system have to take up the slack, adding even more heat to the mix.

For tractor/trailer combinations, this is an even more critical issue, as the physical design of the system uses a network of valves that use air to actuate the brakes. If the valves are not all set to the same pressure point to actuate, this imbalance may cause some brakes to operate while using a light application of the brake pedal, while other brakes aren’t operating.

There is an alternative to controlled braking, which is “snub braking.” When hitting a downgrade, the snub braking method calls for you to gear down appropriately, use an engine brake (if equipped), and have in mind the maximum safe speed for the grade. When that speed is reached, apply the brakes hard, and drop the speed by five miles per hour. Now let off the brakes and coast, keeping an eye on the speedometer. When the maximum safe speed is hit, repeat the process.

The theory behind snub braking is that while the same amount of heat energy needs to be created to slow down the same amount of weight, the time between “snubs” allows the brake system to cool down, thus alleviating the chances of brake fade. For truck drivers, snub braking, by its “hard on the pedal” nature, will force all the valves in the system to open, making it far more likely that all brakes on the rig do their fair share of braking. Depending on their brake controller, RVers who tow may find their trailer brakes actuate more in tune with the tow vehicle with a snub brake – again, creating a better share-the-load situation.

Snub braking doesn’t make up for bad maintenance or “pilot error.” The boiling point of brake fluid is reduced when it contains contaminants. Brake fluid has a great affinity for absorbing water, and water in brake fluid is a combination that can spell disaster. For that reason, don’t keep the cap off the brake fluid (or the vehicle’s fluid reservoir) any longer than necessary when servicing brakes. Even if you’re careful, though, moisture will just naturally find a way to worm its way into your brake fluid.

Follow the recommended fluid change interval based on your owner manual, and know that if you live in a humid climate, changing the fluid sooner, rather than later, is best. For less than $10, you can get a brake fluid tester (here’s one from Amazon): just dip it in your rig’s brake fluid and the indicator lights will tell you where you stand.

Ensuring that your brake pads and drums or rotors are up to snuff is critical. For those who tow a trailer, this means a regular maintenance routine. If your trailer axles are equipped with an “easy lube” system, forgo the “easiness.” Jack the rig up, pull off the wheels, and inspect the brakes. Make sure your brake controller is properly tuned – both the tow vehicle and the trailer should share the load. Drag out the owner manual and educate yourself on how to properly adjust the system. Manual vanish? Google-search it: You’ll likely find the instructions on the web.

And as to pilot error: That old trucker’s maxim applies to RVers of any stripe, be they motorhomers or dyed-in-the-wool fifth-wheelers. You can’t go down a steep grade too slowly. Keep in the slow lane, drop down the gears, and use common sense. The faster you drive, the more heat you’ve got to scrub off to slow the rig down to a comfortable zone. If you use the snub system and find you’re having to snub your brakes every few seconds, you’re going too fast. Drop a gear, drop the speed, and get to the bottom with a smile on your face.

##RVT906;/##BG56

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Roger
6 months ago

As I recall, ABS systems have tiny orifices that can be clogged by the rust formed by water in brake fluid. For that reason, I flush ours every 2-3 years.

David Kendall
6 months ago

This article describes why it’s scary for an unknowledgable and inexperienced driver to drive an RV. This should be included in all training. Tow/haul is not terrible but I’m far more secure doing manual mode when I want. We take terms such as RPMs as common sense. Spouse says, “what’s common sense to you isn’t common sense to everyone. “

Joe Allen
6 months ago

I always look for the sign on the ascent or descent grade and shift appropriately for the event! Rule of thumb, what ever gear you climb a hill, use the same gear in the descent! We have a retarder in our coach and you need to watch your transmission temps, your RPM’s and your puck factor!

Alvin
1 year ago

Strange this article didn’t mention the Tow-Haul, feature, installed on pretty much all RV’s today going back many years. It’s a life saver if there ever was one installed on an RV. Use it, learn how and when to use it. Read your manual its all in there. Your downhill problems are pretty much a thing of the past.

Graybyrd
1 year ago

Good points, all. Would like to add: trucker advice is to descend the grade one gear lower than it takes to climb the grade. If in doubt, start down the grade in a lower gear than you might think appropriate. If it proves too slow, it’s easy to upshift. Unless you’re a double-clutching expert, it’s not so easy to downshift to a lower gear. BUT, if necessary, stand on the brakes and slow down enough to get into a lower gear. Don’t wait until it’s all but hopeless! Slow down and get control while you still can!

As for curves, slow down before the curve; give yourself an extra margin of safety by “snubbing” your speed down before entering the curve, then let the rig roll through at a safe speed. Avoid braking during the curve; it tends to worsen the cornering effects.

Be aware of how your rig (whether auto or manual shift) handles a long grade, and be ready to cope. Also, study the signs at the top of the pass: will it be a 5%, or a 6% grade? How will your rig brake and hold back going down a 6% grade? Some roads in the west have 7% and 8% grades. A few (I’ve encountered them in Wyoming and Colorado) have 10% grades!

For those with internet access, it’s a good idea to research a particular state route to see what comments apply. For instance, State Route 9 in Colorado goes over Hoosier Pass at 11,500-ft elevation, with 10% grades!

Sadly, all this is “preaching to the choir”… wise drivers will be prepared; a few will heedlessly go on to sing with the choir.

Alvin
1 year ago
Reply to  Graybyrd

Tow-Haul – that’s all.

Gordy
1 month ago
Reply to  Graybyrd

I drove semi for almost 35 years and I agree with what you said, but I would like to add too it. If you have never been down the grade, it is harder to start out too slow than to start out too fast. The higher the percent for the grade, the lower the starting speed also watch the distance of the grade. Do not let the passing traffic determine your speed, you do not know their weight or stopping capabilities as compared to yours.Above all do not let your speed get out of your comfort zone. Also, when you travel, READ THE ROAD SIGNS at all times. Make it a habit that you do to the point you do it all the time, weather on grades or on the flat land. It could save your life! Safe travels to all!!

Montgomery D Bonner
1 year ago

In cdl class, the rule is never go down any faster than you went up, but I try to keep it at 40-50, engine brake on, and in 4th gear. If two speed engine brake, you can shift from low to high and back, and almost never touch the brakes, if you start out slow enough. You can over rev a diesel engine using the engine brake, so never let MPH or RPMs get over 2100 or about 51 mph.

Mark
1 year ago

It’s a shame that most people don’t know about how fast a 36′ motorhome towing a heavy van that’s full cannot go down a steep grade as fast as a car. I drove big rigs for 18 years….I know how to get our rig to the bottom without issues. I will always remember going down a very long grade in Colorado that unfortunately had only one lane and no passing lanes with lots of corners. When I finally reached the bottom, having to hold my speed at 30mph tops, I had a line of cars that was ridiculous behind me. I can’t count the number of drivers who were finally able to pass me at the bottom that flipped me off!!

Wolfe
1 year ago
Reply to  Mark

Having just rolled my 35′ TT through the backroad hills of the Allegheny in PA, this is quite fresh in my mind… And yes, I ABSOLUTELY endorse engine and snub braking over flaming wheels.

As for impatient people flipping off slow trailers, I really don’t care as long as we’re all alive to see it at the bottom. “I’m not responsible for their ignorance, only for not copying it.”

Tommy Molnar
1 year ago
Reply to  Mark

Mark, they were just telling you you’re #1.

Jeff
1 year ago

Just a word of advice for those people who still drive Manual Transmissions! NEVER Downshift while going down a hill or steep grade! You should set your downhill gear at the top of the grade before starting down and leave it there! Try to downshift while descending is a recipe for disaster, you will not be able to get your transmission back in gear!

And SNUB or STAB Braking is the preferred method to descend any grade! Controlling your RIG will prevent that “WHITE KNUCKLE” Adventure down the Hill!