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.
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 about $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.
There is a 3rd, more common, type of brake fade found on drum brakes. The cast iron drum heats up and expands away from the shoes. This is by far the most common and dangerous.
Also, snub braking is not recommended. Intermittent braking is more desirable. The technique is to apply brakes just to a point of definite slow down which assures all the relay valves are opening. Then, release a few seconds (5 mph below your “safe speed” and repeat.
One other important point: when you see a downgrade sign, pay attention to BOTH the percentage AND the length. The percentage is how HARD you have to brake. The length is how LONG you have to brake.
2 more tips… turn on your A/C and headlights to create drag. Both act like engine braking.
Start slowing down as soon as you reach the top of the hill and begin your descent… and start shifting down at least one gear, two if you have to. Stay in the right hand lane and don’t worry about cars passing you on the left….let them go….
Yes, don’t ride the brakes all the way down.. not advisable…if you burn up your brakes and can’t stop you’ll wind up in a horrible accident.
It’s a good idea to have your brakes checked BEFORE you leave on a long trip or at least once per year. Keep a record of what percentage you have left and monitor this carefully. The money you’ll save trying to get the last few miles on your brakes is not worth the risk of failure. If your assessment is less than 20 percent, have your brakes replaced… that’s my opinion
I had a CDL for over 40 years and never heard of stab braking. I was taught to go down a hill in the same gear you went up it in. With experience you begin to know that if the sign says 5% or 6% grade which gear to be in and down shift to that gear at the top of the hill. If you need to slow the rig down ease into the brakes to slow the rig down. On a air brake system the only valve that usually has a delay is the front axle. On a fluid brake system they either have a proportioning valve or the ABS controls the amount of braking front to rear.
Tow haul is not just for braking. It changes the fluid pressures as well as the shift point on the transmission
I grew up in the mountains quite a few years ago, and we sure must have been taught differently in driver’s ed. We were taught NEVER to ride the brakes! I’ve never even heard of controlled braking. We were taught to downshift. What you refer to as snub braking only came after that.
Thank you for this article and all the following comments. The description of snub-braking, gearing and rpm/mph is invaluable for me and many others I imagine. Life and brake saving.
In addition, plan your route wisely. I use my AllStays app, which usually tells me the degree and length of grades I should consider. If we are traveling in the MH, we may avoid roads that we would not be concerned about when driving the car.
AND, if you double your speed, you quadruple (4X) the stopping distance. If you double your weight you quadruple (4X) your stopping distance. If you double your weight and your speed it’s (4X4) 16 times the stopping distance.
Thanks for the important information, Impavid. Have a great day! 😀 –Diane at RVtravel.com
This summer we traveled Route 22 through the Teton Pass to Jackson Hole, WY with a 10% grade for ~3 miles up and ~3 miles down with sharp curves and long drop-offs in our 40′ DP and a 6K Toad. Net/net was doable however SLOW and 2nd gear at most going down is my advice. https://flic.kr/p/2ody2SG
What ever gear you climb a hill in, you should be in that same gear on the down ward grade or less. Long grades can be a real pitfall for RVers and speed is not your friend! On my 6 speed allison transmission, I am usually in 3 gear by the time I am down that hill with my trans retarder a slight tapping of brakes. Drive safe out there!
I slow down near the top of the hill and set my cruise to this new speed. I then ensure that my engine brake is engaged and seldom even touch the brakes on the way down. Let the engine do all the work. That is if you bought enough truck to have an engine brake, IMHO.
SLOW DOWN at the top of the grade. If you start down at the speed you drive on flat land, you will get in trouble. Starting down, always turn cruise control off, slow to 40 mph, downshift and use engine braking if you drive a diesel. Do not ride the brakes! You and your rv will be much happier when you reach the bottom.
You are 100% correct. If you slow down at the top of the hill before starting down, your speed ALL the way down is easier to control.
Very good article, you’ve either experienced or researched for this article. I salute you for this. Unlike many journalists who select a subject and start typing without researching what they are writing about. Thank you.
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.
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. “
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!
I have never seen an ascent grade sign in my 15 years full timing, sure would a help controlling heat and preparing for the downgrade. Just sayin
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.
I personally find Tow-Haul not that miraculous. While it does slow the vehicle somewhat on down grades, it still will pick up speed and requires use of the brakes. I much prefer manual mode of the transmission which allows me to down shift rather than what I consider “over reliance” on the brakes.
Tow/haul isn’t going to get you safely down a mountain grade. You must use the transmission gearing and brakes. Tow/haul changes shift points in the transmission, not the gearing for a steep grade. Go on YouTube to TFL toughest towing pages and see how much tow/haul doesn’t help.
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.
Tow-Haul – that’s all.
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!!
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.
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!!
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.”
Mark, they were just telling you you’re #1.
Don’t worry about getting flipped off driving safely. Those doing it are indicating their IQ level. 🙂
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!