If there is one time I white-knuckle my steering wheel more than others it is mountain driving. I am in no way anywhere close to being an expert on how to drive an RV in the mountains, but I feel like I have learned a couple of things along the way and I want to share those in this post.
Know Your Weights
Safely driving an RV in the Mountains starts with knowing how much your rig should weigh and how much it actually weighs.
GVWR and GCWR
I don’t want to get too technical with the weights, but you need to at least know GVWR and GCWR. GVWR is the Gross Vehicle Weight Rating of the vehicle or trailer itself. If you are driving a motorhome, it’s the motorhome. If you are pulling a fifth wheel, it’s the fifth wheel.
GCWR is the Gross Combined Weight Rating of your primary RV and any vehicles attached to it. If you are pulling a fifth wheel it is the truck and the fifth wheel. If you are driving a motorhome, it is the motorhome and the towed car you are pulling.
Manufacturers tell you the maximum GVWR and GCWR on a sticker in or around the RV. On a motorhome, it is typically (1) on the wall next to the captain’s chair or (2) on a cabinet door in the kitchen area. On a travel trailer or fifth wheel, it is often toward the front driver’s side of the outside of the RV.
Here’s an example of a weight rating sticker
At the top left of the white sticker is our GVWR of 26,000 lbs. Everything in our RV from the steering wheel, to the driver, to the water in the fresh water tank should not weigh more than that.
The GCWR of our RV is 30,000 lbs. I know this because I know our RV can tow 4,000 lbs. The weight of our motorhome and the vehicle behind it should not go above 30,000 lbs if we want to stay within specs.
If you are pulling a trailer or 5th wheel, you will also need to find out the specs for your tow vehicle. I’ve found this to be a bit more difficult than the RV. Sometimes it is in the manual, sometimes I need to look online. Like the RV, the specs you are looking for are GVWR and GCWR.
To match up the weight you should be with the weight you actually weigh, you will need to make a trip to a scale. The times I have weighed I have used CAT scales. They are all across the US and take just a few minutes to use.
With a Motorhome and Towed Vehicle
Pull on to the scale, making sure the front axle of the motorhome is on the part of the scale next to the check-in button, the back axle(s) are on a separate scale, and the towed vehicle is on a third scale. Push the button to let the attendant know you are on the scale. Once they answer, they will ask if it is the first weigh in or second weigh in. I let them know it is a first weigh in and then tell them you are weighing an RV (they would otherwise expect a truck number). Pull out of the way and walk in to pay at the register for the weigh in. The weigh in is about $10.
With a Fifth Wheel or Travel Trailer
You will want to weigh with your tow vehicle and fifth wheel/trailer first, drop your fifth wheel/trailer, and then come back for your second weigh in with just the tow vehicle. The difference in weight will give you the GVWR of your fifth wheel/trailer. The first weigh is around $10 and the second weigh is around $2. Well worth the money.
Use Your Engine Brakes
If you only rely on your brake pads for braking, you will greatly reduce the life of your brakes as well as put yourself in danger if you are on one of those forever mile long 6% or more downhill grades.
Using your engine brakes can be done one of two ways: manually or using Tow/Haul Mode
Manually Using Engine Brakes
When I manually use my engine brakes, I slow down to 40 to 45ish before going down the mountain. I move from automatic down to 3rd gear or 2nd gear depending on how steep of a grade you are about to go down. If it is a 4 or 5% grade for a mile or two, 3rd gear has worked for me. If it is a 6% or more grade a mile or longer, 2nd gear has been even better.
The key is to let the engine do the work. You will see your RPMs shoot up while the engine is doing the braking, but that’s ok. That is what is supposed to happen. On our 26k gas motorhome with a Ford V10, it usually fluctuates between 4000 and 4500 rpms.
Tow/Haul Mode for Engine Braking
If you don’t want to manually downshift, your vehicle likely has a tow/haul mode that can be used as well. You can typically turn on tow/haul mode with a button on the tip of the gearshift.
Once tow/haul mode is on, you will want to slow down at the top of a mountain much like you would if you are manually shifting down. As you press your brakes to slow down and let momentum kick in a bit, you should be able to feel the motorhome downshift and stay in that gear. I would keep braking and downshifting until you are at around 3000 rpms while still flat at the top of the hill and moving at around 45mph. These numbers will vary a bit depending on how steep of a hill you are about to encounter, but it is a good start.
Which to Use?
I’ve manually shifted down and I’ve also used the tow/haul mode. Since I am still getting a feel for what gear is best (3rd or 2nd) on different mountains, I have opted to manually downshift.
The tow/haul mode works, but on one mountain, I thought the RV had automatically downshifted for tow/haul mode enough at the top of the mountain, but it never even got down to 3rd. Tow/haul eventually shifted down to third, but I was already quickly building up speed heading down the mountain which is not what you want. This was likely my fault because I don’t think I braked long enough at the top of the mountain for the RV to automatically downshift.
For now, I don’t want to experiment on how long I need to brake and if/when the RV is going to downshift. I just downshift it myself.
Using Your Brakes When You Drive an RV in the Mountains
You don’t want to use your brakes going down a mountain if at all possible. Let the engine do the work. If you do have to use them, you will want to firmly jab on them for a few seconds to get the speed where you want it rather than lightly push them and riding them to the bottom. Jabbing gives your brakes a rest and keeps them from overheating or giving out which could…well it could be bad to say the least.
I’m not a transmission engineer, but if you are speeding up faster than you would like and your speed is already well over 60 mph, I would have to assume throwing your RV into 3rd or 2nd gear flying down a mountain at 60+mph would not be a good idea. Once you are at the point of 60+, you are probably stuck relying on your tow/haul mode (which you should have on regardless of whether or not you are manually downshifting) and jab braking.
Too Slow, is Better Than Too Fast
Some people recommend going down a mountain in the same gear you went up it in. This is good general advice, but may not work for you if (1) you did not manually choose a gear going up the mountain or (2) the mountain has different grades on each side.
I always try to be aware of when a mountain is coming up on my route the night before so I can visualize what I need to do once I get to that point. You definitely don’t want to be daydreaming of the beach while flying down the interstate and not even see signs for an upcoming downhill portion of a mountain.
I’d much rather be that guy going too slow down a mountain than that guy going too fast.
So far, I’ve only encountered 6-8% grades in the smoky mountains so slowing down to about 40 and then keeping the speed below 50 has worked well. Once we encounter grades above 8%, I may even unhook the towed vehicle and slow it down another step. If you have a lighter motorhome than us (ours is 26k) or if you have a diesel, you may not need quite as much caution, but when it comes to mountains, I don’t think you will ever err on the side of going too slow.