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Understanding and Driving Mountain Grades
If you’ve driven for long, at some time or another you’ve come to a sign that said something like, “7% Grade next 5 miles, Trucks Use Low Gears” You probably know that means there is a hill coming up, but you didn’t really understand exactly what it meant, how it will affect you or how it compares to other grades. In this post, I want to explain all that.
What is a “Grade,” and what do the percentages mean?
Grades are measured in units of 100 feet. If you drive 100 feet and you climb or descend 6 feet in that distance, then that grade is 6%. If you travel 100 feet, and you climb or descend 10 feet, that’s a grade of 10%. Because very few of us think in terms of 100 feet at a time, a more practical way for Americans to think is in miles. A mile is 5,280 feet, so if you drive 1 mile, and climb or descend 528 feet in that mile, it’s a 10% grade. If you climb or descend 370 feet, that’s a 7% grade, or if you climb or descend 264 feet that’s a 5% grade. Carried to it’s extreme, a 30% grade means you go up or down almost 1600 feet in a mile.
I took this graphic from the Mountain Directory West and it explains that a 10% grade means that you climb or descend 10 feet for every 100 feet of travel.
On a long straight stretch of hill, you can just put it in a lower gear and let the engine do much of the work of getting you up or down the hill. But if the hill is full of sharp curves, then you have to slow down to go around the curves. By doing that, you lose much of the momentum you had going into an uphill climb, or it forces you to slow down much more than the engine wants to in a steep downhill. For example, my van can climb 6% grade comfortably at 40-50 mph. But if I slow down to 25 mph for a curve, I can’t accelerate much beyond that unless I come to a level spot where I can accelerate, that means I’m going to climb the rest of the hill at 25 mph. Going downhill on a straight 7% grade, if I put it in third gear I can maintain 45-55 mph with a little use of the brakes. But if that same hill has 25 mph curves, I’m going to be using my brakes very hard to go that slow even in second gear.
This part of the Snowy Range Scenic Byway wasn’t all that steep, maybe 7%, but the sharp curves like this one constantly forced you to be on the brakes to go down them, or to step off the gas to go up them. Once you slow down to go around this curve, many vehicles can’t regain the lost speed.
It’s nice to understand what the numbers mean and the math behind them, but what’s important is that we apply that knowledge to our lives and make it useful. Because all of our vehicles are different, they’re going to mean something different to each of us. For example, if you have a high-powered sports car, none of the grades will mean anything to you because you have so much power you can just fly up and down all those hills. On the other hand, you might have a 1973 Dodge Class C with a 318 V8 towing a Jeep and you will just barely be able to make it to the top of some of the bad hills. And if you do, it will be at 15 or 20 mph and your engine will be screaming the whole time. In fact, on the steepest of them, you may simply not be able to drive up them at all, you’ll need to find a different route.
Most of us fall between those two extremes, we are either living in a van or RV and while they can climb and descend most of hills we come to, the question is how difficult, or even dangerous, will that be? To find out, you need to start studying the hills you climb and even taking notes. I suggest getting a notebook or using your phone and have a page called “Hills”. For each hill you drive, write down the location and description of the hill including its grade and its curviness. After you’ve gone up or down it, take notes on how difficult it was:
- Did the engine temperature rise, did it start to get hot? Even worse, did it steam?
- What gear did you use going up and down?
- What speed were you able to maintain?
- On a scale of 1-10 how much did the engine seem to be struggling?
- Did the brakes start to fade or need extra pressure? Did they get hot or did you smell them burning?
Over a period of time you’ll start to see a pattern and you’ll know how capable your vehicle is for each grade of hill and also learn what speed and gear works best for your vehicle. You can use that to decide which hills you are willing to climb or descend and which you need to find an alternate route.
It should gain you more confidence and extend the life of your vehicle.
Tips for Driving Uphill:
- Hit the bottom of the hill with as much speed as you can and let momentum carry you as far as it can. Sometimes this just isn’t an option but sometimes it is. Take advantage whenever you can.
- Keep your vehicle as light as possible–extra weight just makes the engine work harder going up and the brakes work harder on the way down. Since we are living in our vehicles, everything we own in the world is in them and they are going to be much heavier than the average vehicle. This alone is a very good reason to adopt a minimalist attitude toward your possessions.
- Carry as little gas and water as possible. Sometimes you have no choice but have full tanks, but as much as possible have all your tanks as low as you can. 50 gallons of water and 20 extra gallons of gas in the tank is an unnecessary 560 pounds. Give serious thought if you can climb the hill without it.
- Turn off the air conditioner. The air conditioner in your car draws power away from the wheels and creates extra heat under the hood. Roll down your windows and be hot if you must.
- Plan your schedule around the hills. With some really bad hills that you can’t avoid, you might give thought to climbing them earlier or later in the day when there’s less traffic and its cooler. That way the engine will have an easier time and here will be less traffic to back up behind you. On a really bad hill, you might even give thought do driving it at night.
- Add a transmission oil cooler to your vehicle. Heat is what kills automatic transmissions and the cost of the oil cooler will pay for itself many times over with longer life for your transmission. This is especially true if you are towing a trailer! I recommend U-Haul service centers. They put one on my van and did an exceptional job at a great price.
- Take the transmission out of overdrive and downshift as needed. You want to use the lowest gears possible that will let you maintain the most speed you can. You’ll need to study your vehicle to learn what works best for it, but my van will climb a 5-6% grade in third gear at about 50 mph, and a 7% grade at 35-40 mph in second. It will barely climb a 10% grade in second gear and anything steeper I’ll be in first gear. I never climb any hill in overdrive.
- Pull over and let the engine cool down and give yourself a break. However, some hills are so steep you won’t be able to accelerate up the hill from a dead stop. In those cases just crawl up them as fast as you can without stopping.
A 26% grade means you climb or drop 1372 feet every mile, or 6864 feet in 5 miles. That’s steep!
- What do you do if your engine starts to overheat or if it starts to give off steam, I’ve got to be honest with you and say I found a lot of webpages that gave opposite advice of each other. Many said find a safe place to pull off the road, park it and turn the engine off. Others said not to shut off the engine, but to step on the gas instead and bring it up to a high idle. Since the experts can’t agree, I don’t know what to tell you.
- However, all the experts agreed that you should never remove a hot radiator cap! Steam and very hot water will come shooting out and you could be severely burned.
- A faster way to cool an engine is to turn on the heater. If it’s a hot day you’ll just have to endure it, or pull over, get out and leave the doors open while the heater is on.
- If you have extra water, you can pour some cool water over the radiator to cool it faster.
Tips for Driving Downhill:
- Use a lower gear. People behind you may be pissed off, but you have to stay safe!! Big, heavy vehicles must be careful with their brakes on extended down-grades or you can burn them to the point of total failure and you’ll become a missile flying wildly down the hill endangering you and everyone around you. Newer vehicles have much better brakes than older ones, but the majority of us have older brakes so you’re just going to have to make some people angry. Near Steamboat Springs, CO is a 7% downgrade that lasts for 7 miles. I went down it in third gear at 35-45 mph. I had a line of cars behind me but my brakes were in great shape at the bottom
- Don’t ride the brakes! By riding the brakes I mean having your foot on it the whole way down the hill applying a small amount of pressure constantly. Instead, you want to let the van start to speed up and when it’s going as fast as you can allow because of the speed limit or curves, step on the brake hard to slow down slower than you would ideally like. Then get off the brake entirely and let it accelerate. It may seem like you are not off the brakes enough for them to cool down significantly, but you are. I’ve counted the seconds (one thousand one, one thousand two, etc…) for the amount of time I’m off the brake and the amount of time I’m on, and it’s usually a 3 to 1 ratio. If I’m on the brake for 5 second, to slow it down from 50 to 35 mph, it’ll take 15 seconds for it to accelerate back up to 50 mph where I’ll get on the brake again. That’s enough time for your brakes to cool off and it will get you down the hill safely.
- If your brakes appear to be getting hot or fading, pull over and let them cool off. Our lives and the lives of those on the road around us are worth much, much more than those few minutes it costs out of our busy lives. Just as importantly, it’ll be a great opportunity of practicing Zen and training yourself to actually enjoy your life instead of rushing through it as quickly as you can without thought of enjoying it.
So there you have it, some common sense ideas about climbing and descending steep hills. Now go out there and enjoy the beautiful mountain views to their fullest!
Bob,
Nice post. Good info.
Thanks
You’re welcome David!
Bob
Taking on a hill with momentum, you sound like an old VW bus driver!
I appreciate the percent grade explanation & your remark about stuff. Stuff weights & weight costs, silly to spend money to carry things you don’t use.
On the weight subject, most of the Oregon weigh stations leave the scale on when they are closed. You can drive your rig on and see what you weigh, helps guess why it was so hard getting over that pass heading east from Yosemite NP!
Good to know about the Oregon scales, Rob, free is good!
There are some monster hills going over the Sierras! It’s almost like they are gates to keep the rest of u out, and Californians in!
Bob
I had an experience with a 21% grade on a dirt road with a 2002 GMC Sonoma, two wheel drive, 5 speed, pickup. It was a nice, dry day. At the bottom of the hill is a State fishing access site for the river and a maintained boat launch. I figured if trucks towing boats could make it up the hill, them my truck empty should be fine.
Long story short, I ripped up both engine mounts and the transmission mount. The manual transmission forced me to rev the engine so the truck wouldn’t die, but that meant the wheels spun terribly and bounced the whole way up. If I had an automatic, I could have creeped up the hill and not torn the rubber mounts.
I don’t know how steep of a dirt road a two wheel drive truck can take, but it is much less than 21% grade.
That’s good information Canine, thanks!
Bob
Timely post, I was recently wondering how to do this kind of driving with an auto transmission. Up until very recently, my vehicles have been standard, so I’m used to shifting gears that way.
How would one use lower gears the way Bob describes on the uphills and downhills with an auto trans? Would you start from a stop on D then shift down? I tried it a few times on some mountain trips but haven’t got the hang of it yet.
Thanks in advance for the tips!
Ming, you just move the automatic shift lever into the gear you want. All that does is keep it from shifting above it.So if you put it in 1st gear, it can’t shift out of 1st. That’s mainly important going downhill when the auto wants to be in top gear so you put it in a lower gear to get compression braking. But in some situations it can help going uphill because the engine shifts up and down hunting to find a gear. Better to keep it in the lower gar the and match your speed to the gear.
Some newer auto transmissions work very much like a manual but there is no clutch. I’ve never driven one so I can’t help with them.
Bob
Hi Bob, thanks for the reply. You say that putting it in a certain gear keeps it from shifting to a higher gear above it, but does it keep it from shifting to a lower gear if needed? If I have it in 2 to use the engine braking, does it keep it from shifting down to 1 if I have to slow down for a hairpin turn?
I ran into this issue on a trip up and down a mountain this summer. I was coming down and 2 had it going too fast, and 1 had it coming down too slow. Then when I had to brake for the hairpin turns, that would have been way too slow for 2. In the end I left it in auto and used the brakes intermittently so as not to overheat them – a tip from your blog!
Ming, the engine won’t downshift for compression braking, it doesn’t know anything about that. The only time it will step down from 2 to 1 is if you step on the gas and 2 is too fast it will step down to 1.
That’s why you have to force it down by downshifting. You’ve found the problem with most older vehicles, too long a gap between gears, especially the V8s. That’s why most newer cars are coming with 6-8 speed transmissions, so you can find a gear where it has power. Most of the big increases in MPG are coming from the transmission.
Bob
Thanks Bob, I’ll keep practicing. It’s good to know that it will shift between 1 and 2 if I press on the gas and it’s set on 2. I do sort of try to control the gears on the way up by keeping an eye on the tach, and keeping the revs on the high side with the gas pedal for increased power going uphill.
Yes, more gears would help a lot!
Where is that 26% grade hill?! We’ve gone down a lot of hills but haven’t seen any that steep!
Karen, I just took it off the net with a google search, so I don’t know where it is. The steepest I’ve run across in person is 10% but I know there are steeper ones in the country somewhere.
Bob
A side note Bob, I ordered that led light you recommended & mounted to the ceiling today. Wow! A lot of light!
Good, I’m glad it’s working for you Rob!
Bob
Hey Bob this is a very good piece of info for folks. Don’t forget the hillbilly Jake brake. Turn on the AC and it hold the engine back going downhill. The AC compressor takes a lot to turn it. If it’s cold and you don’t want to run the ac then put it on defrost. This turns the compressor on but does not blow cold air if you have the heat on. The car companies do it so the AC freon does not separate during the winter from the oil in the system.
Also if you heat up going up hill you can turn the heater and fan on high and it’s a auxiliary cooling small radiator.
If you heat up going up hill then when you start down hill turn the AC on because it will also keep you from cooling down too fast and causing problems.
When your brakes are hot and you come to a stop let the vehicle ease forward a few inches so the pads don’t stay on the same place and increase the heat on the rotor or drum, the increase heat in one spot will warp them. Just let it ease forward a few inches while you wait on s light or stop sign or even if you stop just to let them cool before continuing your journey.
Thsnks, Bill n Sadie plus Mic
Those are great tips Bill! thanks!
Bob
Bob,
Great information and explanation of how a grade is calculated, thank you. Where have your travels taken you now? I should be heading toward the southwest sometime in the beginning of October. Currently I’m in California.
Take care,
Omar
Hi Omar, I’m back in Flagstaff, AZ now and we are waiting for the desert to cool off then we will go down to Quartzsite. That’s usually toward the end of October. My next post will be about where I am now.
Bob
Hey Bob.
Where do you recommend a lady and her dog go to live and be safe there in Quartside?
Your information was very helpful.
Hi Fran, a fairly big group of us meet in a little town called Ehrenberg, which is about 17 miles west of Quartzsite for the winter and there are anywhere from 15-25 of us there, about equal number of men and women, but I have seen it be more women than men a few times–and of all ages.
It would be perfect for you. We are all like you, we want to be social but we need our space. It’s a BIG desert, you can be as close or far away as you want, but you can know there are always people around if you need them.
It doesn’t usually cool off enough there until the end of October, so that’s when people will start getting there. My girlfriend and I will be there around November 1.
Hope that helps!
Bob
Hi Bob,
That sounds good. I’ll look forward to your post. I may see you before you get to Quartzsite.
Take care,
Omar
As a civil draftsman by trade its difficult to convert a % slope to a degree angle if you don’t do it often.
Many of us have a easier time visualizing a angel rather than a slope. Most people know what 90 deg. Looks like and most people know what 45 deg. Looks like.
So to convert a % slope to a degree angle….
1. First convert % slope to degree slope:
26% divided by 100 (26/100) = .26
2. (Need a scientific calculator for this part)
Invert tangent of .26 = 14.57422 deg.
So 26% slope is 14.6 degrees
Or just use online conversion programs .
Thanks for that info hotrod!
Bob
Something I leaned from a retired OEM engineer that I never thought about before.
A lot of grades have pull outs at the top. I used to stop at big grades to give engine and trans a rest.
Don’t stop at the top. Your trans temps will appreciate the air from faster speeds when you get back on the level and up to regular driving speed.
Very good point pat, much better to rest the vehicle on the way up or down the hill rather than at the top or bottom.
Bob
Here on Maui we have a nice drive up to Haleakala summit, sea level to 10,000 ft in 38.5 miles Average grade is 5% but there are sections of 10% grade. I drove tours in Ford vans on this road and learned early on to go slow, use 1st gear and not ride the brakes. I’m likin’ this whole series of posts Bob.
Practice makes perfect jonthebru!
Bob
Thank u bob, I have been reading u for awhile trying to talk my husband into ditching the house and running away. Well I haven’t talked him into it yet but this week while driving down to Florida I got to drive down my first mountain. Granted it was in a car that is so new it does anything but drive itself and it was a wussy of a mountian but I remembered this article and remembered what u said about braking and got down with no problems, my brother in-law was driving a u-haul type truck he almost had to use the runaway truck lanes because he didn’t know to down shift it, and he had to stand on the brake. Thank you
Terre, I sure hope you can work out a compromise so you you both can be happy, that’s the goal of a marriage! Glad to give you some tips on driving those mountain roads, they can be dangerous.
Bob