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Steep Descents and Heavy Loads - How to Properly Go Down a Mountain

Updated: Mar 20, 2021

Of all the dangerous things we do as truckers, going down a steep grade with a heavy load can be one of the most hazardous. The lives of everyone on the road are at risk when a rookie driver is heading down a large pass without knowing what they are doing. If a new student driver starts with a company and they get a trainer who only drives in a flat region (like the entire mid-west), there is a good chance that they will never be taught the proper way to drive in the mountains.

So, now the driver gets that 44,000-pound load of beer from Boulder that takes them west on the I-70. Their brakes are already hot from coming down out of the Eisenhower Tunnel, and now they are coming down from Vail. With no proper training, he tries to shift coming down the hill, but forgot to shut off the engine brake. The truck won’t go back into gear. Nothing but the air brakes to slow down the truck. Things can go bad in a hurry.

Mountain Highway with Runaway Truck Ramp Sign

What happens when you do it wrong?

When you are in too high of a gear or out of gear, your brakes soon will begin to get soft and fade. You will notice you have to push harder and harder to get the same amount of stopping response. If you have a brake pressure gauge, you will be able to see that you are applying more pressure each time you brake. Soon after this, you will notice in your side mirrors that there is smoke coming from your trailer tires. The truck is now in danger of catching fire. As the brakes continue to get hotter, the heat will transfer to the drum, then to the rim, then to the tires. If the weather is hot, the tires will already be hot. If you made the double mistake of driving with a tire that is under-inflated, it will be even hotter. Once a tire gets beyond the combustion temperature - up she goes. More importantly, you are in serious danger of losing your ability to brake all together.

An 80,000-pound truck screaming down the side of a mountain is a death machine. You are officially in a runaway truck. There is no control and no hope of a happy ending. The only thing you can do is pray for a runaway truck ramp and no slow cars in front of you. Even if there is a ramp, once you use it, you can kiss your career with that company good-bye.

And remember, it’s not just mountains that can be dangerous. Sometimes a long section of steep rolling hills can cause your brakes to fade. It takes a surprising amount of time to cool off those brakes once they heat up.

Alright, lets walk through the proper way to safely take your truck down a steep grade.

Vail Pass Summit

Before the Descent Begins

One of the most important things you can do every day is a good pre-trip. Making sure your equipment is in good order before you start driving is essential. Additionally, before heading down a large grade, you will want to re-check that your slack adjusters are well greased and your brakes are properly adjusted. On some of the big passes, it is mandatory that you pull over and check. If you think there might be an issue, call for a roadside mechanic. You don't want there to be any chance of an avoidable brake failure.

There are road signs that show you the recommended speed for trucks to take that grade. These speeds are calculated for trucks with heavy loads. If your load is over 35000 pounds, and especially if it is over 40000 pounds, you need to take these signs seriously. Start by slowing down to the recommended speed and adjusting to the proper gear for that speed. If you are driving an automatic, put it into the manual shift setting. The lower the gear you are in, the better the engine will be able to slow down the truck when it’s heavy. With less weight, the truck will be able to slow down in a higher gear. With more weight, you need to use a lower gear. If you are not used to the truck or are new to driving, start the hill at the recommended speed. Make sure the engine RPMs are right around the middle of the RPM range you normally shift in.

Steep Grade Warning Sign

It may seem a little silly on some hills that they are putting such a slow speed when it looks like there is hardly a drop at all. Don’t be fooled. They put the sign where it is because this is the location where you have a chance to slow down. It may be a mile before the grade really steepens or it may be just on the other side of the blind curve you are on. If you wait until it gets steep, it will be too late.

Beginning the Descent

IMPORTANT! DO NOT SHIFT GEARS. Now that the decent has begun, you do not want to change gears. There may be some old pros that say they can do it no problem, but shifting on a steep grade is still a bad idea. It is very dangerous.

The only time I would ever recommend shifting, is if you failed to do the previous step properly and you are in too high of a gear for the hill with the weight you are carrying. You should realize that you are in too high of a gear within a minute of starting the hill. As soon as you take your foot off the brake, the speed and RPM’s shoot up and within a few seconds you are required to brake again. In this case, your engine is not doing a good job of slowing the truck down and you are having to use your brakes much too often.

In the event this happens you want to slow down immediately. Don’t wait for your brakes to heat up before you take action. You will use your air brakes to slow the truck down and shift at the very bottom of your RPM shifting range. This will give you the extra second you need to use the clutch to shift into a lower gear.

Important Note: Make sure your engine brake is off before you shift.

At the moment when you take the truck out of gear to shift, there will be nothing slowing the truck down and it will accelerate very quickly. By having the RPMs very low when you start your shift you should be able to get it into the lower gear before the speed is too much to shift. If you need to, come to a complete stop, get it in gear, and crawl down the hill.

You never want to upshift going down a hill. If you feel like you are taking the hill too slowly, just be patient, stay in the gear you are in and get to the bottom. Losing a few minutes going slower than you needed is much better than taking a risk of taking the truck out of gear and not being able to get it back in again.

Managing Your Speed

Now that you are in the correct gear and you are descending the hill, you will use your engine brake to control your speed. If you are in the correct gear for grade and for your weight, you will hardly need to use your air brakes at all. The engine will essentially hold your speed constant.

You will just leave the engine brake on, watch your speed and RPMs as you go, and occasionally do what is called “Controlled Braking”. Controlled braking is used to keep you inside a specific speed range. The range is usually about 7 MPH. For example, if you are trying to stay at approximately 40 MPH going down the hill, you will watch as your speed slowly gets up to about 40 MPH, then you will gently apply pressure to the air brakes to slow down to about 34 MPH. Once you get to 34 MPH you will let off the air brakes completely and allow the truck to gradually speed back up to 40 MPH. Your speed range in this example is 34 – 40 MPH. The upper end of your speed range should coincide with the upper end of your shifting RPM range. The higher your RPMs, the more stopping power your engine is providing. Just make sure you are not red lining your engine.

Keep doing this all the way to the bottom. Easy day!

The moral of the story is you want to avoid using the air brakes as much as possible. When you do use them, it should be in a deliberate, controlled manner. If you are safe, you can drive down as steep of a hill as is out there with never a problem. Also, be smart and don’t neglect your pre-trip inspection.

It’s a dangerous world. Be safe out there.

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