Driving mountain grades in an RV

Grades are the hazard that doesn't show up on a regular map. The route looks like a straight line on screen, and then you're on a long descent with a full water tank and a toad behind you. The fix is to know where the steep parts are and to have a plan for each one before you reach the top.

1. What the percentage means

Grade is rise over distance. A 6% grade drops 6 feet for every 100 feet you travel, or about 317 feet per mile. That doesn't sound like much until you're on 5 miles of it. Short steep pitches are rarely the problem. Long, steady grades are, because that's where brakes build heat.

Most big-rig drivers start paying attention around 5%, and anything 7% or steeper over a real distance deserves a plan. Watch for the yellow truck-on-a-wedge signs, which usually give the grade and length.

2. Climbing

• Let the speed drop. Big rigs slow down on long climbs. Use the right lane or truck lane and turn on your flashers if you're well under the limit.
• Watch your temperatures. Keep an eye on coolant and transmission temperature. If they climb toward the red, ease off, and pull over somewhere safe to let things cool if you need to.
• Downshift early. Let the transmission hold a lower gear instead of hunting. Many motorhomes and tow vehicles have a tow/haul mode for this.

3. Descending

The rule you'll hear from every truck driver: go down the hill in the gear you'd use to climb it. Pick the gear and speed at the top, before the descent starts, and let the engine or exhaust brake do most of the work.

• Pick a safe speed and hold it. If the rig speeds up past it, brake firmly to get about 5 mph under, then release. Firm, separate applications build less heat than riding the brakes.
• Use your exhaust or engine brake. On a diesel pusher, this is what keeps the service brakes cool. Know how your rig's works before you need it.
• Know where the runaway ramps and pull-offs are. Many long descents have brake check areas at the top. Use them.
• Smell or smoke means stop. If you smell hot brakes, find a safe place to pull over and let them cool.

Weight makes everything on a grade harder. Travel with less water on board when you'll cross a big pass, and know your loaded weight.

4. Know the grades before you go

Look at the elevation for each day, not just the trip as a whole. One day might be all flat interstate and the next might cross two passes. Plan the mountain days for the morning, when you're fresh, and keep them shorter.

How RV Compass shows grades

In the elevation panel, pick any drive to see its own profile, with every steep grade listed: where it starts, how steep it is, how long it runs, and how far it climbs or drops. A grade counts once it's 5% or steeper over at least half a mile, and 7% or more is marked as a danger. Tap a grade to see it on the map.

In navigation, the app warns you about a mile before a steep downgrade starts, so you have time to pick a gear. Low clearances get the same treatment. See clearance and grade warnings for the details, and our big-rig route planning guide for the rest of the hazards.