Mountain Grades, Gearing and Brake Fade

Published October 23, 2026 · Last reviewed October 23, 2026

On a long downhill, gear down before the grade starts and let the engine hold your speed, so the brakes are used only in short, firm applications. Riding the brake pedal turns your momentum into heat, and hot brakes lose their grip, which is called brake fade. If the pedal softens or the brakes smell hot, stop at the next turnout, and if control is lost, use a runaway ramp.

What a long descent asks of the brakes

Going downhill, the energy your rig gained climbing comes back as speed, and the brakes convert it into heat. A loaded motorhome or a truck pulling a heavy trailer carries a great deal of that energy. On a long grade there is no pause for the brakes to cool, so the drums or discs, the fluid and the linings keep heating. Past a point they stop gripping well, the pedal gets longer or softer, and speed climbs while you press harder. That is fade, and it can arrive without warning at the worst part of the grade.

The cure is to take most of the work away from the brakes before they heat. That means a low gear and engine braking, and for towing rigs a properly set trailer brake system.

The descent procedure

Before the top of the grade, stop somewhere level and safe, and read any posted signs about steep grades, truck speed limits and brake checks.
Check that the trailer brake controller is connected and working, if you tow, and that your tow/haul or equivalent mode is on if the vehicle has one.
Slow down before the descent begins, then select a gear low enough that the engine holds your speed with little or no braking.
Let the engine and any exhaust brake do the work, and add the foot brake in firm, short applications, then release fully, so the brakes can shed heat.
If speed still builds, drop one more gear, or use the trailer brake lever briefly, rather than keeping the pedal down.
Pull over at the next safe turnout if you smell hot brakes, feel the pedal soften, or just want a rest, and let everything cool before you go on.

Rig sensitivity

Roughly, the more weight you carry and the more it has to stop, the more you must plan. Rig: Van / B-class, Class C Low to moderate, with less mass, though a fully loaded rig near its limits is not light. Rig: Travel trailer, Fifth wheel Moderate to high, because the combination is heavy and trailer brakes must carry a real share. Rig: Class A High, especially a diesel pusher with a heavy tow vehicle behind, and gasoline models without an exhaust brake rely heavily on gearing.

Decisions, in priority order

Action: Choose your gear at the top, not halfway down. A rule of thumb is to descend in the gear you would use to climb the same grade.
Why it helps: Engine compression and friction are a free, heat-free brake. Once speed has built, it is harder to slow the rig by gearing alone.
Verification: At the first part of the descent your speed holds steady with little or no pedal. If it creeps up, you chose too high a gear.

Action: Use the exhaust brake or engine-braking mode if your rig has one, and read the owner manual for how to engage it. Gasoline engines depend on lower gears; use any tow/haul or grade-braking mode the vehicle offers.
Why it helps: These systems add retarding force at the engine so the service brakes stay cool.
Verification: The dash shows the mode engaged, and the rig slows noticeably when you lift off the throttle.

Action: Brake in short, firm applications, then release fully, instead of dragging light pressure the whole way.
Why it helps: A firm press followed by a full release lets air move over the brakes and shed heat. Constant light pressure keeps friction and heat going the whole way down.
Verification: Speed drops by a clear margin with each press, and you reach the bottom with the pedal still firm.

Action: If you tow, test the trailer brakes before the grade using the controller’s manual lever at a low speed, and set the gain so the trailer assists without locking its wheels.
Why it helps: Trailer brakes take a share of the load off the tow vehicle. If they are not working, the tow vehicle carries all of it.
Verification: You feel the trailer pull back on the hitch when you press the lever, and the controller shows output. Never use the lever alone as your main brake.

Action: Stop at a turnout when anything feels wrong: a hot smell, smoke, a soft or low pedal, or a sizable wheel-end temperature difference.
Why it helps: Brakes that have started to fade rarely recover while you keep using them. A pause lets heat leave.
Verification: You wait until the brakes are cool enough to hold a hand near, the pedal feels firm, and there is no leak or smoke. Call roadside help if you doubt the system.

Runaway ramps and signs

Many steep grades have runaway truck ramps, also called escape ramps, usually a gravel or sand bed on an uphill spur. If you cannot slow the rig, steer into one early, sound the horn if you can and hold the wheel straight. Damage to the rig is far less costly than a crash at the bottom. Heed the posted grade signs and any brake-check area at the top; they are there because earlier drivers failed to slow down. If you are unsure of a route, check clearance and weight-limit routing first.

How it works

A vehicle going downhill has potential energy that must go somewhere. Three things absorb it: air drag and rolling friction (small at moderate speeds), the engine (through compression and internal friction when it is turning against a closed throttle), and the brakes. The brakes turn the energy into heat in the rotors or drums, and heat has a limit. Brake linings lose friction when very hot, and brake fluid can boil, producing a spongy pedal.

Gearing down raises the engine speed for a given road speed, which raises the engine’s retarding effect. A diesel with an exhaust brake adds more by restricting the exhaust, which makes the engine work harder against itself. This is effective because it costs nothing in brake heat. A gasoline engine has less natural retarding force, so it depends more on the gear selection.

Trailer brakes have their own heat limit too, and they share the load with the tow vehicle only if the controller is set properly. A trailer that is not braking is pushing the tow vehicle from behind, and its brakes, if working, pull back. The goal on any long grade is to spread the work across engine, tow vehicle and trailer so that no single system gets too hot, and to leave margin in case the grade is longer than expected. A cooler brake system also lasts longer between repairs, which matters in the maintenance guides, such as the tire pressure and heat guide.

Worked example

Suppose, as a hypothetical, you are driving a Class A gasoline motorhome with a small car towed behind, approaching a 6-mile downgrade. A sign at the top warns of a steep grade for the next several miles, and you pull into the turnout before it.

You walk around the rig: tires look fine, nothing is dragging. You set the vehicle’s tow/haul mode, drop to a low gear at about 25 mph on level road and enter the grade. Your speed holds with small pedal presses of a few seconds at a time. Halfway down you notice a faint hot smell and see a turnout, so you pull in, wait twenty minutes, and the smell fades. You then continue in the same low gear.

At the bottom the pedal is still firm. Had you started in a higher gear and ridden the pedal, the rig could have reached the same point with fading brakes and no warning. The details here are invented as an illustration, not a statement of any real road or rig. The verification is simple: speed held by gearing, pedal firm throughout, and a pause taken when the smell appeared.

Frequently asked questions

What gear should I use going down a mountain in an RV?

Use a rule of thumb: the gear you would use to climb the same grade, selected before the descent begins. Your speed should hold with little or no braking, and you can drop a gear if it builds.

What is brake fade and how do I prevent it?

Brake fade is the loss of braking grip when brakes overheat, so the pedal needs more effort for less slowing. Prevent it by using a low gear and engine braking, and by braking in short firm applications instead of dragging the pedal.

Should I use an exhaust brake on a long downgrade?

Yes, if your rig has one and the manual allows it, because it adds retarding force without adding brake heat. Gasoline rigs rely more on lower gears and any tow/haul or grade-braking mode.

Can I use my trailer brake lever to slow down a hill?

Briefly, to straighten a swaying trailer or add a little help. It should not be your main brake, because trailer brakes can overheat too and the tow vehicle must still do most of the work.

What is a runaway truck ramp and should an RV use one?

It is a gravel or sand escape lane on an uphill spur, built to stop vehicles that have lost their brakes. If you cannot slow your rig, steer into it early; damage from the ramp is far less than a crash.

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