Best practice for steep downhill freeway grade

[ARVZ]

Heat your brakes up too much and they can fail completely. This can happen on passenger cars and trucks. The foolish helpless feeling of stomping on the brake pedal and having nothing happen is not something you want to risk.


On a long downgrade you can overheat the brakes to the point they aren't able to slow you down enough to get the engine to downshift so you can even use engine braking. This is what the truck escape ramps are for; runaway vehicles that have no way to slow down any more.



The only safe thing to do is to downshift into 1st or 2nd and LET THE ENGINE DO ALL THE BRAKING. If you can get to the bottom of the mountain without touching your brake pedal at all, you have succeeded. This way if you need your brakes for an emergency stop or unforeseen turn, they will be ready to do their best.



A compelling reason for using 1st is we often don't know the road ahead well enough to chose a higher gear that requires some brake pedal to slow us down. Even if you do know the road, accidents or other turning vehicles or deer ahead of you are not foreseeable. You need unused cool brakes to accomplish a fast stop anywhere.



The only penalty for going down the mountain in 1st is a slightly longer trip.



It uses up a lot of brake pad to slow your vehicle on hills, and they can overheat and the friction materials can lose effectiveness even after they cool off. Overheated brakes can take close to an hour to cool off, and that will also make your trip longer.

[Raspy]

Originally Posted by ARVZ

The only safe thing to do is to downshift into 1st or 2nd and LET THE ENGINE DO ALL THE BRAKING. If you can get to the bottom of the mountain without touching your brake pedal at all, you have succeeded. This way if you need your brakes for an emergency stop or unforeseen turn, they will be ready to do their best.

The only penalty for going down the mountain in 1st is a slightly longer trip.

It uses up a lot of brake pad to slow your vehicle on hills, and they can overheat and the friction materials can lose effectiveness even after they cool off. Overheated brakes can take close to an hour to cool off, and that will also make your trip longer.

The problem with this theory is that you can't go down highway grades, like the Grapevine or Donner in 1st gear. There is a penalty beyond a slightly longer trip. It's getting rear ended or causing an accident. Using 1st gear would definitely cause much more danger than flowing with the truck traffic.

Using lower gears is prudent, but it has to be done within reason. And often, the engine braking doesn't match the required force to hold back. In this case, you just apply the brakes occasionally to reduce speed. Then the speed gradually increases until you do it again. The important thing is to not drag the brakes to hold a certain speed.

If the brakes are hot and you don't think you'll need them for a while, keep going. They will cool much more affectively while driving than while sitting still. The wind takes the heat away and most modern disk brakes are ventilated, meaning they actually pump air through the rotating disks to cool.

Drum brakes have the nasty habit of boiling the brake fluid when overheated. When this happens the pedal goes to the floor and is completely ineffective. No brakes at all. Disk brakes, when overheated, begin to boil off the brake pad material as smoke, which then lubricates the surface between the pad and the disc. They can continue to work when hot, but at a reduced amount. And they can recover easier. Electric trailer drum brakes seem to suffer the same fate as overheated disk brakes, but much sooner. There is no brake fluid to boil, but there is a large surface area of friction against the drum and they fade easily.

This whole conversation demonstrates how important it is to have a lot of headroom with your tow vehicle and not be trying to tow a trailer that is at the maximum weight allowed by your vehicle. Also, brakes are much better than they used to be. One of the first things I look at on a truck is the brakes. How big and what type are they on the rear of the truck?Disks are the only type that is acceptable to me and the biggest ones that will fit in the wheels are the ones I want.

Also, again, if you have a trailer that is prone to swaying, the problem will be amplified by holding it back on grades with the tow vehicle. In that situation, the trailer brakes are not working and the speed is variable. The trailer is pushing the tow vehicle. So, be ready to apply the trailer brakes, at the controller, if needed.

A good speed to shoot for on the highway is about 50 MPH max, if traffic allows. A lot of trucks hold to this speed if they can and you can stop if you have to. At whatever speed you are trying to hold to, the engine should be running at about 75% of it's redline RPM. Gas engines hold back fairly well, diesels, not so much, unless they have engine brakes. Engine brakes are one of the finest safety and brake prolonging features available on any vehicle. They easily double the life of the brakes and often mean no brakes are used to slow down or hold back on grades.

[Glenn Baglo]

No need to read any other posts on the subject Raspy.

[Rzrbrn]

I really appreciate your taking the time to go into this much detail Raspy.

I have a 2011 Tundra 4x4 with 5.7L engine and tow package, which requires some braking on the steepest and longest downgrades. I really was not expecting this, but have gotten used to it, at least pulling the Casita. If I can handle the situation pulling the much heavier BF I will keep it. If not I will be looking for a good used diesel such as the Ford 7.3L , Dodge Ram with the 5.9L engine, or maybe a Duramax 6.6L.

[ARVZ]

Raspy makes some excellent points about modern brakes, but my guess is he has never lost his brakes going down a mountain grade, or possibly never had to make an emergency stop near the bottom of a long downhill.


Freeways usually have flatter grades, and usually don't have downhill runs lasting for many miles. Donner Pass is an exception. Two-lane mountain passes are a different animal. Maybe you won't need 1st or 2nd, but it can be a choice you only get to make at the top of the hill.



If your trailer has drum brakes they will dramatically lose effectiveness as they heat up from being applied. This could mean they will not serve to straighten up your rig even if your tow vehicle disc brakes are just barely hanging in there.



What advantage is there is just barely maintaining control of your ($100K) rig just to go a little faster? We shouldn't have to count on good luck to get us to our destination in one piece.



I guess my point is, speed kills. Modern truckers drive too fast for conditions so are not a good example to follow, literally or figuratively. I see lots of truck wrecks in the Cascades and Siskiyous where I live, and the runaway vehicle ramps usually have fresh tracks.

[bootsmacphearson]

Tow mode changes the shift points for smoother shifting when under load. If you use tow mode then on downhill grades put the unit in manual mode the gear you select will be the highest gear that will be used so you can shift down to help control braking using the + - for the shift. Today I came down 16% grades in Utah pulling a Casita 3160 lbs in 3 gear on winding roads using no brakes speed was 35 - 40 mph. ( I did brake some for switch bCK CURVES)

[Civilguy]

Originally Posted by Raspy

Here's my favorite grade, the Sonora Pass on Hwy 108 in CA. 9,600 ft and as much as 26% grade. Especially interesting with the serious drop-offs that wait for those that don't make the curves along the narrow road.

Originally Posted by Rzrbrn

Thank you Raspy. We really enjoy poking around the North East and also the Sierra Nevada mountains. Not sure where we will wind up but your Sonora Pass is pulling me...

Originally Posted by Raspy

Henry, I'm not sure what they mean by that 25' number. But you will certainly be fine. It's the big heavy semi-trucks that cannot make it. I've towed many times over that pass with my Ram and utility trailers, travel trailers, my tractor, a couple of cords of wood in a dump trailer and flat towed my Samurai.

For what it's worth Henry, the easterly side of the Sierras is the steep side, so you might favor taking that side going uphill. It is a beautiful area. I used to frequent the Sierras quite a bit when I lived in the Bay Area. I drove a '72 Dodge van with a 225 slant six and three on the tree, usually just containing a couple of us wiry teenagers with our backpacks. There wasn't a lot of power to spare, but it always got along fine.

John, I presume there was some sensible reason for hauling all that cord wood over that particular route, like maybe something to do with the lack of substantial vegetation in the area immediately east of the Sierras - ?

[Joe Romas]

Originally Posted by bootsmacphearson

Tow mode changes the shift points for smoother shifting when under load. If you use tow mode then on downhill grades put the unit in manual mode the gear you select will be the highest gear that will be used so you can shift down to help control braking using the + - for the shift. Today I came down 16% grades in Utah pulling a Casita 3160 lbs in 3 gear on winding roads using no brakes speed was 35 - 40 mph. ( I did brake some for switch bCK CURVES)

I suggest READING YOUR TV'S MANUAL

My 2017 GMC Sierra 6 speed automatically downshifts when in tow mode using cruise control when the actual speed gets 5 MPH over the set MPH.

[Raspy]

Originally Posted by Civilguy

John, I presume there was some sensible reason for hauling all that cord wood over that particular route, like maybe something to do with the lack of substantial vegetation in the area immediately east of the Sierras - ?

Mike,

I don't always do things that are sensible.

We live east of Topaz Lake and with the 1 ton Ram diesel, and the fact that I love the Sonora Pass, we usually opt for that route if it's open. We have been getting wood at Manteca and the other way around is kinda boring. For a long time I commuted to the Bay Area and Turlock weekly from NV.

It's not just the grade and scenery that make it fun. In summer, with the thundershowers, I've come across tree stumps, boulders and 1' deep flowing water on that road up near the top. One day in winter, I was a few miles up and a Caltrans worker was just swinging the gate closed as we drove up. It was the beginning of the closed season. I got out and asked if he would allow us to be the last one through, and that I was very familiar with the road. He thought for a few seconds and OK. Then he opened it for us and shut off the following car. Later, as we went on, I was beginning to wonder if that was good idea. Snow on that road can be serious.

I've also helped a few stranded motorists that were broken down up there that had no idea what would happen next, or how to get it resolved.

But the most fun parties happen behind the stuck truckers. Drivers that have driven right past the warning signs and are now so surprised that the road is so steep and winding. Cops that are less than patient. And a gigantic tow truck that has to come up 30 miles to drag them back onto the road. Even the contractors that were adding guard rails near the top and needed a Skytrak forklift, got stuck on a clear dry day and had to get help. Hilarious.

BTW, thanks for your PM and comments.

[Steve Carlson]

The only place I have ever had trouble slowing down enough was US 14A coming down out of the west side of the Bighorn Mountains in Wyoming. I was driving an Isuzu Trooper with a 5-speed manual, and even though I downshifted in advance, in 3rd gear I was using the brakes too much until one of the rears started smoking. According to google it is a 10+% grade for 10 miles...

[Glenn Baglo]

Originally Posted by Steve Carlson

The only place I have ever had trouble slowing down enough was US 14A coming down out of the west side of the Bighorn Mountains in Wyoming. I was driving an Isuzu Trooper with a 5-speed manual, and even though I downshifted in advance, in 3rd gear I was using the brakes too much until one of the rears started smoking. According to google it is a 10+% grade for 10 miles...

No trailer brakes?

[Kai in Seattle]

Originally Posted by Steve Carlson
The only place I have ever had trouble slowing down enough was US 14A coming down out of the west side of the Bighorn Mountains in Wyoming. I was driving an Isuzu Trooper with a 5-speed manual, and even though I downshifted in advance, in 3rd gear I was using the brakes too much until one of the rears started smoking. According to google it is a 10+% grade for 10 miles...


What were you towing--or was it just your Isuzu you couldn't get to slow down?


"K"


Besides...we've driven Wyoming...and it is all 10,000 miles of nothing but scrub brush, uphill in all directions.


Not that Wyoming isn't a beautiful state...

[Steve Carlson]

I wasn't even towing - should have mentioned that!

If I had been towing I'm sure I would have had to creep down in 2nd or even 1st gear...

Here in the Midwest I rarely have to worry about it, but I do go out west pretty much every year. In July I will be towing my little Lite House camper through the Rockies on I-70, should be interesting.

[Kai in Seattle]

Steve Carlson,

Since you hadn't mentioned what you were towing, I suspected you weren't...thanks for the update.

I hope this summer's trip goes very well for you, welcome back to the Wild West!

Those little Lite House campers are cute!

"K"

[Steve Carlson]

Yeah, all the ladies call it "cute"

Fortunately it doesn't weigh much - 980 lbs. empty and I don't load it down much - so I am not anticipating much drama going through the mountains, other than the usual stuff like navigating around semi trucks creeping up the hill at 15 mph whilst being overtaken by cars going 70... but I have done it many times before.

[Kai in Seattle]

Steve Carlson,

So you're all set, driving & towing experience, and the cute little babe magnet.

Wishing you an excellent journey!

"K"

[Rzrbrn]

Originally Posted by bootsmacphearson

Tow mode changes the shift points for smoother shifting when under load. If you use tow mode then on downhill grades put the unit in manual mode the gear you select will be the highest gear that will be used so you can shift down to help control braking using the + - for the shift. Today I came down 16% grades in Utah pulling a Casita 3160 lbs in 3 gear on winding roads using no brakes speed was 35 - 40 mph. ( I did brake some for switch bCK CURVES)

Lyle, I don't understand how my 2011 Tundra transmission operates. It will allow me to manually select gears which I usually do going downhill. But sometimes while I am in cruise, going downhill, the truck will slow itself down. I really appreciate this but I can't seem to get it to do that in any reliable and systematic way. I just cannot understand how to get the truck to do this when I want it to.

An RV service tech just told me yesterday that I should have it in cruise, engage tow haul and the truck will then slow itself down. Only it does not seem to do it when I follow these instructions.

I am completely stumped. How is it possible to have the Tundra maintain a steady chosen speed when going downhill? (I know it is supposed to slow down when it goes about 5 mph over the chosen speed. The owners manual says tap the brake at the speed you want to maintain. But when that is done the truck drops out of cruise and does not slow itself down.

[Steve Carlson]

On many of the newer vehicles the cruise will use the brakes to maintain downhill speed. I know my 2008 RAV4 did this.

[Steve Carlson]

Originally Posted by Kai in Seattle

Steve Carlson,

So you're all set, driving & towing experience, and the cute little babe magnet.

Wishing you an excellent journey!

"K"

Thanks Miss K!

[Joe Romas]

Originally Posted by Steve Carlson

On many of the newer vehicles the cruise will use the brakes to maintain downhill speed. I know my 2008 RAV4 did this.

My 2017 GMC Sierra 6 speed automatic downshifts a gear or two under those conditions to slow down.