Going Down Hill or Life in the Fast Lane!! - RV-Dreams Community Forum

Darrell and Judy · RV-Dreams Family Member

Going Down Hill or Life in the Fast Lane!!

Speedhitch · RV-Dreams Family Member

Darrell you know that is the only thing that I hate about the mountains is going down. Before I started RVing I use to think going up would be the hardest....but I soon was to learn that it is the other way around. Your correct in saying that we could all learn something about driving correctly on the down hill side of the road and Life!

Joe and Sherri

RVDude · RV-Dreams Family Member

The best advice I got on the downhill is to observe the posted hill slope (the %) and then think about the speed at which you want to descend BEFORE you start coming down, get in the gear for that speed BEFORE you start coming down and STAY at that speed/gear until you get down. NOT accelerating downhill is the key to downhill control. Point is, don't pick a speed/gear/brake/slope combination that keeps accelerating you forcing you to heat up the wheel brakes and risk brake fade or that forces a downshift midway as doing a downshift under a hill load may be exceptionally difficult and certainly risky in terms of not getting it back in gear - which would be a disaster.

The speeds you choose all depends on the slope and what type of rig you have (5er or MH or combo), diesel or gas, and the braking systems (engine, Jake/exhaust, air/hydraulic) it has.

The idea is (given you have engine or exhaust brakes) is to match a speed (by your gear choice) to the slope so that the engine or exhaust brakes do literally all the work and the wheel brakes are used for fine tuning or emergency control thus ensuring you never overheat the wheel brakes.

You have to experiment with your rig to figure out the speed/gear and slope combinations that your engine or exhaust brakes can manage. In time you will know what gear to be in at what speed for the different % slope hills. Start experimenting on the cautious side (too slow and too low gear).

I can now roll my 44,000 lbs without accelerating downhill (not accelerating is the key to downhill control) using a 2-speed engine brake, 6-speed auto trans and seldom tap my wheel brakes even at 8-9% sustained grades.

Speedhitch · RV-Dreams Family Member

I have a Dodge 3500 Cummings with the exhaust brake. I also can set the gear with the tow haul engaged. Having done all that your saying that I should find a comfortable speed and hold it there using the break to fine tune... correct? I really would have to be going down the grade to know what comfortable is??? I hope to try this in the hill country south of here in the next month. I will get back with you and let you know how I did.....I hope I can get back to you. I may end up in Mexico trying to stop!

Joe

RVDude · RV-Dreams Family Member

Yep... Downhill is all about smooth control and very slow controlled speed changes and NOT rolling up a head of steam and then slamming on the brakes. Further advice is NOT to ride the wheel brakes (this applies for any vehicle) but to apply them when you gain say 5mph so as to slow the 5mph using the wheel brakes and release. Repeat. Hence, the idea is to pick a gear/speed and aux brake level such that you do not gain any speed or do so very slowly (and controlled) so that the wheel brakes are seldom used and or at least have a chance to cool. Remember, the exhaust/engine brakes act solely through the drive wheels and are IN ADDITION to any brake effect applied by the wheel brakes.

PS: If the road is slippery (i.e. wet, snowy) be ULTRA ULTRA careful about too much engine/exhaust brake as you can very easily lock up the drive wheels using the slightest wheel brake application whilst under full load engine/exhaust brake as well. Locked drive wheels = jack-knife or worse. Many engine/exhaust brake systems will suggest turning them off or at least to low positions if there are slippery conditions present. Fresh light rain is the slipperiest rain. I repeat, remember, the exhaust/engine brakes act solely through the drive wheels and are IN ADDITION to any brake effect applied by the wheel brakes.

PPS: Howard will get to experience this wheel brake and gear choice in spades on his (cute) Liberty when he takes it in the bush. A gas engine has "engine" braking action unlike a diesel. He can clearly tell us (or soon will be able to) the difference between 4L and 4H and the xmission gear choice used with each transfer case choice on downhills, especially slippery downhills. He's already mentioned some of these observations in his training from Jack...

Everything he learns about gearing/braking/control in slippery off road downhills in the Liberty will be invaluable lessons for the rig. Hence, four-wheeling training is a great precursor to rig driving. Oppss, Howard got that reversed! Oh well!

-- Edited by RVDude at 17:12, 2007-07-27

Speedhitch · RV-Dreams Family Member

Thanks for all the advise! Good point about the slippery roads...I never would have given that a thought until I jackknifed...Oh that would not be good at all. One thing about Howard is he puts Linda behind the wheel and she gets all the experience...She should be t he 4 wheeler.

Thanks again

RVDude · RV-Dreams Family Member

Good luck! And have fun!

Maybe you should brush up on your Spanish just in case you slide across the border!!! biggrin

One other thought... If you have an ABS (Anti Lock Brake System) on your truck. ABS systems work by automatically releasing and applying the WHEEL brakes. I do not know this but suspect ABS will NOT release the engine or exhaust brake as well in most vehicles. Hence, if that is correct (check your owners manual) ABS will not save the day in a downhill combined engine and wheel brake locked wheel situation. I would further suspect that once you lock the drive wheels simply releasing the wheel brake will not be sufficient for them to regain traction if they are still under engine or exhaust brake. This is simply by the physics of static and dynamic friction - that is, it is far more difficult to initiate a slide (static friction) than it is to maintain a slide and keep on sliding (dynamic friction).

-- Edited by RVDude at 17:30, 2007-07-27

Speedhitch · RV-Dreams Family Member

Hey Dude I will print this out and put it over my visor so I can refer to it as I plummet down the first hill.....Also next to it I will attach the Lords Prayer...Thanks again

Joe

Darrell and Judy · RV-Dreams Family Member

Dude,

That was the kind of information I was looking for. I have the Duramax Diesel with a 5 speed Allison tranny. The transmission does braking when in the tow/haul mode (it will automatically downshift as needed to keep the vehicle at the speed that the computer has calculated based on recent driving patterns). In other words, I don't know what the heck it does, but it slows the vehicle down. What I am not sure of is how much I can rely on this technology. So your information on selecting gears based on speed makes sense (maybe that's what the computer and transmission is doing). I will do some testing as we leave the Adirondacks going through Massachusetts on our way to Maine.

We had gone across Route 9 in Vermont (Green Mountains) and the truck seemed to operate correctly, but the brakes were hot when we reached the bottom (you could smell them). That may have been because we started down the hill at too high of speed (somewhere around 45 to 50). I am not sure what the optimal would be but before we head out west next spring I certainly want to have it figured out.

RVDude · RV-Dreams Family Member

FWIW - on +-8% slopes in my case 30-35mph is the right speed. If my memory serves me right, I'll bet on VT Rt9 45mph+ is way too fast to start and the brake burn smell is a tell tale. Some 18 wheelers are fairly conservative in downhills and might be a good target speed to follow. It all depends on total load and braking ability of the system and even driver attitude. Also, even as little as a 5mph difference at the start makes all the difference between a controlled "steady-state" downhill, an accelerating one (if too fast), or an annoying decelerating one (if too slow). The amount of engine braking is a function of engine RPM as well as gearing so you need to experiment to find what works most comfortably for your situation. Find a big hill with a passing lane so as not annoy our fellow drivers, go at it slow and try several gear/speed/rpm/brake combinations as you are going down and record the results for that slope. Try it several times. It'll also make you more comfortable with what the controls actually do in real situations. Downhills are still a nail biter but with some experience of what the controls actually do, you'll be more comfortable biting them! (your nails that is, not the controls!)

-- Edited by RVDude at 08:28, 2007-07-28

Darrell and Judy · RV-Dreams Family Member

Thanks Dude,

I'll definately be experimenting before hitting the mountain passes out west. It is nice to be able to stop and not get that "special" view as you careen over the side of a mountain. As has been said, "It's not the fall that hurts you, but the sudden stop!" So I suppose you could take some pictures on your way down. Sort of a legarcy!!! confused

Linda · Hostess

Well, it looks like I'm a little late answering this thread. I have been lax in reading the forum. Could it be that I am in the Chatroom a little too often?

First of all, going up the mountain... I listened to my engine and watched the rpms and found the sweet spot and that is what determined the gear I used. It will be different for most trucks so you just have to pay attention.

Second, going down the mountain...I had to find the speed in which I felt comfortable. My comfort speed was 30-35 mph. So I just geared down to obtain that speed. The engine brake and transmission did most of the work. When my speed would creep up to 40 mph I would brake until I was about 20-25 mph and then let off. Again the engine brake and transmission held the speed most of the time. I would only brake when my speed crept up to 40 mph.

That was on a 6% grade with 30 mph curves. I am sure others may feel more comfortable going a little faster but not me, not yet anyway. I never felt out of control the entire time. I think I only hit the brakes maybe 5 times the entire pass.

I think the biggest key is to go slow and don't worry about the line of traffic behind you!!! biggrin

Darrell and Judy · RV-Dreams Family Member

Thanks Linda, the chat room is fun and time can be lost while chatting away but don't stay out of it for very long. You pretty much confirmed my sneaking suspicion. The truck is powerful enough that I haven't had any problems going up the mountains in the east, but those western mountains that seem to climb forever will be a different story. We definately want to know how and when to "gear down" on the downward side of the mountain, your info helps. I was going to ask Howard, but decided to ask the "pro" instead smile

!!!! By the way, what is Howard going to do now that you have a Jeep to transport??? I guess you'll have to put him in the Jeep and take over the serious driving yourself biggrin

blijil · RV-Dreams Family Member

We also have the Allison but on the 8.1 Liter gas engine. The computer is pretty smart and will gear down based upon your brake usage. We also take it out of overdrive while mountain driving up or down. The comments above are pretty good. Keep your foot off the accelerator and off the brake unless necesary. Keep you speed down to a comfortable constant speed if possible. We just love the long 30 mph curve followed by a steep grade posted at 65 mph followed by another 30 mph curve. I don't know who posts these signs but they sure are driving a heavy rig and they sure aren't paying $3+ per gallon for fuel.

Life is an adventure and so is going too fast down a steep mountain.

Life is enough of an adventure for us.
Larry and Jacki