RV Driving On Extreme Mountain Grades

September 1, 2011 by Lug_Nut · 25 Comments  
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A Lug_Nut point of view.  Extreme mountain grade driving is something most RVers prefer to do in their towed vehicle rather than with their motor home or truck trailer combination.  Steep climbs and drop- off downhill grades can turn a pleasant days run into a white knuckle survival experience.  So what exactly is considered extreme mountain grades?




Interstate highways and the majority of state routes are generally limited to 6% to 7% grades.  This means for every 100 feet travelled you would climb or descend six or seven feet.  A long downhill grade of this descent requires a constant resistance of lower gear operation, Pac Brake, Jake Brake and or service brakes.  The heavier the vehicle the harder it is to maintain a reasonable speed.  While you can generally use your brakes to check and maintain your speed in your automobile or light truck, the same cannot be said for most RV rigs.  Brake friction to slow a heavy rig quickly produces excessive heat that may lead to poor braking efficiency or even full brake failure.  While drum type brakes are perhaps more affected by this, disc systems can also overheat and fail.

Driving 014Extreme mountain grades can be upwards of 18%, well over double what you would normally encounter in the U.S or Canada.   These can bring the climb speed of a heavy motor home or trailer combination into single digits on the speedometer at full throttle.  Likewise on the descent an extreme resistance will be required to hold back the vehicle.  So, heat is a concern when climbing for the engine and transmission, while descending, the brake temperature may be the issue.

Last week I experienced some extreme grade driving while travelling through the Gaspe Penninsula in Quebec Canada.  An extreme steep grade out of Perce took my speed from a start of 30 MPH down to 9 MPH.  My coach and tow weighed in at about 52,000 lbs. with a 500 HP Cummins engine.  This already gave me slightly less than the 1 HP per 100 lbs. (A standard considered necessary)  That was further reduced when the fan drive clutch locked up drawing a whopping 70 HP. leaving me with 430 flywheel HP.  I maintained about 9 MPH for most of the climb and gradually picked up speed as I approached the crest and the grade.  Descents on these grades were equally challenging.  With the Jake Brake in “Hi” I reduced my speed to engage 2nd gear at the outset.  Fortunately, the fan drag that worked against me on the up hill climb also automatically engages in the “Hi” mode adding an additional 70 HP braking resistance.  Needless to say, the fuel milage crashed to something less than 5 MPG throughout this day.  Looking back, I think the up hill climbs were more stressful than the downhill.  I hardly needed to engage the service brakes during the descentss at any time.

As many seemed interested in this topic last year, I will repeat some of the techniques in the two earlier articles.

So let’s first look at managing steep mountain grades in your RV.

Tips on Managing Your RV’s Speed on Steep Grades:

All Categories of coaches and trailer tow vehicles: When approaching a grade that is descending substantially and will, or may, cause your vehicle to increase speed above that which you wish to travel, or may be safe, do the following.  Slow to the speed, or slightly lower, that you intend to descend the sloop, prior to reaching the crest. Be aware of what traffic may be behind you and use caution as you reduce speed as not to cause any danger. Select a lower gear to maximize engine RPM and driveline resistance. Now maintain any excess speed by short adequate hard applications of the service brakes. Remember, the wind resistance is now working with you, and can aid you to keep a comfortable speed.

Medium weight exhaust brake equipped coaches and comparable equipped tow vehicles: Same as the above with the exception of manual selection of a lower gear if your unit is configured to auto-select a lower gear. Engage the exhaust brake (Pac Brake) closest to the selected descent speed as your vehicle crests the hill, and is moving positively down (moving forward without throttle, but in favor of gaining speed). Observe both speed and engine RPM during the descent and control same, if required, with short firm service brake applications.

Tip: Get to know your speed in each gear when the engine RPM is about 90% of the maximum governed loaded speed. If you can’t always remember this speed for each gear, or to just make it easier, put a small red sticker piece at each location on the speedometer. Select your grade descent to be one of these speeds. This will normally deliver smoother braking and possibly eliminate further downshifting. If the engine RPM increases to near that listed in your engine manufacturer’s manual as being the maximum RPM during compression brake application (usually 10 to 15% higher than governed speed), apply the service brakes firmly to bring it back to near its original speed. If, on the other hand, the engine RPM reduces near the speed that would cause an additional downshift, shut off the Pac Brake switch. Do not touch the accelerator pedal if your unit is configured to auto-select a lower gear as that will cause an up shift at this point. You can now toggle the brake switch on and off to maintain the desired road speed during the balance of the decline.

Medium heavy full Jake Brake equipped coaches: Same initial approach as earlier discussed, with the following suggested procedure.  Single Jake speed. Follow the same procedure as the Pac Brake. Get to know your speed in each gear when the engine RPM is about 90% of the maximum governed loaded speed. If you can’t always remember this speed for each gear, or to just make it easier, put a small red sticker piece at each location on the speedometer. Select your grade descent to be one of these speeds. This will normally deliver smoother braking and possibly eliminate further downshifting. Two speed Jake. Follow the same procedure as the Pac Brake, except, toggle the “Hi” “Lo” instead of the activation switch.

Tip: This system can provide exceptional downhill speed control. Understanding and utilizing the features that the two speed Jake can provide will give you the full benefits it can deliver.

Heavy coaches, that may be equipped with three speed Jake’s, operate similar to the above mentioned systems. The Jake switch can be multi toggled as required.

Heavy coaches, equipped with transmission grade retarders, should similarly make the same basic grade crest approach. Apply the joystick retarder control at the lowest setting, increasing it as necessary. As many, like the Allison, full grade retarder type transmissions use internal retarders, shift patterns or gear selection may affect the operation.

A word of caution that should be observed in the use of any compression type braking, use only when the road surface provides adequate traction. Even wet roads, particularly just when it first starts to rain, may not be safe for unrestricted use.

Extreme grades are not always a planned route.  Ask other RVers about certain routes as to their challenges.  This can be done through forum such as or  Additionally you can talk to fellow RV enthusiasts that you may meet in campgrounds in your travels. 

You may encounter extreme grades while travelling in mountainous areas and be faced with this challenge, often without the option of turning around.  However, skilful speed management and a cool hand can triumph. 

There are of course other hazards that you may encounter in mountainous areas that you must also be aware of.  Here are a few.

Road Surface Ice Patches:  Temperatures drop as elevation increases at a rate of about 3.56 degrees F. per thousand feet.  This is known as the “normal lapse rate”, or temperature to altitude ratio.  While this is the usual ratio it can vary.  A steeper lapse rate can be experienced when the weather becomes unstable and the ratio may exceed 5 or more degrees F. for every one thousand feet of elevation.  Likewise another phenomena is possible where the lapse rate is very low, nil or even a slight increase may be found.  This may be an inversion, where warmer air is forced aloft.  But never the less, you are far more likely to encounter a normal lapse rate, hence the word “normal”.  So, on a 50 F., day driving over a 5,000 ft. mountain pass, freezing temperatures are quite probable.  This can result in icy conditions if precipitation is present.  But, even on a sunny day ice can form from water running down from the mountains above, particularly in shaded areas.


IMG_1509Wildlife on the Road: While many lower elevation roads present this problem, many mountain roadways have an additional animal, the mountain goat that often wanders on the highway.  Rugged terrain can also make the road edge an appealing passage in some circumstances which may result in an increase of roadway wildlife traffic.  Combine this with the twisty roads and poor forward roadway view, a shorter warning of wildlife is to be expected.




Rock Fall Warning: While a rock slide is highly unlikely, the possibility of encountering some small rock pieces on the roadway can be very real, particularly after a heavy rain fall.   Generally these rock fragments are jagged and can damage or destroy a tire or vehicle.  Reducing speed when such warning signs are posted can increase your maneuvering and stopping ability.  We have all seen the yellow warning signs, but it is surprising how little attention they are given by most drivers.

Precipitation on an Otherwise Clear Day: When operating at higher altitudes in mountain ranges that are snow capped, precipitation can be encountered even on what looks like a clear day.  This can happen when humid air drifts across the snow caps.  The frozen ice and snow reduces the air temperature to, or below, the dew point.  At this temperature some cloud formation will appear and snow or fine rain may fall.

Reduced Visibility Possible: Quite often the clouds are lower than the mountains are high.  If the roadway rises up to, and through, the cloud base, vision may be reduced to near zero.  Slow down and observe caution as you would driving in fog.

Shear Road Edges: Unlike most roadways found in the lowlands, mountain roads occasionally have no shoulders or guardrails in some sections.  These require special care and attention.  Wondering off the road in these areas can have disastrous results.

Engine or Transmission Overheat: Climbing steep grades takes horse power and torque, this causes the drivetrain to heat up. To keep your engine and tranny running cooler, climb grades in a manually selected gear.  This then will allow partial throttle climbs without the automatic up-shift.  Operating your engine at higher RPM will allow the cooling package to run more efficiently during hard pulls.

Fuel and Services: Generally you don’t see fuel and service stations in the mountains.  So, make sure you have ample fuel and that your fluid levels are all topped up.

Affects of High Altitude: Generally there is little affect to most people when exposed to 5,000 feet or so.  But there are far higher elevations in the U.S. that you can drive to, about 12,000 feet or more.  If you are planning a trip that may take you to these extreme elevations, it would be wise to look into altitude health affects for yourself and those travelling with you.   If you plan to camp in the mountains you should be aware of the reduced output that your generator can supply.  For each 1,000 feet of elevation above sea level, a 3.5% drop in output will be experienced.  So, for example, if you have a 7,000 watt unit, you will only have about 5,500 watts at 6,000 feet or 4,500 watts at 10,000.

Well, those are just some of the challenges you may face when travelling through mountainous regions.  The geographic beauty, however, is well worth it.  If you have never ventured on these roads in the sky, you may want to give it a try.  Just drive safe.

Note: The operation, and or tips, herein stated, may vary or not be applicable to all coach or tow vehicle configurations. Always refer to the directions as outlined in the O.E.M. operator’s manual for your specific coach/rig..


Making The Grade   -   Lug_Nut    -     Peter Mercer

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25 Responses to “RV Driving On Extreme Mountain Grades”

  1. Gary on September 1st, 2011 5:06 pm

    will this work this time? I have carefully put in the correct captcha code so here goes. My addage which has always been true to me was: whatever gear you need to go up, is the same gear you need , to go down. Hopefully you have a tran temp gauge to correct any problems. If too hot, shift up or pull over.

  2. Barry engleman on September 1st, 2011 7:08 pm

    Read with great interesting after doing a 14% grade downhill with close switchbacks yesterday in our 40′ Dutch Star with a Jeep Liberty in tow. First gear, about 5 mph average and lots of brake to boot. Brakes never got hot enough to smell and I was happy to go down it with the safest possible feeling. We were south of Shiprock between Red Rock and Lukachukai going down Buffalo Pass into Lukachukai. The road was great, just the steepest road I have ever done. Did 10% over Teton Pass both ways from Jackson to Victor, Idaho last year. Piece of cake.


  3. Lug_Nut on September 1st, 2011 7:09 pm

    Gary, Great advice. Thanks for your valued comment.

  4. Lug_Nut on September 1st, 2011 7:16 pm

    Barry engleman, Great, you’re out doing the slopes! The real steep stuff is usually shorter, but not necessarily. Thanks for sharing your experience with us.

  5. Owen B. McCullen on September 1st, 2011 7:19 pm

    i live in Oregon and there used to be quite a few log truck drivers. They dealt with extreme grades, rough and slippery surfaces and narrow, severely winding roads. Logging roads were usually built in the roughest and steepest terrain with no improvement of the road bed or fill on the grades. They also frequently had brake problems because the volcanic soil types ground brake shoes to bare metal all too quickly. I was taught to drive on grades by one of them. He would not disagree with anything you said but would emphasize starting down grade below the speed you might think was safe or allowable. It is always easier to add speed on a down grade than to subtract it.

    Another trick was to put an air application gauge on a clearly visible spot on the dash or glare shield. What the gauge does is measure the foot pounds of air pressure applied to the brakes, giving a visual prompt as to exactly how hard you are applying the brakes. Without the gauge, it is impossible to know with any degree of accuracy just how much air you are sending to the brakes. Why add a gauge?

    His inviolate rule of thumb was if it took more than 10 PSI to maintain the desired speed, you should gear down to a lower gear and keep doing that until you could hold your load to an acceptably low speed using only 10 PSI of brake force. He believed that you could maintain 10 PSI on the air brakes indefinitely, even on long grades without overheating your brakes.

    I can testify that 10 PSI is very little pressure, perhaps less than anyone would think was applying any braking force at all. However, I have used his system for mountain driving for years. Our present coach is a Monaco Executive with a 500 HP Cummins and an Allison transmission. It has a two speed Jacobs compression brake.

    I prefer too much stuff and we tow, on a trailer, a full size 3/4 ton 4WD diesel GMC crew cab pickup loaded with tools and a 96 gallon flat auxiliary fuel tank in the pickup bed. The combined load, motor home, flatbed trailer and pickup usually weighs around 58,000 pounds. Oregon has a number of free scales for the benefit of loggers and they are always open to any user. So, it is possible to know quite precisely our weight very conveniently.

    We have traveled some very steep grades, particularly in eastern Oregon on old state roads. The system you advocate plus the air application gauge has allowed us to travel with no great worries. Of course, you should watch the transmission temperature closely, too.

    I am sure we all agree that speed is less important than safety. Most any truck repair shop can easily add an air gauge to any motor home with air brakes.

    Finally, he would echo your comments about turning off the Jake when road conditions are slippery. His only accident in many years of driving came about when the Jake literally threw him and an estimated 95,000 load off a grade when there was ice. Fortunately, he survived but the truck did not. What he relates as amazing to him was the extreme suddenness of the event, with no forewarning. One second he was moving along down hill loaded and the next he was in space and bailing out of the cab of his truck only to land on a steep rock face. He had several weeks to think about the situation while he was hospitalized.

  6. butterbean carpenter on September 1st, 2011 7:26 pm

    Howdy LN,

    Thanks, for a completely understandable explanation….. This is for diesel rigs, now what about gas rigs?? There are many people too poor to afford DPs !!! When in
    the ‘hiilly’ country how do you ‘hold-em-back’ on the down-grade, without a Jake or
    exhaust brake?? We usually just downshift, before the crest and try to let the engine slow it down… But sometimes it gets a little ‘white-knuckled’!!!

    Smooth roads, clear skies & balmy breezes !!!!!!!!!

  7. Lug_Nut on September 1st, 2011 7:33 pm

    Owen B. McCullen, Excellent input! Thank you for underlining some important points. I appreciate your great input.

  8. Lug_Nut on September 1st, 2011 7:40 pm

    Butterbean, Yes, I did cover gas rigs, in the following section. Fortunately they are somewhat lighter than some of the diesel units. However, the over 22K gas rigs should perhaps consider an after market exhaust brake. If you wish I would be happy to address the gas market only on this topic. I have been there on these same 18% grades with a 23K gas rig. Thank you for your valued input.

    “All Categories of coaches and trailer tow vehicles: When approaching a grade that is descending substantially and will, or may, cause your vehicle to increase speed above that which you wish to travel, or may be safe, do the following. Slow to the speed, or slightly lower, that you intend to descend the sloop, prior to reaching the crest. Be aware of what traffic may be behind you and use caution as you reduce speed as not to cause any danger. Select a lower gear to maximize engine RPM and driveline resistance. Now maintain any excess speed by short adequate hard applications of the service brakes. Remember, the wind resistance is now working with you, and can aid you to keep a comfortable speed.”

  9. Art on September 1st, 2011 7:43 pm

    Lug Nut, GOOD to see you back on the horse……………see you next month.

  10. Lug_Nut on September 1st, 2011 7:46 pm

    Art, Thanks, look forward to it.

  11. Charles on September 2nd, 2011 9:29 am

    good article I had always wonder how they got the grade. One ouestion when a highway milage sign says 25 miles to next town (not named here) where is that milage to.

  12. Geoffrey Pruett on September 2nd, 2011 10:22 am

    Drove a lot of 30’s and early 40’s trucks with small engines and a lot of gearing, The uphill was a given, slow, the downhill was learned, same gear as at crest for as many yards as it took to cool things down so the drive train no longer smelled like a foundry. The extra air water and oil flow cools things down without stressing things too much. Brakes were seldom a problem if maintained as all of these had 17 or 18 inch wheels and 4 to 5 inch wide shoes. If the fluid was clean and the adjustments were up they would handle gear down stops quite well. Our current 1998 P30 based unit has much poorer brakes than some of these old timers. High pedal pressure in spite of boost and they are supposed to be working correctly. Some times wish we still had our 1979 C on a Dodge frame as the brakes on it would stop as hard as asked right up to opening cabinet doors behind you. Driving around Seattle are this was some times tested. The most important thing still is do not try to make up the time lost going up on the down hill side. We will all get there but I am in no rush.

  13. Lug_Nut on September 2nd, 2011 1:15 pm

    Charles, Glad you found the piece of interest. Generally signs display the distance to the city hall of a named city. Thank you for your valued input.

  14. Lug_Nut on September 2nd, 2011 1:17 pm

    Geoffrey Pruett, Great information. Thank you for taking the time to share that with us.

  15. Chris Clarke on September 2nd, 2011 4:33 pm

    I just got in from a trip in the Rockies west of my home in Calgary. On the trip with our 13,000 lb. fifth wheel I climbed and descended 2 high passes with long downhill and at times steep descents. My 2007 Silverado 2500HD Duramax climbed the passes just fine but the descents were “exciting”. Using the tow-haul mode the rpm reached higher values than I like to see; and even then the rate of speed was increasing. By switching to manual lower gear selection and reasonably judicious use of the brakes and getting out of tow-haul I managed to get down at a comfortable rate with control. But I also think that the wear and tear on the trailer and truck brakes was excessive.

    My questions to you are: 1. which item (PacBrake or Jake Brake) would be appropriate/best for my truck? and, 2. are the exhaust brakes intended for use in tow-haul mode with the Allison tranny?

  16. Lug_Nut on September 2nd, 2011 7:14 pm

    Chris Clarke, Sounds like you did pretty well. The Pac Brake, or similar, is the only reasonable answer to adding to your truck. The Jake requires that the engine alters internally changing the valve timing and action. The Pac Brake is really an exhaust restriction that maintains a high back pressure and there are several good aftermarket units available. While the Jake type is rated at a higher resistance, there is alot to be said about the exhaust brake (Pac). My previous coach had a Pac Brake, and I can’t say enough as to the braking control it delivered. The addition of a good exhaust brake would well be worth the money. Operated correctly it can reduce the use of service brakes to nearly, if not, nil. I can not comment on the “Haul” mode as I believe it is really for pulling torque shift co-ordination, The main thing you want is the torque converter clutch to be locked up, which I believe is accomplished in all gears, save 1st, in normal drive mode. Your question on the “Haul” mode could perhaps be better answered by GM or Allison.
    Thank you for the question anfd for your great input.

  17. Judith Chesney on December 21st, 2011 11:41 am

    I truly wish I had had a computer and had found this information before we left on our trip out West. We went into the Big Horn Mountains and there is were we lost our truck and trailer to high winds and a 10% grade. We were very lucky to come out of the accident alive. Now I realize what went wrong and will look forward to learning more about traveling with an RV.

  18. Lug_Nut on December 27th, 2011 7:18 am

    Judith Chesney, I am sorry to hear of your poor fortune but glad you came through it in one piece. When winds are high, one should weigh whether to travel or not that day. Sometimes it just comes up while travelling. Hoping for a smoother trip for you in the future.

  19. larry miller on March 8th, 2012 11:56 am

    There is one thing that I have not have not heard anyone mention. I have had a lot of experiences driving in the mountains. I can relate some really close calls that shows we have gathered our knowledge the hard way. One was an 18″boulder in our lane going down McClure Pass by Marble CO. We were meeting a vehicle coming our way in other lane, 2000 Dutch Star full speed and braking as much as possible. We only had a split second to respond, as we met the truck, we turned left and just had enough room to go around and not hit them. Another was going Eisenhower Pass and a car goes around and slams on his brakes in front of us. We had to brake as hard as possible, brakes slowed us up some with brakes fully depressed, heat built and then no brakes at all. We got to 90 MPH and just hung on and made the best of a bad situation. I shake all over just relating the stories.

    One thing, that I would like to contribute is this, when going up a mountain, always turn your heater on maximum heat and fan. This takes the heat away from engine, therefore making the engine run much cooler and not shoot temperature up. We use this technique quite often and works every time. A good way to check how much it helps, start up the mountain as you regularly would and as the heat raises, turn the heater to the max and watch the engine temp back off. You will like it,

  20. reverse look up phone numbers on July 27th, 2012 10:53 am

    Hi i think that you should add captcha to your blog

  21. NeXus RV on August 8th, 2012 9:04 am

    Very good article and post, very informative. Thanks for the info!

  22. Momo on August 22nd, 2012 3:30 am

    Big Daddy:Did you use the correct DOT reeriuqd fluid? how did you bleed, bleeder ball, gravity bleed, etc i would re-bleed ensure the correct fluid. make sure you didnt use an old opened fluid, within a short amount of time, old opened fluid, even if capped off, will suck in water, which will make the brakes spongey.i like to use brand new, then throw out whatever i dont use, so im not tempted to try and use an opened bottle down the road. clean your pads and rotors with brakleen, you probalby leaked some. steel braided lines are a must, at least for the front, good call poster above later dude.

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