Let’s Talk About Mountain Driving and Gear Selection. (1 Viewer)

[04UZJ100]

Moving from Chicago to Alaska there are obviously a lot more mountains. On the highway, I frequently drop both the LX and 4R to 4 for increased power and to prevent hunting. The torque converter remains locked and everything is happy.

However, what is the best technique when ascending up winding roads with switchbacks at 25-35mph?

If I leave the truck in D, it will occasionally hunt for gears and keeps the RPMs around the 2k mark. I personally don’t care for lugging up the mountain since the water temp increases and so does the transmission temp.

What I have been doing is leaving the trucks in 2 or 3 which keeps the RPMs in the 2.5-3.5k RPM range. That appropriate?

How about on the descent? Is it OK to utilize engine breaking? I typically leave it in D because I’d rather heat up brakes than damage the transmission.

Any advice would be appreciated.

 

[JayTortugaTee]

We drive quite a bit of Mtn roads to get to our cabin and i do exactly what you mention.
Use manual mode on way up and down, but usually keep it between 3rd and 4th gear.
Makes it way more fun to drive and the truck handles better under engine braking vs traditional.

 

[Cruisin911]

I think you're overthinking this. The transmission can take the downshifting. No need to heat up your brakes. When mountain driving, simply select whichever gear keeps you at your desired descent/ascent speed. I live in colorado and regularly drive in the mountains towing and not. These engines and transmissions are nearly bulletproof. So long as you're not towing something and its trying to push your RPM past redline, you'll be fine.

 

[04UZJ100]

I think you're overthinking this. The transmission can take the downshifting. No need to heat up your brakes. When mountain driving, simply select whichever gear keeps you at your desired descent/ascent speed. I live in colorado and regularly drive in the mountains towing and not. These engines and transmissions are nearly bulletproof. So long as you're not towing something and its trying to push your RPM past redline, you'll be fine.

I’m a recovering Mechanical Engineer. Of course I’m overthinking it.

 

[canyonrider]

^^^Yep, what they said. You want to use engine braking in the mountains. Also keep the ECT/PWR button on, which is much better for climbs (towing or not).

 

[Cruisin911]

I’m a recovering Mechanical Engineer. Of course I’m overthinking it.

I completely understand. I’m a EE and go overboard on wiring. Next project is building my own spod.

 

[TeCKis300]

You're doing it right going up.

I would suggest doing the same and use lower gears on the downhill. Especially on the downhill. With as heavy as these rigs are, and as powerful as they are, definitely use engine braking. If you leave it in one gear, all the energy is translated to the motor. Though the tranny has plenty of cooling capacity too.

I just got back from camping in the mountains last weekend with trailer in tow. Probably 14,000 of rig. Often needing 2nd gear coming into switchbacks. Tranny can handle it no problem.

 

[Dan Higgins]

I'll reiterate what others have said. Definitely use S-mode on the descents and especially when towing. (I tow a 6K# trailer around Colorado mountains and my LC weighs in at about 6700#.) In fact, I sometimes try to see how much I can control my descending speed only using the transmission. When I'm long, curving descents where I want to ensure I maintain control I'll leave the transmission in lower gear and simply use the gas to speed up. The reason for this is that when I back off the gas the engine compression immediately kicks in - more control. BTW, I learned this technique when I had a Land Rover LR4 which was also a heavy vehicle and in my case had the 8-speed transmission. I went through offroad driver training on two different times - once through a Land Rover class and once with a guy named Bill Burke. Both made it very clear that it was best to use engine compression going downhill. This becomes more true when traction may be questionable due to the fact that the engine compression resistance applies to all wheels of the 4WD and thereby is more "steady" than braking which is more likely to lock up.

When I do use engine compression I try to make sure that my RPM are not already too high before shifting so that it eases into it rather than jumping from 3500 to 4500. I use the brake, if necessary, bring the RPM down a bit then shift. I also try not to jump 2 gears at once though usually this won't hurt.

An example, going down the 9-mile, 7% grade with lots of tight (20-25mph) curves on Monarch Pass in CO with my trailer "pushing me" from behind I kept transmission in S2 and sometimes S1 (4H) to keep the speed under control. It might seem overkill going that slow but it only last for about 20 minutes.

I also always use ECT Power in the mountains or at least going uphill. And always when towing.

One final thing for drivers of MY16 and later is that the new 8-speed transmission has "intelligence" (software) that attempts to adapt the shifting characteristics to the drivers "style" of driving. (This may be true of the 6-speed models but I don't have any experience or knowledge on that. I do know that more advanced "intelligence" was also a characteristic of the 8-speed transmission on my LR4.) This "intelligence" can become a bit confused if there is a significant change in driving "styles". So if you change drivers or go from towing to not towing or something like that it may take a bit to "reset and relearn". During those times it may feel a bit confused.

Bottom line - use engine compression going downhill. That is what the manufacturers recommend.

 

[RET2]

I’m a recovering Mechanical Engineer. Of course I’m overthinking it.

This should be enshrined in stone, thanks for the laugh

 

[bloc]

One small point.. the control systems on these transmissions are sophisticated enough to not allow you to downshift if it would harm the engine.

So other than not wanting to deal with the jerkiness or noise of a downshift to a high rpm, there is no reason to avoid it if you need the additional engine braking

 

[Markuson]

Even without towing, I use manual shifting in long mountain descents simply because it’s tge only way my brakes don’t overheat.

I70 into Denver is a perfect example. With 35’s and over 8000lbs, manual shifting and lower gears is absolutely essential, and very effective.

As for ECT power button. Yes. It helps, but keep in mind that all it’s really doing is giving your Electronically Controlled Transmission (ECT!) a bias toward higher RPMs and the gear shift points to hedge toward them. I do leave my heavy rig in ECT...but nothing replaces the usefulness of manual shifting on long climbs, and especially descents.

 

[Dan Higgins]

One small point.. the control systems on these transmissions are sophisticated enough to not allow you to downshift if it would harm the engine.

So other than not wanting to deal with the jerkiness or noise of a downshift to a high rpm, there is no reason to avoid it if you need the additional engine braking

I of course agree. The reason I try not to make too much of a jump is to reduce jerkiness. Simply because I prefer a smoother driving style and also when managing a trailer on a descent. And, BtW, I have certainly experienced some of the intelligent safeguards when I accidentally upshift when I meant to downshift and vice verse.

 

[Dan Higgins]

One the topic of S-mode and using it for engine braking the section in my owners manual (2016 MY) around page 200 touches on this. It implies that one of the primary reasons for S-mode is engine braking. It also states that when switching to S-mode it will got to S4, S5 or S6 depending on the situation. (This being an 8-speed.). Below is a quote from page 201.

“Shift ranges and their functions
● Automatically selecting gears between 1 and 8 according to vehi-
cle speed and driving conditions. But, the gear is limited accord-
ing to selected shift range.
● You can choose from 8 levels of engine braking force.
● A lower shift range will provide greater engine braking force than
a higher shift range, and the engine speed will also increase.”

There is also a reference to AI-SHIFT but I haven’t seen any details on what is meant by AI. It would be nice to see a paper on the “intelligence” built in to the system. Maybe at least the areas and high level functions where it plays and what factors influence it.

 

[coleAK]

I drive all over Alaska and we really have very few true mountain roads unless you get off the paved roads. I grew up in the Sierra Nevada mountains and we have nothing like that up in AK our larger passes are ~1000 vertical feet. Right off hand the largest pass I can think of on the road system is Thompson out of Valdez. I use S mode when towing the camper (<7000lbs) but when I’m not towing just keep it in drive.

 

[Markuson]

I drive all over Alaska and we really have very few true mountain roads unless you get off the paved roads. I grew up in the Sierra Nevada mountains and we have nothing like that up in AK our larger passes are ~1000 vertical feet. Right off hand the largest pass I can think of on the road system is Thompson out of Valdez. I use S mode when towing the camper (<7000lbs) but when I’m not towing just keep it in drive.

That’s really true.
I’ve driven all over including the Brooks Range, and even that part of the Dalton Highway isn’t very steep.

 

[2001LC]

We've runaway ramps for those that have yet to learn transmission have gears for a reason, use them. Your cruiser will love you for it.

Up or down hill using gears/shifting to keep a good constant speed and RPM in a comfortable power band is just good driving. We so often see vehicles slowing uphill with pedal to the metal blowing smoke from the tailpipe never down shifting, then flying by on the down hill with brake lights constantly coming on. I just give them room!

Another mistake often seen with out of towners, is braking (brake pedal or engine) in the turns, planning ahead is key to safe driving. Constant speed or even slight acceleration and vehicle hugs the turns.

My best advice when driving on ice, kept throttle constant. shifting or even letting foot off the gas pedal a little can start a slide/spin, give a little gas and slide the other way. Plan ahead, don't be that guy in the ditch.

 

[Dan Higgins]

^^^

 

[coleAK]

^^^ now winter driving is a different question. I use The manual shifting all the time for engine breaking. Heavy truck+ice+breaks=sled.