Quote:
Originally Posted by Dinop
Very helpful information. We actually test drove a 2017 Tiffin 31sa yesterday along with a . Diesel 31Br. In Knoxville Tn.
My definition of mountains are over 5000’ similar to what you mention in your travels. We have pulled a 5th wheel out west thru Colorado , Utah, etc and to Montana.
Unfortunately when we test drove the Rv we are not towing so it is difficult to judge how well the gaser performs, mph up hill and noise!
How fast can u pull uphill in the Rockies (mph ?) How noisy? How is it descending down the mountain?
I am not looking to race thru the mountains but I also would like to get to my destination in a reasonable amount of time and be comfortable and feel safe.
I appreciate any insight you can offer.
Dino
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So much of this is about personal perception, experience, expectations, and have an understanding of how to drive these things in the most effective manner possible given the conditions. If you think driving a Buick or Lexus is a fine driving experience (numb and isolated) this isn’t it. If you like to be engaged with your driving, and connected to what’s going on, this is a lot of fun.
First, I have never felt the least bit unsafe or have had any sort of so called “white knuckle” driving experience in our coach, other than a terrible road in Nova Scotia, but that’s not relevant
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Next, if I was driving from Denver to Grand Junction on I70 on a regular basis in my RV, I’d probably have a different perspective
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Driving interstate mountain grades is completely different than many of the significant US / State Hwy. grades. When cars are wizzing by at 65 mph and you are in the truck lane doing 30, it can seem to be a long slog up Vail Pass. OK, but the reality is, it’s what, a 10 mile grade, does it really make any difference if you are 30mph vs. 40mph at the end of the day?
I did pass a semi going up Vail Pass, and in the eastern “mountains” (lower altitudes) I certainly easily keep up with and will pass trucks going up if / when it makes sense to do so. I do remember a DP blowing by me on I70 in UT (there are a couple big grades), maybe doing 5-10mph more than I was
.
On the other hand, once you start getting on the secondary roads, the speed limits for everyone is generally slower to begin with, and particularly with any sort of switchbacks, no one in any sort of big rig is going to be going much faster than anyone else. Going up Slumgullion I was down to 25mph a few times, but with the switchbacks, you just are not going to go much faster in a big DP anyway, and they have to slow down even more on the curves.....
A relevant anecdotal story. Going up to Estes Park, as we were leaving Boulder, there were 2 other RVs in front of us as we were leaving town, one of them a DP. As I was the last In line, I was the first to pull over and let a line of cars by, and at that point I didn’t see the other 2 RVs the rest of the way, until, we got to the first stop light in Estes, and guess what, we are all back together again.
I’ll get to downgrades at the end....
Noise going “up” is all up to you and your right foot how fast your want to go and what rpms are necessary to do that. The reality is, that the speed gain gets to be negligible vs. rpm jump at some point, so it’s something you get a feel for. And that’s for any grade, even on flatland interstate, and why using CC can be obnoxious.
On our coach, the normal 65mph cruising rpm is 2250, and you can take that to about 2750 and at those rpms there is no engine noise inside our coach. This is a vast majority of our driving time (over 90%.....)
The next normal jump is 3250 rpms -3750, you hear it in our coach, but it’s negligible, and certainly a very minimal amount of our driving. If you have CC on, it can cause a jump to that 3250 band on “flat land” interstate hills, but if don’t have CC on, you can stay under 2750 and maybe loose 5mph.
The next rpm jump is 4250-4750, and yep, you hear it. You’ll certainly get into this range quite a bit on bigger climbs and steep downgrades. Again, keep in mind just how much of your driving this would consist of. For those that use CC all the time, this is what they really complain about, because it will cause that (often unnecessary kick down to 4250, even on smaller grades.
The last band is 5000+, and that’s all on you to control going up (that’s where speed gain vs. rpm becomes negligible), but you may certainly get into this on steel downgrades. It’s obnoxious. But the reality is, the amount of time you (we, at least) spend driving 5000 rpms (even 4250+rpms) is negligible.
As for driving significant downgrades...... you’ve got to be in tow / haul mode, start slow, force a low gear, and keep the rpms up. If the downgrade speed limit is 35mph, you start down at 20, in a low gear and the engine rpms already spinning like 3500rpms, maybe more, so the engine / tranny are holding you back from the very beginning of the decent. If you start down Wolf Creek pass for instance at 30mph and 2000 rpm in 4th gear, you are already in trouble, and it’s going to be an ugly, white knuckle and unsafe drive, over using your brakes and putting yourself and others in danger.
This is an interesting, and long thread, some of the posts I have a strong disagreement with... but, it’s worth a read.
http://www.irv2.com/forums/f258/gass...is-429977.html
This is an excerpt from my last post in that thread; I don’t remember the source, but I think it does a great job explaining the how’s / why’s of safely descending steep grades.
1)
Downgrades
There’s a limit to the amount of heat that brakes can absorb and dissipate. The highest brake temperatures occur when braking from highway speeds while on long downgrades, or from repeated use of the brakes without enough cooling time between applications. Almost all brake failures and downhill runaway crashes are caused by overdriving the ability of the brakes to deal with heat. In other words, poor speed control.
Whether in town or on a highway, you’ll usually need to descend a hill more slowly than other traffic in order to avoid overdriving your brakes. You should be in a lower gear to go down the hill than used to climb it. Never shift
to a higher gear on a downgrade unless the speed on the grade can be controlled with a retarding device or engine compression.
Select a safe speed that's not too fast for the weight of your vehicle, length, and steepness of the grade, weather, and road conditions. Use an appropriate low gear to hold that speed, and use the vehicle’s retarding device.
If this doesn’t control your speed, and speed is increasing above your chosen speed:
• apply the brakes hard enough to reduce speed by 10 to 15 km/h — the brakes are cold at this point
• downshift to a lower main gear
Continue down the grade, using engine compression, transmission gearing and your vehicle’s retarding device to control your speed. If the speed increases again, repeat this process. Be careful using this procedure on icy roads.
Keep your vehicle in gear all the way down the hill.
2)
Engine braking occurs when the retarding forces within an engine are used to slow down a motor vehicle, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes.
The term "engine braking" refers to the braking effect that occurs in gasoline engines when the accelerator pedal is released. This results in the throttle valve that controls intake airflow closing and the air flow through the intake becoming greatly restricted (but not cut off completely). This causes a high manifold vacuum which the cylinders have to work against—sapping energy and producing the majority of the engine braking force.
While some of the braking force is produced due to friction in the drive train, this is negligible compared to the effect from the manifold vacuum caused by the air-flow restriction.
As soon as the accelerator is released enough to slow the engine, engine braking comes into effect as long as the wheels remain connected via the transmission to the engine. A slipping or disengaged clutch, or a torque converter, would disengage the wheels or absorb braking energy.
The braking force varies depending on the engine, and the gear the transmission is in.
The lower the gear, the higher the braking effect due to higher rpm and the torque transferred through the transmission (higher torque is delivered from the engine in lower gears).
Engine braking avoids wear on brakes, and can help a driver maintain control of the vehicle. Active use of engine braking by shifting into a lower gear can help control speed while driving down very steep and long slopes, saving the brakes from overheating or excessive wear. If it is applied before the brakes have been used, it can leave the brakes available to make emergency stops (or slow when necessary; my edit)
Just to end this, when we are in the mountains, and driving our little gasser, it is what it is. I really enjoy it and take it all in for all it’s worth.
Hole all this helps.
Regards
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