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Old 12-08-2021, 07:34 PM   #71
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My father was a Chemical and Design Engineer in the tire and rubber industry for 47 years and got his Masters in Engineering from MIT in the 1920's, my Uncle was in charge of setting up and maintaining Vulcanizers and Cousins involved in making the presses so I am familiar with how the tire speed ratings get bracketed for short bursts at MAX speed at moderate temperatures until reaching the stated MPH goal. Most of my family was involved in the design and manufacturing of tires for Civilian, Aviation and Military use. The customized rubber formulations my Dad designed for tires set aside for Civil Defense had a 50 year storage life but were much more expensive than the 5 or 6 year consumer tires we get. The tires for vehicles used to fight aviation fires were highly specialized formulations too as were the rubber suits used by the front line firefighters.

Had a senior moment on the speed rating and the MAX common speed rating is 75 MPH for which I would still be considering 65 MPH sustained the reasonable limit especially after the tires were over a few years old. Setting the cruise control at 75 MPH is something I would not recommend on a tire with a just a 75 MPH MAX Speed Rating. If its Temperature rating was below A then I would lower the sustained speed even further to just 60 MPH sustained.

Those unfamiliar and unaware of how things worked might be inclined to misinterpret things as giving them a cart blanch to just put the pedal down and exceed the speed rating of their tires at extremely unsafe levels.

As far as tires are concerned the old adage holds true that the candle that is burned more brightly burns out more quickly which too many people find out the hard way where I live which some consider the blowout capital of the US.
Bravo that is an impressive resume

I never suggested that anyone exceed the speed rating of there tires and never will.

I respect your decision to drive your vehicle how you are comfortable.

Happy Camping, and safe travels.
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Old 12-09-2021, 05:11 AM   #72
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I don't know any Interstate in the south east where you can run 75 mph for any length of time. Wrecks, traffic, or just general dumbassery keeps that from happening.

So, while I will run with traffic at 75 mph in my 2005 MADP 4032, it is never for more than 15 or 30 minutes before a slow down occurs.
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Old 12-09-2021, 06:27 AM   #73
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Driving at 75 mph

I think that driving that speed is taking an unnecessary chance. Even if you donít have a blow out. Most motorhomes just dont have proper maneuvering and braking ability at that speed. And unless we are a trained and experienced professional driver, we donít either. And as truckers drive faster and harder, the catastrophic accident rate keeps going up. You just canít maneuver 30+ thousand pounds with proper safety margins down the road at these speeds. The maneuvering and braking ability just isnít there. And unless you are a commercial trucker, whats the hurry anyway?
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Old 12-09-2021, 08:14 AM   #74
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I think that driving that speed is taking an unnecessary chance. Even if you donít have a blow out. Most motorhomes just dont have proper maneuvering and braking ability at that speed. And unless we are a trained and experienced professional driver, we donít either. And as truckers drive faster and harder, the catastrophic accident rate keeps going up. You just canít maneuver 30+ thousand pounds with proper safety margins down the road at these speeds. The maneuvering and braking ability just isnít there. And unless you are a commercial trucker, whats the hurry anyway?

So, what is a "safe" speed?

As someone on this forum stated - no one wants to ride behind a motorhome.

Every time I try to put the appropriate space between me and the vehicle ahead of me, someone passes me and slots into that space. It happens every single time.

Running with traffic seems safer than running 15 mph slower.
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Old 12-10-2021, 07:24 PM   #75
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Back to the towing issue......I wonder if Allison were to up it's game and come out with an Allison 3000 8 speed, it might be easier to stay in the rpm range.

Another thing I do.....I try and pick up a little speed on certain grades, before I hit the base of the grade. If it's a long grade, the extra speed doesn't help much. I also shift to 5th on almost every grade, set the cruise and let the Allison do it's thing. Once the coach locks in on a speed, in either 5th, 4th or sometimes even 3rd, I manually push the DRIVE button on the shifter. The Allison will stay in the gear you're currently in, even after pushing the DRIVE button. At the peak of the grade, the Allison will start shifting back toward 6th gear. This way, when I top the grade, I don't forget to shift back to 6th.
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Old 12-11-2021, 03:23 PM   #76
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Disapolnted with speed on hills

Could someone be more specific about use of the cruise control in climbing hills?
I only use this on long reasonably level roads with little traffic. I do use the engine break regularly to slow down on descending the hills.
Thanks in advance.
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Old 12-11-2021, 06:09 PM   #77
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I basically drive our rig as DS Don has described and more gears would probably have a larger effect than more HP or Torque on these rigs-6 speeds is just not enough to keep torque in the sweet spot all the time. My 2018 F150 with a ten speed seems to out pull my 2006 Dodge Ram with a Cummins in most situations except at very heavy loads up the steepest hills but those 10 speeds are amazing. Our old RV only had a 330hp Cat with 860 torque and would out accelerate and climb faster than our current 21 DS 4081 without a load behind it. With a heavy tow load, the DS is not affected as much. It basically comes down to power to weight ratio and the higher horse power rigs are usually heavier as well and thus don't necessarily climb much better. I drive our RV like I am on vacation and hauling a bus load of nuns and never out to win the next hill climb. At the end of the day we will all arrive at the campground within 5 minutes of each other.
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Old 12-11-2021, 08:11 PM   #78
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Quote:
Originally Posted by paulwhitaker View Post
Could someone be more specific about use of the cruise control in climbing hills?
I only use this on long reasonably level roads with little traffic. I do use the engine break regularly to slow down on descending the hills.
Thanks in advance.
I've owned three DP's, a 2005 Monaco Diplomat with the 400 ISL and two Dutch Stars with the 450 ISL. The Monaco had an exhaust brake and when you turned on the exhaust brake switch it killed the cruise control. On both Dutch Stars, they had engine brakes which interact with the cruise control, allowing you to leave it on and use the engine brake in conjunction with the cruise control.

With that said, I've been driving all three the same in regards to using cruise control. Since all three were a drive by wire, you could neither feel the engine or hear it. Using the throttle pedal can really waste fuel as you can push the throttle well past where it's providing any additional acceleration.

I use the cruise control about 95% of the time. The minute I enter an on ramp and exceed about 30mph, I engage the cruise. If it isn't already set for freeway speeds, I just bump up the cruise button, as it allows, until I reach my desired speed. My foot is rarely on the throttle.

When approaching a grade, WITH THE CRUISE ON, I drop to 5th gear. After that I let the Allison do the shifting UNLESS it's really steep and I need to shift it to hold some really high rpm's, which isn't that often. Everyone should take a mental note of what the highest speed is achievable in your coach in gears 3 and 4. If you have to manually shift to 4th or especially 3rd, you know how far you can push the speed in that gear.

As I climb and near the top of the grade, I make a determination. Do I need to change the cruise control speed I had set at the base of the grade, or is it too fast for going downhill. Without touching the throttle or brakes, I adjust the cruise control. On my Diplomat with an exhaust brake, I usually had to substantially reduce the speed for the downhill side because it didn't hold as well as my current coach with an engine brake.

Lastly, for those that didn't know, the engine brake on the Freightliner chassis is designed to engage at about 6mph over the set cruise control speed when speed increases going downhill. After it reaches a few mph above that 6mph, it will try and downshift. I always found the 6mph to be way too fast for the brake to start engaging. Consequently, I was bumping the cruise speed down manually about 6 pushes to bring the speed down to the actual speed I wanted to go down the grade.

The setting of 6mph over the set speed can be adjusted by Cummins or Freightliner. They need to have an Incite program that can access the Cummins computer. They simply change the parameters on the cruise control to 1-2mph over the set speed. This makes it much easier to just leave the cruise control set where you want the speed to be going down a grade.

Some of the above sounds complicated, but once everything is set up properly, it's much more relaxing to just let the cruise do all the work and sit back and relax.
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Old 12-11-2021, 09:50 PM   #79
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A boost leak would cause that, ensure all the pipe connections from turbo to intercooler, intercooler to intake are tight. Also make sure its producing the amount of boost its supposed to.
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Old 12-11-2021, 10:10 PM   #80
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That's surprising.....I really wanted an MA for the 500HP and 1800lbs of torque. It's got to pull better than my DS towing my 6100 pound Raptor. The grades out west slow me down to 45-50 mph on 6% and down in the high 30's to low 40's on 7% grades and better.

What speeds are you talking about.
I realize Im late to this thread and this may have been covered, but....
A MA weighs 5000-6000lbs more than the same length DS pretty much negating the 50hp/445tq difference.
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Old 12-12-2021, 05:40 AM   #81
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I have a DutchStar with 450hp and tow a 2019 GMC Denali 4-door pick up and I have no problems with the hills. If you have to lift off the accelerator for just a second, you will lose your head of steam and then you will have a problem keeping the speed up. Your hitch should be rated for 15,000lbs. So a full size pick up shouldnít be a problem. I would have it looked at by Cummins.
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Old 12-12-2021, 06:04 AM   #82
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So many times you get caught behind a semi struggling with a hill and then itís too late and your done. I pulled a 2021 Tahoe with a 2019 DS and once you loose that momentum, itís over. I also was leaning toward the MA and was told by a 2021 MA owner, 50 hp didnít make much difference and they regretted not going to the 605.
That was enough for me to go with a 605 and I can attest, itís night and day over the 450 and even the mileage is better.
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Old 12-12-2021, 06:14 AM   #83
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The allison trans can be reprogramed to better suit the engine power curve. Your local Allison vender can also program the MODE button to a differnet shift pattern better suited for hills and do a eco setting with the light off. every engine model has a differnt peak power point and you can benifit by some slight changes to your combo. rear end final drive ratio , engine peak power RPM and road speed all play a roll in the program.
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Old 12-12-2021, 07:03 AM   #84
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I try to keep the speed up while approaching the hill and I can usually carry the momentum all the way at 65mph. There are times with traffic and other large vehicles that this isn’t possible. When everyone else is bogged you will be too. I have chugged up some hills doing 35mph because of traffic or slow drivers. I don’t find towing has much of an impact on my performance. My mpg is always 10-12 loaded and towing. I pull the hills at the same speeds towing vs not towing. I do find without the car I recover quicker going up hills when I get slowed by traffic. My rig is only 33’ and I only have 210 ponies pushing her. I weigh in at 27k plus 4K when the car is on.
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