Driving habits vs performance

[BernieD]

Tom:

Count me firmly in the school of "leave it in cruise".  "Blowing by" someone else on a hill climb is not within my budget plan.  Likely you have made the right choice for your technique (or your captain's) if speed is the main concern.  I think Bernie hit this issue right on target.  Speed versus economy.  Being retired and fulltiming, I mostly cruise at 55 mph and watch almost everyone blow right by me.  Until I pass them at the truck stop. 

Smoky

Since your Allison won't upshift to 6th until about 60, you are probably doing all your driving in 5th gear. I would recommend your most economic cruising speed to be about 62mph.

 

[Gary RV_Wizard]

Speaking of Allison Transmissions.... On my gas powered rig (not diseal) there is a switch called "Grade Brake" or "Grade Control" (not sure which and can't check just now) which I'm told changes the transmission shift points or rations so as to increase engine braking when going DOWN hill.

The grade brake on the Allison 1000 5 speed somewhat mimics the operation of an engine brake on a diesel. Basically, with the Grade Brake switch on, a tap on the brake pedal triggers downshifting to a lower gear than the normal gear selection for the current speed.  And as you no doubt know, decending a hill in a lower gear slows the rig with less use of the service brakes.  Grade Braking overrides the gear you have selected with the PRNDL lever but will only go lower than the selected gear - never higher.  It essentially does what good drivers already knew to do: downshift when going downhill.  If you have already downshifted to the same (or lower) gear the Grade Braking logic would have selected, there will be no downshift.

Here is an excerpt from an Allison brochure:

Grade Braking ... will assist in maintaining desired vehicle speeds when driving on downhill grades by automatically implementing a shift schedule that utilizes the engine and transmission to slow the vehicle, which reduces wear on the traditional braking system and increases vehicle control.

Grade Braking monitors vehicle speed, acceleration, engine torque and brake pedal usage. Using this information, it detects when the truck is on a downhill grade and the driver desires to slow the vehicle by pressing the brake.

In the pick-up truck version of the tranny, Grade Braking is combined with the Tow/Haul mode switch. The motorhome version of the tranny doesn't have Tow/Haul mode, so there is a separate Grade Brake switch to activate it.  This will be covered in the Allison owners manual that should have come with your rig.

 

[Tom]

For the benefit of those who didn't correctly read my first message in this topic, the improved performace on hills occurs irrespective of whether we use cruise control or not. With cruise engaged, a heavy foot isn't in the equation. The original advice I received here that suggested this technique for hill climbing in fact suggested keeping cruise engaged.

 

[Smoky]

Bernie:

Thanks for that information.  I will look more closely at my cruising speed.

I did note that my mpg increased to 11 on my last leg from what was original about 6.5.  Some of this was due, I am sure, to the flat terrain after exiting the east coast mountains, and some was due to the break in process.  But I never dreamed I would hit 11 and was hoping for about 7.5 to 8. 

I cannot detect any gear shifting above 55 mph, but I will examine this more closely on the next leg.  If I kick in the engine brake, it seems to want to drop below 55 before activating.

Bernie, I am up for anything that will save me money, so I will look closely at your advice.  Keep in mind I am VERY heavily loaded, so this weight might also affect the transmission drop points.  I am hopeful I do not have to increase my speed very much to find the sweet spot for reasons mentioned below in this message.

It is sort of frustrating not to know what gear you are really in.  The Allison instructions I am reading tell me that even though I punch in a lower gear, the transmission does not downshift until I reach a safe speed for making that downshift.  In other words, I might be looking at a 4 or a 5 on the gauge, but the transmission might still be in 6 because the speed has not slowed enough to make the downshift.

I am still not sure what Tom's approach is.  His latest message clarifies that he uses his down shift method whether in cruise or not in cruise.  If in cruise and above the downshift speed, would not the manual downshift be ignored until he applies some braking, taking the coach out of cruise and lowering the speed enough to safely downshift?  I feel certain that is the case in my coach.

If my comments do not make sense, please excuse, as I am still trying to learn all this stuff.

I have learned for myself a technique which seems to work very well for me when cresting a hill.  If I see at the crest there will be a significant downgrade, I simply tap the brake, removing the coach from cruise control, and then turn on my engine braking switch.  This will usually slow the coach enough for the engine braking to do its job.  I found out simply turning on the engine brake switch, without that tap, does not prevent increasing speed on the downgrade, and the still turned on cruise control seems to be the dominant factor.  I do not know if this technique is useful for those cruising above 55 mph. 

I am very content at 55 mph and never in a hurry to get anywhere.  I recall when I used to do commercial boat deliveries.  I was used to my own boat which would cruise economically at about 35 mph, just up on plane.  When I delivered my first diesel trawler I was at first quite irritated by the length of time it took to get anywhere.  By the second day out, I not only became used to the slower speed at about 6 or 7 knots, but discovered I now had a chance to see a LOT more roses along the garden path.  with a much slower required reaction time I could really enjoy a trip and began to notice things I had always overlooked before.

This principle has certainly carried into our fulltiming land adventures.

 

[BernieD]

I am hopeful I do not have to increase my speed very much to find the sweet spot for reasons mentioned below in this message.

Cummins suggests about 1600-1800 RPM as the sweet spot.

It is sort of frustrating not to know what gear you are really in.  The Allison instructions I am reading tell me that even though I punch in a lower gear, the transmission does not downshift until I reach a safe speed for making that downshift.  In other words, I might be looking at a 4 or a 5 on the gauge, but the transmission might still be in 6 because the speed has not slowed enough to make the downshift.

If your tach is reading above 1500 RPM at 55mph, you are in 5th gear, if down around 1400 RPM, you are in 6th.

I am still not sure what Tom's approach is.  His latest message clarifies that he uses his down shift method whether in cruise or not in cruise.  If in cruise and above the downshift speed, would not the manual downshift be ignored until he applies some braking, taking the coach out of cruise and lowering the speed enough to safely downshift?  I feel certain that is the case in my coach.

If my comments do not make sense, please excuse, as I am still trying to learn all this stuff.

I am not sure I follow what you are saying.

I have learned for myself a technique which seems to work very well for me when cresting a hill.  If I see at the crest there will be a significant downgrade, I simply tap the brake, removing the coach from cruise control, and then turn on my engine braking switch.  This will usually slow the coach enough for the engine braking to do its job.  I found out simply turning on the engine brake switch, without that tap, does not prevent increasing speed on the downgrade, and the still turned on cruise control seems to be the dominant factor.  I do not know if this technique is useful for those cruising above 55 mph.

Why not just turn off the cruise rather than tapping the brake? Leaving the cruise control on should have no effect on the PacBrake when you are going downhill.

 

[Jeff]

Smoky:

I have a Cat 3126B engine so I am sure the RPM's are different for your Cummins but if you are over 1500-1600 RPM's at 55 you can be pretty sure you are in 5th gear instead of 6th. At 61 I am showing 1675-1700 on the Cat in 6th and Cummins is usually lower.

A better solution for me was to buy Silverleaf's VMSpc software. Now I not only know what gear I am in but just about any other info I would like to display of the engine/transmission parameters. New toys also make the miles go by with GPS software displayed as well.

Do you calculate leg mileage by filling up or does your coach calculate it? Silverleaf does a running mileage calculation that is quite accurate but if I use one tank refill to calculate what I am getting it varies a great deal because of the level of the m/h, etc, affecting the amount of fuel I can put in the tank. Over several tanks it becomes accurate again.

My average mileage for 76 miles was 8.1 MPG. Our daily mileage varied from 5.2 to 9.3 because of speed, terrain, winds, and city driving. Wind affected that more than terrain.

 

[Phil]

It is sort of frustrating not to know what gear you are really in. 

Sounds like it's time for you to get a Silverleaf monitor, Smoky. 

 

[Ned]

Since the Allison transmission is the same for both Cat and Cummins powered chassis, wouldn't the engine RPMs at a given speed be determined by the rear axle ratio and tire circumference and not the engine manufacturer?

 

[Tom]

Sounds like it's time for you to get a Silverleaf monitor, Smoky.

I'm surprised the OEM version was not standard on a Newmar coach, given all the great things I've read about them.

 

[Tom]

If in cruise and above the downshift speed, would not the manual downshift be ignored until he applies some braking, taking the coach out of cruise and lowering the speed enough to safely downshift?

Smoky, yes it would ignore it if I was trying to downshift at 70mph, which I'm not. The Allison auto transmission will shift in response to a request, although only when it's safe to do so. That doesn't mean I have to brake if the speed and RPM are in the "safe" range.

You can try selecting a lower gear when you're on flat terrain and going, say 50-55 mph and see what happens.  The transmission will (safely) downshift without you applying the brake, irrespective of whether cruise is engaged or not. Cruise control doesn't keep the transmission in a particular gear, it merely applies sufficient throttle to attempt to hold speed. You can tell when the shift occurs by watching the tach.

 

[BernieD]

Since the Allison transmission is the same for both Cat and Cummins powered chassis, wouldn't the engine RPMs at a given speed be determined by the rear axle ratio and tire circumference and not the engine manufacturer?

Ned

Of course, but the rear axle ratio is probably different for CAT and Cummins engines.

 

[Jeff]

Since the Allison transmission is the same for both Cat and Cummins powered chassis, wouldn't the engine RPMs at a given speed be determined by the rear axle ratio and tire circumference and not the engine manufacturer?

Ned:

I'm sure it is but is probably determined by requirements of HP/Torque for the specific engine?

 

[Jeff]

Bernie:

Brilliant minds think alike, eh?

 

[BernieD]

Bernie:

Brilliant minds think alike, eh?

YEP

 

[Terry A. Brewer]

Tom

>>The Allison auto transmission will shift in response to a request, although only when it's safe to do so.<<

That is so true, I have hit reverse a couple of times at over 60....Glad the trans is smarter than me or I would be taking out a loan for a new one.<G>


Terry
At Clark Fork, ID

 

[Tom]

I have hit reverse a couple of times at over 60

Good to hear that Terry. The possibility of hitting the reverse button is like a nightmare for me.

 

[blueblood]

Most of this trip we've followed friends in another Monaco, a different model but the same engine and transmission. We consistently noticed that we'd have to slow down to stay behind them on hills, which I assumed was due to a difference in weight. But it turns out that, taking into account the as-weighed weights of our coaches and the specified weights of our toads, the two rigs are within 700 lbs of each other.

Questioning our friends we found out that they always leave their coach in cruise control and never select a lower gear. Following advice we've received from other diesel drivers here, we select a lower gear when approaching a grade, irrespective of whether cruise is engaged or not. We'll also downshift again to keep the RPM up while climbing.

Am I missing something?

Cummins stated position on this subject at FMCA session last week, in light of fuel cost concerns, was to maximize use of "top gear" i.e.  keep tranny in Mode On and with cruise control On allow engine to lug back to do the work and allow engine temperature to rise - up to the 220 degree range or just before where ever the red temp light or warning sounds. The Interact System (IS..) engines are designed to run hot and have best efficiency at the higher temperatures. Of course, if grade is such that temperature rises to unacceptable levels then increase RPM's to increase cooling. 

Note - I have asked Cummins to permit me to publish the PowerPoint presentation in its entirety on web sites like this one. They are reviewing my request and say they may need to make some changes in order to make it usable for a wider audience. I'll post if they give me permission to do so.

 

[Tom]

Thanks for that report Leo. It surprises me to read that Cummins is recomending running so close to the over-temp point. Hope they allow you to post the presentation. BTW if the file is above 250K the forum software will reject it. If it's large, email it to me and I'll get it uploaded. Alternatively, email me to coordinate a time when I can open up the file size limitation for you to upload.

 

[Ron]

Thanks for that information Leo.  Looking forward to the presentation if they let you post it.

 

[Smoky]

Wow, it is getting so complicated.

I will try my best to answer the messages addressed to me, and some others,beginning with Bernie.

?Cummins suggests about 1600-1800 RPM as the sweet spot.?

Excellent info, Bernie, I will watch that variable closely on the next leg which will begin on Sunday.

Your next comment.

?If your tach is reading above 1500 RPM at 55mph, you are in 5th gear, if down around 1400 RPM, you are in 6th.?

Are you saying if I step up the speed I will reach the sweet spot?  Again I will watch this closely.  I have a feeling that maybe I am running close to the sweet spot at 55 mph, as I am temporarily overloaded and I bet rpms are a tad higher than normal.  I will be very disappointed, once I get down to recommended weight, if I have to run above 55 mph to get better economy.  I really love the 55 mph pace and get to see more.

?I am not sure I follow what you are saying.?

Even after Tom?s latest comments, I am still not sure I agree with him, unless he further clarifies.  If cruise is keeping the coach above a downshift point, then no downshifting will occur when you press the downshift button.  Of that I am pretty sure.  The transmission knows it cannot downshift until a safe speed is reached.  And left with no further instructions, the cruise control will keep on cruising above the down shift safe point.

One would have to override the cruise control in some fashion in order to get the downshift to occur.  If Tom is saying that he has set his cruise control below a safe downshift point, then I would agree with his conclusions.

?Why not just turn off the cruise rather than tapping the brake? Leaving the cruise control on should have no effect on the Pac Brake when you are going downhill.?

So far I have found a way to increase cruise speed and decrease cruise speed, using the cruise stick, but no way to turn it off other than tapping the brake.  I do not have the smart wheel option, so not sure where the turn off button is located.  Would love to know this as your technique would be more professional.  (back to the manuals this evening.)

Leaving the cruise on does have an effect, as the downshift will not occur until the speed slows down.  I am not sure I have a PAC brake.  I saw this on the Monacos I test drove, but the same kind of switch is labeled differently on the Newmar.  All my documentation refers to ?engine brake? and the manual only refers to downshifting.  I obviously need some more education here.

Tom:

?I'm surprised the OEM version was not standard on a Newmar coach, given all the great things I've read about them..?

Yes.  I wish it was standard.

I did not see one on the Monaco either, which was my second choice.  If Newmar had such an option at my price level I would have gladly added it.  Looks like yet another 3rd party item to go out and acquire.  Have you added one to your coach, and if so, how well do you like it?

?The transmission will (safely) downshift without you applying the brake, irrespective of whether cruise is engaged or not.?

Well yes, but the reason it does that on my coach is that applying the brake automatically disengages the cruise control and at the same time brings my speed down to the downshift point.  I sort of like that method. 

I would be uncomfortable (I think) if my cruise control kept trying to override my braking.  Do you have to manually turn off your cruise control to get down to the downshift point, and if so, are you comfortable with that arrangement?

When I brake, I both get my speed down to the downshift point AND turn off the cruise control automatically.

?Cruise control doesn't keep the transmission in a particular gear, it merely applies sufficient throttle to attempt to hold speed.?

Hmmm.  I still believe my documentation explains that speed can be above a safe downshift point, and the Allison is smart enough to know that and withhold downshifting. 

If that is the case, then the cruise control (at least in the indirect sense) does indeed have some say over downshifting.  I hope nothing is wrong with my coach, but I noticed even in my test driving, that even though I downshifted to 5th, the actual downshift did not occur until my speed came down.  Even on the 2005 Monaco I noticed this.  I am worried now that I am way out in left field on my understanding of these issues.  I admit to confusion here and hope you guys can help me get my head on straight.

The good news is that despite my confusion, we are getting really good mileage, and having a wonderful smooth trip.  I just hope I am not damaging anything.  I am really relying on the info I get from this forum.

?Good to hear that Terry. The possibility of hitting the reverse button is like a nightmare for me.?

Aye Tom.  I have not had that problem at high speeds, but a couple times when first learning parking I would hit reverse instead of first applying neutral when in forward gear.  Nice to know that does no harm.  In some of the Velvet Drive diesel trawlers I delivered, one had to be very careful when ?treading water? at closed bridges, not to go from forward to reverse with any rpms above slow idle.

Phil:

Yes a Silverleaf would be a fascinating and useful device.  If they are not too expensive.  I assume they require professional installation?

And Blueblood I am anxious to see that PowerPoint presentation.  Any other way for us to get one from Cummins if they won?t allow publication on the forum?  Seems to me they can only benefit by pushing it out to as many Cummins owners as possible.