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What is up with the questions about gearing?

Discussion in 'Ask An Owner Operator' started by Ridgeline, Aug 26, 2019.

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Wespipes Road Train Member

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I'm 10x more confused now. Thank you everyone

Wespipes, Aug 27, 2019

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Long FLD Road Train Member

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So on these new automated transmissions are the gears closer together across the board or are they closer on the top end similar to a 13? My Promaster van has a 9 speed auto and you can’t even tell when it shifts unless you’re looking at the tach.

Long FLD, Aug 27, 2019

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REALITY098765 Road Train Member

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Wespipes said: ↑

I'm 10x more confused now. Thank you everyone
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LOL don;t let these guys confuse you, they think they are still driving Astro;s with a 318. Someday maybe they will come into the twenty first century.

Last edited: Aug 27, 2019

REALITY098765, Aug 27, 2019

#53

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Ridgeline said: ↑

Omg, it is a rhetorical question.

Something to ponder about .... maybe prompt others to correct people's misconceptions about how a Diesel engine works and what to look for in gearing.

Here is my thinking .... for what it is worth ...

The problem with thinking that gear ratios is the only thing that matters is just plain wrong. Most are not looking at the drivetrain as a whole or take in account the engine and don't set the goal for gearing an engine to hit the bottom of the fuel consumption curve for cruising. Also no newbie is told to use the transmission to take advantage of the gearing when they need power, it seems the threads have answers about just gears and nothing else.

Snowy and a couple others know what I'm talking about but billyjoebob who is thinking a truck is just like a car and wants tall gears to lower the revs on the engine is clueless to how it works and may be disappointed with the results of a tall gear.

Revs do not equate to better fuel mileage that's a fact. Now a days the computer will tell the engine to over fuel if there is not enough torque or when the engine gets out of the power band.

It used to be peak torque hit at the bottom of the fuel consumption curve but with the electronics, that seems to have shifted peak torque a little bit on the high side near the bottom of the curve.

The selection of a transmission is very important, 9/10 speeds are great for those lazy newbies or someone who is tired of shifting but 9/10 speeds have too wide steps to actually be effective to get the best mileage out of a truck, to me they are for local driving. I found 18 speeds are the best, close ratio steps help with keeping the engine within its power band and closest to the bottom of the power curve.

Also to confuse matter even more is the engine size itself, the lower the size, the higher the bottom of the consumption curve in relation to rpm. The 15 l engines seem to have that bottom of the curve at 1100 to 1200 rpm where as the 13 l engines move that up 1200 to 1300 rpm.
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Fwiw I was being sarcastic about the TDC and fuel burn

rank, Aug 27, 2019

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Snow Monster said: ↑

No, just makes me someone who wouldn't drive a neutered truck or be micro managed.
Are you okay with that?
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I’m ok with that

rank, Aug 27, 2019

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snowwy said: ↑

Some of you will want to argue. But I see this 2 ways.

Low rpms. Less fuel burned. SURE. On paper. But let's not forget the powerband.
Engines might have torque but realistically. It requires more pedal in the lower rpm. Powerband requires less pedal in the higher rpm.

On the flat land. Low rpm could work. But not in the mountains.

It takes longer to climb a hill in the low range. That's more time spent at full throttle. A 500 horse engine could pull it off better then a 450 horse engine.

A good test run. For those of us that did it on a somewhat regular basis. Phoenix to Flagstaff.
The 05 w900 ISX450 I was driving at the time. Would do that drive 20 minutes faster and burn less fuel running the powerband range vs. the torque range.

The faster you can climb the hills. The less time spend with pedal to the metal.

Course, if you want to drive the KR method. I'm not sure if you'd save fuel or not. You might be stopping for pee breaks by the time you got to the top.

Which goes to the next note. Engine running time.
55 mph will save fuel over 65 mph. SURE. But how much longer is that engine going to run to get you from point A to point B?
Is there a gallon comparison chart for gallons used to drive 1000 miles? Flat land and mountains. 500 horses compared to 400 horses. Pulling 80k.

Everyone wants to save fuel. But realistically. Some operations don't stand much of a chance compared to aerodynamics pulling vans. Flatbeds and Heavy haul in the mountains and open wind resistance comes to mind. Although the 16 FL I drove did really good on economy compared to the earlier trucks I drove pulling flats. It also didn't require as much travel time.
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As much as I hate this fact, the slower I drive my trucks (3.90’s and 4.33’s) the better fuel mileage I get. It’s almost exactly a tenth better per mph

rank, Aug 27, 2019

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uncleal13 said: ↑

I wonder what effect this trend towards down speeding has on engine longevity. You hear more of trucks needing rebuilds with under 600,000 miles on them, some under 300,000 miles.
I do hear of recent engines going over a million, but I wonder if they have traditional gearing?
IDK, just thinking out loud.
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This is my concern. Mathematics says it works but I do not feel any engine will live at those RPMs. Now mega fleet governed at 65 with twits driving on a trade in before 500k. It makes sense. They are saving over 5,000 trucks and dont own them long enough to care. Just like extended oil changes. The OEM's used to cater to Owner Ops. However the Owner ops buying new trucks in the last 18 years has decreased. They are engineered and built for fleet purchase and secondary uses is not a concern.

jamespmack, Aug 27, 2019

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starmac said: ↑

When Autos first started getting used by the megas, they claimed it was because they it would make it easier ti teach drivers to drive, fuel mileage was not mentioned.
As far as I know the old helmut still holds the fuel mileage record, but it was so ugly no one would drive them. lol
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Autos are yet to provide better economy over a properly shifted manual. A good driver will not see the promised 3% increase. A poor driver will see a increase.

jamespmack, Aug 27, 2019

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rank said: ↑

Jesus really Ridgeline? here we go again.

because every other time a piston comes to TDC, fuel gets burned. Fewer times = less fuel. Simple math as they say
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It's a psi thing too. At 15 psi boost your displacement is effectively doubled.

77fib77, Aug 27, 2019

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Here's a question for everyone.

If you're bucking a wind at desired road speed or pulling a long gentle grade and your turbo boost gauge is showing 25 pounds of boost and your pyro is showing 900º f, and purely by accident, for no reason at all, you flip that little flippity flipper thingy on the gear shifter and notice your road speed hasn't changed but your rpms have gone up and your turbo boost and EGT have gone down, what does that mean to you?

Is your engine working harder or not as hard?
Is it more or less destructive to your engine to run at higher rpm's with less turbo boost and lower EGT's?
Do you think your fuel economy would go up or down?
Are any of you interested in clog dancing?

Inquiring minds need to know!

Snow Monster, Aug 27, 2019

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