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Old 01-15-2019, 05:51 PM   #541
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Originally Posted by Tuco View Post
I apologize if i'm not being clear or not moving fast enough. We can get into more meat and potatoes later. What I think we need to agree on is that there is a torque budget needed regardless of where we get it from (for now). I would also like to clarify what can affect that torque requirement. This is what I think, please add/comment on this (again K.I.S.S.).

1. % of Grade
2. Weight

To move things along, here is the next question to clarify. Now lets get the vehicle moving at 25 mph on level ground. Here we also have a torque and HP budget to overcome friction, wind, drive train losses and such. Excluding the torque (and HP) needed to overcome gravity in the 5% scenario, can we agree that this is the same number in both at the same speed (level ground and 5% grade)? Again, I may not be saying this clearly, but i'm trying.
Again, don't mean to be condescending. Interesting case study. I could humor the question if I had time. But it won't foster any meaningful understanding anyways as the fundamental question is misdirected.

One thing that has to be clear is that torque at the wheels can be just about infinitely multiplied by gearing, regardless of the power source. Just like one can gain enough leverage with a hydraulic floor jack to lift a weight many many times a persons strength. Strength can be multiplied with leverage.. Analogous with torque at the engine multiplied by gearing to apply torque at the wheels to move a load.

At the risk of confusing things with an analogy:

The speed at which one can lift a car with said floor jack is the question here. Speed to lift requires power (HP). Power cannot be multiplied and is equal to a persons core strength (torque) and aerobic ability to do many pumps per minute (rpm).

Intuitively in a speed contest to do this job, I would hire the strongest and quickest guy possible. You could trade a bit of strength (tq) for speed (rpm), or vice versa. But the goal is to maximize the product of the two which is power (hp).

We're saying that a big fat guy is not the right solution, even if he could grunt out 1000 lb ft of torque in one big pump. In order to win, said fat guy has to have aerobic capability too, because maximum ability is when strength (big pumps) and aerobic ability (pumps per minute) is combined to maximize the speed at which the car is lifted - aka HP.
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Old 01-15-2019, 05:57 PM   #542
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One other thing. Thermometers have degrees and you know where you can stick them. Having owned and sold a very successful trucking company and being around men, trucks and towing I would take this experience over any formal education. Don't get me wrong I do value formal education buy when one starts quoting the physics I know I wouldn't want to get behind the wheel with that person. The are drivers and there are those who drive and there is a big difference. I know a few who start quoting physics and I rest my case.
I don't dismiss experience. Experience is always huge.

I wouldn't ever in a lifetime of experience expect a truck driver to get us to the moon.

I would have some faith that a formally educated person could figure out how to drive a truck.

Combine academic ability and experience - that would be a force to be recon with.
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Old 01-15-2019, 06:09 PM   #543
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I don't dismiss experience. Experience is always huge.

I wouldn't ever in a lifetime of experience expect a truck driver to get us to the moon.

I would have some faith that a formally educated person could figure out how to drive a truck.

Combine academic ability and experience - that would be a force to be recon with.
In today's world some confuse intellect with intelligence. Intellect is what you increase when you go to school. Intelligence is a completely different thing and includes street smarts and many other aspects of one's personality. My point was you don't need formal education to decide which tow vehicle you should buy. All you need is a bit of common sense and that seems to be lacking these days.
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Old 01-15-2019, 06:39 PM   #544
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In today's world some confuse intellect with intelligence. Intellect is what you increase when you go to school. Intelligence is a completely different thing and includes street smarts and many other aspects of one's personality. My point was you don't need formal education to decide which tow vehicle you should buy. All you need is a bit of common sense and that seems to be lacking these days.
Common sense.

Generally informed by anecdotal experience.

I invite you to apply intellect to understand objectively.
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Old 01-15-2019, 06:49 PM   #545
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Common sense.

Generally informed by anecdotal experience.

I invite you to apply intellect to understand objectively.
Well I don't even know what that means so I will just pass thanks.
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Old 01-15-2019, 07:01 PM   #546
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What happened to someone doing the math to figure out the torque required to hold on a hill?
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Old 01-15-2019, 07:40 PM   #547
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What happened to someone doing the math to figure out the torque required to hold on a hill?

I'll just drop this here and go make some popcorn.




I reckon it's going to be approximately F(g) * sin(a) * (distance from hub center to ramp surface) ... or the average hub height if they're different. The units are right, at least.

Approximately.

Like within the ratio of a cheeseburger to a Buick level of precision.
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Old 01-15-2019, 08:14 PM   #548
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Well I don't even know what that means so I will just pass thanks.
https://www.vocabulary.com/dictionary/anecdotal

Quote:
anecdotal

Something anecdotal has to do with anecdotes — little stories. Anecdotal evidence is based on hearsay rather than hard facts.

People like to share stories about things that happened to them, or that they heard about, to make a point. That kind of talk is anecdotal: based on small, personal accounts. Anecdotal stories are helpful when you’re trying to give an example of something, but there's a downside to anecdotal information: since it’s not based on facts, you never know if you can totally trust it. So it's best to go beyond the anecdotal and get more solid information.
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Old 01-15-2019, 10:00 PM   #549
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While I have one of the new big diesels, I am sure the big gas engines would perform well with one exception which is a complete deal breaker for me....range. I have towed with gas and it is unsettling when a headwind in Nevada drops your mileage to 7-8 and you are a 100 miles from nowhere. 34 gallons of gasoline is just not enough. 34 gallons of diesel adds 100 miles which helps a lot.
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Old 01-15-2019, 10:08 PM   #550
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A newer LB gas Super Duty holds 48 gallons.
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Old 01-15-2019, 10:22 PM   #551
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A newer LB gas Super Duty holds 48 gallons.
True and that is very helpful but not many people choose the long bed.
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Old 01-16-2019, 01:29 AM   #552
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I'll do my best here to accommodate your request (my wife would say "In a nutshell...Please?" ). Unless otherwise noted torque is measured at the drive wheels.

1. There is a torque requirement for slope and mass to overcome gravity. Lets call that "X". Mass will never be zero, but slope can be.

2. There is a torque requirement for steady state cursing. Lets call that "Y".

3. The total torque requirement will be X+Y, so lets call that total "Z"

The engine has a torque curve where it can provide a certain amount of torque at a given RPM. Gearing changes the amount of torque seen at the drive wheels (this is over simplified I know). At a given RPM if available engine torque is grater than "Z" then the engine has enough extra torque to spin faster and can increase RPM and HP. If available engine torque equals "Z" then you can't increase RPM and therefore cant get more HP, but it can maintain the RPM it has. If available engine torque is less than "Z" then RPM and HP drop until the engine stalls or you down shift. I will pause here for comment and input. (use cases will be next unless there is major disagreement)

Summaries are good. Points 1, 2, and 3 are fine in principle. They all apply to wheel torque, however. You should be using power in this case study; there is a hp requirement for cruising on level ground at a steady speed (friction, air resistance, etc) and then an additional hp requirement to climb the hill (overcoming gravity). Since we are talking about a moving vehicle, at a certain speed, the rate of doing work (measured in hp or kw) is the appropriate unit of measure.

In terms of whether an engine can accelerate when called upon to do so, I think you are coming at it backwards. Torque isn't often increasing with rpm, as power is, at least in the usual operating range. For torque, think about what happens as you lug it down. Your engine torque peak is at a lower rpm than you are likely operating the engine. As the engine lugs, it slows, but a modern diesel has a torque rise. The torque rise is defined as the (peak torque - torque at rated power)/(torque at rated power), and is expressed as a percentage. It is the slope of the line, essentially. That torque rise is what makes the diesel feel powerful to the operator. It means less shifting is required, as the engine "digs in" and pulls. That is simply because there is more torque available as revs start to drop, so operators note "it didn't even need to shift" as it might have had to do if the torque peak was at a higher rpm. Not needing to shift is perceived as being powerful by the operator, when it is really about the torque characteristics, ie the shape of the line, not the torque amount in absolute terms. A gasoline engine might have been lugged in a similar application and then it bogged down, requiring either a shift or resulting in the engine stalling. That is because as revs dropped (when it hit the hill) the torque dropped and it was like falling off a cliff, you needed to shift before you lost too much speed. Note here that the diesel torque value, ie the actual torque figure, isn't as important as the shape of the torque curve. From your earlier examples, we know that the torque that we need is wheel torque, and we can get that with gearing. Flywheel torque is just a step on the way, before we pick the right gear. But the shape of the torque curve provides feedback to the operator. And it is often interpreted as power, even thought the specs on the engine may show it has less power than a comparable engine.

I have attached materials from an introductory course on engine power principles. I am hoping it may save some typing about what hp and torque are. Those are discussed at the beginning, torque curves and torque rise are also covered. The booklet is over 20 years old, but we are still measuring hp and torque the same way, the math hasn't changed.
Attached Files
File Type: pdf Caterpillar Engine Power Concepts.pdf (213.6 KB, 20 views)
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Old 01-16-2019, 08:45 AM   #553
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While I have one of the new big diesels, I am sure the big gas engines would perform well with one exception which is a complete deal breaker for me....range. I have towed with gas and it is unsettling when a headwind in Nevada drops your mileage to 7-8 and you are a 100 miles from nowhere. 34 gallons of gasoline is just not enough. 34 gallons of diesel adds 100 miles which helps a lot.
...I run big trucks for 54 years, I have always tried to stop and do a walk around every 2 hours...my 17 ram with 6.7..does 12.5-14 mpg...34 gallon tank will run me a good days run...I could install an after market 60 gallon tank ..., for what? If I wanted to haul fuel, I wouldnít have retired and I am in no hurry..life is short..enjoy...
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Old 01-16-2019, 10:01 AM   #554
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Summaries are good. Points 1, 2, and 3 are fine in principle. They all apply to wheel torque, however. You should be using power in this case study; there is a hp requirement for cruising on level ground at a steady speed (friction, air resistance, etc) and then an additional hp requirement to climb the hill (overcoming gravity). Since we are talking about a moving vehicle, at a certain speed, the rate of doing work (measured in hp or kw) is the appropriate unit of measure.

In terms of whether an engine can accelerate when called upon to do so, I think you are coming at it backwards. Torque isn't often increasing with rpm, as power is, at least in the usual operating range. For torque, think about what happens as you lug it down. Your engine torque peak is at a lower rpm than you are likely operating the engine. As the engine lugs, it slows, but a modern diesel has a torque rise. The torque rise is defined as the (peak torque - torque at rated power)/(torque at rated power), and is expressed as a percentage. It is the slope of the line, essentially. That torque rise is what makes the diesel feel powerful to the operator. It means less shifting is required, as the engine "digs in" and pulls. That is simply because there is more torque available as revs start to drop, so operators note "it didn't even need to shift" as it might have had to do if the torque peak was at a higher rpm. Not needing to shift is perceived as being powerful by the operator, when it is really about the torque characteristics, ie the shape of the line, not the torque amount in absolute terms. A gasoline engine might have been lugged in a similar application and then it bogged down, requiring either a shift or resulting in the engine stalling. That is because as revs dropped (when it hit the hill) the torque dropped and it was like falling off a cliff, you needed to shift before you lost too much speed. Note here that the diesel torque value, ie the actual torque figure, isn't as important as the shape of the torque curve. From your earlier examples, we know that the torque that we need is wheel torque, and we can get that with gearing. Flywheel torque is just a step on the way, before we pick the right gear. But the shape of the torque curve provides feedback to the operator. And it is often interpreted as power, even thought the specs on the engine may show it has less power than a comparable engine.

I have attached materials from an introductory course on engine power principles. I am hoping it may save some typing about what hp and torque are. Those are discussed at the beginning, torque curves and torque rise are also covered. The booklet is over 20 years old, but we are still measuring hp and torque the same way, the math hasn't changed.
HP is a function of Torque and RPM. At any any given RPM, HP can be from zero to it's theoretical maximum at that RPM. Maximum torque at that RPM determines HP. Throttle position determines the amount of torque and therefore the amount of HP at that RPM.

You have to look at this system as a snapshot. Do we have enough force from the drive train to overcome the forces working against it. Torque is the measure we use to determine those forces. HP deals with time and is not needed in a force balance equation. Either we have more, less or the same amount of force at any given time.
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Old 01-16-2019, 10:43 AM   #555
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HP is a function of Torque and RPM. At any any given RPM, HP can be from zero to it's theoretical maximum at that RPM. Maximum torque at that RPM determines HP. Throttle position determines the amount of torque and therefore the amount of HP at that RPM.

You have to look at this system as a snapshot. Do we have enough force from the drive train to overcome the forces working against it. Torque is the measure we use to determine those forces. HP deals with time and is not needed in a force balance equation. Either we have more, less or the same amount of force at any given time.


Well said and absolutely correct.
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Old 01-16-2019, 11:31 AM   #556
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What I really meant to say is I don't care. No offense. We see the world differently and you may be correct in your version of the world and I hope you are genuinely pleased with your life.

I know I am and with my tow vehicle.
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Old 01-16-2019, 01:10 PM   #557
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HP is a function of Torque and RPM. At any any given RPM, HP can be from zero to it's theoretical maximum at that RPM. Maximum torque at that RPM determines HP. Throttle position determines the amount of torque and therefore the amount of HP at that RPM.

You have to look at this system as a snapshot. Do we have enough force from the drive train to overcome the forces working against it. Torque is the measure we use to determine those forces. HP deals with time and is not needed in a force balance equation. Either we have more, less or the same amount of force at any given time.
Good. There are a few more things determining torque than throttle (boost, for example), but as a snapshot, fine.

Now, on the subject of torque, how about torque rise? Did you read the attachment? Did you note the different torque curves for the same engine, and how to shift them?
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Old 01-17-2019, 12:24 AM   #558
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...so, in summary

Okay, so I am sick of getting notices in my email that this thread is still going.......So let me sum it up in 5 sentences and put it to rest.....

1. Diesels are better at towing than gas motors, but they stink and are noisy.

2. Diesels cost a hell of a lot more than gas motors, to buy, and to maintain.

3. Some folks are happy with their gas powered tow vehicles, and it is all they need.

4. Some folks will spend ungodly amounts of money to have the latest greatest most powerful turbo diesel engine on the planet,even if they do not really need it.

5. This is the Airstream forum..the home of excess and extravagance.....We pay crazy money for fancy campers, and fancy tow vehicles just go along with it.
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Old 01-17-2019, 07:17 AM   #559
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Okay, so I am sick of getting notices in my email that this thread is still going.......So let me sum it up in 5 sentences and put it to rest.....

1. Diesels are better at towing than gas motors, but they stink and are noisy.

2. Diesels cost a hell of a lot more than gas motors, to buy, and to maintain.

3. Some folks are happy with their gas powered tow vehicles, and it is all they need.

4. Some folks will spend ungodly amounts of money to have the latest greatest most powerful turbo diesel engine on the planet,even if they do not really need it.

5. This is the Airstream forum..the home of excess and extravagance.....We pay crazy money for fancy campers, and fancy tow vehicles just go along with it.
I agree with all of the above statements and I am guilty as charged!
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Old 01-17-2019, 07:39 AM   #560
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Okay, so I am sick of getting notices in my email that this thread is still going.......So let me sum it up in 5 sentences and put it to rest...
If you don't want email notifications from a particular thread you can easily turn those off. While in the thread go up to "Thread Tools", click on it and then select "Unsubscribe". In fact you can choose not to receive any emails from subscribed threads. Go to "User CP", Settings and Options, "Edit Options", "Messaging & Notification" , "Default Thread Subscription Mode" and choose "No Email Notifications". Or, you can choose to totally ignore a thread, also under "Thread Tools".


You can also use 'Thread Tools" if you want to subscribe to a thread without making a comment.
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