Diesel vs gas towing capacities

[Ray,IN]

Originally Posted by Gary RVRoamer

Pretty much, at least on the technical level. Diesels do have some advantages for towing heavy loads, e.g. oodles of low RPM torque & Hp, but the primary reason that most diesel motorhomes have higher tow ratings (larger GCWR) is that the chassis and transmissions used in them are more robust (and more expensive because of it). As already noted here, gas engine pick-ups and larger SUVs typically have substantial tow ratings, often10,000 lbs or more. It's not solely the engine or power that determines the tow capacity.


As an example, the 6.7L diesel-powered Freightliner MC chassis has a GCWR only 3000 lbs greater than its GVWR, so the tow rating would be only 3000 lbs if the chassis/motorhome was fully loaded. The limiting factor in that one is the Allison 2350 transmission and associated axle and frame structure. The 6.8L gas-powered Ford F53 chassis, on the other hand, has a GCWR that is 4000-10,000 lbs greater than its GVWR (depending on the configuration) and has commensurately higher tow ratings.


In other words, it's the sum of all the components used and not just engine.

This is the best explanation the OP will receive!

[asuperheat]

Basically The chassis overall capacity minus the curb weight of the vehicle determines towing capability. It is not as simple as gas vs diesel. The entire driveline, brakes, cooling system, tire load capacity ect all play a part.

Typically diesel characteristics make it perferd over gas when towing heavy.

[UTTransplant]

I would also like to mention that diesels have exhaust brakes, or at least most do. To me, ltrabeling frequently in mountainous terrain, I would buy a vehicle with an exhaust brake no matter what else I had to compromise on. (Luckily, diesels don’t really require compromise on horsepower, torque, or fuel economy.) Towing a trailer with a Diesel engine is so much easier! We towed small trailers for years with gas engines, then got a trailer that was officially only 80% or so of capacity(yes, we weighed everything TJ, but it was a dog at towing, and it required a lot of effort gearing up and down for mountains. Bought a 3/4 ton diesel, and life was rosy again.

[egwilly]

As the owner of a one ton diesel pickup, I will tell you that it tows much better than my last gas pickup with a 5.4 gas motor..... Way better.

That said, if you go diesel, be aware of the expense and issues if something goes wrong. I have been lucky my warranty has covered the DPF and SCR system so far.

Example: if you get water, or pump gasoline instead of diesel into the tank, and start the engine, that's a $13,000 repair to replace the fuel system components. The high pressure fuel pump will fail and pump debris into the system.

Some folks delete the DPF, EGR and SCR systems in their trucks....I can't due to annual smog inspections in Calif.

Good luck with your decision...think of the future when you decide. Bigger is usually better.

[EA37TS]

Originally Posted by MtCamper

Diesels make torque, torque tows trailers.

With enough gearing, you can tow with your Yugo, but you won't be a Happy Camper.

Get a diesel if you plan to tow much and want to be a Happy Camper.

Torque gets the load moving, Horse Power keeps it moving at high or low revs.

[schad]

Originally Posted by EA37TS

Torque gets the load moving, Horse Power keeps it moving at high or low revs.

Torque, or more generally force, does both of those things. Newton's first law.

Power is literally just torque times engine speed. That's it. Since engines don't produce torque unless they're spinning, in this context there is absolutely no difference between power and torque. They are completely interchangeable. The only reason to prefer one is that sometimes the math may be easier with a particular form.

[Itchytoe]

Originally Posted by schad

Power is literally just torque times engine speed. That's it. Since engines don't produce torque unless they're spinning, in this context there is absolutely no difference between power and torque. They are completely interchangeable. The only reason to prefer one is that sometimes the math may be easier with a particular form.

Horsepower isn't torque times engine speed. It's torque divided by time. It's the rate an engine produces torque. This is easier to see if you use the metric units, like the vast majority of the world uses. Torque (ft lbs here in the US) is a force (kg) applied at a distance (meter) from a pivot point. Force times distance is kg meter. Same thing as lbs feet, just metric. 1 metric horsepower is 4,500 kg meters per minute. It's quite literally torque (kg meter) divided by time (minute).

Using the SI units (cuz #Merica!) 1 horsepower is 550 foot pounds per second. Again, it's literally torque (foot pounds) divided by time (seconds). Notice how engine RPM was never even considered. That's because engine RPM isn't a factor in horsepower.

It just so happens that RPM has a unit of time in it, specifically minutes. Well, there's 60 seconds in a minute, but we still need to deal with the dimensionless "revolutions" part of RPM. To use RPM, we need to convert it to "something per second". The only thing we can really convert it to is radians per second. There are 2*pi radians in a full revolution, and 60 seconds in a minute, so to convert RPM to radians per second, we multiply RPM by (2*pi/60) which is .10472 radians per second. Now we have a conversion factor! To get horsepower (550 ft lbs per second) from torque (lbs ft), divide 550 ft lbs by 0.10472 radians per second which yields 5252. That's where the magic 5252 number comes from. It's just a combination of a few conversions. It's not how horsepower is defined, despite gearheads claiming otherwise.

Horsepower and torque are not interchangeable in any context. One is how much work can be done, the other is how fast that work can happen.


https://auto.howstuffworks.com/question622.htm

[Mr_D]

Originally Posted by hohenwald48

There are even Wranglers with more than 5,000# towing capacity.

Not according to the charts Jeep publishes. Highest on their charts is 3,500#'s

[Marine Les]

Originally Posted by Motor joe

I'm weighing the differences between gas and diesel tow vehicle and I can't find anywhere where it says a diesel engine vehicle can tow more weight than a gas engine. Is that because the amount it can tow is not dependent on the engine of the vehicle? In other words, I would expect a diesel engine to be able to pull a heavier trailer than a gas engine, but maybe it's not dependent on the type of engine. Is that correct?
Thanks,

Motor joe your ? is much too open ended for a meaningful response. Are you pulling with truck or motorhome/ class c or a. How heavy is your toad?

[Gary RVRoamer]

Horsepower isn't torque times engine speed. It's torque divided by time.

The physicists and engineers don't agree. The standard formula is HP = Torque x RPM/5252 Since rpm inherently includes time (it's per minute, right?), the time factor is already included, e.g 500 rpms is 500/minute. If you have more torque at a given rpm, you also have more hp.


https://www.wikihow.com/Calculate-Horsepower

[Itchytoe]

Originally Posted by Gary RVRoamer

The physicists and engineers don't agree. The standard formula is HP = Torque x RPM/5252 Since rpm inherently includes time (it's per minute, right?), the time factor is already included, e.g 500 rpms is 500/minute. If you have more torque at a given rpm, you also have more hp.

https://www.wikihow.com/Calculate-Horsepower

I don't think you read the entire post. Physicists and engineers do agree with me. 1 horsepower is, by definition, 550 foot pounds per second. Quite literally torque divided by time. The formula you're using is a derivation of several conversions all packed into one so that it's easier for laymen to figure things out as it relates to vehicle engines. Horsepower itself doesn't require a turning engine. You can simply push a box across a table and generate horsepower without any rotation at all. All you need is 550 foot pounds per second.

https://en.wikipedia.org/wiki/Horsepower

If you're going to site Wikipedia, at least use the correct page. Notice the links to other pages, like hydraulic, mechanical, electric, and boiler horsepower. It's a measure of force over a time period.

Go talk to an actual physicist about horsepower and tell him/her to not use a rotational engine as an example. If that's even possible, horsepower can't be defined by RPM.

[Redapple]

Each platform has its benefits and application. It is NOT a cut and dry answer.
Diesel engines generate peak torque at far lower rpm than an equivalent gasoline engine. This means much less stress on the engine. Diesel generates more energy, btu's joules, whatever form you wish to measure than gasoline, approx 23% more. This means more power.

That is just one set of variables, there is also application, what are you towing. Where are you towing it, how often. How long and heavy is the item being towed or hauled. Commercial or private, and at
what price point, and cost to operate

I think these are just some of the questions each of us need to ask before a decision is made.

I have driven and towed with both, GM 5.7, 6.0, and Two Duramax platforms and a V10.

All got the job done.

Which is better...gonna give my Engineering answer...it depends

[schad]

Originally Posted by Itchytoe

Go talk to an actual physicist about horsepower and tell him/her to not use a rotational engine as an example. If that's even possible, horsepower can't be defined by RPM.

It took me a while, but I understand the problem now.

When I said that "power is literally just torque times engine speed," you seemed to understand that as a claim that power is defined as torque times engine speed. That's not what I meant, and it's not what I said, either.

I made certain assumptions based on the fact that we are all talking about gas and diesel engines. I also made certain simplifications based on the fact that this is a forum about RVs, for goodness sake, not a physics textbook.

Here's your example, by the way: If you drop an object from on top of a building, you'll see power but no torque at all.

[Rhagfo]

I will throw in my $0.02 here now, I see we have gotten into the HP vs Torque deeply.

Originally Posted by Motor joe

I'm weighing the differences between gas and diesel tow vehicle and I can't find anywhere where it says a diesel engine vehicle can tow more weight than a gas engine. Is that because the amount it can tow is not dependent on the engine of the vehicle? In other words, I would expect a diesel engine to be able to pull a heavier trailer than a gas engine, but maybe it's not dependent on the type of engine. Is that correct?
Thanks,

Based on the statment above I assume that the OP (Motor Jo) is referring to a "Tow Vehicle" and is looking to tow a TT or 5er.

Originally Posted by MtCamper

Diesels make torque, torque tows trailers.

With enough gearing, you can tow with your Yugo, but you won't be a Happy Camper.

Get a diesel if you plan to tow much and want to be a Happy Camper.

While a person that tow with gas will state it is HP, it truly is torque.
To start with a diesel with the same gearing as a gas of similar or lower HP will be rated to tow about twice that of the gas engine.
Gas engines need deep gears and RPM's to get tow ratings, 4.10, 4.30. 4.88, they use those deep gears to turn HP into torque at the rear wheels.


An example is our 2016 Ram 3500 with 3.73 gears, it is rated to tow 25,000#, with gas I would be rated about 12,500#.


Gas can get some decent torque numbers with turbo charging, as in the Ford EcoBoost, but fuel mileage when working suffers, do that to a large gas engine and fuel mileage towing 16,000# would likely be about 6 mpg.


Last is the bonus of an exhaust brake on all newer diesel tow vehicles, and can be added to older.
Going down steep grades, without using the service brakes is a great and relaxing feeling.