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-   -   Tow Limits (http://www.airforums.com/forums/f238/tow-limits-174222.html)

slowmover 10-30-2017 02:55 PM

Quote:

Originally Posted by Len n Jeanne (Post 2027844)
If you're driving in the mountains of Colorado, you definitely do not want to be under-powered driving up a steep grade. Even in 2nd gear behind the big trucks.

When we got out 19'FC, we also traded in our Tacoma for a Tundra. Now the towing is a breeze, with no straining up the long steep slopes.

A "common" justification. So I'll borrow it as representative.

For the OP:

The ascent doesn't mean much. It's the descent that matters.

Let's make it simple: on the ascent no matter the speed the lash-up is under tension. The TT stays relatively well in alignment (better than on level ground) AND travel speed is reduced (meaning handling problems reduced).

How fast up the hill isn't directly relevant to "safe". That's inexperience as considers it a problem.

On the descent, the trailer is trying to pass the TV. The tension is reduced so that any adverse wind can put the TT into sway. One must have some room to accelerate.

Brakes matter. Not engine power. Gear choice is everything past target descent speed.

OP, if you want some fun, try one of those, What did you name your Airstream, threads. Think that cute name will suffice as they see the bitch coming around in one of the mirrors? Ha!

A VPP hitch mitigates nearly all sway problems. Cheap at twice the price. But even here one needs application of TV service brakes.

So other half-baked stuff includes those who "love" a Diesel engine exhaust brake OR Tow/Haul shift programming + compression braking. That's only good while solo, basically. They're aids used as substitutes versus "good practice" descents. It's keeping the trailer both upright and lane-centered that matters. And that's hitch tension.

And back to the beginning: solo duty reigns supreme. The most time and miles, thus the greatest emphasis on stable design and can also tow the AS.

.

Adventure.AS 10-30-2017 02:55 PM

Quote:

Originally Posted by kendrick.l.j (Post 2028278)
I have read every post and have a question. If tow limits are not to be believed why bother having them?
When I decide I was going to get the AS, I knew exactly what model I wanted. I went to the RAM dealer with a long list of requirements including and most importantly what it needed to pull.
If tow limits are meaningless than why do all the truck and car manufacturers list what the limits are?

You might find these two videos from FastLane Truck concerning "magic towing dust" (which explore how tow ratings are determined) informative.

https://www.youtube.com/watch?v=IqzQ...hB32dnoKakg27A

https://www.youtube.com/watch?v=uOOH...hB32dnoKakg27A

kendrick.l.j 10-30-2017 05:21 PM

Adventure— thanks for the links. I did watch both. Wow. I honestly had no idea that there is no standard being used (except by Toyota ) and that it all just erroneous numbers. Very disappointed.

jcl 10-30-2017 05:36 PM

Quote:

Originally Posted by kendrick.l.j (Post 2028278)
I have read every post and have a question. If tow limits are not to be believed why bother having them?

Well, they sell trucks. And they do provide some comparative value IMO (two truck models from the same manufacturer, one has a higher tow rating, and an analysis of what the mechanical differences are, eg larger transmission cooler, can provide some illumination)

The problem is that many people believe that a larger tow rating, in and of itself, adds safety or a safety margin. Proof that advertising works. I am not saying a tow rating has no value. But it is only a starting point, it isn't the finish line.

My last SUV didn't come with a tow rating. The manufacturer didn't see it as adding value, ie they wouldn't sell more vehicles. So they didn't even put one on the vehicle. But they did sell a hitch through their dealers, and one could infer that the hitch rating was at least as good as what they thought the truck could tow.

My daughter got a new Toyota car. I realize not many here tow with cars, but some do tow with Toyotas. Toyota is even referenced in the post above, although that is about pickups, and I don't think any manufacturer is applying the SAE tow rating standards to their other vehicles. Anyway, I read the Toyota owner's manual (old habit). I saw a reference to towing that I thought was interesting. So I looked it up. But I got a non-Canadian site for Toyota. Different figure. So I researched it. The car isn't built in Canada. But the same car, in three markets, came with three tow ratings and approaches to towing, all from local Toyota organizations.
1) Don't tow. Very bad. Don't do it. Vehicle isn't designed for it. etc.
2) Use only the Toyota receiver (which had a middle of the road tow rating), as it is designed for your vehicle.
3) If you tow, understand the following. Details were then provided for tongue weight limits, trailer weight balance, where to attach your receiver and a dimension drawing showing where the blind nuts were installed in the chassis for you to attach your own receiver. It was a factory drawing. It included electrical hookup instructions. So, apparently the vehicle was designed to tow. Tow rating provided here was about twice the figure given in (2), but varied with trailer frontal area, etc. Someone had thought about this.

So, that example showed me that tow ratings are, shall we say, subjective. I think that the manufacturer's marketing group in (1), which was in the US, wasn't serving their customers particularly well. (2) was in Canada. More open, but limited info. (3) was the corporate site, ie rest of the world. They were the ones who actually had the factory design engineers. But all the customers in region (1) and region (2) only had what their dealer, and the national marketing organization, told them, to go on. Imagine the forum wars when three people from three geographies all got together to discuss towing with the same car. IMO, essentially the marketers in (1) and (2) didn't consider that a tow rating was going to sell more vehicles, so why bother. I have a hard time faulting them, they are probably right, but it does illustrate some of what goes on behind the scenes.

J. Morgan 10-30-2017 09:50 PM

I am all for tow limits, eight years is enough for everyone. :)

Countryboy59 10-31-2017 04:05 AM

Quote:

Originally Posted by kendrick.l.j (Post 2028278)
I have read every post and have a question. If tow limits are not to be believed why bother having them?
When I decide I was going to get the AS, I knew exactly what model I wanted. I went to the RAM dealer with a long list of requirements including and most importantly what it needed to pull.
If tow limits are meaningless than why do all the truck and car manufacturers list what the limits are?

Because the average person with a 7,000 lb trailer and a truck that can tow 10,000lb usually just hooks up and goes. I did that for years.

kendrick.l.j 10-31-2017 04:11 AM

I am for standardized tow rating as well but from the above video it doesn’t look like that is going to happen. Only Toyota is following them while everyone else is just throwing darts at at the board and picking a number out of the blue.

Andrew T 10-31-2017 04:29 AM

The part of tow ratings that will never work is that they use weight alone which is a relatively small part of the towing equation. Aerodynamics, Balance, suspension, braking and hitch system are all more important. A 9000 pound loaded 34í Airstream is much safer and easier to tow than a 3500 pound stick and tin box trailer.

As someone mentioned earlier if vehicles were truly engineered to tow the vehicles with the highest ratings would look nothing like a pickup truck.

Andy.

slowmover 10-31-2017 10:11 AM

SAE J2807 is chock full of holes. Drive a pickup thru those:

Pre-determine the "answers" by ignoring valid concerns as questions.

And, don't test less profitable vehicles than pickups. Assign to those a low random number, if any.

And, use a trailer in testing not at all representative of he RV market.

Change WD hitch guidelines to not only favor the above, but to actively discourage the use of other vehicles. Even though it took fifty years to "discover" the problem cited as need for that change.

That "standard" is a dead end.

.

uncle_bob 10-31-2017 10:45 AM

Quote:

Originally Posted by kendrick.l.j (Post 2028479)
I am for standardized tow rating as well but from the above video it doesn’t look like that is going to happen. Only Toyota is following them while everyone else is just throwing darts at at the board and picking a number out of the blue.

Hi

Keep in mind that those videos are from 2013. The "next change" the Ford guy is talking about in the video has already happened. There are far more J2807 certified trucks on the market than was the case when the videos were made. There are a few references in the video like "everybody tests on the same roads". What was being done was not totally insane.

Indeed as noted above no standard (especially a brand new one) is going to really cover everything. The testing was better targeted at the 150/1500 size trucks than at the larger versions. That lead to a bit of back and forth and some revisions.

Bottom line seems to be that when the standard went into effect, the ratings changed by a couple hundred pounds. To some degree this is why some of us get a bit excited when people run to within a hundred pounds of this or that rating. They simply are not that precise a thing.

Throw on top of that the fact that I only care about an Airstream. I really do not care about pulling anything else (until I suddenly buy a boat ... :) ). No standard will ever have a "pull a 30' Classic over the PA turnpike" category. That's the category that matters to me :).

As mentioned in the video, trailer brakes matter. That's only one item on a very long list of things that matter. Those things will not impact every TV the same way. What is fine on this TV that tests out at 10,000 lb may be totally wrong for the next TV that also tests out at 10,000 lb. We spend a *lot* of time talking about sway .... that's very much a combined effect between hitch, trailer and TV.

Lots of variables.

Bob

KK4YZ 10-31-2017 11:40 AM

Quote:

Originally Posted by Andrew T (Post 2028480)

As someone mentioned earlier if vehicles were truly engineered to tow the vehicles with the highest ratings would look nothing like a pickup truck.

Andy.

Andrew,
That begs the question: what WOULD a designed-for-towing vehicle look like?
THAT would make for interesting discussion, but Iím interested in your thought.
Thanks
Jim

bono 10-31-2017 01:39 PM

https://i.imgur.com/5y9vb4W.jpg?1

Quote:

Originally Posted by KK4YZ (Post 2028627)
Andrew,
That begs the question: what WOULD a designed-for-towing vehicle look like?
THAT would make for interesting discussion, but Iím interested in your thought.
Thanks
Jim


KK4YZ 10-31-2017 02:30 PM

Quote:

Originally Posted by bono (Post 2028664)

Run on fuel cells or kryptonite?

70CT 10-31-2017 02:31 PM

1 Attachment(s)
Attachment 298038

uncle_bob 10-31-2017 02:41 PM

Quote:

Originally Posted by KK4YZ (Post 2028627)
Andrew,
That begs the question: what WOULD a designed-for-towing vehicle look like?
THAT would make for interesting discussion, but Iím interested in your thought.
Thanks
Jim

Hi

Keep in mind that you likely would re-design the trailer for optimum towing as well as the TV. The pictures above begin to get into that part of it.

Since this is a microscopic sized market (by car or truck standards) .... what you see is what you get. Modify or not as you see fit. Dedicated tow vehicles to match with custom RV's are not something I'd hold my breath waiting for.

Bob

jcl 10-31-2017 04:04 PM

Quote:

Originally Posted by KK4YZ (Post 2028627)
That begs the question: what WOULD a designed-for-towing vehicle look like?

My take:
  • Low centre of gravity
  • If more than 2WD was desired or required, it would be AWD and not 4WD, resulting in no heavy transfer case, and being built closer to the ground
  • It would have virtually no rear overhang. Think of tow trucks, often built on 350/3500 platforms as are discussed here, but which have to deal with much more than 10% tongue weight, and so have the weight of the tow applied very close to the rear axle.
  • If a box was required for cargo, the rear axle would still be pushed out to the rear of the truck. In the '70s, Ford (and maybe others) had a longer wheelbase on the F350 pickup, with the exact same overall length. Some people found that out when they tried to swap boxes and found the wheel wells were in the wrong place. They did it prior to dual rear wheel pickups, to spread the load between the front and rear axles better given higher loads for things like slide in campers. It would work for towing as well as for carrying cargo.
  • It would be designed for much better handling when not towing, on the basis that adding a trailer rarely makes something handle better, and it is better to start with a good platform
  • The vehicle stability control system would work together with the trailer brakes, and be able to apply them independently in the event of a sway event
  • The vehicle would have onboard weight measurement at each corner, with feedback to the driver

There could be lots more items included, but there is a start.

Len n Jeanne 10-31-2017 04:16 PM

slowmover, obviously safety is the biggest concern when towing, period. We don't dispute that, and you've got a great description of towing on the downhill side of the mountain. However, we live in the mountains and tow through the mountains pretty much wherever we go. On a long steep ascent, you do feel whether your vehicle is under-powered. And we normally stay in or near the right lane at 60 mph on a long steep pass. With multiple lanes of traffic on long steep uphill grades, it is really helpful to be able to pass a slow-moving truck. Or just not feel like the vehicle is straining.

slowmover 10-31-2017 11:32 PM

Quote:

Originally Posted by Len n Jeanne (Post 2028723)
slowmover, obviously safety is the biggest concern when towing, period. We don't dispute that, and you've got a great description of towing on the downhill side of the mountain. However, we live in the mountains and tow through the mountains pretty much wherever we go. On a long steep ascent, you do feel whether your vehicle is under-powered. And we normally stay in or near the right lane at 60 mph on a long steep pass. With multiple lanes of traffic on long steep uphill grades, it is really helpful to be able to pass a slow-moving truck. Or just not feel like the vehicle is straining.

I used your post as example, understood? We'll do it again that way:

So, now, "you've" (whomever) not questioned the assumption of why it's "important" to pass a slow-moving truck. It isn't, and you know it. That's where the problem lays. Emotional anxiety. Neither safety nor inadequate vehicle performance apply.

35-45/mph on a long and/or steep ascent isn't meaningful. It's better than "adequate". It's "good" in fact, where 80% engine load isn't reached.

That is if one understands how to spec a tow vehicle. That that isn't a subject in itself shows the failing of every RV board.

And it's objective. Saying, "well, your idea and mine aren't the same" takes it right back to where I started.

It isn't opinion in the sense of uneducated. It's where the deficiencies also found in a tow vehicle badly chosen crop up.

The point is that in having met that test (speed on a grade at X percent power) the range of "good" vehicles is covered no longer by engine power, but by suspension and steering sophistication. Etcetera and so forth. There is a list of things to be checked off in vehicle spec. Not one thing to the exclusion of others.

Solo duty is what matters. Towing is occasional. (This is fundamental, not accessory). Thus, wrong metric applied per "safety".
.
I get it about inexperience and "well, the vehicle is straining". That has definitions. A feedback device like a Scangauge or UltraGauge OBD reader can show Engine Load percentage if the dashboard wont. 80% is a handy number, and while there's nothing wrong with hitting 100% in a climb, controlling for speed (at or above minimum) is the metric. Climbs at 45-mph at 80% or less? Good. Same otherwise, but at 100%? Adequate.

It's like learning to read the tachometer to manually shift an automatic transmission is part of an ascent or descent to make best headway with the vehicle that's Adequate. To make a somewhat higher speed with the one that's Good. Etc. (One shifts high enough in the rpm range that it enters the next gear as close to Peak HP as possible).

The engine has operating guidelines. Enough rpm to climb above peak TQ and below peak HP is great. (Done. Check that off list). A vehicle that needs most or all of its HP to do that isn't being abused. It won't last any less long just because the rpms are high. It's doing what it's supposed to do. As are you. (Thus also Done, check that off list).

Road speed. Engine rpm. Both have targets or boundaries, be they 45-mph or engine rpm redline. Together, the test is clear. Because other traffic -- solo vehicles -- don't enter into this.

You have the vehicle you wanted. But "safety" was down the list. It doesn't correlate to excess engine power.

(For which there's also a test. 0-60. Thirty seconds is Adequate. 20-seconds is Good. More than that isn't useful compared to having had a more stable-by-design vehicle. As most miles and time will be spent solo.

That you feel better isn't a bad thing in and of itself. It's the common delusion, however.


.

KK4YZ 11-01-2017 06:43 AM

Quote:

Originally Posted by jcl (Post 2028717)
My take:
  • Low centre of gravity
  • If more than 2WD was desired or required, it would be AWD and not 4WD, resulting in no heavy transfer case, and being built closer to the ground
  • It would have virtually no rear overhang. Think of tow trucks, often built on 350/3500 platforms as are discussed here, but which have to deal with much more than 10% tongue weight, and so have the weight of the tow applied very close to the rear axle.
  • If a box was required for cargo, the rear axle would still be pushed out to the rear of the truck. In the '70s, Ford (and maybe others) had a longer wheelbase on the F350 pickup, with the exact same overall length. Some people found that out when they tried to swap boxes and found the wheel wells were in the wrong place. They did it prior to dual rear wheel pickups, to spread the load between the front and rear axles better given higher loads for things like slide in campers. It would work for towing as well as for carrying cargo.
  • It would be designed for much better handling when not towing, on the basis that adding a trailer rarely makes something handle better, and it is better to start with a good platform
  • The vehicle stability control system would work together with the trailer brakes, and be able to apply them independently in the event of a sway event
  • The vehicle would have onboard weight measurement at each corner, with feedback to the driver

There could be lots more items included, but there is a start.

Kinda makes me think of a larger Chevy SSR.

KK4YZ 11-01-2017 06:46 AM

Quote:

Originally Posted by uncle_bob (Post 2028679)
Hi

Keep in mind that you likely would re-design the trailer for optimum towing as well as the TV. The pictures above begin to get into that part of it.

Since this is a microscopic sized market (by car or truck standards) .... what you see is what you get. Modify or not as you see fit. Dedicated tow vehicles to match with custom RV's are not something I'd hold my breath waiting for.

Bob

Bob, Iím not turning blue yet, cuz I donít expect it to happen either.


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