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Old 07-12-2009, 04:17 PM   #1
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The 80% tow rule. Where did it come from?

OK, This may open a can of worms but I would like to know.

If the manufactures state a certain vehicle will tow a certain amount, wouldn't you think that it is safe to tow that amount?

Wouldn't you think that they would have a margin of error into their tow ratings. (they don't want to get sued do they?)

So with the assumption that the manufactures say it's safe to tow at their rating why do so many say that it is only safe to go up to 80% of that tow rating.

Where did this rule of thumb originate?

Look what we use to tow with in the 60's and 70's. People are towing with cars and having no problems.

SO WHY THE 80% RULE....

And just to be safe isn't the right answer, you might as well say 50% then.
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Old 07-12-2009, 04:50 PM   #2
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i always considered the 80% rule as stupid. i agree with you someone just made this up. never made sense to me. everyone on here always seems to go overboard when it comes to tow vehicles.
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Old 07-12-2009, 05:00 PM   #3
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There are no "rules." You tow with what you have or what you're comfortable with.

Personally, I like the 80% guideline because I know I can drag my Airstream and all my gear wherever I want to go without a problem, like Independence Pass or Lizard Head Pass in Colorado.

But that's one of the great things about having brain cells. You can rub them together, evaluate your choices and use your judgment.
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Old 07-12-2009, 05:02 PM   #4
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I guess I look at it as 80% will easily cover you in the flatlands. However once you get into conditions that require more muscle, those situations will cover that 20% gap. For example if I'm pulling 100% of my towing capacity in the flatlands, what happens when I go into the Ozarks with grades much steeper than typical Interstate standards? I would expect that that load I'm pulling acts as if it is much heavier because I'm not only fighting rolling and air resistance, but I'm now fighting gravity. If I'm at 100% in the flats, then I'm over 100% on the grades. That causes more heat in the tow vehicle and more strain on the transmission and other components.

That's sort of my take of why you want some reserve. Now if you a flat land tower, then 80% many not be necessary. If you are a Rocky Mtn tower, you may need more reserve.

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Old 07-12-2009, 05:15 PM   #5
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I guess I look at it as 80% will easily cover you in the flatlands. However once you get into conditions that require more muscle, those situations will cover that 20% gap. For example if I'm pulling 100% of my towing capacity in the flatlands, what happens when I go into the Ozarks with grades much steeper than typical Interstate standards? I would expect that that load I'm pulling acts as if it is much heavier because I'm not only fighting rolling and air resistance, but I'm now fighting gravity. If I'm at 100% in the flats, then I'm over 100% on the grades. That causes more heat in the tow vehicle and more strain on the transmission and other components.

That's sort of my take of why you want some reserve. Now if you a flat land tower, then 80% many not be necessary. If you are a Rocky Mtn tower, you may need more reserve.

Jack
Not sure I understand what you mean by reserve. The max tow load is the max tow load whether you are on a hill or on the flat. I'm sure the vehicle manufacture doesn't expect everyone to tow on flat ground.

I can see if you want to pull at 70 mph on the flat and on the hills too. Then the 80% would help. It would also put less strain on stuff, but then it's like what I said, why not make it 50% then you have even more reserve...
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Old 07-12-2009, 05:53 PM   #6
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Not sure I understand what you mean by reserve. The max tow load is the max tow load whether you are on a hill or on the flat. .
I think another example would be a military pilot. When he comes out of a steep dive and pulls the nose up in his plane, the movement going up and the resultant force of gravity makes him feel much heavier. The same muscles that raise his arms now have to now overcome that additional pull of gravity (much like his weight increasing).

It's really not all that different in towing in that the tow vehicle components now have to expend much more force in moving that trailer as you go uphill. While the trailer may technically not weigh more, the force required of the tow vehicle to move that trailer has to be greater to overcome the pull of gravity. I can guarantee you that if I have a tow vehicle rated to tow up to 10,000 lbs., if I'm going up a steep hill, I can reach the top of that hill faster with a trailer that weighs 6000 lbs. than one that weighs 8,000. Flat ground wise I can pull both trailers at 60 mph. The difference is that the extra effort that is used to pull that trailer up the hill faster comes from the unused towing capacity of the tow vehicle.

So the 80/20 rule is not locked in as gospel. My current tow vehicle is probably more like 85/15 when rated against my current Classic slide out. While it is adequate for my area of travel and is withing GM specs for rated load, it wouldn't be the tow vehicle of choice if I lived in Colorado. Which for all intents means that my choice of a vehicle might have more of a 75/25 spread.

The 80% not only deals with load but it deals with performance and being able to handle conditions that may always not be ideal. Also keep in mind that components that are stressed at a 100% load factor probably may require servicing more often than something stressed at 80%.

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Old 07-12-2009, 06:04 PM   #7
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Trying to start a load moving on flat ground is much easier that uphill.
Never has been a "rule", but max load= no margin for error= no safety margin.
Yes, in the 50's/60's, sedans were used to tow, but there were 1/3 the number of vehicles on the hwy's then, and at lower speeds. Todays speeds, and traffic density calls for heavier vehicles, with better brakes, to control heavier trailers, with less room on the road.
Am constantly amazed at the number of people who want a tow vehicle to be; small, lightweight, low payload, soft riding, great mileage,,,and "cute".,,,, They haven't a clue.
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Old 07-12-2009, 06:12 PM   #8
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I've wondered about where this "rule" came from also (purman and I both live in the same rural county, so it may be something in the air or water or from all the cows). Sometimes it's 80/20, sometimes 85/15. I think it's "conventional wisdom" which isn't wisdom at all, but just repetition for so long we tend to believe that someone actually figured it out long ago.

I don't know how manufacturers come up with capacities—some may bloat them, some may be conservative. If they built lousy trucks that have low capacities, they are probably the same people who would lie about capacities to sell trucks—that is the marketing people make the decisions, not the engineers. They don't listen to lawyers who worry about liability; if companies listened to lawyers, there would be many fewer bad products. On the other hand, companies that make reliable trucks, have more of interest in telling the truth because they have nothing to lose. My Tundra appears way overbuilt for a 1/2 ton truck, so I expect the numbers are very conservative. But a certain company just emerging from bankruptcy put WD hitches on trucks that cracked, so their numbers were a fantasy in the real world.

My rig is about 60/40 for towing capacity, but probably around 90/10 for payload according to Toyota's numbers. It's true as Jack posted—closer to a vehicle's capacity, the more wear you can expect, but also true you can tow with a truck so big that it manhandles the trailer. That's like getting a hug from a linebacker when you have osteoporosis. Finding that sweet spot is a challenge, partly from logic, partly from what feels good.

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Old 07-12-2009, 07:21 PM   #9
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Jacanavera, I understand the physics of gravity playing a role, But then not towing is even better that towing. so why is it set at 80% I agree with your perception of the 80% and agree it is a good idea to have a little in reserve but others make it a hard fast rule, WHY?

I still contend the the manufactures must take into account that not everyone tows on the flats.

Now,my set up is probably just past 55% of my tow load but I have max it out towing a mini excavator, and I felt under control at 50-55 mph. Sure I couldn't stop as I normal do without towing something, but then I leave more space between me and the car in front of me.


Now if my TV was all I had, and I am willing to tow it to the max what is wrong with that?


It seems here, there are plenty of people who call it reckless and dangerous, to the tower and others on the road.

Why is this so? if the Vehicle manufacturer says it's not!!!!!


I'm not trying to start an argument, I agree it's best not to max out your TV, but some people have no choice.
I am just wondering where this rule comes from because it is brought up some much when talking about towing...
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Old 07-12-2009, 07:31 PM   #10
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I just had a great idea, I think I'll get one of those new 30'classics, they have a gvw of 10,000 lbs. And, that Tundra, well, it's rated to tow that, it even has brake discs about the same size as the F-350 powerstroke,,,, and it's got 40 more horsepower,,,,, would certaintly be a better TV, right??, I'll bet it rides better too.

Or, I bet if I see those guys up in Canada, they could make me a set-up, so I could tow it with my Trailblazer, or Bronco, and get great mileage too,,,,,yeah, that's the answer.

Right,,,,,NOT
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Old 07-12-2009, 07:41 PM   #11
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My 80/20 rule....

80% common sense....

20% seat-of the-pants...

Works for us...


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Old 07-12-2009, 07:54 PM   #12
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Well, the Tundra can tow from 10,100 to 10,500 lbs. depending on the model, so there would approximately 1 to 5% safety margin. The tongue wt. of the '08 30' Classic is only 670 lbs., so payload may not be a problem. Tongue wt. on the slideouts was more than 1,000 lbs, but they don't make them anymore. Keeping the cargo weight down in the Classic would give more of a margin. It can carry 2,900 lbs. of cargo, so by limiting yourself to 1,900 lbs., you have a margin of around 11 to 15%. So, actually it could be done, though I wouldn't do it. As for a mid sized SUV, no. The Canadians tow them with two snowmobiles in tandem.

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Old 07-12-2009, 07:55 PM   #13
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Jacanavera, I understand the physics of gravity playing a role, But then not towing is even better that towing. so why is it set at 80% I agree with your perception of the 80% and agree it is a good idea to have a little in reserve but others make it a hard fast rule, WHY?

I still contend the the manufactures must take into account that not everyone tows on the flats.

Now,my set up is probably just past 55% of my tow load but I have max it out towing a mini excavator, and I felt under control at 50-55 mph. Sure I couldn't stop as I normal do without towing something, but then I leave more space between me and the car in front of me.


Now if my TV was all I had, and I am willing to tow it to the max what is wrong with that?


It seems here, there are plenty of people who call it reckless and dangerous, to the tower and others on the road.

Why is this so? if the Vehicle manufacturer says it's not!!!!!


I'm not trying to start an argument, I agree it's best not to max out your TV, but some people have no choice.
I am just wondering where this rule comes from because it is brought up some much when talking about towing...
When it comes right down to it, I don't believe anyone knows why 80% became "the right percentage". Obviously I didn't go by it since I'm over that limit. My previous van had a 6,500 lb. limit and the Safari I pulled weighed 6,000 lbs. I personally would'nt call it reckless and dangerous if you don't adhere. I think what we've seen is some tow combos where it's not a good mix.

Just an example is me back before my Airstream days. I bought a 30' aluminum framed SOB that weighed about 3,800 lbs. I pulled it with a Chevy Astro EXT van that was rated to pull 6,000 lbs. The van had a premium gas V6 with a 4.10 rear axle. So I was in the 80% range. Was it a good tow vehicle for that trailer. No! The reason was the mass of that trailer was so large that even with excellent sway control equipment, the trailer pushed that van all over the road when the wind was blowing. It acted as a big sail. So yes it's rated to tow, but not that trailer. I dumped it after one season because not only did it physically wear me out while towing but I finally figured out there is much more to consider than pure towing muscle.

In many cases some of us here are critical of tow vehicles that while fitting the capacity side, are no match for a travel trailer of size.

Jack
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Old 07-12-2009, 08:01 PM   #14
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I think what Jack may be saying is that every combination is different and in the end, you have to try it. If he didn't say it, I am. Having the hitch set up correctly makes a big difference. All the numbers can be perfect at 80% or less and a poorly set up WD hitch will result in not enough weight transfer to the front wheels of the truck, a trailer than isn't level anb/or poor sway control. After I set up my hitch (the dealer did a crappy job), WD distribution is correct, the trailer is level and the rig rides much better.

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