Are They Meaningless? Tow Limits, Payload and Axle Load

[ROBERT CROSS]

There is no 'DOT' script on my door's, I'll continue just as I have for the last 33yrs.

Bob
🇺🇸

[BayouBiker]

Originally Posted by camp-n-family

The engineers and technicians don’t make the ratings. The lawyers do.

Nah, for the most part, the Engineers set the ratings and the lawyers enforce them.

[Bruce B]

Originally Posted by BayouBiker

Nah, for the most part, the Engineers set the ratings and the lawyers enforce them.

I have to believe you are correct Brian!

[HappyHapgood]

Interesting. One of my takeaways from this is that some of the larger tow vehicles (those with 10k or greater GVWR) often have more lenient guidelines in acceptable Performance. For example, vehicles less than 10k GVWR can’t lock up their ABS systems unless going slower than 10 mph. But the bigger trucks can lock up at 20 mph.

So... maybe the tests (and therefore ratings) aren’t even really apples to apples.

Matt

Originally Posted by Profxd

Stated simply yes so here are some details to consider.
The most important FMVSS 105 braking test here https://www.nhtsa.gov/sites/nhtsa.do...105-03_tag.pdf

SAE j2807 here
https://fifthwheelst.com/documents/t...ds-2016-02.pdf

To say that payload (GVWR) is just a suggestion is just wrong, but hey it comes from those that think they are experts not real engineers.

[BayouBiker]

Many of the differences you note are geometry related and really are Apples to Apples. The ABS lockup for example is because larger vehicles tend to have larger diameter tires and thus lower angular velocity. to accommodate similar instrument considerations they need higher speeds.

I've seen real engineers and experts make that and similar statements..... Go figure.

[dst]

"Are They Meaningless? Tow Limits, Payload and Axle Load"

I don't think a jury is going to think they are meaningless if you get pulled into court for being in a wreck. I don't think "I read on the internet not to worry about it" is going to remove your liability. Even if the wreck was not your fault, a lawyer will try to shift fault your direction since you were operating outside of the manufacturer's posted guidelines. Somehow they will make that a contributing factor, even if it is a crazy statement like "he could not swerve to get out of the way of my drunk driver client because he was overloaded".

[2008AS]

Can Am lost me when he suggested using what has turned out to be one of the worst trucks ever produced.

The engine that is likely better suited to RV towing is the 5.0 litre Cummins that is in the Nissan Titan.

Amazing that someone made this guy god of towing.

[starpicker]

BTDT. Ignore the ads and brochures, even for that make and model. 2nd time around I learned from these forums all you need to know in one regard: Go by only what is shown on the driver’s door pillar. Do your calculations from there. The numbers matter and setup your hitch properly.

[Tireman9]

Originally Posted by jaybauman

We should also keep in mind that manufactures' limits are in-part determined by the weakest link in the chain.

I recall a conversation I had with a few automotive engineers back in 1999 or so. I took a long weekend and rode my motorcycle from Santa Fe to Denver, taking the long and twisty back way. After crossing a particular pass, I stopped at a gas station / convenience store to fuel up and stretch my legs. While walking around, I spied a funny-looking dually truck that I couldn't quite identify so I walked up and started talking to the "owner".

It turns out that this was a 2003(?) future GMC Sierra 3500HD with Duramax and a team of GM engineers was measuring performance data at extreme conditions. The body panels were somewhat fake, since the body design was still in progress. The interior was gutted, with 3 or 4 laptop computers bolted to console and dashboard. The team had been in Death Valley the previous week, and now they were pulling a heavy trailer through 12k passes. IIRC, they were specifically working on engine cooling and HVAC (but I don't really remember all the details 20 years later). I do recall those young engineers were having the time of their lives and were not looking forward to heading back to Rochester when they wrapped up the data collection.

Since most of us do not tow at maximum trailer limits in these extreme conditions, it could be easy to fall into the "I can exceed TV limits--I do it all the time" mindset; we don't ever run into the engineering failure break points with our usage patterns. Maybe this is a false sense of security, or maybe it's legitimate since we're not really pushing overall design limits.

In summary, there is likely additional towing bandwidth available as long as you're not at the extreme operating conditions. But I would like to hear from real automotive design engineers on this topic.

Back in the '90s I participated in two cross-country "prototype runs". These involved 6 different cars, 12 engineers from various areas of vehicle design and suppliers plus a follow truck that carries some spare parts and all our luggage for the week.
The cars included the current model, 4 competitor cars considered comparable models plus a "prototype". I was told the prototype cost $250,000 because it was all custom one-off parts.
There were 2 tire engineers, an engineer from the suspension dept evaluating shocks & springs, a couple of engine guys, transmission guy and the "cup-holder" guy who was involved in the various interior panels, including their fit and finish. A couple other specialists were involved for a day or two and would then swap put with a different specialist.
Each day we would drive a car for 1/2 hour then ride in that car 1/2 hour as we completed our multi-page evaluation sheet then we would switch to a different car and continue the rotation till we have evaluated each of the 6 cars.
The trips started in Detroit and wound across the US via locations such as Memphis, Dallas, Denver, Phoenix, Vegas and ending in LA or San Francisco. I would estimate that 90% of the travel was on state route or even secondary roads with only 10% on Interstate. We had a specific route that included all kinds of roads and surfaces.
The tire engineers would be evaluating ride, noise, handling, steering response etc while also noting other items such as engine response and transmission shifting. I remember being in the prototype when it was confirmed that the cup-holder location made it impossible to tune the radio if there was a "big-gulp" drink cup in the holder. In one of the controls we observed that the shift into 5th had a similar problem when a drink cup was present.
One section included acceleration and shifting runs up to Eisenhower Summit on I-70 in Colorado.


As you can see there was a lot involved and these types of evaluations are a normal part of new car development. They are also expensive which is probably why this type of evaluation is seldom if ever done in the RV world.
I often wonder if any RV company has engineers live in a motorhome and drive it across the US or has people spend a week in a prototype new model trailer. When I read comments or look at new RVs it just doesn't appear that much time has been spent actually living with the various features and workmanship found in many RVs.

You can see that we were doing a thorough evaluation.


I will cover the question of the various performance, durability limits and testing done specifically on tires in a separate post.

[Bruce B]

Originally Posted by Tireman9

...

You can see that we were doing a thorough evaluation.


I will cover the question of the various performance, durability limits and testing done specifically on tires in a separate post.

I am looking forward to reading that post!

[dayner]

Yes they are important. Research how legal tow and capacity ratings are determined and tested for verification. They are not "rules of thumb", "goals", nice to know but not applicable cause I bought bigger tires & an exotic hitch, dont apply cause my rig was modified by some guy in Canada, I know how to drive better than most folks, I have always done it this way and never killed anyone, etc. They are there to not only to help protect you and your rig from damage, but also there to protect the general public from you and your rig.

[jcl]

Originally Posted by Tireman9

Back in the '90s I participated in two cross-country "prototype runs". These involved 6 different cars, 12 engineers from various areas of vehicle design and suppliers plus a follow truck that carries some spare parts and all our luggage for the week.
The cars included the current model, 4 competitor cars considered comparable models plus a "prototype". I was told the prototype cost $250,000 because it was all custom one-off parts.
There were 2 tire engineers, an engineer from the suspension dept evaluating shocks & springs, a couple of engine guys, transmission guy and the "cup-holder" guy who was involved in the various interior panels, including their fit and finish. A couple other specialists were involved for a day or two and would then swap put with a different specialist.
Each day we would drive a car for 1/2 hour then ride in that car 1/2 hour as we completed our multi-page evaluation sheet then we would switch to a different car and continue the rotation till we have evaluated each of the 6 cars.
The trips started in Detroit and wound across the US via locations such as Memphis, Dallas, Denver, Phoenix, Vegas and ending in LA or San Francisco. I would estimate that 90% of the travel was on state route or even secondary roads with only 10% on Interstate. We had a specific route that included all kinds of roads and surfaces.
The tire engineers would be evaluating ride, noise, handling, steering response etc while also noting other items such as engine response and transmission shifting. I remember being in the prototype when it was confirmed that the cup-holder location made it impossible to tune the radio if there was a "big-gulp" drink cup in the holder. In one of the controls we observed that the shift into 5th had a similar problem when a drink cup was present.
One section included acceleration and shifting runs up to Eisenhower Summit on I-70 in Colorado.


As you can see there was a lot involved and these types of evaluations are a normal part of new car development. They are also expensive which is probably why this type of evaluation is seldom if ever done in the RV world.
I often wonder if any RV company has engineers live in a motorhome and drive it across the US or has people spend a week in a prototype new model trailer. When I read comments or look at new RVs it just doesn't appear that much time has been spent actually living with the various features and workmanship found in many RVs.

You can see that we were doing a thorough evaluation.

In October 1996 Ford introduced the 1st Generation Expedition. Towing was a part of their target market.

In summer of 1996 we drove the Alaska Highway from Dawson Creek to Anchorage and back, with detours down to Skagway, and up through Chicken to Dawson City. We were driving a 1996 Explorer. I spotted what looked like a larger Explorer in Whitehorse, downtown; I identified it as an unreleased Expedition, and spoke to the test team who were validating it for towing. They had a non-Airstream trailer hitched up, around 28 or 30 feet IIRC. The testing and validation was largely done, they said they didn't have a lot of surprises, but they had wanted to do the length of the Alaska Highway, towing, to see what else came up. They were good guys to talk to. All engineers. I got photos, but don't know where they are now. We saw them at numerous locations on that trip, along the highway, over the next several days.

I went home and got in line, and bought one of the vehicles in the first shipment of 1997 Expeditions to our town when they arrived. It towed well I thought, but not great on power. The higher output engines came in subsequent years. I had a second Expedition in South America, working at elevations up to 16,000 feet. That is where they should have validated it, they would have moved to turbocharging much earlier. A full load made for a slow climb to the mine sites, and I wasn't towing at that point.

[rgwatkin]

Originally Posted by switz

Looking at manufactures web sites, one looks at their suggested tow ratings and wonders if the profit motive for upselling drives the number. As an example, my 2012 Ram has a GVW of 9,600 pounds. After adding just one leaf spring on the rear it suddenly has a 11,000 pound tow rating. No other parts are changed.

But a 3500 model sells for more $$$

When people express concern on 1/2 ton axle overweight I always have just one question, when is the last time you heard of someone breaking an axle...answer...never. I bet the safety margin on axles is 2x.

[jcl]

Originally Posted by rgwatkin

When people express concern on 1/2 ton axle overweight I always have just one question, when is the last time you heard of someone breaking an axle...answer...never. I bet the safety margin on axles is 2x.

The limit is also reached with high dynamic loads, and those are typically reached at high vehicle speeds.

Mercedes SUVs are designed for autobahn speeds, and are capable of those speeds. They have an official load rating. They also have a supplemental higher rear axle maximum load rating for the same vehicle, noted in the manual, and applicable only when towing. They know that owners won't be towing at 150 mph, and so seem to be comfortable telling customers they can tow with higher rear axle loads. Typical towing speeds will likely be more like half that top speed, although the higher axle rating when towing doesn't mention speed, just that the owner is towing.

[jcl]

Originally Posted by dayner

Yes they are important. Research how legal tow and capacity ratings are determined and tested for verification. They are not "rules of thumb", "goals", nice to know but not applicable cause I bought bigger tires & an exotic hitch, dont apply cause my rig was modified by some guy in Canada, I know how to drive better than most folks, I have always done it this way and never killed anyone, etc. They are there to not only to help protect you and your rig from damage, but also there to protect the general public from you and your rig.

I think it would be great if people researched how tow ratings are determined. Legal is a separate issue, but sure, that too.

My favourite tow rating anecdote relates to tow ratings (GCVWR), how they are calculated, and them not being mandatory. It is up to the manufacturer in some cases. If the manufacturer doesn't specify a GCVWR, the regulations tell the owner how to calculate the legal one. You take the GVWR of the tow vehicle, and the GVWR of the attached trailer, add them together, and that is your legal GCVWR. Simple. I came across this again most recently when I looked up GVWR for Maryland, where another recent poster notes they reside, in relation to a claim about these ratings. Maryland uses that approach to determining GCVWR. It is derived from a US federal statute.

Makes a mockery of the claim that GCVWR is necessarily a safety number. Certainly, tire and axle loads are legal and safety limits. GVWR is a legal number when one is a commercial operator and subject to those regulations, and for vehicle licensing in many locales, and also IMO as a general safety limit whether or not one is not a commercial operator, but when one is solely hauling a load (eg not towing, and also when towing without WD).

GCVWR is a safety number in one key sense. It is used to license the operator. A heavier nameplate rating requires a more highly trained operator, the maintenance of operator log books, stops at weigh scales at the tops of big descents, and so on. The rating doesn't refer to the vehicle (except for some specific test criteria) but it does refer to how the vehicle is used.

All of us are capable of obtaining a higher level license (CDL in the US), of stopping at truck brake stops, of using weigh scales to confirm loads, and so on. We don't have to have a higher GCVWR to do those things.

[s1000pre]

There are tow ratings from manufacturer which are then broken down and outlined per body style and trim level. The F-150 is a perfect example. Ford is currently boasting best in class 13,200 lb. available towing. ...WHAT...is that a 50lb. Kid driving a short cab 2wd, no washer fluid and 1 gallon of gas ��. My 2019 f150 limited has the lowest..as the numbers reflect, I can barely get away with pulling a fully loaded 25FB which has a weight of just over 5,300lbs. I have done the math, kids dogs, payload, gas, full tanks(worst case scenario). It isn’t that I’m only close to my max towing, I’m also reaching my max payload of only 1,270lbs. I guess those low profile 22’s are looking for any excuse to blow its bead! If I load it down and hit the perfect rock or pot hole...it’s all over!!! This is a perfect example of why not to exceed limits. A 1970’s station wagon can pull an Airstream. The question is, how well does it stop from 65mph in an emergency situation. Or how does it handle on a 55mph mountain pass around a corner with a Semi passing. Look...I would stick with the manufacturers specs! If specs of your vehicle layout, trim level and all asterisk’s (*) state that you are within your limits...this includes all payload including occupants...you should be able safely tow... The discrepancy is power. If your within specs...you can pull it!!! the difference is: Will it struggle going 50 up the mountain pass, or can you pass someone going up a steep grade at 75mph. The more power & torque...the better it will perform. Anyone should be able to make this decision without consulting the forum again and again for the correct towing vehicle. Aviod the onslaught of personal opinions on the forum regarding tow vehicles. Everyone has an opinion...I have mine! It’s going to be a lot less exhausting, shopping For your tow vehicle without everyone’s contradicting opinions! Get out the calculator, add up the numbers...be conservative with weight of cargo. Then decide how much power you really “want” if within specs they will all get the job done!!!

[dznf0g]

Originally Posted by camp-n-family

The engineers and technicians don’t make the ratings. The lawyers do.

Wrong! The marketing managers and engineering do during the "white paper" phase of product development.

[dznf0g]

Originally Posted by rgwatkin

When people express concern on 1/2 ton axle overweight I always have just one question, when is the last time you heard of someone breaking an axle...answer...never. I bet the safety margin on axles is 2x.

The "safety" margin may be, but the durability margin is not.

[CanyonMan]

Originally Posted by rideair

Tow ratings are meaningless until one of two things happen.

1. Stop by police with a set of scales.
2. Have an accident and the attorney of the family you killed looks at the numbers.

Enjoy,

I would be interested in any first hand accounts of either of those scenarios happening.
Canyon

[GettinAway]

Originally Posted by ROBERT CROSS

Can I get an Amen from the Congregation...😇

Bob
🇺🇸

Got mine.. AMEN! Now I have to read the next 7 pages and see if this statement has been totally trashed.