Are They Meaningless? Tow Limits, Payload and Axle Load

[Collyn]

Originally Posted by BayouBiker

It is common in the towing community to hear that towing and hauling load limits from the manufacturers are all over the place with little or no relevance to vehicle ability to pull a trailer down the road. You often hear the numbers are meaningless and you hear this from novices, those who are seasoned and experienced and some who are considered experts in the field of towing.

One group notably absent from this group are the engineers and technicians employed by vehicle manufacturers who directly determine, test and establish tow and haul ratings.

How can this be that there is so much disagreement outside of the pool of those who establish these limits?

The claims seem to get started by the large group of people who don't understand how the limits are established nor how to interpret the limits. Many who do have some understanding seem to prefer to perpetuate the rumors and myths for some reason or another. The rare Engineering expert (Collyn for example) comes along from time to time and tries to shed some light on the topic.

So this thread will once again attempt to discuss and explain the meaning of these numbers and why they seem to be all over the place with no obvious basis used to establish or apply them.

Brian

Travel trailer towing is a tiny proportion of those who tow trailers. Most are military and (what we call in Australia) trades-people. They pull trailers that are far shorter and weigh a typical laden two tonne. Vehicle makers, by and large, set tow ball weight limits - and ensure their products can stop and restart on a (defined gradient) hill - but that's about it.

I can elaborate on this if there is interest.

Collyn

[DewTheDew]

Not sure about Andy's claim that GVWR is an "arbitrary number" at the end of that article.

[switz]

On the drive home from the selling dealership, I stoped at Keldermans in Iowa and had the 2012 Ram 2500HD Cummins converted from steel springs to all air bags. Due to weighing the truck at the end of each modification, I found the air bags and compressor and their steel parts added 100 pounds to the empty weight of the truck despite the removal all front and rear steel stock suspension parts.

So the rear suspension now consists of 10,000 pound rated air bags that provide a level ride and can be dumped so, as a short person, I can load things into the bed of the truck. However, the axle was not upgraded so that is the actual weight limit for the rear end. The factory selected tires "just" exceeded the axle rating by 20 pounds, which is legal.

I also know the rig is under the GCVW rating with the 2014 31' Classic attached and fully loaded for camping. Limits may get pushed when heading to the dump station with all tanks full.....

There are many "tow vehicles" where there seems to be great payload, but the GVW loaded tow vehicle number subtracted from the combined gross weight number is much lower than the maximum trailker vehicle weight in the literature. In some cases, subtracting the heaviest trailer weight from the maximum combined weight means bringing a single tooth brush for the two skinny passengers (Note, try and find the 150 pound person in a vehicle as that is the "standard" weight for driver and or passengers).

I have seen five "porkers" get out of a car that had overloaded the vehicle way beyond the safe load numbers on the door jamb.

So attempting to comply all the time with the displayed numbers requires a membership at the local truck scales or purchase of your own two sets of four scales like I acquired.

To be correct, one also needs to know what load is on each end of each axle. That data can come as a surprise to see which side of trailer is actually heaviest due to placement of appliances. A tire on the heavier side might actually be overloaded.

[BayouBiker]

Originally Posted by Prettygood

I am not suggesting exceeding stated limits. What I am suggesting is that those posted number still have a margin built in on actual capabilities. If you stay at the states numbers, the vehicle should be able to handle it well. Exceeding them places you in an unknown and dangerous spot.

There are so many people that say ‘only use 50%, only use 80% of published numbers’. I’m suggesting that isn’t really required to still be safe.

I understand your point better now.

One aspect of towing limits when they are not drive train limited, is they generally apply to trailer styles that pull more easily than travel trailers due to cross section and the distribution of weight throughout the trailer (inertial moment). To address this some people recommend derating. Others note with trucks in particular, they are just more pleasant when you're not towing at the limits. I think these are both valid to an extent.

Edit: To DewTheDew's point I agree GVWR is not arbitrary, but I also note when towing it does not apply as well as a towing specific number could.

[kgottleib]

Originally Posted by Bruce B

I often wonder about design duty cycle and margins when I read these towing discussions. There are an awful lot of variables in the real world. No small one being the driver.
In my business we maintained European autos. Even within a single brand/model/year, we encountered huge variation on life cycle. How could that be? Given good maintenance, I typically attributed different failure rates to the driving habits of the owner.
These were very expensive, highly engineered vehicles that were not subjected to towing or even the Autobahn speeds they were designed for but rather, were used for transportation in and around New England.
One person could drive 100,000 miles on a set of brake pads and rotors and another could not get 20,000 miles to a set. Some suspensions felt tight at 100,000 miles and 5 years, some were awful in 2 years and 40,000 miles.
It seemed that the vehicles that were driven well had very few problems in general. Those that suffered a rough driver had all kinds of “premature” service needs.
Manufacturers who build vehicles designed for towing must be aware of the vast spread of ability different drivers bring to the table.
I suspect than if you were able to closely observe the driving habits of say a random group of 100 drivers, you would be appalled at some of what you learned.
I am no engineer but I have to believe that manufacturers assign numbers like payload to account for the vast range of possibilities given a very large pool of variables.
My educated guess is that if you choose to exceed a number of any kind, that you better be ready to trade “some thing” off. It might be brake wear, differential life, handling under duress or something you never thought about. Perhaps you will be fine if you are one of the truly gifted, smooth and capable drivers.
Perhaps you will find that reason for the number the manufacturer assigned.
My problem is that I have limited tools to bring to my assessment of a tow vehicles driving dynamics. I have studied math, physics, chemistry and more but I have zero experience applying it to the very dynamic models of towing.
I do know that the best feeling tow vehicle I have ever driven was the heaviest truck I owned. My seat of the pants tells me that bigger is better.
My Audi Q7 was a lovely, lovely vehicle to drive. I preferred towing with my RAM 2500...
My experience maintaining autos leaves no doubt in my mind that subjecting a smaller vehicle to towing will shorten its life. That life may still be long, but it will not be as long...
I do love reading these threads when people keep their cool and remain polite.

hey hey back when i was in my 20s and even early 30s I was that driver that wore out a vehicle in just 2 yrs, now in my 50s the brakes on my last Jeep GC lasted 100k miles, the local shop that i work w for repairs was amazed.. we all learn at our own pace, slow is ok as long as we are learning I actually pay attention to NOT using brakes unless needed, never tailgating and coasting to stop, and watch my ave mpg fuel efficiency at all times..

[DewTheDew]

Originally Posted by BayouBiker

I understand your point better now.

One aspect of towing limits when they are not drive train limited, is they generally apply to trailer styles that pull more easily than travel trailers due to cross section and the distribution of weight throughout the trailer (inertial moment). To address this some people recommend derating. Others note with trucks in particular, they are just more pleasant when you're not towing at the limits. I think these are both valid to an extent.

Edit: To DewTheDew's point I agree GVWR is not arbitrary, but I also note when towing it does not apply as well as a towing specific number could.

Perhaps, but my point is that the sum of axle loads is not necessarily appropriate as an indicator of being "within safe limits". Those axle loads are max so if you put a snowplow on the front or a trailer with no WD hitch on the back, for instance. In those cases you may overload an axle without reaching the GVWR so that is another "check" to prevent customers from doing silly things. The axle numbers are individual measurements and the capability of the truck as a whole (which includes how ALL of the load-bearing and drivetrain parts of the vehicle respond) is defined by the GVWR. That statement of Andy's at the end of the article was a bit of sand in my craw. Yes, I realize that there is a factor of safety but I think setting up a rig that deliberately exceeds the published limits of a vehicle as set by the manufacturer is risky from a safety and legal standpoint.

[jcl]

Several manufacturers offer, or have offered, options for alternate GVWR stickers on new vehicles. This is usually so purchasers can avoid taxes or registration fees associated with heavier vehicles.

That pretty much defines those GVWRs as arbitrary.

[dznf0g]

None of the rating are arbitrary, nor meaningless....with all due respect to the authors, experts and posters. Some may not come into play for the AS tower...but they "could" if they are careless. None of you all are considering point loading of a TV. We discuss tires axles and receivers a lot, but when a vehicle is designed, more is taken into account.

For example, one could have 4 occupants in a truck and an even "water load" in the bed and be over payload, but under on axles and GVWR. This isn't probably a horrible situation, as the load is pretty evenly distributed over the frame (aft of the front axle) and the rear of the bed. But what about the guy who loads a welder against the front wall of the bed and has one occupant, where the welder weight puts the truck over payload, but under the axle. GVWR and tire ratings. What is the stress on the bed structure and frame at that location? Will it fold in half today? Probably not, but it will fatigue over time.
Case in point. I can't tell you how many F450s I saw with just such an effect. Ford uses the front frame structure from an F350 and just welds on larger rear frame rails. Fleet accounts would, arguably inappropriately, load the truck from a weight distribution standpoint...and yes they do fold nearly in half.

What does all this mean for us? I very hesitantly, say probably not a whole lot. But NONE of the numbers are meaningless, nor arbitrary. I NEVER saw a dart board in any engineering meeting rooms!

Watch your loads...distribute your loads, and try...I say try, to stay under payload...and certainly stay under axle, tire and GVWR vehicle posted limits.

And yes, THE MOST IMPORTANT issue of this and some other threads, discussing handling, CoG, vectors, oversteer/understeer, is the "loose nut" located 2 feet behind the steering. Drive to your combination, load, geographic condition, and weather conditions. SPEED kills.

[dznf0g]

Originally Posted by jcl

Several manufacturers offer, or have offered, options for alternate GVWR stickers on new vehicles. This is usually so purchasers can avoid taxes or registration fees associated with heavier vehicles.

That pretty much defines those GVWRs as arbitrary.

NEVER!!!! That is where the lawyers come into play. That is a violation of federal law. Only final vehicle manufacturers (upfitters & RV manufacturers) who build on incomplete chassis can change the ratings. Then they are the "certifier" and are under the same federal requirements.

[jcl]

Originally Posted by DewTheDew

Perhaps, but my point is that the sum of axle loads is not necessarily appropriate as an indicator of being "within safe limits". Those axle loads are max so if you put a snowplow on the front or a trailer with no WD hitch on the back, for instance. In those cases you may overload an axle without reaching the GVWR so that is another "check" to prevent customers from doing silly things. The axle numbers are individual measurements and the capability of the truck as a whole (which includes how ALL of the load-bearing and drivetrain parts of the vehicle respond) is defined by the GVWR. That statement of Andy's at the end of the article was a bit of sand in my craw. Yes, I realize that there is a factor of safety but I think setting up a rig that deliberately exceeds the published limits of a vehicle as set by the manufacturer is risky from a safety and legal standpoint.

I agree that simply summing axle load ratings is not the full answer. I would go further and suggest that focusing on any of the numbers by themselves is not a sound approach.

If GVWR defined the maximum power train capability, then the vehicle wouldn’t be safe to tow anything. If GVWR defined the maximum tow vehicle braking capability, then it wouldn’t be safe to tow an unbraked trailer, eg one of 2000 lbs.

You make a point about looking at the truck as a whole, and not just the components. Fair comment. But now take a step further. Look at the combination, and not just the truck. I think the error for some is in looking almost exclusively at just the tow vehicle and its ratings, and not sufficiently at the setup of the connection in a combination unit. If they aren’t comfortable with the feel or performance of their vehicle and trailer, some think the first thing to do is get a bigger heavier truck, instead of resolving a setup issue.

[jcl]

Originally Posted by dznf0g

NEVER!!!! That is where the lawyers come into play. That is a violation of federal law. Only final vehicle manufacturers (upfitters & RV manufacturers) who build on incomplete chassis can change the ratings. Then they are the "certifier" and are under the same federal requirements.

I sad new, not already sold. The reduced 10,000 lb GVW rating on one ton trucks is a good example. They are reduced ratings, not increased ratings,

[dznf0g]

Originally Posted by jcl

I agree that simply summing axle load ratings is not the full answer. I would go further and suggest that focusing on any of the numbers by themselves is not a sound approach.

If GVWR defined the maximum power train capability, then the vehicle wouldn’t be safe to tow anything. If GVWR defined the maximum tow vehicle braking capability, then it wouldn’t be safe to tow an unbraked trailer, eg one of 2000 lbs.

You make a point about looking at the truck as a whole, and not just the components. Fair comment. But now take a step further. Look at the combination, and not just the truck. I think the error for some is in looking almost exclusively at just the tow vehicle and its ratings, and not sufficiently at the setup of the connection in a combination unit. If they aren’t comfortable with the feel or performance of their vehicle and trailer, some think the first thing to do is get a bigger heavier truck, instead of resolving a setup issue.

To be clear, GVWR is not the spec for maximum powertrain and braking capability....GCWR is. (although braking assumes trailer brakes on trailers over 2K).
Simplistically, GVWR, Axle, tire, and payload ratings cover static "vertical" loads. GCWR covers dynamic "horizontal" loads. Of, course GVW and GTW make up GCW....then the other specs come into play under GTW and GVW, such as GAWs of each unit, effective receiver weight, payloads of each....etc.

[jcl]

Originally Posted by dznf0g

None of the rating are arbitrary, nor meaningless....with all due respect to the authors, experts and posters. Some may not come into play for the AS tower...but they "could" if they are careless. None of you all are considering point loading of a TV. We discuss tires axles and receivers a lot, but when a vehicle is designed, more is taken into account....

Watch your loads...distribute your loads, and try...I say try, to stay under payload...and certainly stay under axle, tire and GVWR vehicle posted limits.

And yes, THE MOST IMPORTANT issue of this and some other threads, discussing handling, CoG, vectors, oversteer/understeer, is the "loose nut" located 2 feet behind the steering. Drive to your combination, load, geographic condition, and weather conditions. SPEED kills.

I generally agree that not all ratings are meaningless, but some ratings can be arbitrary, like the reduced GVWR label designed to avoid registration fees, or a reduced rating associated with a light duty receiver. That rating can still be meaningful, but more in reference to the receiver, not the overall vehicle. The references to payload being less meaningful were about when towing, not when applying point loads in a truck bed. The thread title was designed to provoke, not clarify, IMO.

The biggest issue I have with tow ratings is when posters relate them to “guaranteeing” their safety. They don’t, and I think it is misleading when some suggest they do.

[dznf0g]

Originally Posted by jcl

I sad new, not already sold. The reduced 10,000 lb GVW rating on one ton trucks is a good example. They are reduced ratings, not increased ratings,

Yes, that is true...I misunderstood...but I cannot ever remember such a situation with light duty trucks at GM (1500 - 3500 series)...and it's not for taxes nor registration. It is for DOT driver licensing and certification requirements. 4500 series trucks were offered at 16k GVWR as that is the cutoff for commercial driver licensing and DOT regulations...for commercially registered trucks. The same physical truck may be offered at a higher GVWR. The company buying the truck has a decision to make. Are they ever going to load the truck over 16k? If they do, then they, and the driver, would be fined, as they are subject to DOT weighing. Doesn't matter if the truck is capable of a higher GVWR....they are skirting the law for licensing and company certifications. And that is not arbitrary nor meaningless.

Since there are no DOT nor certifications required for retail sales, labelling doesn't matter....which always boggled my mind. Grandpa can crawl out of his Cadillac, and into at 30k# GVWR motorhome without any experience, training, weighing, licensing nor certification....and a professional commercial driver can't do his/her job without?????

[jcl]

Originally Posted by dznf0g

To be clear, GVWR is not the spec for maximum powertrain and braking capability....GCWR is. (although braking assumes trailer brakes on trailers over 2K).
Simplistically, GVWR, Axle, tire, and payload ratings cover static "vertical" loads. GCWR covers dynamic "horizontal" loads. Of, course GVW and GTW make up GCW....then the other specs come into play under GTW and GVW, such as GAWs of each unit, effective receiver weight, payloads of each....etc.

Agreed about GVWR, that was the point I was making.

As to GCWR, if the trailer frontal area, profile, CoG, and other characteristics are specified, then I think the GCWR is likely closer to the actual vehicle capacity. If they aren’t, then there are a lot of assumptions built in to the number. If arbitrary is considered too strong a word, perhaps necessarily imprecise would serve better.

Just as an example, when I see pickup tow ratings published with a maximum trailer frontal area spec, I think to myself that they are getting closer.

[jcl]

Originally Posted by dznf0g

Yes, that is true...I misunderstood...but I cannot ever remember such a situation with light duty trucks at GM (1500 - 3500 series)...and it's not for taxes nor registration. It is for DOT driver licensing and certification requirements. 4500 series trucks were offered at 16k GVWR as that is the cutoff for commercial driver licensing and DOT regulations...for commercially registered trucks. The same physical truck may be offered at a higher GVWR. The company buying the truck has a decision to make. Are they ever going to load the truck over 16k? If they do, then they, and the driver, would be fined, as they are subject to DOT weighing. Doesn't matter if the truck is capable of a higher GVWR....they are skirting the law for licensing and company certifications. And that is not arbitrary nor meaningless.

Since there are no DOT nor certifications required for retail sales, labelling doesn't matter....which always boggled my mind. Grandpa can crawl out of his Cadillac, and into at 30k# GVWR motorhome without any experience, training, weighing, licensing nor certification....and a professional commercial driver can't do his/her job without?????

I would say that GVWR came from DOT, but it has been appropriated by licensing and tax authorities in many jurisdictions, including mine. We don’t even have a DOT.

When you note that the same physical truck is offered at different GVWRs, then I suggest that the lower rating may thus be arbitrary in terms of defining the vehicle capability. It isn’t arbitrary in terms of DOT requirements, certainly.

[DewTheDew]

Originally Posted by jcl

Several manufacturers offer, or have offered, options for alternate GVWR stickers on new vehicles. This is usually so purchasers can avoid taxes or registration fees associated with heavier vehicles.

That pretty much defines those GVWRs as arbitrary.

Okay, so we can say they are arbitrary but only one direction. They will not offer the option of a higher GVWR sticker. So sure, if you are buying used you might want to know if this was "de-rated". But the discussion is about 1/2 ton trucks and I doubt those are de-rated because the increased registration and taxes do not apply in that category. Am I incorrect?

But in the example Andy used in the article there was no claim of de-rating via sticker. This was the maximum GVWR of the vehicle as sold. He set it up in a manner that exceeded this significantly under static conditions. It is what it is. I am happy that it handles well but hit a good bump at highway speed and you will be exceeding limits even more and in an dangerous situation if something breaks.

I get that it can be done, but those numbers are not arbitrary and they are set by people who designed the system. Strengthening the hitch assumes that the hitch was deliberately under-designed wrt the rest of the vehicle rather than deliberately set at that level as a weak link because the next weak link is more dangerous/expensive if it breaks. Go ahead and get an Audi engineer who set that limit to come on here and tell us that it is under-rated. Otherwise I will go with the specs. I don't know about you but I have a healthy respect for German automotive engineers, having owned a number of BMWs, Audis and Mercedes over the years for road and track use.

[DewTheDew]

On a side note, I am a materials scientist. When a steel or aluminum producer supplies material there is a range of acceptable specs for composition, strength, ductility and so forth for a given alloy and heat treatment. These are not especially narrow. Therefore the factor of safety of a mechanical design will also take into account the variability of the material (as delivered, as formed, as installed) as well. Perhaps that batch was at the strong end of the range, perhaps it was at the weak end. The factor of safety has to design for the weak end (and yes, some big customers may require a higher standard for their material but in my experience mainstream vehicle manufacturers will not do that because it costs more).

I just wanted to point out that it is more than just the design, it is the material.

[dznf0g]

Originally Posted by DewTheDew

On a side note, I am a materials scientist. When a steel or aluminum producer supplies material there is a range of acceptable specs for composition, strength, ductility and so forth for a given alloy and heat treatment. These are not especially narrow. Therefore the factor of safety of a mechanical design will also take into account the variability of the material (as delivered, as formed, as installed) as well. Perhaps that batch was at the strong end of the range, perhaps it was at the weak end. The factor of safety has to design for the weak end (and yes, some big customers may require a higher standard for their material but in my experience mainstream vehicle manufacturers will not do that because it costs more).

I just wanted to point out that it is more than just the design, it is the material.

Sure. I (perhaps mistakenly) consider material and supplier costs as part of the overall resultant design specs....as cost is important to the Marketing Line Managers, in order for the product remain competitive with its peers in the marketplace.

[dznf0g]

Originally Posted by jcl

I would say that GVWR came from DOT, but it has been appropriated by licensing and tax authorities in many jurisdictions, including mine. We don’t even have a DOT.

When you note that the same physical truck is offered at different GVWRs, then I suggest that the lower rating may thus be arbitrary in terms of defining the vehicle capability. It isn’t arbitrary in terms of DOT requirements, certainly.

Correct. I didn't notice your are from Canada. I don't know much about Canadian requirements. My commentary is US only. My only involvement with Canadian vehicles were with fleets who operated in both US and Canada regarding reciprocal warranty coverage.....and some gray market vehicles. Discussion not related to this thread.