Payload margin of error engineered in???

[Daquenzer]

Originally Posted by pteck

This is a great question. And the answer is absolutely.

Part of any cars specification and validation is the factory fitted tires. Along with associated inflation pressure typically documented on the door jamb placard. The fitted tires and pressure can certainly be the limiting factor that dictates payload, as the OEM seeks the balance of performance, NVH, or whatever else that may have dictated the fitted tires. The tire selection and inflation pressure itself can often be a balance of those qualities and gross vehicle weight rating.

So yes, if the limiting factor had been tires, upgrading to a LR-E tire can potentially expand capacity. So can increasing stock inflation pressure (which is never a bad idea anyways for more stability). But one should be cognizant and analyze potential other constraints including GAWR, suspension, etc., to understand what is another or next bottleneck or constraint.

Again...not touching the can of worms that is regulation.

I would agree. So when I was building my 2020 F150 I wanted a heavier hitch weight capacity. The ONLY thing different on my 2020 vs my 2017 was I went to 20” tires. That’s it. That gave me 200lbs more on the rear axle weight.

And this is where I have problems with the payload sticker at times. If modifications that small can make a difference, then I would think other modifications could be made. Having said that one would need to be careful, because there’s always the weakest link. But as one previous post stated the difference between an 3/4 ton and a 1 ton are the tires a few more leaf springs. Not really that significant.

[Northsite]

Unfortunately, some people do not read their posted limits or don't care about them. Here is one case that I saw. I was driving toward Tupelo on US 45 S at 60 MPH. An F-150 pulling a trailer way to large for it went by me, probably going close to 70. About half a mile down road he went across a bridge that had a bump. The trailer started to articulate and the F-150 couldn't handle it. They left the road and did a slow roll off to the side. He never found out if the excess weight damaged his truck, but the crash did.

[BillTex]

Welcome!

“Payload” is a somewhat meaningless value. You are limited by your axle rating (RAWR). On a half ton truck this will, in fact, be the rating of the semi-float axle itself. Most half tons are around 3900# or so.

On HD trucks your “axle rating” is usually limited by your tires/wheels as the axles themselves can be rated for ~ 10,800lbs-12,000lbs depending on setup. The OE tires may be rated from ~ 7000 lbs - 8160lbs (LI 129 tires. Available now in 18” and 20”). You can of course upgrade to 19.5” tire/wheels to gain even more capacity but i can’t imagine you would need this for towing and the “G” tires come along with other issues you need to deal with (where to keep a spare?, the squirrelly ride, etc).

Bottom line is it’s easy to upgrade the tires/wheels on a HD truck to gain capacity and still not reach the capacity of the full float axle. Not so easy to upgrade the axle on a half ton truck to gain capacity.

Hope this helps,
Bill

[DAVSCH]

We’ve had these threads before. I’ll say this again. The vehicle engineering has some fudge factor in it in the tow vehicle. Not a lot, but it’s there. Now for my part. I have several policemen friends who have told me their standard procedure for a vehicle wreck with a trailer in it. They check the capacities listed on the tow vehicle!!!!! If you are towing Beyond the limit of the tow vehicle, you will be cited regardless if the wreck was your fault. The doubting Thomas’s here will say “OK, a ticket”. If you are solely involved in a single vehicle accident with NOTHING else damaged, yes, a ticket. If anything else is involved, the lawyers are going to eat your breakfast for the next several months. Can you say LITIGATION???? Do your tow vehicle and your pocketbook a favor. Don’t exceed weights!!!!!

[Martee]

When I first used my Flying Cloud 25FB, I loaded up the Toyota Tundra, carefully honoring the Airstream stated tongue weight of 860lbs for my trailer. Only to find much later and after the trip was completed, the actual tongue weight was closer to 1240lbs or 380lbs more. I used a Reese Steadi Flex hitch with 1400lb bars for towing, and the weight distribution hitch moved about 120lbs off the tow vehicle and back onto the trailer. So that entire trip, I was 260lbs over weight, and never noticed any affects or issues on the tow vehicle. It tracked exceptionally well at speed limits and without any sway.

[Bill M.]

My guess is that there is none. The payload limit is indeed the payload limit.

But at the same time I do not think the car is engineered to fall apart or wreck if you go over the payload.

[Mollysdad]

Originally Posted by SnowWanderer

How much of a margin of error or safety margin do vehicle engineers factor into their payload maximum decisions?

IMO, when designing a truck the engineers provide a payload number. Let's say 1500#. Those engineers don't know if that 1500# will be bags of gravel or an Airstream hitch. However, a WD hitch takes some of that 1500# of hitch and uses leverage to move it to the front axle and the rear trailer axle.
However, you don't have a good way to know what that safety factor is.
I accommodate extra payload by less highway speed and more control on downhill sections.
Payload is dynamic. Let's say you're right at your published payload. As you're driving, you hit a pothole. That wheel, axle, spring, and suspension bits go flying up causing the real world number to skyrocket for a short period of time. Obviously, the axles don't snap off. The engineers took that into account.

That's my $0.02

[richard5933]

I'm no engineer and have no idea how these things are set, but I always think of it more like the 'Best By' date on food at the grocery store.

Will it kill you if you eat it after the 'Best By' date? No, but it probably will not taste as good as it did just a few days ago. However, if you exceed the 'Best By' date by too much, then you better be ready for a date with the porcelain bowl.

I think of the weight limits in a similar way. Exceed them a little and you'll likely be alive the next day, but you're going to sacrifice things like handling, ride, and longevity of the vehicle. As the amount you exceed the limit increases, the safety level decreases till you reach a point where bad things start happening fast.

We all like to have a black/white decision point. The manufacturers give us one on the placard in the form of the GVWR, etc. Go beyond that placard at your own peril.

[fastrob]

"Stupid is as stupid does," Forrest Gump.
Truck scales are cheap. $12-15, and will tell you what you got.
Slow and steady, nice and easy, what is the hurry?

[cru-in]

Originally Posted by BillTex

Welcome!

“Payload” is a somewhat meaningless value. You are limited by your axle rating (RAWR). On a half ton truck this will, in fact, be the rating of the semi-float axle itself. Most half tons are around 3900# or so.

On HD trucks your “axle rating” is usually limited by your tires/wheels as the axles themselves can be rated for ~ 10,800lbs-12,000lbs depending on setup. The OE tires may be rated from ~ 7000 lbs - 8160lbs (LI 129 tires. Available now in 18” and 20”). You can of course upgrade to 19.5” tire/wheels to gain even more capacity but i can’t imagine you would need this for towing and the “G” tires come along with other issues you need to deal with (where to keep a spare?, the squirrelly ride, etc).

Bottom line is it’s easy to upgrade the tires/wheels on a HD truck to gain capacity and still not reach the capacity of the full float axle. Not so easy to upgrade the axle on a half ton truck to gain capacity.

Hope this helps,
Bill

Rear Axle rating on my Ram 1/2 Ton is 4100 pounds

[cru-in]

To the Op's question. As an engineer who leads aircraft modifications, I want the end user to stay within the specified limits of the system. I never want a user to assume I (we) designed in a safety factor. The safety factor is for unexpected events, not daily operation.

[BillTex]

Originally Posted by cru-in

Rear Axle rating on my Ram 1/2 Ton is 4100 pounds

Sounds about right. As noted “around 3900 lbs” for half tons.
Again , the limiting factor for half tons is the actual axle-which is not practical to replace.

Visit the scale and see what your weights are. “Payload” for half tons varies widely from as little as 900lbs to around 2000 lbs. A stripped, single cab, 2wd truck will result in greatest available “payload”.
Ford used to offer a 7700 lb GVWR that had an upgraded axle for the half tons. Don’t know if that is still available.

I don’t want to get too far off topic, as this is a “payload” thread. But there are a lot of other reasons to go to an HD truck if you tow much more than 6000-7000 lbs.

[CapriRacer]

Originally Posted by cru-in

To the Op's question. As an engineer who leads aircraft modifications, I want the end user to stay within the specified limits of the system. I never want a user to assume I (we) designed in a safety factor. The safety factor is for unexpected events, not daily operation.

X2!!

I've always thought of "Safety Factor" (What a BAD name!) as 3 different things:

1) To account for the things engineers can't or don't quantify in the design process.

2) To account for variations in manufacturing.

3) To account for end user ..... Ahhhh ..... Mmmmm ..... miscalculations.

This means it is sacred and shouldn't knowingly be violated.

[RedSHED]

Originally Posted by cru-in

To the Op's question. As an engineer who leads aircraft modifications, I want the end user to stay within the specified limits of the system. I never want a user to assume I (we) designed in a safety factor. The safety factor is for unexpected events, not daily operation.

This.

If it has a different part number, safely assume it's different. Part numbers cost money - Ford or whomever isn't going to create a new part number just because it's Tuesday and they're bored.
If it's different, safely assume it has different characteristics. You can sub Douglas Fir for Sitka Spruce in aircraft spars while rebuilding a Champ or a Stearman, for example, but the weights are different and there will be an impact on performance.


The numbers are going to be a compromise - longevity, production cost, marketability, and capability are all pulling at rated loads -- and pulling at them in different directions. If a truck maker specs the gross weight of their truck at 8600 lbs instead of 8400, it might have as much to do with CAFE as it does with an engineering analysis. Or maybe it really does have to do with the engineering. The only way to really be sure is to become a VP in that company and make the decision yourself.

[cru-in]

" The only way to really be sure is to become a VP in that company and make the decision yourself."

Love this sentence! : )

[dznf0g]

Originally Posted by CapriRacer

X2!!

I've always thought of "Safety Factor" (What a BAD name!) as 3 different things:

1) To account for the things engineers can't or don't quantify in the design process.

2) To account for variations in manufacturing.

3) To account for end user ..... Ahhhh ..... Mmmmm ..... miscalculations.

This means it is sacred and shouldn't knowingly be violated.

In fact, it is so sacred, as a trusted (it took many years) applied technology field guy at GM, I could never get my engineer friends to tell me exactly what the margin is. I have a pretty good idea, but I don't violate it for the reasons above.

[pteck]

Originally Posted by cru-in

To the Op's question. As an engineer who leads aircraft modifications, I want the end user to stay within the specified limits of the system. I never want a user to assume I (we) designed in a safety factor. The safety factor is for unexpected events, not daily operation.

This is the right answer. Definitely agreed based on the way the question is framed.

I take a more pragmatic interpretation to the question. As we know in systems, every component is not magically aligned to the same limits. The system taken as a whole has specific constraints that drives the spec'd payload capacity. Identify and upgrade these limiting items, and potentially more can be had.

Therein lies the crux. Without OEM analysis and data, it would take some liberties and educated assumptions to safely expand the operational envelop.

[Joe T]

Payload is derived from the gvwr which is put in place for many reasons. Weight of vehicle minus rating.

Then you need to look at the axle GAWR ratings and tires as that is really important because overloading that can cause an immediate safety issue.

Some manufacturers add both axle capacities and come up with a gvwr. Usually lighter class vehicles. Works fine unless you plan to make a clown car.

Then some advertise GAWR that if met would exceed the gvwr. People sometimes use these and combine their trailer gvwr and get a GCWR of their combo and stay under the gcwr and axle/tire ratings. That would probably answer your question as no one would suggest you exceed those under any circumstances. Licensing and tongue weight puts built in limits on all this and that is where the engineers come up with the numbers.

And yes you can actually pull your trailer right up the street at 20mph exceeding those weights and not get in a wreck but why damage your vehicle?