F450 vs F350 SRW payload

Grit dog wrote:
Not sure I agree with tire load ratings not having a factor of safety applied to them.
As an Engineer, I can't think of a single assembly or component of most anything that isn't designed with a factor of safety. With the exception of intentional "weak links", for example shear pins. You want to rely on it breaking at a certain stress to protect the rest of the assembly from overloading.

I'll say tires 100% have a substantial factor of safety built into their published load ratings.

While everything has some form of factor of safety, what I meant is tire ratings are never "sandbagged" for marketing purposes.

In the context of OEM axle and GVW ratings, where ratings are low to meet a "class" or boost sales of a higher class - I've never seen Michelin sand-bag a 245/75r16's rating to boost sales of 265/75/16 tires! So we can safely assume all tire ratings of equal factors of safety.

This is not the case with the axle - as per Ford's chart, an F450 rear GAWR has nearly 200% factor of safety, ON TOP OF whatever factor of safety is already built into the axle (as we ca safely assume the F550 won't fail at 50 lbs over rating).

Grit dog wrote:

I'll say tires 100% have a substantial factor of safety built into their published load ratings.

You can buy the SAE standard if you really want, but essentially boils down to:

Tires are tested at their rated load, and not higher, for 1 hour at their rated speed, in a room heated to 100F. There is no additional safety factor required for validation. The safety factor is essentially up to the automakers, by specifying a tire load and/or speed rating that is higher than needed for the specified use. A tire manufacture may perform a Step Up Test beyond the target certification but this is not required, nor am I aware of it even being common. I supposed that some tires may be validated at a speeds and loads lower than ultimate failure, but this would place them in a sales disadvantage since tires will be selected by standardized ratings.

If you really think tire makers are over-designing tires, I suggest this read:
https://jalopnik.com/goodyear-knew-of-dangerous-rv-tire-failures-for-over-20-1824997252

carringb wrote:
"I don't agree with the idea that overloading tires means imminent tire failure at high temperature and speed as I've found there to be a pretty large safety factor incorporated into tire ratings. "

Tire rating really don't have any safety factor designed in . But it's important to remember that heat is a function of Loading AND Speed. Most of us are not running at full loads anywhere near max speed ratings (which are validated for 30 minutes). On that note... Ford worked with Continental originally to produce a 19.5" tire with a a higher speed rating, specifically for the F450, and now other tire makers are matching that. The original F450 was governed at 75 MPH due to the tires, which caused some buyers to "downgrade".

Not sure I agree with tire load ratings not having a factor of safety applied to them.
As an Engineer, I can't think of a single assembly or component of most anything that isn't designed with a factor of safety. With the exception of intentional "weak links", for example shear pins. You want to rely on it breaking at a certain stress to protect the rest of the assembly from overloading.

I'll say tires 100% have a substantial factor of safety built into their published load ratings.

“Commercial” truck tires max speed ratings are at maximum load for the tire.

"I don't agree with the idea that overloading tires means imminent tire failure at high temperature and speed as I've found there to be a pretty large safety factor incorporated into tire ratings. "

Tire rating really don't have any safety factor designed in . But it's important to remember that heat is a function of Loading AND Speed. Most of us are not running at full loads anywhere near max speed ratings (which are validated for 30 minutes). On that note... Ford worked with Continental originally to produce a 19.5" tire with a a higher speed rating, specifically for the F450, and now other tire makers are matching that. The original F450 was governed at 75 MPH due to the tires, which caused some buyers to "downgrade".

RoyJ wrote:

4x4ord wrote:
^^^^ The thing is the GAWR of the F450 pickup is the same as the GAWR of the F350 4x4 pickup.The 4x2 F350 is a little more. More than likely the axle rating is limited on the F450 not by the axle itself but by the truck's rear suspension. We always talk on this forum about what it is to overload a truck .... is it going over the axle rating? or the tire rating? or the GVWR? and when it comes right down to it the little bit of weight that most of us consider putting on our trucks would never hurt anything anyway. An F450 is certainly more truck than most any RVer will ever need. Even my little F350 SRW has had 11,000 lbs of payload on its back and the tires didn't pop, the frame didn't break and as far as I know there was no ill consequence. If I had an F450 I certainly wouldn't be afraid to load what needs loading on its back.

In the order of consequences, 1) being most severe for "overloading":

1) Tires. Going over can mean imminent failure at high temp / speed. There is zero marketing built into tire load capacities

2) Axle limit from axle OEM - mostly driven by bearing load and housing strength. Again, very little marketing - when was the last time we saw a full page Dana S110 on social media?

3) Truck OEM axle rating - which includes suspension, brake, and the above. Now we're starting to see affects of marketing / legal / EPA / SAE...

4) Truck OEM GVW rating - heavily affected by factors beyond pure engineering specs, i.e. to fit within a "class"

According to this, the F550 uses the exact same 1.64" M300 as a F450 pickup, with a 14,706 lbs rating. So with upgraded leaf packs, I feel you can safely load well above the 9,900 lbs factory rating:

I appreciate what your saying hear Roy. Basically you're pointing out that with upgraded suspension a f450 could be loaded significantly beyond its rear axle rating and still fall within the design limits of all its components.... An f350 SRW may be capable of handling significantly more weight than what its RAWR suggests as well but not without violating the design limits of some of its components.

I don't agree with the idea that overloading tires means imminent tire failure at high temperature and speed as I've found there to be a pretty large safety factor incorporated into tire ratings. Obviously it depends how much one loads a tire over its rated capacity. Here's a couple pics showing my srw's tires and springs while the truck is loaded to more than double its rated payload ie with a 7000 lb pin weight placed on its hitch .

4x4ord wrote:
^^^^ The thing is the GAWR of the F450 pickup is the same as the GAWR of the F350 4x4 pickup.The 4x2 F350 is a little more. More than likely the axle rating is limited on the F450 not by the axle itself but by the truck's rear suspension. We always talk on this forum about what it is to overload a truck .... is it going over the axle rating? or the tire rating? or the GVWR? and when it comes right down to it the little bit of weight that most of us consider putting on our trucks would never hurt anything anyway. An F450 is certainly more truck than most any RVer will ever need. Even my little F350 SRW has had 11,000 lbs of payload on its back and the tires didn't pop, the frame didn't break and as far as I know there was no ill consequence. If I had an F450 I certainly wouldn't be afraid to load what needs loading on its back.

In the order of consequences, 1) being most severe for "overloading":

1) Tires. Going over can mean imminent failure at high temp / speed. There is zero marketing built into tire load capacities

2) Axle limit from axle OEM - mostly driven by bearing load and housing strength. Again, very little marketing - when was the last time we saw a full page Dana S110 on social media?

3) Truck OEM axle rating - which includes suspension, brake, and the above. Now we're starting to see affects of marketing / legal / EPA / SAE...

4) Truck OEM GVW rating - heavily affected by factors beyond pure engineering specs, i.e. to fit within a "class"

According to this, the F550 uses the exact same 1.64" M300 as a F450 pickup, with a 14,706 lbs rating. So with upgraded leaf packs, I feel you can safely load well above the 9,900 lbs factory rating:

Roy, I think I read that the new Ford frames are 10.7 in^3 section modulus.

^^^^ The thing is the GAWR of the F450 pickup is the same as the GAWR of the F350 4x4 pickup.The 4x2 F350 is a little more. More than likely the axle rating is limited on the F450 not by the axle itself but by the truck's rear suspension. We always talk on this forum about what it is to overload a truck .... is it going over the axle rating? or the tire rating? or the GVWR? and when it comes right down to it the little bit of weight that most of us consider putting on our trucks would never hurt anything anyway. An F450 is certainly more truck than most any RVer will ever need. Even my little F350 SRW has had 11,000 lbs of payload on its back and the tires didn't pop, the frame didn't break and as far as I know there was no ill consequence. If I had an F450 I certainly wouldn't be afraid to load what needs loading on its back.

4x4ord wrote:
No Ford claims the F350 has a higher carrying capacity than the F450 has ..... it's some of us on here that have a hard time believing Ford is being up front with what they're talking about.

Cummins,
What would you say is the limiting factor on what an f450 can carry? Is it the suspension? The Frame? What about the F350? I think the F450 is limited by its suspension. I think the F350 is also limited by its suspension and I'm guessing they both have the same rear srings, unless you go to the 2 wheel drive f350.... then you get suspension rated to carry a little more. The f450 has more braking, stronger axles, more wheel bolts and same frame. The tires I don't know, but I'm guessing maybe the 19.5 tires are rated to carry more than 17's even though the 17's have bigger tire to road contact point.... the 19's can likely take more air? Without modifying the f450's suspension I don't know how you claim it is built to carry more than what its suspension is rated for?

Not 12Vcummins, but here's my 2 cents.

I highly doubt the axle / brakes / wheel / tires are the limiting factor, as we all agree it's an upgrade. Leaving frame as the only possibility. Since Ford doesn't release all the specs, we have to performed educated guesses.

A pre-gen F550 used 36,000 psi steel with 10.1 in^3 section modulus. Multiply we get 363,600 in-lb, or 30,300 ft-lb of bending moment before the frame snaps in half.

Ford claims the new SD frame is between 50,000 - 80,000 psi, let's take 65,000 psi as average. We don't know section modulus, but GM HDs use 6.811 in^3, let's assume they're similar. 65,000 x 6.811 = 442,715 in-lb or 36,893 ft-lb.

So the new F350/F450 pickup frame is roughly 20% stronger than an older F550, which carried up to 19k lbs GVW. I don't see frame a a limiting factor either.

In conclusion, I'd feel pretty safe loading up to the rear GAWR on a new F450. Beyond that it'll be difficult to compare as the chassis cabs use a different axle.