xcntrk

So I built this comprehensive spreadsheet that allows you to track and monitor all your trailer towing weights, and measure those against the maximum specifications for your model. The spreadsheet assumes you have 3 sets of (CAT scale) measured weights: the base vehicle weight, the TV plus Trailer weight (without WD), and the TV plus Trailer weight (with WD). That spreadsheet is attached at the bottom if anybody wants to use (or improve upon) it. [UPDATE, available HERE]

What I keep coming up with is that my rear axle GAWR is my limiting factor. Realistically I can only tow around a maximum of a 7500lb trailer and be able to support the estimated 1070lbs of tongue weight before maxing out my RGAWR. That's rather pathetic for a Max Tow version with a 11,200lb tow rating.

As I researched more into what makes up my rear axle GAWR, I came up with the following specific component ratings:

• Rear Axle unit w/E-locker and 3.73 = 4800#
• Rear Springs = 4050#
• Rear wheels (20" 6-lug) = 4050# (2025ea)
• Rear Tires 275/55R20 (P-scorpion) = 4806# (2403ea)

Surprisingly the rear axle unit is rated at 4800lbs and is presumably the same as what's found with the HD-Payload package (minus the 7-lug hubs). This includes all the internals such as size of axle shafts and number of splines, etc. Another surprise is that the crappy Scorpion P-rated tires have a max load of 4806# combined, which is well above what the rear wheels or springs can handle. This is surprising as the first thing folks seem to upgrade in an effort to support more weight is the tires (to LT). Lastly, the big limiters are the springs and wheels. Springs aren't so much a problem as they can be supplemented with air-bags/RAS/etc to increase capacity. The bummer with the wheels however is that all of the 6-lug wheels (13 available in 2013 models) are rated at 2025ea with the minor exception of the Raptor wheels.

So theoretically, the only way to improve RGAWR would be to replace the stock wheels and supplement the suspension. You could then theoretically increase the RGAWR closer to the 4800# range.

Sources:
https://www.fleet.ford.com/truckbbas...0Raptor_SB.pdf
https://www.fleet.ford.com/truckbbas...F-150_v1-1.pdf
http://www.tirerack.com/tires/tires....=Scorpion+ATR#

smurfs_of_war

I built a similar sheet. Did you take into account what the WDH will move across the axles? The full tongue weight without WDH will theoretically be spread across the axles (front and trailer) and your sheet should show that using a formula. You'd be surprised how much of a difference that would make. I find it hard to believe that you are maxing over your RGAWR unless you are piling the bed full. I have a 3900lbs RGAWR and with an overloaded payload (a LOT) and a 5500lbs trailer tied (600lbs tongue +/-), I am still under it. Don't forget that the cabin load is distributed differently based on passenger orientation and position of the seats on the frame.

xcntrk

I did take that into account, sort of. If you haven't looked at it, the spreadsheet is a little different then what you describe in that it's not predicting WD advantages, instead it's expecting the user to provide that input (via CAT scale measurements) and the spreadsheet will compute the WD advantages.

But to your point, WD definitely changes things although it's not quite as you describe. All WD does it take some percentage of the tongue weight and redistribute it back into the trailer axle(s). The amount of distribution can range from 10-20% depending on how much leverage is dialed in via the trunion bars. So let's say you have 1000# of tongue weight, with WD in place you can effectively reduce that tongue weight by redistributing 150# (15%) back into the trailer and off the tongue. So the TV now only sees 850# instead of the original 1000#. The benefit to the TV is less weight on the rear axle thereby enabling the front axle to better share in the overall load on the tongue. This is the obvious part with WD, but here's where it gets complex:

As for how hitch weight is distributed across the TV steer & drive axles, this is based on the principal that the more hitch weight you incur the more imbalanced the distribution of weight is between the two axles. For example, think of a teeter-totter with the front and rear axles being the fulcrum point in the middle. As you incur 1000# of hitch weight on one side, that rotates the teeter-totter to the aft end and the entire rear axle has to bear the weight - plus it also now incurs some small portion of weight that has transferred from the front-end. So now you have both the original hitch weight + percentage of weight from the front end to contend with. This is why with scale readings typically the steer axle is lighter with a trailer in-tow then without (due to the front-end weight shifting to the sagging rear). So when you add in a WD hitch, you're reducing the tongue weight (as it's redistributed back into the trailer) and this has the effect of less hitch weight incurred on the rear axle and therefore less transfer of weight from the front-axle. This is where the concept of a more balanced ride comes from with WD hitch marketing.

The point of all this is that a WD hitch is not directly redistributing any weight back into the Tow vehicle front-end some how. To do this it would need the same multiple mounting points and leverage (trunion bars) back to the tow vehicle as it does with the trailer. Instead the WD is enabling a more balanced ride by simply reducing tongue weight.

smurfs_of_war

Interesting. I will take a peek after work and see. Admittedly I haven't yet since I am on my phone, but I would like to. I want to compare notes

11screw50

I think the 4800# rated axle is only with the 8200# GVWR (page 8 of 15 in the pdf I have stored locally for 2013). Page 9 shows that a 4x4 has either the 4100# rated axle or the 4800# axle. You might need more than just wheels and springs (and even if you upgraded, the sticker on the door doesn't change.).

I do understand your frustration though.

Buck50HD

Re-read the original post. He states that the axle unit alone is rated at 4800 lb but not the springs and wheels. The HD payload package can say 4800 on the sticker because it has the springs and wheels to match.

When I first bought this truck, I had myself convinced that there was something special about the HD payload 9.75" rear end but I was wrong. It even has the same bearings as the standard axle which I am not too happy about. At that same time, I know the axle was designed for 4800 so it should be OK. Typically, axle failures are from lateral impacts or bearing failure, not normal operating loads. I have also not had much luck finding instances of failed semi-floating axles in searches. Actually, what typically comes up are bearing failures of full floating rear ends where the hub came right off after the bearing disintegrated. Either way, there's some risk.

11screw50

Right, I've looked at the pdf and I understand that the lowest of the components determines the rating however under the rear axle it is listed as 4100/4800 so I had assumed there were two different axles.

xcntrk

That's due to the different center differentials. Standard (open) diff 3800, limited slip diff 4100, and E-locker diff 4800. All still within the same axle housing. As Buck50HD mentioned, it's the same rear axle just different hubs and outers including the 7-lug setup on the HD. Another interesting note, the Raptor has thicker axle shafts w/more splines but a lower payload rating. The bigger shafts are obvious, to support the 35" tires (and monster jumping), but it baffles me what produces the lower payload rating when it appears to have the same size ring & pinion as the Max/HD version. Weird Ford numbers game...

Buck50HD

You are right... they do show different axle rating. I'll be honest, after all the reading I've done, I'm still not certain about the differences in the HD/non-HD 9.75 rear. The axles seem to be the same except for the extra lug and the bearing is the same so that's the limiting factor to me. The housing actually has a different P/N so it's possible there's some extra meat.

It would be great to hear from someone that knows for sure and prove that there is something unique, aside from the 7 lugs.

smurfs_of_war

Solid vs pressed and pinned? This topic has me intrigued. I'd like to look at them now.