Years ago it was thought that “equal squat” on the front and rear of the TV was the correct way to adjust WD. This concept on purpose drove the front end down below unhitched height and weight.
Tests by RVIA and SAE have since shown this is not a good thing to do any more. Actually back in the 70’s the NHTSA hads a towing study done pulling TT’s by TV’s of the time. The firm who did the study for NHSTA reported the same thing now that SAE has concluded. If you want, I can find that NHTSA study on line and link it here. I printed it off a few years ago and I still have the 1” thick report down in the basement.
To summarize this, the concerns are oversteer in the TV. Understeer and oversteer - Wikipedia, the free encyclopedia
When the front end of the truck is heavier then unhitched it creates more grip to the road. While this may sound like a good thing, it can be a really bad thing when towing a TT. The concern is the front end will “bite in” so to speak in a sharp turn and rather then sliding some like normal, it does not and sends the truck into jack knife. While this was known in the early 70’s by that NHTSA report, it never made it to a formal recommendation until a few years ago. This directly conflicted with the equal squat theory.
Equal-I-zer is now on board with “not” overdriving the front end below unhitched. In fact the actual directions state the front end should be above unhitched. On page 17 and 18 http://www.equalizerhitch.com/pdf/eq...anual_0111.pdf
Equal-I-zer states the front end to be higher than unhitched.
Here is a link to what an RV member has claimed Equal-I-zer wrote him. The verbiage used and technical nature of the content suggests it is factual. It also matches page 17 and 18 of the Equal_I-zer manual.
RV.Net Open Roads Forum: Towing: Advice on setting up Equalizer Hithch...
Ford has also got on board with this same type of recommendation for WD adjustments. Here is right out of a 2012 F150. See page 276 under weight distribution hitches
GM, is still stating to return the front end to unhitched height as this time.
The days of overdriving the front end are gone or going quickly.
There is also steering geometry involved. If you adjust the WD hitch to return to unhitched height or weight to slightly above, the steering geometry and tire wear is normal as your truck is riding around unhitched. Now there is another realization about a WD hitch. The WD on the front of the truck is changing as you tow. If you always towed on perfectly flat land then the WD would stay the same. The reality is, we go up RR track crossings, down steep hills, up over bumps, hard banked turns, any type of turn where the TT is on a different level of ground then the TV in a turn etc. When the truck and TT are at and angle to each other WD changes. The front end gets driven down or up pending which way the angle was between the TV and TT.
So if you are 120# heavy on purpose now, when you go up a quick hill like some RR track crossings, the WD bar loads up more and that 120# over drive can turn into 240# or higher over drive. Now you are really biting in if this is a turn as well. We cannot stop this shifting of WD, it just happens however we can control to not make it worse than it already is by not overdriving the front end.
Then there is the rear of the truck breaking free of traction in wet and or slippery conditions when the camper is pushing the truck. When this conditions happens, that extra weights on the rear axle helps more prevent a lose of traction then having extra weight on the front axle.
The truck receiver is in the middle of this too. If Toyota declares the front end to be returned to unhitch height and you have an OEM receiver, they may have designed that receiver to match up with the WD recommendation in the owner’s manual. They know a WD hitch takes a lot of ups and downs and make it heavy enough to take that. However they may not make to extra heavy to over drive the front end plus the normal towing dips and hills.
Toyota on the older Tacoma’s had a 750# rated WD receiver. I helped a few RV’ers with that truck after they bent their receiver up in the air. In this case one of them was using 1,000# WD bars on a 750# receiver. When these back flexes happen the receiver has to take it or permanently bend and his did. The other buddy had a Reese round bar head and a DC. He had a double whammy. The Reese round bar head has very little rear tilt. And his older Taco receiver really flexed. Basically with 750# WD bars he could not get his front end anywhere close to unhitched height on a 700# tongue weight. He was way high. He bought an aftermarket receiver and now all is OK.
I’m not saying your new receiver has the issues of the older ones, just don’t on purpose overdrive the front end for the reasons listed above.
Your spare weight set # 4 is a lot better. Basically with are back to unhitched weight on the front end. I would go with that setup.
Ticket #1 - truck with no trailer: (truck had full tank of gas, 400 lbs of passengers and 75 lbs of tools/spare tire.)
Steer Axle - 3,580 lbs
Drive Axle - 2,700 lbs
Front 120# heavy
Ticket #3 - truck & trailer with WD hitch hooked up:
Steer Axle - 3,700 lbs
Drive Axle - 3,280 lbs
Front 20# heavy
Ticket #4 - revised setup truck & trailer with WD hitch hooked up:
Steer Axle - 3,560 lbs
Drive Axle - 3,480 lbs
Hope this helps