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Old 02-23-2013, 09:44 PM   #1
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Test: Measurement of Resulting Drop from added Rear Axle Weight

In my continuing quest to determine how much TT my Tacoma can handle, I decided to conduct a test to simulate what 650lbs of tongue weight (which is my TV max) will do to my rear suspension. Based on other posts, it sounds like using a WDH can move around 20% of the weight off the rear axle, which means the weight should be around 520lbs. I put 6x50lb sandbags in the back of the truck bed and stood on the hitch (I'm a little over 200lbs). The resulting hitch drop was about 3 inches (went from 17" with no weight to 14" with myself and the sandbags).

So, assuming my TT has a hitch weight of 650 loaded, if it is true that a WDH will only move 20% of the weight off the rear axle, does that mean a WDH in itself will not be sufficient, seeing as the rear end will still drop 3"? Should I be looking at going the extra mile and installing Firestone/Airlift air bags to keep the back end from dropping? Or is a 3" drop acceptable (i.e. will not cause porpoising, etc)?

Thanks,
Dan
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Old 02-23-2013, 09:50 PM   #2
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With a WDH properly adjusted, you can bring your Tacoma back up to level.

Actually, if setup improperly you could lift the rear of your truck off the ground.

A WDH will do the job.

JMHO,
Doug
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Old 02-23-2013, 09:55 PM   #3
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Maybe I just don't understand exactly how a WDH works. I assumed it just moves some amount of weight off the rear axle, depending on how it is adjusted. From the other people on the JOF who have posted actual before/after WDH weights, it seems like they are only moving 20% or so. I guess there is more to it than that.

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Dan
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Old 02-23-2013, 10:06 PM   #4
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Dan,
Maybe that's all they needed to move.
I had a conversion van once with a 24' TT. I could nearly pick the rear up off the ground with my WDH.

When you get your WDH, measure front, the center of your wheel to the fender well before you attach your TT

Attach your TT and adjust your bars until your back to 0" to +1/2" of your unloaded measurement.

CAT scale readings with quantify exactly what you've changed before and after.

Best regards,
Doug
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Old 02-23-2013, 10:39 PM   #5
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Dan,

For the moment forget about percentages, because not all TV/TT combinations are created equal and everyone has different loading habits, plus different TV suspensions react differently to loaded weights.

How a WDH works:

The main function of a WDH is to return the same weight that was removed from the TV's front axle do to the "effect" of the TT's loaded tongue weight being placed on the TV's hitch ball (TV's front rises, rear squats). The importance of returning the same weight removed back to the TV's front suspension is to re-establish the steering integrity and TV handling characteristics.

Under most correct WDH adjustments, the TV's rear will still be handling some added weight so the TV's rear will still squat 1" to 2" (normal, but not as much squat without the WDH) even though the TV's front suspension has been returned to it's original condition (weight & height).

The WDH when engaged will distribute (remove) weight off the TV's rear axle then distribute the proper amount of weight back to the TV's front axle and a lessor amount of weight back to the TT axles. The weight being distributed in most cases is less than the loaded tongue weight value (not all TV/TT combinations are created equal). NOTE: The loaded tongue weight originally placed over the TV's hitch ball remains fairly constant, the WDH doesn't move weight off the TV's hitch ball.

If you look at the WDH ball mount where the spring bars are inserted into the ball mount sockets, as the spring bars are engaged there will be a for/aft force taking place within the sockets thus transferring force through the TV's receiver and the TT's A-frame.... this in turn translates into weight being distributed off the TV's rear axle. The tongue weight sitting "on top" of the ball mount remains constant.

Sometimes folks will say that about 20% of the tongue weight was distributed back to the TT's axle, but in reality the actual weight comes off the TV's rear axle. Depending on the TV/TT combination, this could be a 10% value.

The only way to confirm the weights being distributed is a visit to a CAT scale, which everybody should do. The CAT scale will confirm all weights and confirm the WDH is adjusted correctly.

Hope this sheds a little light on the WDH (a lot to digest). If I can clarify anything, please advise.

Bob

On Edit: When you have some time, walk yourself through the CAT scale weigh-in process and how given weights are compared, may be helpful: https://www.jaycoowners.com/showthrea...igh-Your-tt-tv
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Old 02-24-2013, 01:39 PM   #6
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Thanks for the explanation. There is definitely more physics involved than I had originally thought. The dealership will be installing and adjusting the WDH for me when I pick up the TT. I plan to measure the wheel wells before I go to the dealership, then make sure the front remains unchanged and the rear is no more than 1 or 2" down after they make the adjustments. Then I plan to take it directly to the CAT scales, which will hopefully tell me if I need to add/remove any chain links.

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Dan
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Old 02-24-2013, 03:29 PM   #7
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My understanding is that the TV should sit level with the WD engaged (assuming it sits level without the trailer). The front drop and the rear drop should be the same. The TT should sit level or very slightly nose down- never nose high.
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Old 02-24-2013, 05:04 PM   #8
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Sailor,

Your correct about that ideally the TT should tow level, or slightly nose down...., but in the case of the TV things have changed over recent years, obtaining equal squat is a challenge to say the least.

As mentioned in my prior post, the most important objective of the WDH is to return the TV's front suspension to it's original (unhitched) weight condition. The WDH will however raise the rear of the TV a little (reducing degree of squat), but in most cases it won't return the TV's rear fender height back it's original unhitched height ..... do most in part to these newer frame/suspension designs.

Bob
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Old 02-24-2013, 05:26 PM   #9
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Dan,

There's actually more physics going on then I mentioned, especially what is taking place with the TV's frame & receiver when the WDH is engaged...., and the same with the TT's A-frame.

Keep in mind when you depart the dealership your TV/TT combination will be in an unloaded condition, a CAT scale visit at this time will only address your unloaded TV/TT state. Once your TV/TT combination is under "loaded" conditions (ready to camp), this will be the most important CAT scale visit confirming all weights and your WDH adjustment. In most cases the WDH will have to be re-adjusted one last time under loaded conditions.

Watch over the tech's shoulder as he adjusts your WDH, and make sure they give you all the WDH installation documents.

Also, when you reference the WDH chain at the snap-up brackets with the RV tech or others, reference chain links "under tension" to minimize any confusion.

If you have any questions in respect to the RV dealer's adjustment of your WDH, take a couple of close-up side view photos of your WDH with the TV/TT hitched up, and feel free to post them if you want another pair of eyes on it.

Bob
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