Weight Distributing Hitch ?

Originally Posted by Bill

My feeling is that anywhere in the 600-1000 pound range is appropriate for TMs.

Bill's "feeling" is validated by the calculations. I tried changing various parameters in my WDH spreadsheet calculator and this is what I found:

(The main criteria for these calculations is that the WDH is adjusted for the net load change on the TV front axle to equal the net load change on the rear axle. This should be pretty close to what happens when you follow the WDH adjustment instructions to achieve an equal change in height of the front and rear wheel suspensions. Calculations might actually be too conservative - i.e. you don't need as much WDH force as stated - if rear suspension is stiffer than front suspension)

- Generally, you will need more force from the WDH bars for:

- higher tongue weights
- more weight in the TV trunk/bed
- longer TV wheelbases
- longer TMs (i.e. longer distance between tow ball and TM axle)

- Case 1: for short TM (e.g.2619), short wheelbase TV (106"), 550lb tongue weight, 50lb in trunk, you need WDH force of about 575 lbs per bar
- Case 2: for long TM (e.g 3324), long wheelbase TV (130"), 700lbs tongue weight, 100lb in trunk, you need WDH force of about 980 lbs per bar.

So, this bears out Bill's statement that 600lb to 1000lb bars should be sufficient for pretty much all TM/TV cases.

Other things to note:

- For case 1 the load transferred to the TM axle is about 245 lbs
- For case 2 the load transferred to the TM axle is about 315 lbs
i.e. not a huge change across the range as expected (it goes up with tongue weight but down with TM length), but it is generally more than the 1/3 of tongue weight we've been assuming.

- In the second case, if you adjust the WDH for say 800 lbs instead of 980lbs, you get +500/-750 front/rear axle download due to WDH ( i.e. 500lbs load put back on front wheels and 750 lbs load taken from rear wheels) instead of +610/-920. So even for a big long TV, the longest TM and 800lbs of tongue+trunk load you could get great benefit from even the 800lb bars inasmuch as all the missing weight (350lbs in this case) from the front wheels has been put back on and more, (i.e. steering ability recovered) and the rear wheels have been relieved of a lot of the TM tongue load. This would be probably be similar to the case where you adjust the WDH so that the rear goes down a little more than the front does which is quite acceptable and is preferred by some. Also the TM axle load increase is now only 260 lbs instead of 315 lbs, (not particularly important maybe for the 3324 with its dual axles, but this type of adjustment to minimise transferred load to the TM axle might be preferred for say a 2720SL).


-Paul

(PS.. I've had to make some assupmtions in these calculations where I don't have a real measurement. If anyone can give me the tow ball to axle distance for TMs other than the 2720, I can be more accurate..thanks)