xcntrk wrote:
---So wouldn't the hitch weight actually be different between WD and without, therefore consuming less payload from the TV with WD in place?
I get that there's leverage involved at the root of the WD system and that the actual tongue weight of the TT doesn't physically change. But where I'm trying to make the comparison is between tongue-weight and hitch-weight, which I think could be two different values with WD involved.
"Hitch weight" is equal to tongue weight minus the load which is transferred to the TT's axles. I apparently didn't do a very good job of explaining that in the first two paragraphs of my respone in
this post.
Perhaps a numerical example would help:
Let D1 = Tow vehicle wheelbase = 130"
Let D2 = Distance from TV's rear axle to ball (a.k.a. "ball overhang") = 65"
Let D3 = Distance from ball to mid-point between TT's axles = 130"
Let TW = Tongue weight = 1000#
With trailer attached and no WD applied:
Load removed from TV's front axle = TW*D2/D1 = 1000*65/130 = 500#
Load added to TV's rear axle = TW*(D1+D2)/D1 = 1000*195/130 = 1500#
Total load added to TV = -500+1500 = 1000# (100% of TW)
Assume WD is activated to transfer (add) 250# to TT's axles (250# chosen to return front axle to unhitched load).
Due to leverage effects:
Load added to front axle = 250*(D2+D3)/D1 = 250*260/130 = 500#
Load removed from rear axle = 250*(D1+D2+D3)/D1 = 250*390/130 = 750#
Total load
removed from TV due to WD = -500+750 = 250#
IOW, the amount of load removed from TV equals amount added to TT.
The combined effect of TW without WD plus effect of WD is:
Net load change on front axle = -500+500 = 0
Net load change on rear axle = 1500-750 = 750# added
Net load change on TV/receiver/hitch = 0+750 = 750# added
Net load change on TT's axles = 0+250 = 250# added
Ron
