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RockyMtnRay · 07-31-2004, 09:29 AM

[quote author=Denny_A link=board=20;threadid=1379;start=msg15180#msg1518 0 date=1091246405]

If a WDH is used, the vehicle stays level. The proportional braking feature is defeated.
[/quote]

With all due respect, I disagree with your conclusion. Although a WDH transfers part of the hitch weight to the front wheels, some (a third if the WDH is correctly setup) does remain on the rear wheels. Hence, although the tow vehicle remains level, the rear of the tow vehicle does indeed drop (by comparison to an unladen vehicle), and the brake proportioning valve does thusly increase the amount & percentage of brake force applied to the rear wheels. Therefore a properly setup WDH does not defeat the proportioning feature...although the increase in rear braking is not as large as if a WDH hadn't been used.

The real problem with the brake proportioning valve (BPV) comes not with a WDH, but rather with the use of air bag type rear suspension boosters to "level" the tow vehicle. If a WDH is not used, two things happen to the tow vehicle: the rear of the TV does drop and, equally importantly, the front of the TV rises (because of the teeter-totter effect of applying substantial down force well behind the TV's rear axle). In many cases, the front of the TV rises by 1 to 2 inches. If an airbag system is then used to raise the rear of the TV so that the TV is level, the overall ride height on both ends of the TV is now 1 to 2 inches above that of an unladen vehicle! Since the rear is now lifted by as much as two inches, the BPV is now almost entirely closed and the rear brakes are providing only 5 to 10 percent of the braking force of the TV instead of the 20 to 30 percent they normally provide (or the 50 percent they should be providing when the TV is loaded). I consider airbags as completely evil devices if they're being used to "level" a tow vehicle.

07-31-2004, 09:29 AM	#18
RockyMtnRay TrailManor Master Join Date: Jul 2001 Location: Colorado Springs, CO Posts: 816	Re:Toyota 4Runner replaces Honda ODY [quote author=Denny_A link=board=20;threadid=1379;start=msg15180#msg1518 0 date=1091246405] If a WDH is used, the vehicle stays level. The proportional braking feature is defeated. [/quote] With all due respect, I disagree with your conclusion. Although a WDH transfers part of the hitch weight to the front wheels, some (a third if the WDH is correctly setup) does remain on the rear wheels. Hence, although the tow vehicle remains level, the rear of the tow vehicle does indeed drop (by comparison to an unladen vehicle), and the brake proportioning valve does thusly increase the amount & percentage of brake force applied to the rear wheels. Therefore a properly setup WDH does not defeat the proportioning feature...although the increase in rear braking is not as large as if a WDH hadn't been used. The real problem with the brake proportioning valve (BPV) comes not with a WDH, but rather with the use of air bag type rear suspension boosters to "level" the tow vehicle. If a WDH is not used, two things happen to the tow vehicle: the rear of the TV does drop and, equally importantly, the front of the TV rises (because of the teeter-totter effect of applying substantial down force well behind the TV's rear axle). In many cases, the front of the TV rises by 1 to 2 inches. If an airbag system is then used to raise the rear of the TV so that the TV is level, the overall ride height on both ends of the TV is now 1 to 2 inches above that of an unladen vehicle! Since the rear is now lifted by as much as two inches, the BPV is now almost entirely closed and the rear brakes are providing only 5 to 10 percent of the braking force of the TV instead of the 20 to 30 percent they normally provide (or the 50 percent they should be providing when the TV is loaded). I consider airbags as completely evil devices if they're being used to "level" a tow vehicle.