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Date:         Wed, 10 Mar 1999 14:45:09 -0500
Reply-To:     "G. Matthew Bulley" <gmbulley@BULLEY-HEWLETT.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "G. Matthew Bulley" <gmbulley@BULLEY-HEWLETT.COM>
Subject:      Not exactly...was: towing with a vanagon
Comments: To: Bill <Bill@FREEHOLDER.COM>

Bill wrote-- "If you paid attention in physics, you know that as far as braking and acceleration are concerned it makes absolutely no difference whether the weight is inside the vehicle or a trailer. The only difference is the added friction of another set of bearings, which is minimal."

Not a flame, especially since the wife and I had a nice evening with Guillermo and his wife and he is always right on the dice with his posts... but the above statement isn't EXACTLY correct.

I don't have time to write out all the details (some of you just breathed a sigh of relief). But the physics of one object pulling another through a pivoting tether are *quite a bit* different from the physics of accelerating and decelerating a single, self-contained mass, like a van full of seat-belted passengers and safely stowed gear.

In particular, during emergency braking, the van's brake-proportioning valve relies on a spherical mass that moves farther and farther up a little ramp the harder you stomp on the brakes. If the load is self contained (in the van), all is well, the load shifts forward, the little ball in the valve rolls WAY up the ramp, and the greater portion of the braking effectiveness is directed to the front wheels.

If the load is tethered to the rear of the vehicle, the valve may not sense the forward shift in mass accurately, and in fact, the rear of the van may be likely to have an increase in load, as the mass on the trailer tries to remain in motion, and shifts forward, pressing down on the tongue.

In this scenario, you are far more prone unpredictable brake response, and loss of control. It is precisely for this reason that the internal load capacity of our van is so high, and the trailed capacity is so low.

Accelerating and maintaining the speed of a load behind our van's is not the issue...emergency braking is. I would propose that it takes only one episode of trying to panic stop with a heavy load in an over-laden vehicle to convince one that using a properly equipped vehicle is a far safer policy.

Back to work...

G. Matthew Bulley Bulley-Hewlett & Associates Cary, NC USA www.bulley-hewlett.com (888) 468-4880 toll free

-----Original Message----- From: Bill [SMTP:Bill@FREEHOLDER.COM] Sent: Wednesday, March 10, 1999 10:09 AM To: vanagon@GERRY.VANAGON.COM Subject: Re: towing with a vanagon

<<<SNIP>>> This time of year, the trout fishing is great, and the bass will be starting to hit soon.

Bill (SE Arizona) (Bill@freeholder.com) HTTP://www.freeholder.com ---------------------------------------------------------- You can't do everything, but you can do something. You can't help everyone, but you can help someone. Even one candle helps to push back the darkness.


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