Date: Fri, 8 Aug 2008 12:35:45 -0700
Reply-To: Mike Elliott <camping.elliott@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike Elliott <camping.elliott@GMAIL.COM>
Subject: Trailer loading and tire pressure testing
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi all,
I don't to join the legion of unskilled trailer haulers who find
themselves in a terrible jam because they were dozing in Trailering 101.
So if anyone wants to check my work to see if I overlooked something, that
would be helpful.
TRAILER: 270 lbs. (Small fiberglass-bodied single axle utility trailer.
Empty weight: 270 lbs. This was derived from weight on tongue = 30 lbs,
weight on one tire 120 lbs. It's safe to say that the other tire had as
much weight on it.)
PAYLOAD: 218 lbs.
TOTAL COMBINED WEIGHT: 488 lbs.
The rule of thumb seems to be to have 10% to 15% of the gross weight on
the tongue, so I balanced the load to get 55 lbs on the tongue.
TIRE PRESSURE
Too much pressure = bouncy ride, too little = hot sidewalls and possible
kablooey. Each tire is carrying (488 - 55)/2 = 240 lbs. These tires are
ST175/80R13, and according to the load inflation chart at
http://tinyurl.com/6lg2oy 15 psi is more than enough. Refer to the chart
if you don't believe me -- these are beefy tires for such a little
trailer. Heck, 15 psi is good up to 670 lbs per tire.
So I aired each tire to 15 psi and took the loaded trailer for a 7 mile
ride, half of it on the freeway. At the end of the ride, the sidewalls of
the van's tires (aired to spec) had risen to 97F (ambient here is around
76F), and the sidewalls of the trailer tires read about 90F. This suggests
that the tires are not underinflated, which is in agreement with the load
inflation chart.
However, the pressure in each tire had risen to 20 psi, a 33% increase.
A list member had p-mailed me a couple days ago about a tire pressure rule
of thumb: if the pressure goes up more than 10% after a fast 5-mile drive,
the pressure is too low.
So...according to the rule of thumb, the tires are underinflated.
According to the chart, they are nowhere near being underinflated.
According to the comparison to the sidewall temps of the van's tires, they
are not underinflated. Anyone want to comment on that?
Oh -- by the way, the trailer towed like a dream. No side to side
oscillations which indicate that there is too much weight to the rear, and
no excessive bouncing. It followed along like a little sweetheart.
--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR
