----- Original Message -----
From: <mblair1@home.net>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Sunday, November 12, 2000 23:45
Subject: Re: [MV] M34 vs. M35A2
>
> DDoyle9570@aol.com wrote:
> > While I have never seen tabulated data to support this, I suppose the ground
> > pressure is lower on 10 900x20's is lower than that supported on 6 1100x20
> > (although the gross weight of the 6 wheeled vehicle is 410 lbs less than the
> > 10 wheeler).
>
> I think you're correct. According to my 1965 M44-series operator's
> book, the recommended highway pressure for singles is 70 PSI, and it's
> 50 PSI for multifuels with dual tires.
>
> I think that with pneumatic tires, the ground pressure will be roughly
> equal to the tire pressure (ignoring support due to the rigidity of
> the sidewalls, which I would guess is negligible for most common
> tires). The air in each tire will apply an equal force to each square
> inch of the interior of the tire, and the tire will flatten until the
> area of the contact patch times the tire pressure is equal to the
> weight supported by that tire. Thus, the ground pressure will roughly
> equal the tire pressure, with the total area of the contact patch
> varying depending on the load and the tire pressure.
>
> I'm no tire expert... I'm just applying a bit of physics to the problem.
> Mark J. Blair, KE6MYK mblair1@home.net
The following is sent after working a graveyard ( 3rd ) shift. I am no
mathematician or physics expert but lets say your truck weighs in at
24,000 lbs., it rides on 10 tires therefore each tire supports 2,400 lbs.
If your truck has 6 tires than each tire supports 4,000 lbs. You can see
the need for larger tires. Each tire where it meets the ground, ( footprint) ?
uses X number of square inches. So lets say your 10 wheeler @ 2,400 lbs.
per tire with a footprint of 10 square inches now has a footprint of 240 p.s.i.
If your truck has 6 tires , with a footprint of say 16 square inches now
uses a footprint of 250 p.s.i. When you air down for operation in sand you
increase the size of the footprint and decrease the p.s.i.
The above numbers were just made up for the sake of working this out
and in no way should be taken as actual weights , square inches, and
p.s.i. Another way of looking at would be to take a M-48 Battle Tank
with its large track sitting on the ground only uses 11.87 p.s.i. of ground
pressure. If anyone can explain it better please do.
Jim Wiehe , VA3JHW
mail to : j.wiehe@sympatico.ca
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