Tracks vs Wheels in snow and ice.

> At 9:40 PM +0100 1/16/02, Oerjan Ohlson wrote:

The only great benefit CTPR systems give is that you can trundle along on
black top, then go off onto soft ground with out having to get out and run
around. One is still limited to a certain range of
pressure based on rim configuration and if the tire/rim combo has
bead locks or not. But the argies very well could have climbed out and lowered
the pressure with a gauge then pumped them up later just like early DUKW
drivers did.

> What the Armor article does say is that the SISUs (XA-180s) could

> They added snow chains, but that's it. I would've thought that

Probably depends on the Freeze conditions too. Could it have been
especially icy? If so according to the article M-113 tracks didn't
grip very well. However, the SUSV tracks did grip just fine.

What I want to know is why the wheeled XA-180s were nice and mobile
and yet the HEMTT wrecker wasn't so mobile. What really seems to be at issue
is the type of tracks and availability of snow chains for the vehicles in
question, tracked or wheeled.

> A bit heavier than the M113 IIRC... not particularly light, no. The

But it doesn't appear to be a floatation issue. It appears to be a traction
issue.

> *Why* the Bradleys are too heavy to swim isn't very relevant, is it?

One thing that effects vehicle mobility is ground pressure. If I have a big
heavy tank with long thin tracks, then I'll have a higher ground pressure than
if I put wider tracks on the same tank. Compare the difference between the
HVSS and VVSS on the US tanks in WWII. There was a great deal of "Thank god
for those wider tracks" from many US tankers when the newer tracks started
making their rounds on the later makes of Sherman (and other types with that
chassis).

Ground pressure applies to wheeled vehicles as well. A central tire pressure
regulation system allows a driver to lower the pressure and increase the foot
print of each tire for softer ground. BeadLocks allow for a lower pressure.
More wheels along each side also affects this pressure (as one would expect).

The ground pressure of each is: BV206 (SUSV) 1PSI (front) 2 PSI (rear) M113
8.63 PSI LAV 52.5 (nominal it goes higher...)

I cannot locate the ground pressure for the SISU XA-180, perhaps
someone else can locate it...

Now, traction in snow and ice is such that even if I have a wheeled 4 Wheel
drive vehicle with a low ground pressure, I'll still slide if I hit hard snow
and Ice. If I add spikes or chains, I will not slide. The same thing goes for
tracked vehicles. Compare the tracks on the SUSV to those on other vehicles.

See: http://sites.netscape.net/chrisyateschris/snowcat.htm

From reading your cited article, it appears that the M113's problem was in
fact traction and not bogging down. Otherwise the M113 wouldn't have performed
so well in Vietnam in the jungle and in areas of marshland. Looking at the
tracks of the CV90 (also a Hagglunds product) I see some grippier tracks that
likely work just as well in snowbound conditions.

Now perhaps the US army would be better equipped in snow bound conditions
getting some special track pads for snow and ice for the
M113 and M2/3 series vehicles as well as investing in snow chains for
each of the primary vehicles. A further step would be to get the BvS10 which
is an armored version of the Bv206.