FTE 61-79 - soft brakes

61-79-list-digest Saturday, May 9 1998 Volume 02 : Number 258

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Date: Fri, 8 May 1998 07:48:00 -0700
From: "Chris Samuel"
Subject: FTE 61-79 - Another take on wheel speed

SNIP
Please pardon the ignorance of an old farm hand but In my experience
wheel speed just gets you stuck faster.........?? Maybe dirt tracks
at fair grounds aren't bottomless mud pits? Speed makes friction so
it make for more bite? (not much friction in muck :-))

The following is long and my opinion, YMMV
Wheel speed is my friend in Bottomless Mud Pits, but not with "Tractor
Tires" there is too much digging action to a chevron type tractor tire and
not enough flotation.
When running "Boggers" or just "Swampers" wheel speed is critical to
making it or sinking it. The same factors apply as in the pulling
explanation except the rearward displacement of Muck at just the right speed
will propel the truck forward. Too much and you go too fast (out of control)
or straight down; too little and you go too slow and then down! The
balancing factor is the amount of flotation required by the truck.
Way back when the ruts were only a 33 tire deep we could get away with a
tall skinny tire, the theory was that you reached down and grabbed the
bottom. This is hard to do when the truck in front of you is running 44's
and you have "only" 36's. So Flotation becomes key to this equation, get
enough, but not too much. 75% of the time there is no such thing as too

much, that is until you experience it on wet pavement or snow, I just love
it when the tail end decides to lead!!
Here is another observation if the tire is of the all terrain
type like a BFG Mud Terrain you need to error back to the skinny side and
get your flotation with diameter. You are getting the same PSI at the
contact patch but you have more tread engaged to provide energy transfer.
This is because the tread is shallow and only semi-aggressive.
Ether way the wheel speed is going to be higher then expected, though it
generally slows down as the tread gets more aggressive. To go back to the
Chevron Tractor tire; the tread is vary aggressive, or the Tread to Void
Ratio is low (big voids) the tread will displace muck at a high rate, so the
tire digs if the speed is too high for the amount of forward momentum.
Stop to think about the original design application for each tire design.
The Tractor Tire a relatively heavy low powered tractor, that operated at a
low speed.
The Bogger A moderate weight rig running at a high power output at high
speed.
Put a set of boggers on the tractor and it may just sink due to the reduced
flotation offered by the Boggers and the tires may just slick-up with mud
because the tractor will not normally be running enough wheel speed to clean
the tires. Put the tractor tires on say Sleddogs puller and drop the hammer
in soft muck and the tires simply displace all of the muck below the tire
> before they can begin to provide forward movement and then Sleddog is going
to make us dig his truck out and spend 2 days washing it to get it back to
pulling weight.
There are a ton more factors Power, Weight, $$$ Available, Suspension,
etc...
and every time I say that wont work some arse goes and does it just to mess
with me!
Of course I could just be observing the wrong things, and my experiences
could be nothing more then a long string of anomalies.

Chris
79 Bronco
>

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