Re: more Ta'rs questions...

[phile@stpaul.gov (Philip J Ethier)]

Peter_C_Schulz@ccmail.ed.ray.com writes >
 
> I had always been told that the best tires for snow are those that are 
> narrow and tall with plenty of small and deep elements (siping) to break 
> up the snow and "punch thru" it. 

Right.  You want to get to the hard surface underneath, not float on top
of the snow.

> My office mate has driven with his mudder tires on his 4x4 in the snow 
> (big, chunky tread blocks, lots of open tread area. Granted, the tires 
> are oversized, and probably have a much lower ground pressure per inch 
> than "normal snows". 

Don't underestimate this effect.

What mud tires are designed to do is provide floatation in mud.  You and
I, driving our cars on snowy roads, want to reach down to the solid
bottom.  Mud racing in a truck, there IS no bottom.  Without huge tires,
the truck sinks until the floatation is provided by the chassis.  Then you
have to winch it out.

My brother-in-law went to truck pulls and mud races with his 3/4-ton
8600-GVW package Chev pickup.  He had huge balloon tires for that.  Come
winter, off they came.  He had some large diameter skinny tires for
plowing snow.  He always told me that the truck was murder to drive in
snow on the big mudders and would not plow snow at all with them.  He
lives in Rochester, Minnesota, (Mayo Clinic Town) where they seem to get
heavier snowstorms than here in the Twin Towns, although I would not be
surprised to find that Rochester, NY, (Kodak Town) gets more snow.

> Any way, what I learned about his tires would 
> indicate that they should be at least ok in the snow.
> Well, not in his experience.  He said that absolutely no snow sticks to 
> them, and to "drive well in snow, you need the snow on the ground 
> sticking to the snow in the tire.

Not exactly.  He has two much snow between his tire and the road
surface.  If there is heavily packed snow, the big ribs on the tires
drive themselves into the snow and push the car like paddles.  If the snow
sticks to the tire, it packs up the grooves and does not allow the tire
ribs to penetrate.  Your tire turns into a treadless slick.  His tires are
providing too little pressure to the snow to make it pack so the rib can
push off of it.  At the same time, the wide tire is also unable to push
the snow out of the way so it can get down to the road to get some grip.

Of course, it also takes more power to carve through the snow with a wider
tire, so more traction is required to provide forward motion.

Bottom line to all effects is that the best tire for snow is:

Tall (lots of ground clearance)
Skinny (less snow to move, more pressure on the road surface)
Noisy on smooth pavement (big lateral grooves and ribs to grip in hardpack,
and clear themselves of snow for the next grip)

All the rest are compromises for other purposes.

phil.ethier@stpaul.gov