RE: BMW and driving in snow

["Fadeev, Alex" <Alex.Fadeev@xxxxxxx>]

> My 325i ("standard" 205/55 R 15 87V tyres) has excellent
> drivability (straight line, cornering, braking etc) in the dry.
> If there is a limitation it seems to be that the back end
> breaks away first on turning (seems to go quite "light"). 

John,
It's not the car, it's you!
If anything, your car will be understeering like a pig. If your car suddenly
oversteers during a turn on a slippery surface, barring any suspension
upgrades, that means your are WAY too fast with your right foot!

> However in the wet its very easy to lose traction - more than
> you'd expect even given the reasonable amount of torque available
> at the wheels.

Ha?
How is increased torque supposed to increase traction???
Respectable amounts of torque will _de_crease traction (throttle-on
oversteer) if you are not careful.

> In the snow it's probably one of the poorer performers I've
> driven and I don't think it's entirely my driving :-)

wanna bet?

> I've owned many other cars, most with lesspower I must admit. (And I
> wouldn't swap my BMW). But before anyone goes bananas at me about not
> having the correct tyres for snow please wait - - I know that already,
> but I'm comparing with other  (lesser) cars that didn't have snow 
> tyres either. 

yeah, but did all those cares have the same size/width/design/model tires?
if not, you are comparing apples to bricks.

> Now to my question (at last): *why* is it that larger (wider 
> footprint) tyres seem to be (are) poorer performers in terms of
> grip, in the snow (and wet)?

Because they have a harder time pushing through water/mud/snow/slush to the
surface of the road. 
The wider the tire, the larger the contact patch with the road. 
The weight of a car is constant. The larger the contact patch, the lower the
weight per square cm/inch of the contact patch. This is great news for dry
traction.
However, the lower the weight per cm2 of contact patch, the lower a chance
that a tire will push through water/mud/snow/slush to the surface of the
road. The less grip a tire appears to have in rain/mud/snow. 

alex f

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