Re: Funny quote about the SAAB 9-3 based Cadillac BLS

As far as the Aero is concerned, the only quasi-solution is to get skinnier/higher profile snow tires and put them on 16" rims. That should soften up the ride somewhat, whilst also resolving any ice/snow slippage. I say "should" because I've not yet tried it. As winter is (hopefully) winding down here, in Boston, I'm waiting until September to outlay the money for it.

When I purchased the car I had also tried the Linear and Arc flavors (both on 16" rims). I hadn't noticed them to be all that much softer in the ride department. But I admit, that wasn't of dire concern at the time and that would have been only one aspect I was paying attention to, amongst many.

- tex

Where do some people get the idea that a narrow track ( or Tread) makes a better snow tire?

Have they forgotten the elementary formula that friction + the coefficient of friction X the force(that is the mass of the car)normal to the surface.

It is independent of the area in contact. The bigger that area the more the force (mass) is spread out.

Malcolm

Malcolm,

A skinner, taller tier (185/65) tire is the most classic Saab tire in Gislaved.

It is a proven fact, look at all of the Land Rover adventures, notice their skinny yet tall tires to get them in and out of the much.

SaabGuy

Because the >tension< is higher.

Yes, correct f = F/N, coefficient of friction = Fricton (force) / Normal presure (weight/mass of car) or F = f x N

Exactly, but friction F is a force, working on an area; the larger the area the smaller the pressure, as pressure = F / A Why do people use studded tires on ice? What knife cuts better; a sharp one (with small A) or a dull one (with larger A) ?

-- MH '72 97 '77 96 '78 95 '79 96 '91 900i 16

Malcolm

I think you are looking at this to simplistically. On a nice clean street the forces to roll a wheel are more complex than that, and once you add in a few inches of snow the formulas really get complicated.

When driving in snow, you will be applying a force to move forward. The snow you are running over will be pushing the wheels back the other way (higher rolling resistance from packing down the snow). Wider tiers have to compress more snow, so need to apply more force to the road to get to the same place, increasing chances of slipping.

Also, don't forget that the skinnier tier has to move less slush to get down to the road. Once the tier makes contact with the road, slipping is much less of a problem then when riding on a half inch of slush. Narrow tiers are far less likely to hydroplane than wider ones.

-- Stephen B.

I'd say empirical study probably came into it, rather than just theory?

Nope, but what you've forgotten is that the smaller an area the weight of a car is sitting on, the higher pressure in pounds per square inch there is, given the same weight of car. A wider tire will "float" on top of the snow - and the friction of snow is a lot less than that of pavement. Gotta cut through the snow to the pavement, and skinny tires are great at doing that.

Independant, until you lose contact with the road.

For STATIC friction which is the case if the tire is skidding. Since most of use care about ROLLING (static) friction where the coefficient of friction *does* depend on the normal force.

Sorry, but you have fallen victim to the oversimplification found in many introductory Physics texts.

Bill

They get the idea through many, many years of trial and error. As the old hookers will tell you, experience counts for something.

Exactly right. So tell me, do you want the mass to be widely spread out so it can better float on the surface of the snow or do you want the mass to be applied to a narrower area with the intent that the tread will better penetrate that same snow?

-Fred W

skinny yet tall tires to get them in and out of the much.

All that i can say is that the extra height must be devoted to deeper lugs and tires like that must really sing on pavement.

Narrower tires would not cut . They are lat on the bottom. The best you could get is a water film or ice.

Malcolm

Um, no.

Do you drive in snow at all, Malcolm?