Widewing

When discussing a tire's ability to gain traction on ice, one must understand the physics involved. Is it wet ice or dry? Static or dynamic friction?

Let's just make it simple. Friction is not dependent upon area. Friction is dependent upon load and whether or not there is mechanical interference between the two surfaces. If you double the area, you halve the load, thus no increase in friction. A good example of mechanical interference are studded tires.

Ice is hard. Ice cold tires are relatively hard as well. There is not any significant mechanical interference between the surfaces. Wet ice is worse as it results in a lubricated surface. Winter tires have gozillions of sipes to squeegee out much of the water, reducing the lubricating effect of the water. But, winter tires offer little to no improvement over normal tires on dry ice.

High performance summer tires get grip by using a very soft compound that generates a lot of mechanical interference (at the molecular level). In short, they are termed as being "sticky" for a reason. When at optimum operating temperature, they are sticky. However, these compounds dramatically harden when cold and lose their ability to adhere at the molecular level.

In short, it does not matter what your tire pressures are when on ice. The coefficient of friction doesn't change with increased or decreased area.


My regards,

Widewing

Gravel Gertie

Thank you Widewing for your very enlightening explanation. I learned something today. What you said makes perfect sense.

White Widow

here in colorado they race jeeps on lake dillon i will try to find more info on what tires they use and tire pressure. i would think they have spikes in their tires

White Widow

actually buy a pair of these tires if you are going to drive on the ice.
got these pics from westword.com

hig4s

I've been here 11 years, the 40 before that were in Michigan. Six of those, including the years I learned to drive, got my first drivers license and got my first car were all in the Garden peninsula of the upper peninsula of Michigan. Where most of the winter it is so cold salt will not melt ice, so you just drive on it. Generally with studded tires, if you actually wanted to go anywhere.

BlackNorthernJK

ok...truthfully, I'm just jealous as all hell that you live in Florida, we're back down to -27C(-17F) up here in not so sunny Edmonton...sucks

JNMLLE

I would assume that with any surface (other than asphalt, of course) one would DEFLATE the tires, as the softer they are the more traction they'll provide. The harder the tire (inflated) the more slippery, and the softer the tire (deflated) the more grip. I'm no expert, but something tells me I'd slide all over the place if I were to hit an icy patch of road with asphalt-inflated tires. The softer the rubber the better the grip, and reversely, the harder the rubber the more slick. The tire becomes softer as it's deflated, therefore creating more traction and the ability to "pull" (it's "mushier"), as opposed to slipping due to the hardness of over-inflation. It would be like trying to walk on an ice rink with hard-soled dress shoes versus softer-soled basketball shoes. And even if the dress shoes had the same traction as the basketball shoes, the key here is that the basketball shoes are SOFTER, and that makes all the difference.

Widewing

Don't assume anything about ice. As I stated earlier, friction is independent of area. Load, not area determines friction. It doesn't matter if you air down or up, the load factor remains unchanged. Friction is limited, as it cannot increase above the coefficient of friction between the two surfaces without a modifying factor (sand, studs, or water, which lubricates the ice), regardless of load.

To gain traction, one must introduce a mechanical interaction. In other words, the vehicle must penetrate the surface of the ice to get a mechanical bite. Tires alone cannot do that because ice is the harder surface. Studded tires, or cable chains (not as good as studs) will do that. Rough ice can offer some traction as the tire tread can get some minuscule bite. Sand is a great help because it interacts both with the ice and the tires.


My regards,

Widewing

BlackNorthernJK

Thanks for all the work on this Widewing, you are an engineer correct? I'd say you have a pretty good idea what your talking about.

Mariner

widewing has got it right, i use a double row studded winter tire as we get a lot of ice on the back roads. over the years i have tried a number of combinations airing down, up wide and narrow tires and nothing comes close to a good studded winter tire.