Tires: winter tire widths, ford f 150, rim diameter

Question
in your opinion is it better for winter conditions to have a wide tire 285 or narrow 245.  Also can a 245 tire be mounted on a rim that has a 285 on it now.  i have ford f 150 w/ 20" rims, for winter would 18" be better or is over all diameter more inportant
thanks

Answer
Scott,

It depends.

If we start with the assumption that the traction generated from the road surface - no matter how small the contact size - is more than the traction generated by contact with snow, then it would be extremely important to cut down through the snow to get to the road surface - and that would mean that narrower tires are better.

But if there is no chance of getting to the road surface, then more contact area with the snow would generate more traction - ergo, a wider tire would be better.

Can a 245 tire be mounted on a rim that has a 285 now.  There is some overlap, but it is highly dependent on the exact rim widths involved.

And if you change rim diameter, you can keep the same overall diameter of the tire, so there's no clear cut answer there as well.