Effective friction is a function of weight and coefficient of friction between the materials. Interestingly the surface area of the contact is not part of the equation.
On a flat surface a truck and a car using the same tire compound should have identical stopping distances. The issue comes when you are going downhill.
That is why you see racing cars with big fat tires, because it's more grip and the relationship is not linear.
> That is why you see racing cars with big fat tires
If you mean drag racers those tires are glued to the ground, and do not work off of friction. Other than that, what race cars have big fat tires?
Tires are usually sized so that the ground pressure of the tire is in the 40 to 100 psi range (which is also the tire inflation pressure). That's simply to keep the ground from deforming and the tire from popping. It does not affect friction.
This is also why off-road tires have lower pressure - the sand and mud they work on is not strong enough for a higher pressure. It is NOT for increased friction, it's because the surface they drive on can't handle it, so you spread out the weight, and reduce the pressure.
Road-going tires won't get hot enough unless you're skidding far below 7% slip.
The explanation in fact relies on deformable surfaces. If you imagine keeping the normal force constant and reducing the apparent contact area, the pressure on the surfaces will be increased which will cause the surfaces to deform more, resulting in more microscopic points of adhesion.
Well according to the article they don't have identical stopping distances, so let's figure out what would fix it.
> The issue comes when you are going downhill.
That just changes the angle of gravity. Why would it affect trucks and cars differently? I thought the point was that going downhill exacerbates differences in stopping distance, not that is causes them.
For one thing an 18 wheeler has 10 brakes, not 18. So that's an obvious thing to fix.
> Why would it affect trucks and cars differently?
The weight of the truck acts as an acceleration force when going downhill. The tire friction of a car and truck is the same - but then the truck has extra force trying to accelerate the vehicle when it's downhill.
Realistically, surface area does come into play because things deform and heat up, but I can’t say how much.
