Tire pressure and friction?

Question

Can somebody explain to me the relationship between tire pressure and friction? Specifically, I had a conversation with my professor today regarding an off-road vehicle deflating his tires a bit to lower the tire pressure and give him better grip when rock-climbing. My professor contended that the lower tire pressure did not increase the friction between the tires and the rocks. This makes little pratical sense to me since one would 'just know' that the lower tire pressure would indeed help in the rock climbing.

Please help!!

Thanks!

Answer 1

I think this is a case when your experience, beats your teachers book-knowledge. He is probably thinking of the formula that says that the friction force equals the normal force times the coefficient of friction.
According to this formula, the surface area doesn't matter. In real life it does.
Sharp rocks will press deeper into soft tires, creating friction. Even on flat tarmac, larger surface area, creates larger friction. That is the reason why sports cars use wide tires.
The formula he uses is only an approximate way to calculate the friction. It does not give an exact answer and it does not work for all conditions.
We still use that formula to get an estimate, because it is easy to use and most of the time it gives a fairly good number for the friction.

Answer 2

Lower tire pressure does increase friction. The tire will flatten more on the ground, increasing the contact patch. Lowering the tire pressure off road is more for preventing punctures, and ride comfort.

Answer 3

Specifically what happens is that in lowering the tire pressure the sidewall collapses a little. When the sidewall collapses a greater area of the tire touches the ground. With greater area comes greater friction.

For off-roading, less pressure allows the tires to "grip" around things as oppose to bounce over them. Maybe (i don't know) you're less likely to puncture a tire too.

Answer 4

I have to agree with you. Lower tire pressure increases the amount of contact your tire has with the surface, thereby increasing friction. Give that professor a failing grade. :)

Answer 5

This is a case of needing common sence not book sence. Lowering the pressure does create more friction but more importantly makes the tire have more give which gives better traction.

Answer 6

The air filled in cycle tire keeps the frame of the tire aloof from the road's surface,So the friction decreases.When the pressure is decreased then the metal frame comes near.& everybody knows that friction happens more with hard or metallic good............hope i helped.

Answer 7

The decreased air pressure allows the tire to flex more so it conforms to the shape of the ground, rocks, etc. better and as the tire spreads-out it has more surface area in contact with the ground.

Answer 8

Please see the article below. I believe your professor is in error. The reason that lowering tire pressure results in increased traction is that the tire has more surface area on the ground. This increased area results in increased friction.

Answer 9

friction is depends on your road condition and resultant weight of the vihecle.may b you right coz lower pressured tire takes little bit more space in the road.that makes friction bit high but that small amount is not a big diff. in a offroad jeep.but mainly friction depends on road condition and the weight.so lower tire pressure doesn'y do much work.your prof. is correct.