"Inflation pressure does not affect grip": Autospeed article.

[dcb]

Lol, I think the jist here is on-road use. Letting the air out of your tires is a hokey way of approximating tank tracks, which of course is NOT a good choice for on-road, but which would be able to handle the extremes of offroad better than any tire.

[vtec-e]

Originally Posted by CapriRacer

1)

Tires get a lot of their grip by penetrating the macro texture of the pavement. When pushed to an extreme, the rubber is torn off the tire - with subsequent increases in force. As a result, it is possible to get more than 1g forces.

But wouldn't a tire with higher pressure push more into the road surface, due to there being more pressure per unit area between the tire and the road?

And anyway, if it were dangerous and grip was compromised at higher pressures, wouldn't there be a load of test data to prove it?
Instead all we get is people telling us it's dangerous.

ollie

[thatguitarguy]

"Except in aquaplaning", is a huge caveat. When you are sliding on ice, snow, or slush, you are actually hydroplaning. You can slide very easily on rough ice, while maintaining perfectly good traction on very smooth dry glass. The difference here is a microscopic layer of water between the solid ice and the tire. The pressure caused by the weight of the vehicle will "squeeze" or "melt" this layer of water from the ice, so that it will nearly always be present in those conditions.

It is why an ice skate will glide over the ice instead of digging into it.

[thatguitarguy]

Originally Posted by vtec-e

But wouldn't a tire with higher pressure push more into the road surface, due to there being more pressure per unit area between the tire and the road?

A vehicle with more weight or downforce will push more into the road surface. With weight and downforce being a constant, higher tire pressure only reduces the size of the contact patch.

Therein lies the argument of traction. Higher pressure = smaller contact patch, and vice versa.

[Christ]

Originally Posted by orange4boy

In fact, according to these tests Higher inflation pressure reduced stopping distance and increased coefficient of friction...Scroll down for stopping distances.

FEA chapter III. tire pressure survey and test results

Unfortunately, higher pressures were not tested.

(Poor Cara. Sorry Christ)

FEA chapter III. tire pressure survey and test results

Not quite. I don't have ABS. I can stop faster than similarly equipped vans with ABS, too.

At least in this case, ABS was an exercise in "Make it look good, and sell it for more."

[jamesqf]

Originally Posted by shovel

Possibly not relevant to on-road discussions, but with regards to off-highway driving on extremely rough surfaces anyone who says inflation pressure doesn't affect grip can stop talking immediately if not sooner.

But there it's a different mechanism at work. You're generally driving on something that's fairly loose - think dirt spinning out from under the tire - so a larger contact patch reduces the force on each unit area of the dirt.

[Ryland]

I thought it felt like my tires had better grip, my snow tires are rated for 51psi and I try to keep them at that, 3rd winter on this set and the tread wear is dead even.

[orange4boy]

Oh, for sure, off road is a different animal. There you often want to increase contact patch so you don't sink or so the tire can cover medium size bumps and not get stuck between two peaks of a rock, for instance.

On ice, you want a cold tire. The minute you spin and heat up the tire you lose most of your traction.

With chains, lower pressure so the car does not vibrate excessively.

"Except in aquaplaning", is a huge caveat. When you are sliding on ice, snow, or slush, you are actually hydroplaning.

I think most people think of aqua planing as on a hard surface with liquid water. To slide on ice there does not have to be a liquid layer, but there often is.

There are a lot of "it depends" when it comes to tire traction and pressure. The best would be a variable pressure system. I think the Porsche 959 had this.

[Christ]

Variable pressure = something more to go wrong, waste fuel, and weigh more.

[orange4boy]

Edit: Something to note, this article seems to have no empirical testing, which I think is important in this kind of situation. Issues related to tires and fuel economy can often have the books cooked via mental exercises, which, while seemingly sound, are crucially lacking various pieces of the puzzle. Colour me skeptical.

I'm always skeptical which is why I will keep looking for better and better info on this. Please post better info if you have it. My later post has actual data although they didn't test above max sidewall.

1) Unfortunately, had they done a little research, they would have found this:

Fact or Fiction? Tire contact patch and air pressure.

That directly contradicts Item #1 - and has data to back it up. So it isn't a myth!

True, It does contradict item 1, but not the statement that inflation pressure does not affect grip. Obviously this is a general overstatement. Inflation pressure does not affect grip (very much). Let's find more info. I'm not completely satisfied by the AutoSpeed article or the one you posted.