Short tire pressure story

[Tony Raine]

Originally Posted by gascort

I'd argue still that when you have a smaller contact patch, you drive water out from under your wheel faster due to increased pressure on the water. When I switched from 245/45/17 to 315/35/17 tires in my mustang (got bigger wheels for looks and altering the car's stance only - I've never believed in contact patch - friction relationships) I lost rain performance. I can hydroplane all the time now in that car.

I'm sure there is a speed at which the greater pressure just won't matter due to the water's viscosity, but I haven't ever experienced it.

thats the way i've always thought it was. less tire on the road, means more weight in a smaller spot, means more traction. have your wife/girlfriend/random woman on the street, stomp on one of your feet with the heel of a tennis shoe, and the other with a stiletto.

when fourwheeling, i've found a skinnier tire "digs" down to solid ground (if its there ) and a wider tire "floats" on top.

[Johnny Mullet]

We had a heavy downpour here a few days ago and it was so bad we were getting flash floods. I was traveling down this road and seen the right half was under water and I had an oncoming vehicle. I thought to myself that I am screwed since I got 44 PSI in my tires, but I splashed right through the deep water at 50 MPH with no problem.

[atomicradish]

Thanks for the story, Daox. This is one of the primary concerns people have expressed to me about inflating your tires to the sidewall maximum.

If only they knew... if only...

[NeilBlanchard]

Hello,

I think that the tire itself has a lot to do with good wet traction and less hydroplaning. I've had tires that hydroplaned badly at 45mph in just a little water, and others that work great at faster speeds and/or in much deeper water. Wide channels that are well shaped to let the water escape, and the right structure in the tread and sidewall also affect it, I'll bet.

Different tires can be wildly different in the rain; no matter what their internal pressure is. So, just because person has no issues with high pressures, doesn't mean that we all will be okay.

Not all rain storms are the same: from motorcycling, I learned to be very wary in the afternoon cloudburst after a hot day -- the water lifts all sorts of oil out of the pavement, and the surface is close to ice.

[MetroMPG]

Originally Posted by MazdaMatt

Everything in life is an optimazation problem. I don't drive a minivan because I don't need 7 seats. I can't go telling a family of 7 to go buy an econobox. if you air up your tires for psi, you have to drive more carefully, if you do so, you have no loss. You optimize your mileage and lose out on some other aspects. no biggie as long as you know your car's limits.

Well said, Matt. That's it in a nut shell.

[Concrete]

a over-inflation (a bit) is better in almost every way to under-inflation

simple demonstration
Tire Tech Information - Air Pressure vs. Wet Performance
but I do agree with Neil - each tire is different

the autocross guys over-inflate not under-inflate and they certainly would not accept a performance loss.

if you are running 32psi because your door placard tells you and your tire says more, you are probably under inflated and that IS dangerous.

if you run 32psi because your tire side wall says so - you are on the verge of under-inflation the moment it gets cold or you have any kind of leak, and that could be dangerous.

if you are 5 psi over the side wall - that has got to be minimally significant for safety or we would have people killing themselves because of low accuracy tire pressure gages. If you really want to pop a modern tire (with out help of a nail etc.), you have to run it low.

60 psi in a 32 psi tire - well... that is an optimization issue as stated

personal data:
bought truck and started running 55 psi in 44 psi rated tire on an S10
wear pattern improved - handling improved - rolling resistance improved
ride rougher and road noise higher pitched and more noticeable
wet traction was poor before and I have not notice a change - hydroplaning reduced

[WheresMyGas]

Originally Posted by Daox

Everyone on the highway slowed down to around 40-50 mph.

Wait... Aren't you going already going 55mph to save gas? What was your speed drop for your quick braking?

sidenote: WOW you're nearly doubling your Paseo's epa. That's crazy.

[Daox]

The road is a 65 mph freeway. I average 60 mph on it normally.

The slow down was actually while we were going around 45 mph and everyone slowed to about 20 mph because the rain suddently REALLY picked up.

[PaleMelanesian]

I also run 60psi, and I've had nothing but good experience in wet weather. In the past, at 35psi, I've been slipping around much more than now.

[dremd]

I did recently notice that my ABS has to work harder (shorter pulses) at 55psi than at 45 psi when on poor surfaces. No testing, just an observation.