Let air out of tires for better winter traction?

I would not reduce air pressure for normal winter driving.

There are two schools of thought for traction in snow. Either have a very large tire and try to stay on top of the snow or a narrow tire to cut through the snow to the hard surface below.

With a large tire you would want low air pressure to increase the contact patch and lower the pressure per square inch. This is the same method used with off-road vehicles in sand. The Prius will not allow for a wide enough tire to float on top and this method is only good for deep, undisturbed snow.

That leaves the narrow tire as your only option.

As a personal side note, I grew up in Michigan and we always changed our tires for winter. On both sports cars and trucks the tire of choice was tall and narrow.

 

for ice driving, most of us ice-racers run really low tire pressures. I think it has more to do with keeping the tires flexible and able to grip the small bumps on the ice. I've run around 20 pounds pressure on my Prius for ice-autocrosses using Blizzaks. On the street I still run 40/38.

 

I only know softer tyres are better in mud. I think that may be more to do with staying on top of it and it allows the tread to self clean.

 

A current thread at CleanMPG discusses this, but with a different vehicle and tires. That person found optimum traction at less than the max sidewall psi, but above the vehicle mfr. rec.

More testing with Prius would certainly yield useful info.

 

-ALL- tire manufacturers recommend running tires in snow at the "standard pressure", as seen on the door placard.

The reason is they are designed to "clear" snow from the tread best at some optimum pressure, which is usually the pressure seen on the door placard. More pressure wouldn't have much effect on this. Less pressure would trap snow in the tread (the tread bows upward when the pressure is low, closing the grooves). For ice you want the tire to contact the ice optimally, and this also usually occurs at the door placard number. You also don't want the tire to heat up, so lowering the pressure is not a good idea, as it causes the tire to flex more and thus heat up. This melts a small amount of ice, causing a loss of traction. If you were crawling on ice, lower pressure may help as the low speed won't heat up the tire, but most of us try to keep up with traffic, and -that- isn't crawling!

Now I'm not sure if this applies to the stock tire, as it ISN'T a winter tire. If you are driving in snow, you shouldn't be using the stock Integrities! A set of good quality winter tires, even with wheels added in, cost less than sliding into something!

If you are driving on sand or thick mud you want lower pressure, as it "traps" the medium -under- the tire, allowing the vehicle to "stay on top". Until the nut behind the wheel panics and floors it.

Last fall I "threw away" the stock Goodyear Integrities and put on Nokian WR tires in the stock size. Yesterday I had a chance to drive on the highway in icy conditions, though this wasn't my intention . When traveling with the wind to my side I thought I had a flat tire. Nope. The highway was icy. Many drivers didn't slow down. Some were sorry they didn't, looping off the road. I arrived at my destination without incident. I also got to drive in an unplowed field (Christmas party in the country) without any problem. The snow was only 5-6" deep, and yes, I did plow a bit, but it's powder so didn't stop me.

 

your best bet for a traction improvement is to get a set of dedicated winter tires and run them at the recommended sidewall pressure. it makes a WORLD of difference over all seasons, in both the getting traction to go AND to STOP!

(dont even get me started on the freak early snowstorm where i got caught with my summer performance tires on my current car (taurus SHO). i had to leave the car and walk.