I live in New York, where winters can be brutal at times. Because of this, I plan on keeping my tires at 37psi front, 35psi rear. My personal advice is that high tire pressures and snow and ice are not a good combination. I may boost pressures in the warmer months, but I will not run high pressures in the winter due to traction considerations.

Harry

PS: I am getting 50 mpg highway mileage on a brand-new Prius, and averaging 47+ mpg overall.

 

hummm... I find that extremely surprising.

In my experience in extreme cold climates (involving slush, snow and ice), the tire traction decreases with a decrease in tire pressure. Again, that is not very safe (according to the Department of Transportation) for motorists in the northern climates.

In my vehicles the minimum pressure I choose is max sidewall-4psi. Anything less makes traction noticeably reduced in deeper snow. In icy surfaces having somewhat less pressure does help a little but in our 5 month long winters it does not help enough to offset the advantages of a properly inflated tire.

As far as I know, the only other time when low tire pressure is beneficial is when off-roading... particularly when negotiating rocky inclines - Obvioulsy not with our Prius .

Cheers;

MSantos

 

First, notice that I am running tire pressures above what is recommended, not below, so I am not running low tire pressures.

Some Googling comes up with various tidbits:

"RAY: But there are no circumstances when overinflating the tires will help you get more traction. Overinflating leads to a narrower tread patch, less friction and less traction ­ which is why it's associated with slightly higher fuel economy."

from here http://content.hamptonroads.com/stor...778&ran=144851

At the same time, it is unwise to reduce tire pressure for snow and ice:

from here:http://www.gm.com/company/gmability/.../you/tips.html

more:

"An executive of Drivers.com recently bought four used tires from a dealer and was told to keep the pressure four psi (pounds per square inch) higher in winter than in summer. Not so."

from here: http://www.drivers.com/article/354/

My point is that traction is critical in northern climates on snow and ice. You can't run tires too low or too high. Inflation needs to be reasonably close to what the vehicle manufacturer recommends. I am getting excellent fuel economy running my Prius tires at 2 psi above recommended pressures. I won't run them any higher than that in the winter due to concerns over traction and safety.

Harry

 

Checking further, I notice the max pressure on my Prius OEM Goodyear Integrity tires is 44 psi.

I found a web site that suggests (max pressure - 10 %) as a good tire pressure to try.

"What's the "correct" tyre pressure?
How long is a piece of string?
Seriously though, you'll be more likely to get a sensible answer to the length of a piece of string than you will to the question of tyres pressures. Lets just say a good starting point is the pressure indicated in the owner's manual, or the sticker inside the driver's side door pillar.I say 'starting point' because on every car I've owned, I've ended up deviating from those figures for one reason or another. On my Subaru Impreza, as outlined above, I got much better gas mileage and no difference in tyre wear by increasing my pressures to 40psi. On my Honda Element, I cured the vague handling and outer-tyre-edge wear by increasing the pressures from the manufacturer-recommended 32/34psi front and rear respectively, to 37psi all round. On my Audi Coupe I cured some squirrelly braking problems by increasing the pressure at the front from 32psi to 36psi. On my really old VW Golf, I cured bad fuel economy and vague steering by increasing the pressures all-round to 33psi.
So what can you, dear reader, learn from my anecdotes? Not much really. It's pub-science. Ask ten Subaru Impreza owners what they run their tyres at and you'll get ten different answers. It depends on how they drive, what size wheels they have, what type of tyres they have, the required comfort vs. handling levels and so on and so forth. That's why I said the sticker in the door pillar is a good starting point. It's really up to you to search the internet and ask around for information specific to your car.

The Max. Pressure -10% theory.
Every tyre has a maximum inflation pressure stamped on the side somewhere. This is the maximum pressure the tyre can safely achieve under load. It is not the pressure you should inflate them to.
Having said this, I've given up using the door pillar sticker as my starting point and instead use the max.pressure-10% theory. According to the wags on many internet forums you can get the best performance by inflating them to 10% less than their recommended maximum pressure (the tyres, not the wags - they already haves inflated egos). It's a vague rule of thumb, and given that every car is different in weight and handling, it's a bit of a sledgehammer approach. But from my experience it does seem to provide a better starting point for adjusting tyre pressures. So to go back to my Subaru Impreza example, the maximum pressure on my Yokohama tyres is 44psi. 10% of that is 4.4, so 44-4.4=39.6psi which is about where I ended up. On my Element, the maximum pressure is 40psi so the 10% rule started me out at 36psi. I added one more to see what happened and it got better. Going up to 38psi and it definitely went off the boil, so for my vehicle and my driving style, 37psi on the Element was the sweet spot.

from here: http://www.carbibles.com/tyre_bible.html

I may wind up going to 40 psi front, 38 psi rear. For now I think I'll stick with 37 psi front, 35 psi rear.

Harry

 

I think we're all pretty much in agreement that proper tire traction in winter is not helped by low pressures. In fact, I firmly believe in tire pressures that approach (but not meet or exceed) the max sidewall pressure listed on the tire.

The only negative about high tire pressues that we should be aware of is accellerated suspension wear. This may affect shocks, springs, control arms and joints. Other than that we may get a noticeably harsher ride which is something for each of us to decide on what pressure value is more bearable.

Cheers;

MSantos

 

We just had our first deep freeze (10 degrees) with a very light snow that made the roads a sheet of ice. The Anti lock brakes worked fine and the vehicle stability control light was constantly flashing. But it did not fishtail or spin around like the pickup that was behind me did. But it does slide more easily than our maxima. (Gee, could be the extra ton or so of weight the maxima has)
The biggest problem was an idiot slammed on her brakes ahead of me ( I am glad I gave her a lot of room) with a long line behind us including the pickup truck on my tail end the whole way.
She slams to a stop to allow cars from a store on the right and road on the left to pull out. Our road is a state route with no stops. She decided to stop and almost cause a big pileup. All because she had to try and be nice and let people out on a major road.
I had given her a lot of room (I knew I could stop easily behind her) but, the truck behind me was sliding fast towards me. I looked into the other lane and saw it was clear so as I slammed on the brakes The vehicle stablility control light went crazy, the anti lock brakes went crazy (Both worked great) and I controlled the skid into the other lane until I was away from where the truck was sliding to where I used to be. With one exception. All the heating fans etc. shut down during the slamming of the brakes.
In other words all the safety systems worked great. But it does tend to slide quite a bit upon starting and you can feel the back end get loose.
I also learned you need to really baby this thing in the cold the first few miles because it sounds like crap getting up to speed.
I am more concerned about the very low ground clearance up front when we get our major snows. I think if we get over 7 inches that front bumber is coming right off.
Also can anyone answer this. at 10 degrees the tire inflation light comes on. Then when it warms to 30 degrees the light goes off. The pressure is right in the middle of the range when I check it.
Also would filling the tires with nitrogen help keep the pressure more stable in the up and down weather we have.

 

Hi,
WOW!!!

I'm wide awake now!

I can't help you about the tires and nitrogen but I'm impressed by your "close call." Good presence of mind!!

Bob Wilson

 

I had an interesting experience this morning. It was snowing lightly and there was a good coating (1" or so) on the roads. But I set off on my usual route to work anyway, it being the first snow of the year and hence forgetting about the consequences of such things.

I was going up the large hill between home and the main road to work, and I began to notice that I was going slower and slower. In the Prius, when you push the gas pedal and the tires are slipping, the engine doesn't race like a conventional car, so I didn't have that verbal cue as to what was going on. Soon I noticed that I was flooring it, and was still going only 5 mph and getting slower. Then I stopped. I was sitting there, on an uphill, flooring the accelerator, and going nowhere.

I let the truck following me pass, and then put it in reverse and backed up about 10 feet. Then I tried again. The whole experience was weird, without the sound of the engine racing or the sound of the tires spinning (I heard neither). But the Prius started going very slow, the VSC was kicking in, and no matter what I did with the steering wheel it kept correcting to get me going straight. And no matter what I did with the gas pedal it kept providing just enough of whatever to keep me going slowly forward. I got to the top of the hill this way, and started down. Whenever I began to slide, the VSC kicked in and kept me going straight (I was going very slowly down, on purpose).

I am very impressed with the way this car handles snow and ice. It is my first non-4WD in 15 years, and I am not at all trepidatious about driving it in moderately nasty conditions. I feel like as long as I keep it slow (and use common sense, and my 4WD Hybrid Escape, when it gets REALLY bad), I'll be OK.

My Prius (maybe I should call it Fawkes, now that it has been reborn from the ashes - but that's my other post) seriously rocks! I don't think I will even consider any other car for a LONG time.

(oh, and my mileage figure for the Prius, see below, is not at all accurate - I averaged about 52 mpg in the summer, but stopped posting my tanks months ago for other reasons! now that it's cold again I'm back to about 48-49. The Ford is pretty accurate, it was created over an entire year.)

 

Now that's quite an experience you had driving uphill and not making it! It's something good to know/watch out for/be prepared for.

The day after I posted this thread we had a couple inches of snow (Chicago and North of Chicago got the brunt of the storm) and our steep driveway hadn't been plowed when I had to take my son to school. I was concerned about making it back up the drive into the garage....NOT TO WORRY! The car drove right up with not as much as a spin of a tire. It handled wonderfully on the roads too. I was definitely impressed. My last car would never have made it up the drive. I am so lovin' this car. Our driveways are so steep that when one of our neighbors parked his car on his icy drive it slid down out into the middle of the street! I think my Prius is going to be great. I'm also impressed at how the engine slows down when you remove your foot from the gas. Very little braking is required. I also used my engine brake to slow to a stop light without having to hit the brakes and I liked it. It worked great. It's like downshifting to 1st gear in a manual transmission.

Anyway, thanks for your input. Great story and information that's good to have.

 

GEEZ! I always say that it's the OTHER PEOPLE who don't know how to drive in the winter that you have to watch out for! They're crazy.

On my way to taking my son to school yesterday I pulled up to a stop light only to witness 2 cars colliding and one of them spinning out on the slick road. It was BITTER COLD here and we had had a light dusting of snow the night before and the roads were a sheet of ice. Since that happened on my route to school I had to turn around and take a different route. As I pulled up to another stop light I witnessed ANOTHER accident! An SUV rear-ended a car at the stop light. Within 5 minutes, I witnessed 2 accidents because of slick roads. I always worry about being rear-ended by someone who doesn't know how to drive on winter roads.