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Discussion Starter · #1 ·
Hello, I'll be making a couple of trips to Lake Tahoe. I live in San Francisco so it's not economical to get winter tires. I know by dropping tire pressure a little bit, you will expand the surface area which will make contact with the ground. So how much should I drop?

Stock spec says tire pressure should be at 32psi... I was thinking I'll drop down to 28psi?
 

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I don't drop my psi at all... and I drive in tons of snow. Of course, I run all seasons which may help a bit, but I really don't think its necessary to drop the psi. In fact, a skinnier winter tire will perform better than a wider one. So, keeping the psi up would accomplish the skinnier effect, rather than letting air out and giving the tire a wider footprint.
 

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You're likely to encounter potholes so I'd suggest increasing the pressure to prevent possible rim damage. I'm running winter tires @ 38psi, the softer rubber requires more pressure to keep sufficiently inflated.
 

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when driving through snow its often better to keep your tires a little overinflated anything. as others before me stated it helps prevent rim damage and in snow the less surface area you have the better (more weight per area on tires = better traction in snow). I personally keep my tires at about 4 psi over the recommended amount, so 38 in front and 36 in the rear. The stock tires do ok in small amounts of snow, but anything more than a couple inches i'd be very very careful! Be safe and have fun in tahoe!
 

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There's one problem with dropping pressure, the cold causes the air to become denser, meaning that 32psi turns into 30psi, or maybe 28psi.
 

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Discussion Starter · #7 ·
I'm only asking because the Top Gear guys were advised to do so, of course their condition was far more extreme (North Pole)
 

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Yes you should drop your Tire pressure in the winter. You have a larger tire footprint for and a bit more more traction. Also having more give in the tread of your tire helps to release snow and keep it from building up in your tread. But if you have the summer only tires, I'd say go rent a car for the trip. Don't go below the lowest recommended pressure and don't do any High speed driving (over 90 mph lets say).
 

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[quote author=Werty link=topic=134349.msg2888659#msg2888659 date=1232855334]
I'm running winter tires @ 38psi, the softer rubber requires more pressure to keep sufficiently inflated.
[/quote]
this makes no logical sence. your saying that because the rubber compound is soft you need to raise the pressure? your not running bias ply tires dude. they are radial tires and the compound has 0 bearing on proper pressure.
[quote author=japrussianjew link=topic=134349.msg2888790#msg2888790 date=1232861949]
when driving through snow its often better to keep your tires a little overinflated anything. as others before me stated it helps prevent rim damage and in snow the less surface area you have the better (more weight per area on tires = better traction in snow). I personally keep my tires at about 4 psi over the recommended amount, so 38 in front and 36 in the rear. The stock tires do ok in small amounts of snow, but anything more than a couple inches i'd be very very careful! Be safe and have fun in tahoe!
[/quote]
exactly. this is the same reason why many people up north often "down size" their tires in the winter to slimmer widths. the smaller the foot print "in reason" allows the tire to bite threw the snow and into the gavel/pavement below.
 

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You don't actually bite down to the pavement in snow. You have 2 kinds of tire traction Mechanical and Adhesive. Mechanical traction comes from your tires biting into the snow. as long as your tire treads are reasonably clean this is where most of your snow traction comes from. Its why you have no traction on ice, No bite and no adhesion.
 

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Actually the reason why narrower tires work better is more weight of the car on a smaller patch DOES allow it to bite below the snow. Unless you live on the North Pole... most people I know, drive on roads and are looking to get through the snow/slush on the road and contact the pavement. That is why you see groves of pavement during a snowstorm on well traveled roads. Yes tread helps... but that is not the only thing, narrow tires help too. If wide tires really worked in the snow then you would see WRC cars running huge tires, instead they run skinny tires.

Your ice example isn't applicable... if the tires have studs then they work better once they reach the ice, so you would want the tire to push through the snow.
 

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[quote author=jarry link=topic=134349.msg2892513#msg2892513 date=1233027585]
Yes you should drop your Tire pressure in the winter. You have a larger tire footprint for and a bit more more traction. Also having more give in the tread of your tire helps to release snow and keep it from building up in your tread. But if you have the summer only tires, I'd say go rent a car for the trip. Don't go below the lowest recommended pressure and don't do any High speed driving (over 90 mph lets say).
[/quote]

That is incorrect, a wider tire is much worse...and a larger footprint does not mean more traction. You cut a better and deeper path with a more narrow tire.

I do agree that a rubber compound intended for winter conditions (M&S rated will suffice) is more flexible than a summer tire which gets extremely hard and slick in temps below freezing.

You can get a weekend rental from Hertz for a great deal, usually under $50 for a weekend...ot bad.
 

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FYI, the manual says to add 4psi of extra pressure (yes, I know that nobody reads those, I think the manual actually says 4.7 psi, don't know where they got the .7 from). Your tires will look under inflated at 32psi and will probably squeal at every turn on dry roads.
 

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So your contention is that less tire area on a snowy road is better? Can you get more specific about the mechanics of how that is better? Do you want your drive tires different from your non drive?
 

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Let's start out with this: more air pressure essentially makes the tire taller, and thus more narrow.

Now, a more narrow tire sinks deeper because of it's different proportions of length and width of the contact patch's shape. A narrow tire's contact patch is long and narrow, maximizing steep and minimizing sloping edges. This minimizes flotation and the tire sinks into the hard packed snow underneath where the tread's lugs can get a bite.

A wide (low-profile) tire's contact patch is short and wide, minimizing the steep and maximizing the gently sloping edges. This increases flotation and the tire's tread stays in the loose upper layers of snow.

Basically, you're pushing more snow (resistance) and not getting as much adhesion because the tire can not dig down enough.

All 4 should be the same, regardless of drive wheels...remember, it's more about stopping than accelerating. For RWD, you could get away with tires on the drive wheels as there is weight up front. But FWD you'd be better off with 4 unless you want the rear end to be sliding all over the place.
 

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Just a note that defy's logic. page 8-35 of the '08 mazda3 owners manual says that Overinflating your tire creates a greater possibility of damage from road hazards.


If you want a stiffer tire for driving in snow, why does siping help you get better traction?

With higher pressure your sidewalls are stiffer which doesn't allow your tire to warm up as much while driving.

The tread section of your tire that is generally designed to help you turn are toward the outer part of the tire and having less weight on those because you have more crown on your tire will lessen your ability to take corners.

A stiffer tire is less able to conform to minor bumps, grooves and irregularities making it more likely to have an instant traction loss.

With a lower pressure you have more Tread distortion which helps keep your tires free of ice buildup and snow and your tires get warmer and stay a bit more pliable.

A wide track with wide grooves help you push more snow out of the contact areas. Floating comes from not having enough voids in your tire or having your voids iced up completely.
 

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so you got like half the people saying drop pressure and other saying increase. i took my rx8s 8" wide off and went to a 6.5" wide wheel. kept same pressure at 32psi.
 

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[quote author=jarry link=topic=134349.msg2894505#msg2894505 date=1233101284]
Just a note that defy's logic. page 8-35 of the '08 mazda3 owners manual says that Overinflating your tire creates a greater possibility of damage from road hazards.


If you want a stiffer tire for driving in snow, why does siping help you get better traction?

With higher pressure your sidewalls are stiffer which doesn't allow your tire to warm up as much while driving.

The tread section of your tire that is generally designed to help you turn are toward the outer part of the tire and having less weight on those because you have more crown on your tire will lessen your ability to take corners.

A stiffer tire is less able to conform to minor bumps, grooves and irregularities making it more likely to have an instant traction loss.

With a lower pressure you have more Tread distortion which helps keep your tires free of ice buildup and snow and your tires get warmer and stay a bit more pliable.

A wide track with wide grooves help you push more snow out of the contact areas. Floating comes from not having enough voids in your tire or having your voids iced up completely.
[/quote]

Of course OVERINFLATING a tire is not good... we are not talking about exceeding the tire's recommendation. If you increase the pressure of the tire within the operating range it will not be negative, no crowing or anything, which negates all the stiff tire issues you mention. We are also not saying siping does not help - of course it helps. Again, if a wider tire helped get traction in the snow you would see WRC cars run them.

A tire with wide grooves does not push more snow out, it allows a place for the snow ... otherwise you would see summer and winter tires have similar designs. Winter tires have DEEP groves for the snow to go in and evacuate as the tire roles... in theory, these deep groves allow the tire to go beneath the surface snow and contact a harder substrate... ie pavement.

I'm also a puzzled how a tire with 4-6 less psi would retain heat better... that doesn't make any sense. Once a tire reaches its rolling temp... that is what it is. Having a stiffer tire will not affect its operating temp.
 

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Not to mention snow is, by definition, below freezing. Any heat you get in the tire will quickly be drawn out by the cold temperatures of the environment.

Bottom line, increase your pressures a bit. Two reasons, like was said a narrower tire is better in snow, and second, if you don't your pressures will drop a few PSI as the tires cool.

Now, if you're driving on solid ice its different, you want to drop your PSI a little bit in order to get a larger contact patch.

But the odds of driving on a 100% ice surface are slim to none. Moral of the story, raise the PSI for 99.9% of winter circumstances.
 

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Who believes that WRC teams are driving on the wrong tires in the snow?



Skinny tires = more pressure on the contact patch. If you increase your tire pressures, you decrease your contact patch and apply more pressure to the snow.

TIM
 
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