"Inflate snow tires 4 psi more than recommended tire pressure"

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[Linked Image] While looking up lug nut torque spec in a 2016 Mazda 3 today, I noticed the owner's manual says inflate snow tires 4 psi more than the recommended tire pressure. Anybody know why?

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I see what you mean. I am going to read it the way I want, instead of the way it's written. And this is how I am going to read it. DO NOT: *Go faster than 120km/h(75mph) while driving with snow tires. OR *Inflate snow tires more than 4psi more than the recommended tire pressure label, etc. That's how I read it. However, I think that it is bad advise the way they've written it and it has slipped through the editors and certainly needs an addendum to that page in the owner's manual. Our resident tire guru(s) may chime in with information that I am completely unaware of.
 
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Over the years there's been lots of problems with language translations. I just bought some folding lawn chairs and one of the 'warning tags' starts with "Do not standing on chair"...
 
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I think it is because the snows generate more friction with the road surface and generate more heat. I have seen that printed in several manuals going back many years.
 
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I think the reason why they wrote that is 2 fold: 1) A smaller footprint is more likely to penetrate the snow and get the tire in contact with the pavement - which always has more grip. 2) Because people don't like to adjust their tire pressures when it's really cold out there, this 4 psi more covers 40°F temperature drop - the tire will never be under inflated.
 
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The tread compound used for snow tires is really soft so perhaps they've found that an additional 4 psi will compensate for thing such as heat and turning response.
 
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Mazda unqualified statement is confusing and generally incorrect. Or just plain wrong on the 4psi over placard. Ne'er on any car Ive owned over 50 years have snowtires provided good traction inflated over placard. Never. In fact it was dangerous. Since it doesnt usually dive below 10F often where I am in the early AM. I try to run snows at about 3 psig under placard Cold (measured typically at 18deg F.) That ends up around 28 - 29 psig . These have been either 70 series or 65 on minus 2 steel rims fitment. I would never venture out and drive below -20F. I could see in cold parts of Canada that if inflated at STP ( say, a garage) you would want the tires over placard due to the 1psig/10deg drop. Then the tires would be 4 UNDER placard This show the inadequacy of not specifying the ambient temp for a cold fill, and the assumption of STP conditions. A chart is really needed here. Now here is a instance where it would be good NOT to read the O.M. smile
 
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Only logical reason I could think of is-snow tires tend to have thicker, squirming tread, which a little more PSI can help negate? Otherwise it makes no sense to me!
 
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I don't see ambiguity in the way it's written. It plainly says the door sticker applies to summer/all season tires and not to snow tires. Pretty simple advice if you ask me. Now, as to why, that's open to debate.
 
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hyundai owners manuals said the same thing for years. On a car that recommends 30 or 32psi, 34 or 36 is still fine IMO now on my jeep that spec 36, no way I would put 40psi in the blizzacks.
 

Pew

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Originally Posted by ARCOgraphite
Ne'er on any car Ive owned over 50 years have snowtires provided good traction inflated over placard. Never. In fact it was dangerous.
In my experience snow tires don't grip properly when underinflated on a passenger car. It becomes very noticeable in deep(er) snow or very patchy spots where the car starts to wander towards corners that aren't properly inflated.
 
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An underinflated squished tread closes the knobs of the tire and it doesn't bite or cleanout the same. And yes thinner tires work better in snow than wide ones.. To the "Follow the manual" nanny types that disagree with the spec i would ask ...so you think you know more than the engineers? This verbiage they have thrown on occasion.
 
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The only circumstance I lower tire pressure is off road, where lower pressures increase traction immensely. I do treat deep snow like deep mud in regard to tire pressure however, running about 3 PSI in my Mickey Thompson Claws. On the street, I maintain my daily drivers at the recommended placard pressures. I mounted Vitour Iceline snows on my daughter's 200 and they work wonderfully at the recommend pressure.
 

snow_shovel

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Originally Posted by Ded Mazai
Why didn't you question the first sentence that you cannot go faster than 120 km/h? Does it make more sense than the pressure staff?
Slow down for safety I guess?
Originally Posted by ARCOgraphite
Mazda unqualified statement is confusing and generally incorrect. Or just plain wrong on the 4psi over placard. Ne'er on any car Ive owned over 50 years have snowtires provided good traction inflated over placard. Never. In fact it was dangerous. Since it doesnt usually dive below 10F often where I am in the early AM. I try to run snows at about 3 psig under placard Cold (measured typically at 18deg F.) That ends up around 28 - 29 psig . These have been either 70 series or 65 on minus 2 steel rims fitment. I would never venture out and drive below -20F. I could see in cold parts of Canada that if inflated at STP ( say, a garage) you would want the tires over placard due to the 1psig/10deg drop. Then the tires would be 4 UNDER placard This show the inadequacy of not specifying the ambient temp for a cold fill, and the assumption of STP conditions. A chart is really needed here. Now here is a instance where it would be good NOT to read the O.M. smile
Where I live we get -40F before windchill hide
 
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I run 40-42 PSI cold inflated year round on my A/S Tires. It does snow where I live, I Just drive normally. I also replace my tires when it starts to go down below 4/32nds.
 
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Originally Posted by Kawiguy454
An underinflated squished tread closes the knobs of the tire and it doesn't bite or cleanout the same. And yes thinner tires work better in snow than wide ones.. To the "Follow the manual" nanny types that disagree with the spec i would ask ...so you think you know more than the engineers? This verbiage they have thrown on occasion.
The issue is at what temp is COLD for the cold inflation check. 60F? If its 90F out and they read 4 psig over placard - Ill leave that for Winter Alternative ly If I check andt set my cold inflation at 20 degF and set it at 28psig. That Tire would read 32 Psig at 60 deg cold. and maybe 35 or 36 after my commute. So is 28psig at 20F Under Inflated? If No Ambient spec is given for recommended inflation pressure that means close to NOTHING** ** I say close to nothing as I assume COLD is at Imperial Standard Temperature and Pressure. ( 60F 1 ATM)
 
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Weather does have its seasons... if you only check your pressures once or twice a wear, ie when you put your snows on and the 3-season tires... it's not enough. Because weather fluctuates from season to season and including in between seasons, the more you check the tire pressure, the cold is based on the ambient temperature for that interval you check it...but, let's say you check the pressure in the afternoon, and set the cold temperature to say... for a mildish winter, 40 degrees, will if your average overnight lows are 20, you'll be approx. 2 psi lower than the recommended cold pressure in the morning, which probably won't kill you. Let's say you do it monthly, there is enough data to gather what the average low temperature will be, which you set the cold temperature to, and you change it every month during the winter.
 
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