Winter driving, do you drop your tire pressure?

[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]

I gave you the answer... it's common knowledge among tire manufactures, automotive mechanics, racing teams, auto enthusiasts...and several car forums. I learned about it a number of years ago, from the Volvo forums...the Swedes know their stuff when it comes to winter driving conditions.

Overinflating is a bad thing, yes...but going with something like 38psi is not overinflation. Lastly, you should follow the recommended pressure range on the tire, not the car's owner manual. Especially when you no longer have the OE-equipped tires on the car.

Siping creates several small grooves, it can supposedly help in any condition but I feel it is somewhat of a gimmick. Why don't tires just come from the OE that way?

Tell you what, get some wide tires and keep pressure low...then let us know when you spin in the snow from taking a turn at a higher rate because you feel that tires work the same in slick conditions as they do in dry conditions.

Btw I'm an engineer for a tire company.

Seems like almost everyone who has commented here has relied on secondary information. They read it on a site somewhere or its "common knowledge." I appreciate that you were posting information in an attempt to answer someones questions but if you don't actually know, or you are referencing some other information you found or saw someone else, at least qualify your response so that people can evaluate it. Even though I'm an engineer I don't assume I know everything there is to know, and when I put out my opinion I make sure its labeled as an opinion.

After posting my comments here, I asked the questions because I was interested to see where everyone is getting their information from. I went digging around the internet and couldn't find much of anything. There really isn't anything anywhere on how winter tires work and why they work. If you do find references to snow driving and tire pressure, go ahead and link them.

Siping is made to trap very small pockets of snow and ice because nothing adheres better to snow and Ice than more snow and Ice. If you question this go make a snowball, and then try to stick it to something else. This goes back to Adhesive vs Mechanical traction.

Rubber has a low heat transfer rate so even though it is in the "freezing snow" the tires are in fact well above the temp of the snow. Tires tend to hold in heat and that is actually one of the biggest considerations in designing tires. Deflection of a tires sidewall is a form of work and creates heat. Tire pressure has a huge effect on tire temperature because if your tires are deflecting more they are doing more work and more heat gets stored in the tire.

The racing car with the narrow tires also has spiked and studded tires. So digging through the snow and getting down to ice and possibly ground is much more effective for them. But we don't have spiked studded tires. If it were a real advantage, we'd all have 4 donut spares on for winter driving.

The 4.7 psi drop is from some engineer getting too picky with the numbers.
The idea is to hold your tires at a constant Volume between Summer and Winter. So basic chem, ideal gas law PV=nRT. To hold the V constant ,n and R are the same so P1/V1=constant and you can set the 2 equal. P1/T1 =P2/T2. Temperature has to be in an absolute temp scale so you have to change degrees Fahrenheit to Rankin. If you are looking at the difference in tire pressure from 10F to 80F. 10F=470R, 80f=520r. P2/35= 470/50. P2=31.6 psi which is a drop of 3.6 psi purely from the temp difference. If you measure from 90F to 0F you get a 4.7 psi drop.

Yes you are right, Tread depth tread width and angle are all important. There are literally thousands of tread designs that give a specific advantage in different situations and are less effective in other circumstances. So to discuss tread design specifics is pretty much impossible. We can just talk in generalities.


And then there are lots of mechanisms that testing is the only way to qualify. Tire design is much less exact and less developed than a lot of other engineering. The amount of testing involved in taking a tire from concept to construction is impressive.

[quote author=jarry link=topic=134349.msg2899638#msg2899638 date=1233286658]
Btw I'm an engineer for a tire company.
[/quote]

Excellent, somebody who ACTUALLY knows what they're talking about here! That's a rare occurrence!

Siping is made to trap very small pockets of snow and ice because nothing adheres better to snow and Ice than more snow and Ice. If you question this go make a snowball, and then try to stick it to something else. This goes back to Adhesive vs Mechanical traction.

Click to expand...

I actually knew that!

The racing car with the narrow tires also has spiked and studded tires. So digging through the snow and getting down to ice and possibly ground is much more effective for them. But we don't have spiked studded tires. If it were a real advantage, we'd all have 4 donut spares on for winter driving.

Click to expand...

I didn't think about digging down to the ice / ground, but I knew the tires were spiked. You win this one. :lol:

The 4.7 psi drop is from some engineer getting too picky with the numbers.
The idea is to hold your tires at a constant Volume between Summer and Winter. So basic chem, ideal gas law PV=nRT. To hold the V constant ,n and R are the same so P1/V1=constant and you can set the 2 equal. P1/T1 =P2/T2. Temperature has to be in an absolute temp scale so you have to change degrees Fahrenheit to Rankin. If you are looking at the difference in tire pressure from 10F to 80F. 10F=470R, 80f=520r. P2/35= 470/50. P2=31.6 psi which is a drop of 3.6 psi purely from the temp difference. If you measure from 90F to 0F you get a 4.7 psi drop.

Click to expand...

Can you translate this for those of us that suck at math? Winter tire pressures up or down?

Thanks for your information though. Now, can you go through the hundreds of "this tire is better than that tire because" threads and straighten them all out? :yap:

TIM

If you are driving off road or on a road with very little traffic you encounter unmolested snow and have to worry more about tire float. But most situations you are driving on a road where someone else went before you and you are encountering a hard packed or iced over section of road. Its this type of road that winter tires are designed to manage. If you are cutting a new path through new snow then you need a different approach and the thin studded tires are right for that. But its better to talk about the general strategies where most of us drive every day and not stress about the rare instances.

You say you live in Sweden? Do you guys do full concrete roads over there? Our roads are HORRIBLE here. I was listening to a story today that said 94% of our roads are asphalt BLAH!!!


Almost everyone in Europe has a summer/winter specific tire and wheel combo for their cars, and in the US its pretty rare that people do (unless they were forced because their MS3 has summer tires). Even in places that absolutely need snow tires people refuse to invest in the extra control and piece of mind. Go buy dedicated snow tires if you are in an area that has a low temp, even if you don't get excessive snow. They offer huge advantages.

The Tire pressure thing is just that, your tire pressure drops when the temperature drops and you have to account for that so check your tire pressure and put it back to the recommended pressure. I even oversimplified the calculation just to demonstrate where it came from. Someone was being a typical engineer and a technical writer was saying "whatever" when they put 4.7 is the exact pressure you need to raise your tires.