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  1. #1
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    Higher or Lower Tire Pressure for Icy Roads?

    So, if you want better traction for dirt or rock, you lower your pressure. But what about snow/ice? Supposedly the reason that narrower tires are better for winter is that they are better able to penetrate through snow and make contact with the pavement underneath...making me think higher pressure would be better because it reduces the size of the footprint. What say you?

  2. #2
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    Which are you worried about snow or ice? That's the problem.
    It's not so much the model year, it's the high mileage or meterage to keep the youth of Canada happy

  3. #3
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    Pure speculation, but i'd say lower. Lower tire pressures will create a less rigid tire that will conform better to the oddities in the road. It seems to me, and let's be clear, I'm talking straight out of my ass with a little bit of intuition guiding me-- that a harder tire would be more likely to stay on top of the ice and not grip, kinda like a smooth ball over a surface rolled down a hill, versus say 3/4s inflated basketball thrown down a hill.

    I don't know, but I think the answer is lower pressure.

    You also have to account for the fact that in cold weather, the pressure of the tire will reduce a bit, due to the way gases work, fwiw, so you may not need to adjust at all, it may occur on its own and return to higher pressure in the summer
    Do I detect a lot of anger flowing around this place? Kind of like a pubescent volatility, some angst, a lot of I'm-sixteen-and-angry-at-my-father syndrome?

    fuck that noise.

    gmen.

  4. #4
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    I would leave the pressure alone for normal drivivng ,I might try lowering it if I got stuck or something

  5. #5
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    The answer is to park the van near the middle school BEFORE it gets snowy or icy.
    "Vagenius"

  6. #6
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    Yeah, but I need to be able to make a quick getaway if the cops show up. Don't want to spin out and have 8-year-olds flying all over the place.

  7. #7
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    Lower pressure. Anecdotally, my blizzaks do a heckuva lot better @ 28psi than 38 psi, snow or ice. It's easy enough to play around with. "Cutting" through the snow being affected by tire pressure has a lot to do w/ the structure and stiffness of the tire itself. Realistically I can't imagine that aspect being material.

    Talking purely out of my ass, it'll allow some "give", softening the margin between sticking and sliding - same rationale as a higher sidewall.
    focus.

  8. #8
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    but what if the car's on a snowy / icy treadmill?

  9. #9
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    The treadmill still won't spin unless the car's able to get enough traction to move forwards.
    focus.

  10. #10
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    Lower pressure = softer rubber. More psi is like running around an ice rink with your ski boots on.

  11. #11
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    Quote Originally Posted by tenB View Post
    Lower pressure = softer rubber. More psi is like running around an ice rink with your ski boots on.
    good analogy. I think the confusion is over wide vs narrow tires. You want a narrow footprint so the snow does not suspend you over the harder driving surface underneath (hardpack or pavement) and spin. You still want a soft tread and a conformable tire carcass, hence the lower pressure.

    Guys that go jeeping in powder snow need fat, balloon like tires so they don't sink down and get high centered, but most drivers will be better off with a narrower profile tire for on road usage. My summer tires for my 4runner are somewhat wider than the studded snows for offroad and sand driving.

  12. #12
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    ^^^^What he said, adding that you can get a "smaller" footprint with a wider tire. Models tend to use gumball tires like Nascar, no tread. Thus assume all equal dimension tires have the same amount of actual rubber inside the patch, so friction-area. Nope. An open tread pattern will have less actual rubber area than a dry road pattern with tiny grooves, even at the same tire dimensions and contact patch outline. And the rubber will squirm around more. So on the road performance is often more about tread design and rubber compounds than patch size per se.

    As far as inflation, footprint/contact patch area is simply car weight/tire pressure. Wider tires have a different shape patch, not more. Some evidence that as inflation drops, wider tires' patches grow faster than narrower tires.

    But here's what I can't quite figure: Underinflating tires will make the patch grow, yet the argument for narrow tires is a smaller patch to concentrate weight. Same as overinflating.

    Anway, far as I can see from here in the northeast, everybody goes for open tread patterns, keeps pressure on the low side. No chains, and few specialty tires. Concentrating weight with narrow tires could be useful if you can actually can reach the road surface (meaning you're talking about typical road snow/slush like you get out west). But if the ice is hard, as it tends to be back here, all the weight will do it melt its surface better (reason a hockey blade glides). You might want more area for less pressure, more friction. Open to correction here...

    Up north, they drive screws through the tire from the inside, slap in some goop to seal them, and go hit the frozen lakes. At least, back when we had frozen lakes...if you've got some short screws and sealant, go for it.

  13. #13
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    Quote Originally Posted by Beyond View Post
    As far as inflation, footprint/contact patch area is simply car weight/tire pressure. Wider tires have a different shape patch, not more. Some evidence that as inflation drops, wider tires' patches grow faster than narrower tires.
    That seems like its assuming that tires have little to no structural rigidity, which is wrong.

  14. #14
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    My intuition would agree with what most people are saying, lower tire pressure will help your tire conform more to the road and get more traction...theoretically. To be honest, I wouldn't go messing with it because the lower pressure will reduce your gas mileage and increase wear on the tires. You're correct about a skinnier tire handling better in snow, but putting extra pressure in you tires probably won't decrease the footprint enough to make a difference.

  15. #15
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    Quote Originally Posted by toast2266 View Post
    That seems like its assuming that tires have little to no structural rigidity, which is wrong.
    Not clear what your "that" refers to, but if you mean the thing about wider tires getting a bigger patch as they deflate, looked at blog with data from Avon, testing their own tires.

    If you mean area=weight/inflation, standard formula throughout the industry, just go Google.

    If you mean shape change with width, that's also standard finding, comes from constant relation of area to weight and inflation. So if you keep weight and inflation constant, area can change shape, but not total size.

    I think the lack of concern with rigidity has to do with its net mathematical contribution compared to vehicle weight or inflation. Also I sense that there's more standardization of rigidity since design went to radial tubeless with wider stances and lower profiles. The sidewall doesn't support the tire anymore. Can't say if that holds for serious truck tires, as in 18 wheelers or earth movers. Talking about tires you can go buy retail as a consumer.

    But agree that there are other variables like cross-sectional shape of the tire, rigidity, rubber formula as it affects friction, etc. Earlier in my post I mentioned how the tread design will depart from model parameters. But far as I can tell, there's a whole cottage industry out there arguing over small effects; Everyone seems to more or less agree that the biggest impact is just weight, inflation.

  16. #16
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    Now the point of snow tire siping is to hold snow in the tread, because snow on snow has more grip than rubber on snow.

    so, lower pressure=larger contact patch=more snow in tread=more grip.
    The whole human race is de evolving; it is due to birth control, smart people use birth control, and stupid people keep pooping out more stupid babies.

  17. #17
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    For normal driving, I'd leave them alone, personally. By the time you change pressure enough to matter, you're getting to ridiculous levels, in both directions.

    The whole "higher pressure is better" thing makes some sense for RAIN, deep water, crowning the tread surface to let it "cut" through is plausible; roadracers (automotive) often talk about this for rainy events, as it resists hydroplaning. I've got some experience with race/rain tires, and honestly, I leave pressure alone. I don't have ENOUGH experience to say for sure (I have tried more pressure in the wet). Seems to me that higher pressure in the wet IS beneficial for puddles/really deep spots, but you give up so much more on the simply wet (but not deep) sections, it is a wash. Keeping them at normal pressures seems to work better - puddles are sketchy no matter what, adjust pressure for the areas you might have SOME grip, go faster.

    Thing is, by the time you add enough to really crown the tread, you're adding a LOT of air, and traction will suffer on packed snow that you're not "cutting through" no matter what PSI.

    Lowering pressure does have some benefits - many years ago, I went to an ice "race" put on by a Jeep club. In the morning, there was bumpy ice and blown in snow (on a lake). There was grip to be had, did Just Fine in my Audi.

    By the afternoon, the surface was polished smooth. I've never seen anything like it. I could put my car in 4th gear and sidestep the clutch at idle, it would just clunk and sit there, some of the tires spinning. Ridiculous.

    The "fast" people were airing down - and it WORKED - but I'm talking 6-10psi. Tires looked flat; enough air to keep the tire beaded, to keep the rim from bouncing off the ground (no bumps, naturally), it really did seem to work (I did not air down, I no longer did Just Fine....). There were lots of Jeeps there, naturally, but a fair number of normal cars, and those who aired waaaay down certainly had a distinct (huge) advantage - but unrealistic for street driving.

    I ran studded Cooper snows on my van (2wd) for years. Towed snowmobiles with it. First few sets were 245/70-16s, IIRC, last set were 215/85-16 - same OD as the 245s, but narrower. Narrower is better, right?

    Nope. The 245s were better on packed snow; FS roads and whatnot. I did not notice the 215s being BETTER anywhere else than the 245s, and I certainly noticed them being WORSE on snowpacked roads - plowed roads, normal roads, no big deal, about the same, but roads that got packed by traffic before the plows got there, the 215s just did not have the traction.

    I'd go a little narrower than stock - 245 section width is the narrow end of normal for a 7800# one ton van - but I'm not going to overdo it again. I never adjusted pressures in the van, ran 65psi front, 80psi rear (load range E truck tires), shrug, it worked, but the 245s worked better than 215s.

    Lowering pressure absolutely works in soft surfaces (sand, snow) and slippery surfaces. Run them at the lower end of recommended, that's ABOUT as good as it gets. To get DRAMATICALLY better, you have to let a LOT of air out, IME; an unrealistic amount for anything close to normal driving.

    Now, if it is a blizzard and nasty and you absolutely have to get there, sure, it is a good trick to have in the bag, but good tires gets you 97% of the traction; getting the last 3% through pressure changes is possible, but taking 5psi out is not going to make or break anything.

    IMHO, YMMV, etc. I'm a tire nerd.



    Iain

  18. #18
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    From TireRack.com:


    Higher Tire Pressures for Winter Driving

    Lea esta página en español

    Several vehicle manufacturer's owner's manuals recommend operating winter tires several psi (typically 3-5) higher than their recommended pressures for summer and all-season tires. While none of them actually provide the reason why, there are several scenarios that would support the practice.

    First and foremost is that winter tires feature more aggressive tread designs, softer tread compounds and are often molded with deeper beginning tread depths than summer or all-season tires. While the combination of these design elements allows winter tires to remain more pliable in sub-freezing temperatures to provide more traction in snow and on ice, it often results in tires that have somewhat reduced responsiveness to driver input. The 3-5 psi higher recommended inflation pressures increase tire stability and help offset the reduction in responsiveness.

    Additionally ambient air temperatures in winter typically range 40- to 50-degrees Fahrenheit colder than typical summer temperatures for the same location. The lower ambient temperatures allow tires to be more efficient at radiating heat and the tires will run cooler, building up less hot tire pressure. In this case, the 3-5 psi higher recommended inflation pressure increase helps offset the reduced hot tire pressures resulting from less heat buildup.

    And finally, all tire pressures are intended to be measured cold, which means when the tires are at the same temperature as the air outside. Unfortunately, unless you park your vehicle outside or in an unheated, detached garage, and measure its tire pressures first thing on dark, cold mornings, the influence of attached garages or higher ambient air temperatures later in the day often means that drivers are actually measuring tires that are not completely cold. In this case the 3-5 psi higher recommended inflation pressure increase helps offset the reduced tire pressures associated with the conditions in which the tire pressures are typically measured.


    I don't know whether this helps.
    IMHO, Tire pressure is tire pressure. It is the tread, and the weight on the tires that will give you better traction
    "My policies are based not on some economics theory, but on things I and millions like me were brought up with: an honest day's work for an honest day's pay; live within your means; put by a nest egg for a rainy day; pay your bills on time; support the police." M. Thatcher (RIP)
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    Judges smoke it, even the lawyer too...So you've got to legalize it..." Peter Tosh

  19. #19
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    Quote Originally Posted by schindlerpiste View Post
    I don't know whether this helps.
    Given that it's a two and a half year old thread that Mannix decided to reply to, probably not...But good info lives on, I guess.

  20. #20
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    Whoops! Thanks
    "My policies are based not on some economics theory, but on things I and millions like me were brought up with: an honest day's work for an honest day's pay; live within your means; put by a nest egg for a rainy day; pay your bills on time; support the police." M. Thatcher (RIP)
    "...
    Judges smoke it, even the lawyer too...So you've got to legalize it..." Peter Tosh

  21. #21
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    oops.

    Was searching for info on Conformable liners, saw that, shrug....


    Iain

  22. #22
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    wtf is with all the old thread bumps of people answering 2 or 3 year old questions?
    No longer stuck.

  23. #23
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    All y'all haven't tried 29ers??

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