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Old 12-17-2010, 05:31 PM   #1
duffkid27
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Default new tires!

i just put ws70's on my car today. what should i run the psi at on the pavement cold, and snow cold. they feel super soft but i geuss thats how they get traction on ice. i have the psi at 40.
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Old 12-17-2010, 07:03 PM   #2
LGT+WRX
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Hit up Luke of Tire Rack, he might have some specific data for you....

Outside of that, it'll be trial-and-error. You don't want to over-inflate, as it will decrease footprint, which will compromise traction on ice and hardpack, as well as through the deepest fresh powder.

In addition to precise vehicle model, you'll want to also let him know of your wheel sizing.

In the mean time, while you're taking a few days/weeks to figure out an optimal pressure for you (I typically do either the "Max - 10%" or start from the recommendations on the door-card, jumping in increments of 2 PSI), here's some interesting reading, too:

http://legacygt.com/forums/showthrea...es-149238.html



Also, FWIW, the dual-compound WS-series Bridgestones often garner that comment: that they just feel more "wiggly" or imprecise. Unfortunately, it's a concession made to that near-wonderous top-layer.
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Old 12-18-2010, 02:06 AM   #3
JTraction
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Everyone on nasioc seems to love high tire pressures. I run my winters and summers both at 36psi.
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Old 12-18-2010, 11:02 AM   #4
LGT+WRX
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^ Agreed. I think that a part of that goes back to subjectivity - that we want to somehow eliminate that "squishy sidewall" feeling, which is something we all hate, on our "summer" sets.

But the problem, of course, is that not only is there typically much more sidewall with our winter sizing, we're also, in doing so, trying to combat something that's simply in the nature/design/construction of these winter tires (that their sidewalls do "give" more, and that, what's more, independent of the sidewall, their tread architecture even contributes to that imprecise and "squishy" feel, and cannot be countered via higher pressures).

What we know now, for certain, is that there can both be too much and too little: sure, that seems obvious, but it wasn't until more recent times that we've actually had hard data to back up these observations.

What we don't have data on, however, is how much does over- or under-filling affect traction: i.e. is there a "greater sin" of the two, and exactly what doing one or the other would compromise (we can make some good assumptions, based on logical extrapolation of the implications of what over- and under-filling should translate to, at the contact patch: but so far, that's assumptions without data).
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Old 12-21-2010, 11:02 AM   #5
Luke@tirerack
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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.
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