The science/physics/math/safety behind overinflated tires...

[Brian K]

<div class='quotetop'>QUOTE(akim @ Jun 28 2006, 05:32 PM) [snapback]278235[/snapback]</div>

What are people's thoughts of driving with maximum (e.g. 42 psi) inflated tires in the snow?

I would think that during the winter months, one would want to lower tire pressures to 'Toyota recommended' ranges for better traction in ice and snow. Safety over mpg?
[/b]

We ran or Graspic DS2s this past winter at the same 44/42 we run during the summer on the Integrities. Traction was phenominal, no problems whatsoever. Snow, ice, slush, rain, OK on all. I call it our 2wd 4x4. We have a circular driveway, one part is a gentle climb, the other is for 4wd in the winter, and only if one must. Heck, the Prius made it up that AND under lousy conditions! This in rural Maine- think boonies, bear, deer, moose, our road gets plowed by Darrel if the town is having a good day, that kind of rural.

[theorist]

I believe most would agree that a highly inflated tire will wear less on the shoulders and perhaps wear more in the center than a less inflated tire would.

Often a car's tires wear faster on the shoulders than the center of the tread, due to the car's allignment specifications, out of spec alignment, agressive driving, or lots of cornering). In these cases, which seem common with Prius owners, couldn't higher inflation pressure extend the life of the tire by protecting the shoulders at the expense of the center?

Of course if the tire is so highly inflated that the contact patch shrinks to the point of creating frequent scrubbing from braking and even acceleration as well as turning, such higher pressures could cause more treadwear across the tread. (Perhaps another reason nobody glues tread to flat wheels? :P

[theorist]

While these tirerack articles focus more on comparing underinflation with proper inflation, I found them excellent.


This one includes great photos of the water between a Hydroedge tire and the glass surface it was driven over at different inflation pressures. It also describes the handling characteristics at different pressures from a comparative road test.
http://www.tirerack.com/tires/tirete...e.jsp?techid=3


This one focuses on dry traction and handling at different pressures.
http://www.tirerack.com/tires/tirete...e.jsp?techid=2


This gives an overview of tire pressure effects and mentions that in autocross or competition, drivers use higher pressures for better cornering.
http://www.tirerack.com/tires/tirete...e.jsp?techid=1


This talks more about customizing pressure selection for handling and performance. It recommends increasing inflation 6-10 psi for wet traction.
http://www.tirerack.com/tires/tiretech/tec...e.jsp?techid=58

[Tadashi]

Oh wow. I did not realize it was a cold psi rating. I guess I will turn it up a notch.

Here is a question... Should I rotate my tires since it costs me about $20 each time. Some say it would be cheaper to just buy new tires. Note I do not change them myself. Not a matter of ability unless you count the ability to overcome my laziness.

[DaveinOlyWA]

i rotate my own tires. if done in 20 minutes or less, it can be a nice workout. (5 minutes of that is adjusting tire pressures) jacking up car on back jack point will lift both wheels off the ground

[mcbrunnhilde]

<div class='quotetop'>QUOTE(Tadashi @ Jun 28 2006, 05:45 PM) [snapback]278338[/snapback]</div>

Oh wow. I did not realize it was a cold psi rating. I guess I will turn it up a notch.

Here is a question... Should I rotate my tires since it costs me about $20 each time. Some say it would be cheaper to just buy new tires. Note I do not change them myself. Not a matter of ability unless you count the ability to overcome my laziness.
[/b]

When I got my car, I took it immediately to Discount Tire (America's Tire) and paid $10 per tire for "lifetime" (of the tire) rotation and balance. Every 5,000 miles I do my own oil and get it to Discount for the free rotation/balance. If you get 40,000 out of the tires, that's 7 services for your $40. Probably any tire chain will do the same, even for tires that you don't purchase there. If you don't have Discount/America's try a Goodyear store--the OEMs are their tires, and they should be willing to service them for something like the above fee.

[DaveinOlyWA]

$10 per tire for lifetime of the tire is very very cheap

[mcbrunnhilde]

<div class='quotetop'>QUOTE(DaveinOlyWA @ Jun 28 2006, 07:42 PM) [snapback]278410[/snapback]</div>

$10 per tire for lifetime of the tire is very very cheap
[/b]

I think I've heard that Wal-Mart is even cheaper, but some folks prefer not to darken their doorstep....

[tnthub]

Tire gauges are almost never accurate. Always use the same gauge for your tire inflation pressure. Each gauge will be accurate to itself. I highly suggest a digital gauge with backlit readout that measure in half pound increments. Gauges do not have to be expensive.

I say this because a half pound or pound difference at the drag strip can significantly alter the outcome of a race. The amount of flex in the sidewall can make the difference between a tire hooking up and spinning. It also alters the reaction time of the vehicle. In a front tire the slightest change in diameter alters the "rollout" at the starting line also changing the reaction time of the driver and vehicle.

After eight years of racing I have tried all types of tire gauges and so have many of my fellow competitors. Sooner or later we all misplace a gauge and borrow one to get through the day. Each time the actual tire pressures were checked by different gauges the results would differ by as much as two pounds. However, the difference in pressures was measured by each gauge as the same in relation to the original reading.

In other words, if one gauge read 14.5 pounds cold and another read 15.5 pounds cold, when hot the 14.5 pound cold reading went to 15.5 pounds and the 15.5 pound cold reading went to 16.5 pounds.

Always use the same gauge. just because two gauges of the same make and model are used does not mean the results are the same. If the measurement basis is not accurate each time, then putting 40 pounds of air in one month and going to 42 pounds of air the next month may actually be incorrectly based on a gauge that reads two pounds low...

[Wildkow]

<div class='quotetop'>QUOTE(Brian K @ Jun 28 2006, 04:59 PM) [snapback]278308[/snapback]</div>

We ran or Graspic DS2s this past winter at the same 44/20 we run during the summer on the Integrities.
[/b]

Brian K is that a typo?