Hi all,

So I noticed this morning after not checking tire pressure for a few months that it was all the way down to 33/31! I had been running 42/40, but of course during the last few months the temperature around here dropped about 50 degrees, and due to that pesky ideal gas law , there was a corresponding drop in tire pressure.

My question is, is it still safe to reinflate to somewhere between 40/38 and 44/42 during the winter? What effect does it have on traction? Is there a larger tire temperature (and thus resulting pressure) range in winter driving that would make this unsafe?

Looking to reclaim a few lost winter MPG ,
_Jerad

I plan on running 50lbs in my civic this winter (I checked mine this morning and had similar results to what you posted) My thinking is that the narrower a tire the less likely it is to hydroplane and to slide on snow. I'd think underinflating them would be much worse than over inflating. I don't know for sure though. When I end up wrecking my car I'll be sure to post to warn others of over inflating

My hydroponics experiment

You ever notice how hard it is to lip read cartoon characters?
"Crazy is what the sane call Delta Flyer"

lol. let's hope you don't end up as a poster child for what-not-to-do.

So are you saying I'm wrong? I realy don't know. To mee it seems less surface area of tire means deeper penetration in the snow. Oh well. Its not like I have great traction with the sp20s now anyway

My hydroponics experiment

You ever notice how hard it is to lip read cartoon characters?
"Crazy is what the sane call Delta Flyer"

Snow traction actually happens more on the edge of the tire (if you examine the all-season tires they have 'notches' on the edge, summer tires don't) so over-inflation may not help in terms of gripping loose snow, but hydroplaning is absolutely correct. I had super-skinny tires on my old Colt and it could go through any puddle (or sometimes road-lake) at any speed without hydroplaning, but now on my Colt I got wide tires (wider than stock) and it hydroplanes on most puddles, but snow grip is excellent.

2001 Prius Photos       2005 Prius Photos
1992 Mitsubishi Delica Diesel-WVO Hybrid Photos

Not exact science, but:

"As temps drop, so does the pressure in the tires, as much as 1 pound-per-square-inch (psi) for every 10 degree drop in temperatures."

http://www.safetycenter.cmsu.edu/winter_tips.html

But 1 psi for every 10 degree drop doesn't seem like much? Aren't members on this forum posting a greater drop than that?

<Best Tank Economy!><Best Tank Endurance!>

As an avid 4x4 competitor. I can tell you that low press is more traction and vice-versa. A 50psi tire is going to slide around a lot more that a 32. I run 12 psi off-road and 32 on road for the lifted bronco. I need all the traction I can get. Foot print of the tire is decided by the pressure. If you want traction go low, FE go hi. It is an individual choice that each drive must make. Braking distance is also reduced by the higher pressure because the foot print of the tire is reduced and the ABS must reduced the stopping force that it can apply before tire skidding occurs. Do a web search about tire press and tire foot print to see actual results. You will be supprise. I don't think I will go over 36 on the Prius. My Wife has rear-end 2 cars in 8 years. (and no she wasn't drafting) I think the lower psi foot print ABS factor is more important for her than the FE gain with 40+ psi.

Prius 06 Black Pack#2

--

I'll give you that things might be very different for little car tires and my truck tires that are over 35" tall. I accept your polite corrections and will search the forum for the tire press threads you mentioned.

Prius 06 Black Pack#2

My little experiment with PSI shows that you are only saving a tiny tiny percentage of gas per mile. I ran my car at max PSI for an entire month and only noticed on a couple of tanks that I got 10 miles more than running at +5psi all around. While FE didn't increase dramatically as expected, handling did... but at a price. It's a harsher ride, but I can take corners much faster.