tire preasure confussion

[coratz]

ok, stock recommended tire preasure is 32 psi front and back. question, for tire longitivity/fuel economy, shouldnt the tire preasure be at max 42 psi??9or higher on some tires) another question, for the best possible grip what should the tire preasure be?

[NovaResource]

PSI stands for Pounds per Square Inch. As you raise the pressure in the tires, you reduce the tire patch area (square inch) since the weight of the car stays constant. For example, the Vibe weighs about 2900 pounds so there is 90.625 square inches of tire contact to the road at 32 psi (2900 pounds / 32 psi). Divide 90.625 by the 4 tires and you get about 22.65 square inches per tire. If you raise the pressure, the contact patch gets smaller: 2900 pounds / 35 psi = 82.85 sq/in of tire contact (about 20.71 sq/in per tire. So by raising the tire pressure by 3psi, you have lost 2 square inches of tire contact per tire.When you raise the pressure, the center of the tread gets worn out quicker. Raising the tire pressure creates less rolling resistance and less heat in the tire (due to less contact to the road) however, it lessens grip.Lowering the pressure can create more grip by creating a larger contact patch however this only works up to a point. Because if the pressure is too low the tire tread can cup and actually pull the center of the tread up off the road. This causes the tire to wear out quicker on the outside of the tread. Also, lowering the pressure raises rolling resistance and heat the tire generates (more tire touching the road). This loweres fuel economy.

[MadBill]

What Scott says is all true, but still doesn't give you a magic pressure number for "best cornering" (which also involves the pressure -dependent internal spring rate, stiffness, response of the tire, etc.) Lots of racers spend lots of time trying to answer this question, and still end up (in NASCAR racing, for example) making minute adjustments at each pit stop. One approach is to hang out at/enter Autocross or similar events and see what you can learn from the competitors. Another (if your tire manufacturer supports amateur racing to any extent) is to ask a tire company rep. A third is to chalk the tread/sidewall area to see how far the tire rolls over, find a nice deserted stretch of road with a good low to medium speed corner and lots of run off room, set the tire pressures say 6 psi above stock for a start and begin pushing your car through the turn faster and faster. When you reach the apparent limit, re-chalk, add 2-3 psi to the end that's sliding (likely the front, in the case of front-drivers like ours) and see if it sticks better. If it does, add 2-3 more and repeat. When you have that end at its best, start on the other and repeat the process. Most "Showroom Stock" road racing cars usually go with somewhere in the 40 psi cold range, plus or minus 10%. Although this approach will eventually give you a good set up, as well as an appreciation for your car's and your own capabilities, it does have a few drawbacks: 1. Grinds off a lot of rubber. 2. Possibilty of car damage when you overcook it. 3. Cops/busybodies may hassle you. 4. Car may ride like it's on mahogany instead of rubber with the resultant pressures.Good Luck!<insert weasel words re non-responsibility for ensuing damage/liability here>

[Chris]

Coratz, you've got the right idea but the wrong car. If you check out the tires an insight or other 'ultra high mileage' type car (honda had a civic that used lean burn tech... forget what it was called), you'll notice they have skinny, higher pressure tires on them to give exactly as you indicate, low rolling resistance and great economy.Our Vibes, however, are designed for a combination of comfort, load carrying and performance so the tires are wider (better handling) and softer (better ride). If you crank pressure in stock vibe tires you'll have terrable traction in wet or icy conditions as the tires are not designed for that. For ultimate dry weather traction (autocross), you're on your own!For the street, keep them at what the manufacture suggests - usually somewhere around 32.

[mu_ohio]

To answer your original question. The manufacturer recommends the optimal pressure for mileage and longevity. If a tire is over inflated, it will wear out faster and under inflated lowers gas mileage and wears the tire out faster as well. The sidewalls themselves are designed for support which does as much for you as the tire pressure.

[noginsk]

Hi all. I was recently reding on http://www.suzukiaerioforum.com and found this topic to be interesting. The post was on page 2, near the bottom by Mr.Bill (no, not MadBill). This is the link to the page http://suzukiaerioforum.com/ae...rt=20This is what he said:"I'm tellin' you guys it's your tire pressure. When I went on a trip to LA I got 372 miles on one tank of fuel. (AWD even) Filled up when I got there, and the car only took 10.4 gallons. But before I left I filled all my tires to 40 psi. (the tires say max is 44) Car rode fine, the steering was more responsive and the car manuvered crisply. I wouldn't be at all suprised if when the EPA tests cars for fuel mileage, they are inflating the tires to their maximum recommend pressures and ignoring the sticker in the door jamb. Besides, aren't those only broad overall suggestions? It's not like Suzuki manufacturers Yokahama tires, and knows what they can take or are rated for. It's like a "legal" sticker. Because you may buy tires that aren't rated as high a pressure as the OEM tires. So they just use the 32 psi as a general rule. If you guys haven't noticed, but when our tires are at 32 psi, the look flat and the sidewall rubs the pavement. I'm a firm beliver that the day of 32 psi is fading along with leaded gasoline. Today's tires are computer generated, they use a more sophistocated wrapping processs and hi-tech materials. They are designed and engineered with newer rubber/composite compounds to give longer wearablilty as well as outstanding over all traction in multiple conditions. It was not long ago when it was unheard of to have a tire that could be used safely in the rain, and still stick to the dry pavement. I'm not saying that the Geolanders are at the forefront of tire technology, it's just that every "NEW" tire that I've bought in the last few years has a way higher maximum rating than 32 psi. Because on tires of old, they say do not exceed 32 psi. So I'm not dreaming this stuff up. I had purchased some cheapy Korean tires (Nankangs) for my other car, they were a 40 series, and even on those the recommended tire pressure was 40 psi. It's like no one wants to make a commitment one way or the other. The tire companys say, "Inflate your tires to the auto manufacturer's recmoomended pressures." and the Auto manufacturers are saying just the opposite. I'm sure it's all legal crap. Because no one wants to be at fault when it comes to an accident when a tire fails. Remember Firestone? Firestone said that the SUV's were prone to flipping over and showing sings that they were not tire friendly. While Ford on the other hand said that their SUV's wouldn't have flipped over if Firestone's tires hadn't blown. Back and forth, back and forth. I'm keeping my tires at 40 psi, and I will continue to reap the benefits of getting a consistant average of 28 mpg with my AWD Automatic!Last edited by Mr.Bill on Fri Mar 28, 2003 8:56 am, edited 1 time in total"I then did a search on genvibe.com to see what people here have to say, and pulled up this thread. http://forums.genvibe.com/zerothread?id=2032In here, novaresource says that raising pressure reduces the contact patch which gives less rolling resistance which equals better fuel economy and that lowering pressure gives more rolling resistance (which says to me it gives better traction) as long as the pressure stays above the tire "cupping" level.In the next post below, MadBill goes on to say that when finding ideal pressure for best cornering, slowly add pressure to the tires that slip until optimal is found. That tells me that adding pressure gives more rolling resistance which is better traction.So, which is it? If I am reading MadBill right, higher pressure = better handling? If I am reading NovaResource right, I see the opposite. Both seem to agree on less rolling resistance equals better fueleconomy. Back to the aerio page, this Mr.Bill uses 40 psi in his tires which can handle a max of 44 and the aerio says to use 32. Both the 44 and the 32 numbers are the same as the vibe. This guy is claiming about 3-4 MPG better by using 40 psi instead of the OEM spec 32. Can that be done in the vibe safely?