Tire Pressure

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Jul 14, 2005
My van has tires that can hold a max PSI of 44lbs. The door recommends 35psi when cold. I basically do a compromise betweent the two and keep them inflated at 38 or 39psi when cold. Is this acceptable, safe? Will it prolong the tread life as well if I keep them a bit above what the door jam recommends?
It's a trade-off of handling, comfort, fuel economy, tire wear, load capacity, and maybe even suspension component life. If it's still comfortable at higher pressures and the tires still wear normally, you'll have the benefit of better handling and fuel economy. It's definitely safe; higher pressure gives it more load capacity.
The severity of impacts on front-end and suspension components will increase with higher tire pressure. But I think it's unlikely that an extra 3 or 4 psi will have a noticeable effect on the life of your parts.
i suppose you could wear the center of the tread out on a radial by grossely over inflating however i tend to agree with you that it isnt going to happen as long as you stick to reasonable adjustment. radials just dont wear the center down when moderately overinsflated like those old fashoned bias plys did in the bad old days. ex: dont use 44psi in a car that specs 26psi.
I read that bit about over inflating tires wearing down the middle back when bias tires dominated the American market, and thought it made good sense. I have run mostly radials since 1966, and have stuck to the recommended pressures. It has long bothered me that the manufacturers recommend the same pressure all around on the notoriously unbalanced FWD cars. How can 30 PSI be right for both the back and front of my Cavalier? Does GM feel their owners can't cope with complexities of a differential? I have worn out several sets of tires on FWD cars and never noticed the fronts wearing on the edges and the rears in the center. What do other manufacturers recommend for their FWD? Trucks are another matter. Sometimes I think to jack up the rears on mine to the sidewall when hauling a heavy load. Do the recommendations reflect that most trucks always run empty?
"What do other manufacturers recommend for their FWD?" Here's a quick survey from Tire Guides: Acura - Same or at most 2 psi lower in the rear Honda - Same or at most 2 psi lower in the rear Hyundai - Same Infiniti - Same or at most 3 psi lower in the rear Kia - Same Lexus - Same or at most 4 psi lower in the rear Mazda - Same or at most 4 psi lower in the rear Mitsubishi - Same or at most 4 psi lower in the rear Nissan - Same or at most 4 psi lower in the rear Subaru = 2 or 3 psi lower in the rear Toyota - Same VW - Same or at most 2 psi lower in the rear If I read this correctly - "same" wins. But I think LabMan hit the nail on the head - "Does GM feel their owners can't cope with complexities of a differential?" I think they do and so do I and I have ample experience to feel comfortable that for every guy who pays attention to inflation pressure and could cope (and that would be pretty much everyone here at BITOG), there are 2 dozen who can't. And the worst part is that there are some of those 2 dozen who are arrogantly defiant with that position!
It *is* possible to inflate even a steel belted radial so that it wears "down the middle". Don't ask me how I discovered that little truth. [Big Grin] Having said that, I'm the first to agree that within reason, all my cars have driven much better with higher air pressure than recommended. The Neon is a small, fairly lightweight(~2600 lbs?) FWD car, & the sticker recommends 32 psi all around. Well, I've routinely run 35-37 psi in front, and 32-35 in the rear(in 188K miles, I've had rear seat passengers about 2 times!). Think about it, in many(most?) FWD cars, the front tires support about 1 1/2 to almost 2 times the weight supported by the rear tires. Handling & driving are much improved, & MPG is helped a little too. So, just remember that tire inflation, like much else in life, is a balancing act. Don't be afraid to experiment a little- but keep it reasonable, if the sidewall says 35 PSI Max, don't inflate to 50 PSI! [Wink]
How can 30 PSI be right for both the back and front of my Cavalier?
Because both axles will have approximately the same weight/load when all seats are filled and there is a couple of hundred pounds of luggage in the trunk. Almost everybody here seems to be forgetting the fact that the recommended pressures are for a FULLY loaded vehicle. And then they want to go even higher than the recommended pressures even though most of their driving is with a mostly empty vehicle. Too many people equate a quicker initial steering reponse as "better" handling. And while this may be the case for "some" maneuvers such as a quick lane change on dry roads, higher pressures are not going to allow more grip in corners especially on slippery or rough surfaces. I prefer to use the proper pressure for the load based upon the load/inflation tables.
Load/inflation tables for car tires (actually all tires) are maintained and published by The Tire And Rim Association. Their year book costs $70+. The tables along with much other tire/wheel/vehicle application info is REpublished every year by Tire Guides Inc. tireguides.com. Cost= $16. Most "good" tire stores/dealers will have a recent edition and sometimes some older ones kicking around to look at. The newest one that I have is from 1999. I got it in 2001. I asked my tire dealer if he had any old ones that might be on their way to the recycling bin. You can find LT and truck tire tables on line but I've never seen a full P tire list on line.
How can 30 PSI be right for both the back and front of my Cavalier?
This all depends upon the "roll couple distribution". One can alter the RCD by raising or lowering the ride height, raising or lowering the suspension pick up points, changing of the springs, and changing of the anti-roll bars. Different suspension geometries work differently so the adjustment has to be done with respect to the geometry at hand. The final adjustment the manufacture performs is to specify a tire inflation pressure. You can be sure of several things with respect to the manufactures suggested tire inflation pressures: A) they are safe, B) they favor ride comfort over actual handling, C) these setting sacrifice grip for predictability. Your priorities may vary for their priorities.
I'm surprised that no one has mentioned that you should run a little higher PSI for sustained high speed driving (70 MPH +) for certain speed rated tires (T and below). I run my vehicles tires at a +3 at x degrees outside temp for the lowest expected temp for a given season. For example, my Matrix calls for 32 PSI. I have AEM Eagle F1's (94W) which call for 35 PSI. The lowest temp I would be driving at in SC is about 20 degrees. Therefore, I run 38 PSI at 20 degrees. Now before everyone jumps, the max PSI on the side wall is 51 so I'm well within that. As the seasons change, you adjust to compensate. Also, for every +/- 10 degrees in outside temp, there is a +/- 1 PSI change. If you inflate your tires to 30 PSI in a warm garage (say 60 degrees) and then go for a drive in 30 degree weather, your pressure will drop 3 PSI. Your tires will be underinflated. Will the PSI increase with tire temp? Probably but I wouldn't want to ride that long to find out. As a former LEO, I trusted my life to tires. The V rated RSA's we ran on the Vic's were set for 35 (up from Ford's 32) to allow for high speed driving at speeds in excess of 100MPH for extended periods. This is just my 2 cents on the topic.
I always run a few lbs under max, ie: a 44 max psi I run at 40 or so and a 35 max I run around 33. I find that running lower results in the sides wearing prematurely whereas the slightly higher pressure will wear evenly for me. Just had a major hassle with Firestone, got caught out of town on a Sat with a nail in tire, they refused to patch it saying nail was on side, nail was over an inch from the sidewall into the thread and they had me over a barrel, no choice but to replace, a rip off. Further, they refuse to put in my 40 lbs stating that was overinflation on a tire with a max psi of 44. I will never see a Firestone outlet again if I can help it.
Spector, You should not be using what's written on the sidewall of a tire for anything other than the maximum. In other words, the pressure on the sidewall of the tire does not mean anything relative to the load on the tire. You should be referencing the placard inflation in some fashion as this directly relates to the load on the tire. Personally I use 3 to 5 psi above the placard value. Also, the issue about the puncture - The Rubber Manufacturer's Association says you're not supposed to repair a tire near the edge of the belts (the most highly stressed area of the tire) So to give folks a guide, they've said that repairs should not be made in the outermost rib of the tread- which is usually about an inch and a half in from the shoulder. So don't be too hard on the Firstone store, they were just trying to do what's right, even if it meant not doing what the customer wanted. [ March 20, 2006, 10:37 PM: Message edited by: CapriRacer ]
On my Acura Integra GS-R, the recommended pressure is 35 front/33 rear. I go with 38 front/36 rear. On my Honda Pilot, the recommended pressure is 32 front and back. I go with 36. My opinion is that you should use the recommended tire pressure (what's printed on the driver's door) as the minimum and what's printed on the tire as the maximum. Whatever you select is all going to be tradeoff between ride/comfort and gas mileage/handling.
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