The sticker inside my car’s driver’s door says 29 p.s.i.
The info on the sidewall of the tire says 35 p.s.i.
Which pressure should I maintain? Please help settle this debate with my S/O. I say the sticker on the car - he says the number on the tire …
Thanks,
S.
Owner’s manual.
The number on the tire is usually the MAXIMUM pressure. You put that much air in an you’ll wear out the tire pretty quickly.
You should go by what it says on the car. The pressure on the sidewall is the maximum pressure.
Go with what’s on the car, not the tyre. It should also specify differences between front and rear, if they’re appropriate.
wow … quick answers … thanks!
Since McDeath filled them to the number on the sidewall, I’ll have him vent some of it out to get the pressure to the recommended p.s.i. on the car.
hee hee … i love being right! 
Strong disagreement with previous posters is voiced. The owners manual and door sticker data is valid only when dealing with the tires embraced by said manual or sticker.
Radical example would be looking at the manual for an auto manufactured in the 1950’s when it has been fitted with modern radial tires. The book was written for tires which didn’t exist back then.
More recent example is my own truck. It was fitted with passenger car tires when new, with a maximum inflation of 32 PSIG. I’ve replaced them with extended load range tires, inflated to 41 PSIG. If I ran them at 32, I’d have replaced them over 10K miles ago, instead of the 40K they have enjoyed.
Actually, raising the pressure in your tires will increase mileage, since you aren’t losing as much energy as the tire deflects at the smaller contact patch. The tire will also run cooler due to this, which is a good thing in hot weather.
Lower pressure will give a better ride (more cushioning).
Higher pressure (to a point) will make the car corner better. If I don’t run 38 psi on my front tires when road racing or autocrossing, the tires will roll over to the point where the sidewalls are wearing on the pavement. Higher pressure stiffens the sidewalls, preventing this.
So if a mix of comfort and economy is your goal, go with the manufacturer’s, but feel free to add a few pounds (up to the tire’s max pressure limit) before long highway trips to save some gas.
I also completely disagree with the previous posters. The door sticker states pressures for the stock tire rating. What if you upgrade wheels and/or tires, or just replace your original tires with new ones? Your winter tire will probably have a different rating then that of an all-season radial. My tires say 44psi MAX. I don’t fill it to that point, I’ll put about 38-40psi. Please don’t go by your door sticker.
aaaaaaaaaaaaaaaaaaaaarrrrrrrrrrrrrrggggggggggggggggghhhhhhhhhhhhh
I SO wanted to be right. 
I guess we’ll just compromise and put the pressure somewhere in between.
I also must respectfully disagree with some of the earlier posters. I have seen a small range of acceptable tire pressures which vary depending upon the tire. My old FIAT came with stock tires that recommended 30 psi, but the aftermarket replacement Pirellis recommended 36 psi.
That having been said, regardless of what the owners manual says, you should not exceed the maximum safe pressure listed on the side of the tire.
I asked the guys who do my tires. They say 38psi for my tires regardless of what the car sticker says.
If I remember correctly, during some of the investigation into the failure of Firestone tires on Ford Explorers, there was some discussion of the pressure Ford inflated the tires and recommended. My memory gets hazy, but maybe Firestone told Ford to increase the recommended pressure because the pressure they (Ford) set was too low and could contribute to failures.
Ford’s reasoning for setting the tire pressure low was to soften the ride – the Explorer had a bouncy road feel to it from its frame and suspension, which was largely unchanged from their truck categories.
So, as far as I know, manufacturers decide on a recommended tire pressure taking into account the tradeoff between comfortable ride and fuel efficiency (and probably tire lifespan).
But, on preview, I see zlexiss has already said this more consisely.
In addition, even if you start with a lower pressure it won’t necessrity stay that way. Lower pressure results in more flexing and more flexing raises the temperature which raises the air pressure. If you drive around town at low speeds for short trips the temperature won’t get all that high and the ride will be smoother. But if you go our on the highway and run continuously at high speed my guess is that the tire pressure builds up to almost the same value for all reasonable starting pressures.
I run my tires at a couple of pounds below the max. given by the tire manufacturere and accept the slightly, but only slightly harsher ride.
I was assuming stock wheels and tires, but you know what assuming gets you. 
Once upon a time, I started an identical thread.
Based on citations from tiremakers, I reached the conclusion that the smart money is on “Listen to your automaker, not your tire maker”. Also, both Goodyear and Michelin say to pay attention to the car’s manual or doorjamb placard, rather than their tire’s maximum inflation pressures.
This was the URL for the aforementioned enlightening thread on tires inflation:
http://boards.straightdope.com/sdmb/showthread.php?t=154452&highlight=tires
Now as far as what to do with a vehicle that predates radial tires, I still don’t know.
I have always filled my tires, when cold, to at or near the maximum pressure labeled on the tire. This increases tire life by reducing heat generation (through less flexing).
Too many people believe that all tires should be filled to ‘26 psi’ or some other magic number, simply because that’s what most tires used to require. This was a contributing factor to the rollover accidents with southern SUV’s – high ambient temperatures + improperly inflated tires + long distance high speeds = greater chance of failure through excessive heat.
My last sports car had ‘V’ rated tires. Max pressure was listed as 44 psi, and I filled them to 41 or 42. I had to watch those yahoo’s at Jiffy Lube or Les Schwab – they were always trying to lower the pressure.
Tires have changed, and even regular passenger car tires now require higher pressures. 36 psi is not uncommon. The manufacturer is more interested in ride quality (filling the tire up to maximum gives a noticeable harshness to any cars ride) than tire life. Tire manufacturers are complicit in this, since they stand to sell more tires that way.
In the case of the SUV rollovers, neither side was going to admit any liability, since big dollars were at stake. IMHO, all parties share some blame; Ford and Firestone for recommending too low a pressure and for making the sidewall so high to increase ground clearance (like many Explorers saw any use off-road); and car owners for running the vehicles with low tires – even lower than recommended.
i am in the fill the tire to the tire manufacture’s specitied pressure,because the tire was designed to run at whatever the specified temperature is.Why wouldn’t the designers know the proper way to use the item they have designed ?
Also,2 more things i must mention,the pressure showen on the sidewall is max.pressure -cold- not after the vehicle has been run for hrs.,and the second thing is if you fill the tire to more than the max. cold pressure in hopes of getting a few xtra tenths of a mile to the gal. you’re going to change the tire’s footprint,which will lessen your brakeing ability,not a good trade off in my book.
Think,than do what you feel is right.
Actually, frictional force is, in general, independent of the contact area.
Cite:
http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html
Also, if you’ve got a tire that states 44psi MAX, and it’s a steal belted radial, and your car sticker says something like 32psi, this could be a serious safety hazard as steal belted radials, without the proper inflation, will “cup” up in the center of the contact patch. Basically making your tire riding on it’s outer edges and not getting the correct traction it needs. This is the reason that they may generate more heat, and become garbage after 20,000 miles, just a thought. Some seem to think that this increases traction and performance. This is true, but only limited to the older bias ply type tires. And similiar to those found in race cars, such as slicks, and those monster sprint car tires.
I respecfully disagree with this, using the “exceptions” link as my justification, where the trapeziodal shape, small end down, is digging into the surface.
A tire riding on pavement is not two smooth surfaces in contact. Rather, both the pavement and the tire (deflecting through the weight of the car on the contact patch) are like two interlocking sets of hills and valleys.
A larger contact patch will give you more of these “interlocking” surfaces to hold on to, providing better traction.
Ultimately, this interlocking is why dragsters can launch themselves with forces greater than 1G, and some autocross cars can corner harder than 1G, both without the assistance of aerodynamic downforce due to low speeds. It was thought that this would be impossible until people started doing it, then a look at what was really going on led to a newer understanding of tire traction.
Tires don’t always behave in the proportional manner of simple friction physics. Another good example is that all other things being equal (same tires, same suspension design, centers of gravity), a lighter car will have more “grip” around corners than a heavier car. The extra weight on each tire gives some increase in traction force, but it’s not fully proportional - twice the weight gives less than twice the traction.
There’s some good discussion of this in a book by Fred Puhn titled, “How to Make Your Car Handle”
-Jeff