There is more than you'll ever want to read about it my tire pressure thread, linked in my sig.
What model is it, what is its curb weight, and what size tires are on it?
Auto manufacturers recommend the minimum pressure required to avoid lawsuits, in order to sell vehicles to people who like a smooth ride. From
http://www.gassavers.org/showpost.ph...01&postcount=4 :
Quote:
Originally Posted by theholycow
 Buried deep in many manuals and publications is the recommendation for increased pressure for more demanding conditions -- speed, load, road condition, tire condition, etc.
As far as I can tell, the default recommendation by the automaker is made by the marketing department to sell cars with a softer ride, limited by the legal department (who consults the engineers for the bare minimum) to avoid blowouts. Remember the Ford/Firestone debacle? They either forgot to consult with the legal department, or the lawyers forgot to ask the engineers... |
I'm not sure about this, but I think big-box tire retailers don't expect their employees to think too much and tell them to just recommend 35psi for everyone no matter what since it's a pretty safe number. It's high enough to handle most configurations, and low enough that every tire they sell is rated to handle it.
You should do your own experiments. For FE, the best pressure is usually the highest pressure that doesn't exceed the tire's maximum, doesn't cause ill handling or uncomfortable ride, and doesn't cause uneven wear. For best handling, one generally finds even higher pressure than that is helpful (hence why autocross racers and police cars run often far higher pressures, sometimes even beyond the tire's rated maximum).
In my pickup, I run 80 front (tire's maximum rating) and 72 rear. GMC recommends 35 all around. I have been doing it for ~125,000 miles, worn out lots of tires, and have not had center wear yet. In my VW I run 51psi (tire's max).
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