I have a 2000 honda civic ex on 15' oem si rims wraped in 205/50/15 dunlop direzza's. How do i know what air pressure is correct for the tire? Do i go by the stock pressure on the door or do some research and get tire pressure for that specific tire?

 

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I've always kept my tires at 32 PSI. It's just one of those things that's stuck with me since I was a kid... Dad did the same thing.

 

32 psi is very low if you want good steering and handling response.

The car manufacturers recommended psi is mostly set with a soft ride as a higher priority than steering and handling response. It's perfectly safe to use the tyre manufacurers maximum setting (as written on the sidewall), though ride may become too harsh for many.

From a wear perspective, with correctly cambered wheels, radial tyres aren't very sensitive to inflation pressure (high or low, unless very high / low), but as psi goes up do become more sensitive to static and dynamic camber angle (more so with lower profile / stiffer case construction), and this will be both from a wear and handling perspective.

My personal recommendation would be to inflate to 10% below the tyre sidewall max psi, and use this as the starting point for experimentation (up or down). Nobody can tell you what psi to use because nobody else knows what your tolerance for increased harshness might be relative to your desire for sharp steering / handling. Only you can find what you like through experimentation.

Check out this dscussion:

http://www.eng-tips.com/viewthread.c...=220757&page=1

PS Get a good quality pressure guage, don't rely on servo guages, they're often wildly wrong.

PPS The tyres won't explode, and the car won't try to kill you at the max tyre sidewall psi, and some tyres really work a lot better at high psi (especially tyres with soft sidewalls), don't be afraid to at least try the tyres at their max psi.

 

Not true. Low to mid thirties is an excellent "performance setting" for most cars. For example, the Integra Type R and GS-R are both performance models, whose recommended tire pressures are not much more than that, at 35F/33R. And those tire pressures work out very well for those cars when you take them out on the track.

That statement is true, but not of the 32 psi level mentioned. Cars that are more family-oriented do indeed have recommendations made with a soft ride as a higher priority. For example, base model Integras have a recommendation in the high twenties. So on such models, you still have the ability to raise your pressure by 4-6 psi, which will give you better handling without being anywhere above the unsafe level marked on the tire sidewall.

Absolutely NOT TRUE at all; in fact, it's quite dangerous indeed. The reason is that tire pressure is measured when the tires are cold, i.e. they haven't been driven on. Once you start driving and the tires warm up, they exceed that maximum, which can lead to excessive stress, heat, and tire failure. This is BAD ADVICE and it's UNSAFE. DON'T DO IT.

Furthermore, using the maximum pressure can also lead to an extremely hard ride, and actually REDUCES steering and handling response. There is no reason to use the maximum pressure. DON'T DO IT.

Again, the tire pressure recommended for your car is a good starting point. You can adjust from that point, generally increasing for a more sporty feel and handling, decreasing for a more comfortable ride quality. As a general rule, I have never heard of any cases where you would ever need to go more than 6 psi above the recommended pressures for street use. (Track and autocross use are a different story, especially when you're using R compound track tires.)

There's no need to listen to one individual on the internet, someone who may be totally ignorant of tire knowledge and lacking experience (and who provides links to his own ignorant posts on other forums, claiming them as "evidence"), when there are recognized, reliable sources on manufacturer and retailer websites that include the best experts in the business. For example, the folks at the Tire Rack know better than anyone else; not only do they try out all the tires they have in all different conditions - they have their own test track at their headquarters in Indiana - but quite a few of them are racers at the accomplished amateur and professional levels. As noted on the Tire Rack's website at http://www.tirerack.com/tires/tirete...e.jsp?techid=8 :

You can find links to lots of advice on their website about setting tire pressure, with an index at http://www.tirerack.com/tires/tiretech/tiretech.jsp to the following sections:

Air Pressure vs. Dry Performance
Air Pressure vs. Wet Performance
Air Pressure – Correct, Underinflated and Overinflated
Air Pressure, Temperature Fluctuations
Air Pressure, Time Fluctuations
Air Pressure/Load Adjustment for High Speed Driving
Air Pressure: When and How to Set
Checking Tire Inflation Pressure
The Influence of Altitude Changes on Tire Pressure
We're Checking Who's Checking Tire Pressures

Under the heading "Competition Tire Information", there's also a section on:

Air Pressure for Competition Tires

as well as sections with recommendations for specific makes and models of track tires.