Tire Pressure questions

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Originally Posted By: NMBurb02
Here in the People's Republic of California (not sure if elsewhere as well) shops are required to check tire pressure whenever they service a car and adjust the pressure as necessary. The GP calls for 30 psi front and back, but the independent shop I use fills to 40 psi every time. It makes for a harsh ride but is below the max psi on the tires (50 IIRC) so I'll typically drive around with it at 40 for a while and then bleed to 33-35 when I get around to it.

The Burb's tires are slightly oversized (1 inch/3% taller, same width) and I've never been able to figure out how I need to adjust the placard pressure of 35 psi to account for the difference in volume, despite reading advice on multiple sources (some say higher pressure, some say lower). I tried the chalk method but messed it up somehow and plan on trying it again.

I believe Costco fills with Nitrogen and the one time I purchased tires there is probably the only time I have used nitrogen.


I would still run the recommended pressure for normal driving with slightly taller tires. I wouldn't try to adjust unless it shows uneven wear, or you are racing, towing, or off-roading.
 
Ill bet you go to a dealer for a tpms light for low air/nitrogen. Your going to get air only. If you check your tires regularly you won't have an issue. Nitrogen is good but not worth the hype in passenger cars.
 
Originally Posted By: 63Marauder
You use the pressure number that is on the tire. Cold.


That's just plain wrong.

For example, the tires on my Land Cruiser have a Max pressure of 80psi; but recommended pressure is a little less than half that - 39psi.

If I ran my tires at 80psi as you suggest, they would wear unevenly (heavy wear in the center of the tread and almost no wear on the edges), ride terribly (stiff and rough), brake less efficiently (longer distance to stop) and have overall less traction.

So please, hold the uninformed bad advice.

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You really need to figure out what's right for your situation. I use the door jamb recommendations as a start. I've seen some that came with separate recommendations for a basic load or higher for the max load (something like 800 lbs load). My '95 Integra GS-R came with a rather high recommendation for 35/33 PSI front/rear and I basically stuck to that because I could tell it was high.

Some find that aftermarket tires respond differently than OEM tires. Almost every high performance tire I've had on my 2004 WRX seemed to do better with maybe 3-5 PSI more than on the door jamb. The one thing is that they do recommend 2 PSI more on the fronts, and I try to keep it that way.

I remember with my '89 Integra the 26 PSI recommendation always seemed low, so I just upped it to 30-32. There was nothing particularly wrong with it, and I always got decent tire wear.
 
Originally Posted By: 63Marauder
You use the pressure number that is on the tire. Cold.


The number that says MAX PRESSURE? That doesn't seem right for normal DD....
 
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It's been my experience the numbers on the door jamb are for the OEM tires. If you get other tires that have a much higher max pressure rating than the OEMs then the door jamb numbers may be too low.
 
So much wrong in this thread. BITOG is great for oil information, but apparently not for tires!

Here is a link on the use of N2 in tires:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=191

Oxidation is not a factor in normal driving and normal cars.
Using N2 means you may have to add air to your tires a little more frequently. But you should be checking that anyway.

Of course you can mix N2 and regular air....they are already.
And you will note from the tire rack article that O2 gets into tires just as N2 leaks out.

Yes, the tire pressure is checked with cold tires before driving and you use the manufacturer's recommendation on your door jam.
 
Originally Posted By: SHOZ
What's wrong?


The rating on the tires is maximum pressure they can withstand as per the manufacturer.
The pressure to fill your tires is based on the car manufacturer NOT the tire manufacturer and it's based on vehicle weight and power, etc.
 
If there is a huge difference in the tires then the factory recommended pressures go out the door. IMHO. Some are stiffer sidewall, some shorter or taller sidewall.

A 51 max psi tire (@35 psi) will not perform like a 35 psi max tire.
 
I'm sorry to say this but SHOZ has no idea what he's talking about. He's confused between max pressure a tire can handle and recommended pressure a tire should be inflated to.

Yes, you can play around a little bit with some tires. For instance, the recommended pressures for my car are 35psi. I have conti DWS which are known to have soft sidewalls. Therefore I inflate them to about 37-38 to givea me the kind of handling I am looking for.

But to say the factory recommended pressures 'go out the door'? Aside from being a bad pun this is potentially dangerous advice to people who may not know better.
 
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I'm sorry but I do from experience know that it is not dangerous advice. Dangerous advice would be to keep the tires under inflated. What's dangerous about putting a bit more pressure in a tire that it's rated for?

Have you ever gone from some factory 35 psi tires to a 51 psi tire? If I ran my winter Michelins at the factory pressure it's like diving with a half inflated tire
 
Originally Posted By: SHOZ
I'm sorry but I do from experience know that it is not dangerous advice. Dangerous advice would be to keep the tires under inflated. What's dangerous about putting a bit more pressure in a tire that it's rated for?

Have you ever gone from some factory 35 psi tires to a 51 psi tire? If I ran my winter Michelins at the factory pressure it's like diving with a half inflated tire

There are many, many variables. The worst thing about riding with overinflated tires is that it reduces the contact patch. That may cause premature wear down the center of the tire if there isn't negative camber dialed in as well as poor dry handling. I remember getting some tires after a service that were inflated way too high, and the steering felt really jittery rather than smooth. Putting in too much air can also make it more likely to suffer pothole damage.
 
Originally Posted By: SHOZ
Still not unsafe. When I would take the car out on the track the tires go up and when heated are generally above the max rating.

And I'm not advising anyone. My post are just stating my experience. Just another example of when you want to increase the pressure.

Air Pressure/Load Adjustment for High Speed Driving


That link suggests 1.5 psi additional pressure if you are traveling at 124 mph and no addtional pressure below that speed.

Just how does that relate to daily highway driving where speeds are rarely more than 80 mph?

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