: Another tire pressure question



Joey'sVee
10-28-05, 10:11 AM
Ok, I still have the run flats and they still have some tread left on them so I will be keeping them for another 6 months or so. I have 8K mi on them. Now here are my questions...

1. The tire pressure should be 30PSI (cold) for the front and rear, correct?
2. The tire pressure is independent of the kind of tire you have (run flats, toyos, etc.), correct?
3. When they say 30 PSI (cold) what temp are they talking about?

When the car is parked for 3 hours but it's 70F my tire pressure is like 31PSI but on a cold morning when it's 30F the pressure is 25PSI...so I'm not sure what temperature it should be when I make sure my pressure is 30PSI, ya know. :rolleyes:

Thanks for the help! :o

tedcmiller
10-28-05, 10:35 AM
"Cold" tire pressure is the pressure in the tire when it at the ambient temperature regardless of what that temperature is. This occurs when the tires have not been run for a reasonable time, like eight hours or so, and have not been exposed to other factors that could cause unequal heating. Unequal heating can occur when, for example, one side of the car is in direct sunlight while the other side is shaded. Thirty psi is the correct "cold" pressure. Set the cold pressure to 30 psi for the lowest temperature you will normally incounter. If you will normally have temperatures of 25F in the morning, set the pressure to 30 psi at 25F. All of the tires should be set to 30 psi when they are all at the same "cold" ambient temperature.

Joey'sVee
10-28-05, 10:48 AM
So if I set at to 30PSI at 25F after sitting all night then won't the pressure get up to high when driving down the interstate on a hot day say around 90F?

dqw1
10-28-05, 10:49 AM
Joey, you stole my thread I was about to post. Thanks for beating me to it. I'm in the same situation and the tire pressures are driving me nuts. I put them at 31 and after they warm up and They only get back to 29. Thanks Ted for the answer. How long do you have to run before you get a hot tire temp? I'm doing short drives to work and back home, less than 5 miles, temps in the morning is in the mid 30's this week. Sorry to ride your thread Joey.

Florian
10-28-05, 10:50 AM
Ok, I still have the run flats and they still have some tread left on them so I will be keeping them for another 6 months or so. I have 8K mi on them. Now here are my questions...

1. The tire pressure should be 30PSI (cold) for the front and rear, correct?
2. The tire pressure is independent of the kind of tire you have (run flats, toyos, etc.), correct?
3. When they say 30 PSI (cold) what temp are they talking about?

When the car is parked for 3 hours but it's 70F my tire pressure is like 31PSI but on a cold morning when it's 30F the pressure is 25PSI...so I'm not sure what temperature it should be when I make sure my pressure is 30PSI, ya know. :rolleyes:

Thanks for the help! :o

30PSI, after sitting overnight. Front and back.
TPS is a stand alone item, and can be used with any tire.

Let your V sit overnight and start it up, check the tire pressure and run it to the nearest air pump to get em close to 30psi. If you have a compressor, do it yourself.

F

Joey'sVee
10-28-05, 10:57 AM
How long do you have to run before you get a hot tire temp?

Until the temp stops increasing...I'd say 20 min on the interstate.:D

benjet
10-28-05, 12:22 PM
2. The tire pressure is independent of the kind of tire you have (run flats, toyos, etc.), correct?


The sensors are independent of the tire, yes. Recommended tire pressure is different for each make/model of tire (i.e. you would NOT want to run GS-D3's @ 30 PSI).

ctsvett
10-28-05, 01:42 PM
I run my BFGs at about 32-34 psi cold..

The way to test tire presure is to check it in the morning after the car had not been driven all night.

Reed

CTSVONFIRE
10-28-05, 06:02 PM
I have always had low pro's on all my cars, and I set my tire pressure when they are hot. B/c that's what I want my tire pressure 2 be when they get hot. But that is just how I do it.

Joey'sVee
10-28-05, 09:34 PM
See how confusing it is....to me anyways, lol!

CTSVONFIRE
10-29-05, 11:21 AM
Yeah just come up w/ your own method. That's the best way. I look at my tires alot b/c I have a staggered offset and can't rotate my tires.

Joey'sVee
10-29-05, 08:34 PM
The sensors are independent of the tire, yes. Recommended tire pressure is different for each make/model of tire (i.e. you would NOT want to run GS-D3's @ 30 PSI).

See even the mods disagree on this. One says it depends on the tire...the other says it doesn't (do a search). So should I make sure its 30 PSI at 29F early in the morning or should I set it after the car has sit for a few hours eventhough it's 70...knowing it gets up to 90F some days? :hmm:

Dennisscars
10-29-05, 10:46 PM
I run a couple lbs under sidewall max checked after overnight in garage, no matter what brand or size. The sidewall cold press figures in run temps. They put it there for a reason...

Dave's V
10-29-05, 11:36 PM
The owner's manual says to check the tires when they are cold (sitting for more than 3 hours and driving less than 1 mile). 30 PSI is the standard pressure unless you drive a loaded vehicle at more than 130mph (tire pressure would then be 32/34 cold).

TPS tend to act goofy at times so it is best to check them the old fashioned way once a while.

Merle Corey
10-30-05, 07:25 PM
One thing to say about the run flats and low profile tires... don't take many strokes at all with a modern bicycle tire pump and the better ones have gauges with great definition at the pressures we use.

Dennisscars
10-30-05, 08:22 PM
Go ahead and spring for a digital tire pressure guage. They run them on sale at Sears every so often. Tell the wife they make good stocking stuffers.

Throw away the cheapo one the tire store gave you with their name on it. It basically registers on/off.

tedcmiller
10-31-05, 04:30 PM
Joey'sVee,
Where are you going to go from 25F to 90F in the same day? I suppose you could start in Canada on a cold winter morning, drive like hell for 24 hrs and end up somewhere in Mexico, but I thought you were talking about a normal drive around the area where you live.

Joey'sVee
10-31-05, 06:09 PM
Within the past 7 days it has been ranged from 30s to 80s. Should I set it for 30sF or 80sF? I don't wanna change the tire pressure every few days.

tedcmiller
11-01-05, 10:33 AM
Is that 30F or 39F? In any case, set the cold tire pressure for 30 psi at whatever the ambient temperature is at the time. They will not get too hot even driving around at 80F. If the average cold ambient temperature drops to a lower value over a period of several weeks, causing the cold pressure to drop by a couple of pounds, you can adjust the pressure again or you can ignore it. As long as the cold pressure is within a couple of psi of 30, the tires and the tire wear will be fine. The recommended pressure of 30 psi assumes a cold pressure, and the pressure will increase fairly quickly to a normal running pressure as the car is driven. All of this assumes the tires are Goodyear F1 run-flats or an equivalent. Run-flat tires have a stiffer sidewall and as a result flex less during running so the pressure increase is less than with a non-run-flat. Non-run-flat tires typically need a higher cold pressure setting than run-flats to achieve even proper tire wear.