Confused about tire pressure
10-10-2015, 02:12 PM
#21
Senior Member
Tell that to the families of the people who died in the Firestone-Explorer fiasco because for recommended under inflating tires to make a smoother ride. No body knows the tire better than the tire manufacturer. I always run the max pressure stated in the sidewall after taking into account increase pressure from heat.
10-10-2015, 02:51 PM
#22
Bad advice. The number on the side of the tire is the max psi the tire can run, not the amount that must be used. When the same tire is used on two different vehicles, heavier vehicle needs more air than a lighter vehicle. Too much pressure and you will wear the centers out...Once again, if in doubt do a chalk test.
Last edited by 77Ranger460; 10-10-2015 at 02:57 PM.
10-10-2015, 03:19 PM
#23
Senior Member
Oh yeah! My OEM sidewalls are imprinted with 51 PSI. At that pressure my Fusion would be bouncing down the road like a Goodyear dirigible in a hurricane, not to mention providing a jaw-breaking ride and rapidly wearing center tread. Doesn't the sidewall PSI myth ever die?
10-10-2015, 06:58 PM
#24
WindowGuy
that seems like the worst way possible to check your tire pressure... define lukewarm? do you check with your hand, a thermometer, your D? tires will heat up faster if it's hot outside, or if you drive aggressively, etc...
set your tire pressure when cold and adjust as needed for load / temperature changes (from +20C to -20C for example, you'll lose a few psi)
set your tire pressure when cold and adjust as needed for load / temperature changes (from +20C to -20C for example, you'll lose a few psi)
11-29-2015, 06:24 PM
#26
Not trying to hijack the thread. But I had a question about the nitrogen!
When i bought my truck, i distinctly remember cycling through the PSI of the tires in the cluster and they were at 40. Now that was back in late may 2015.
Now that its cold out its reading 29 PSI! I feel like thats such a huge jump for the nitrogen.
I was thinking should I just go to the dealership and see what they say. All of the tires say around that PSI 29/30. The door says cold tire pressure should 35 PSI!
When i bought my truck, i distinctly remember cycling through the PSI of the tires in the cluster and they were at 40. Now that was back in late may 2015.
Now that its cold out its reading 29 PSI! I feel like thats such a huge jump for the nitrogen.
I was thinking should I just go to the dealership and see what they say. All of the tires say around that PSI 29/30. The door says cold tire pressure should 35 PSI!
11-29-2015, 07:56 PM
#27
Senior Member
When i bought my truck, i distinctly remember cycling through the PSI of the tires in the cluster and they were at 40. Now that was back in late may 2015.
Now that its cold out its reading 29 PSI! I feel like thats such a huge jump for the nitrogen.
Now that its cold out its reading 29 PSI! I feel like thats such a huge jump for the nitrogen.
Or have you been checking your pressures regularly, and suddenly the tire pressures all dropped 10 psi?
Anyway:
The pressure in nitrogen filled tires will change when the temperature changes, just as it does with air filled tires, because nitrogen and oxygen respond to changes in ambient temperature in a similar manner. For example, when your vehicle is parked it will lose a similar amount of pressure for every 10 degree change in temperature, whether the tires are filled with nitrogen or air.
The calculations for this change are based on the Ideal Gas Law. A good rule of thumb is this: For every 10 F degree change in temperature, the pressure will change by 1.9%. If a tire is filled to 32 psi at a temperature of 75 F degrees and the temperature drops 10 degrees, the tire pressure will drop to 31.4 psi; a difference of .6 psi. If a 100 psi tire is filled at 75 F degrees and the temperature drops 10 degrees, the tire pressure will drop to 98.1 psi; a difference of .9 psi.
These fluctuations will occur as the temperature rises and falls no matter what the inflation gas. Fortunately, tire manufacturers are well aware of these conditions and design their tires and recommend their cold inflation pressure accordingly.
However, nitrogen does not contain the moisture and other contaminants found in compressed air so, as you drive and the tires heat up, nitrogen filled tires will fluctuate less in temperature and pressure than air filled tires while driving. The bottom line is, you will still see pressure changes with nitrogen but, overall, your tires will run cooler and at a more consistent pressure than if they were filled with air.
The calculations for this change are based on the Ideal Gas Law. A good rule of thumb is this: For every 10 F degree change in temperature, the pressure will change by 1.9%. If a tire is filled to 32 psi at a temperature of 75 F degrees and the temperature drops 10 degrees, the tire pressure will drop to 31.4 psi; a difference of .6 psi. If a 100 psi tire is filled at 75 F degrees and the temperature drops 10 degrees, the tire pressure will drop to 98.1 psi; a difference of .9 psi.
These fluctuations will occur as the temperature rises and falls no matter what the inflation gas. Fortunately, tire manufacturers are well aware of these conditions and design their tires and recommend their cold inflation pressure accordingly.
However, nitrogen does not contain the moisture and other contaminants found in compressed air so, as you drive and the tires heat up, nitrogen filled tires will fluctuate less in temperature and pressure than air filled tires while driving. The bottom line is, you will still see pressure changes with nitrogen but, overall, your tires will run cooler and at a more consistent pressure than if they were filled with air.
11-29-2015, 08:00 PM
#28
Senior Member
What is the right tire pressure? And why?
When I picked up my truck the tires were nitrogen filled at 40psi. I got my first oil change this week and noticed that the tires were reduced to 36psi. 36psi does match the sticker on the door, and is what I have always used in my car tires. But, I keep reading about higher and higher pressures.
When I picked up my truck the tires were nitrogen filled at 40psi. I got my first oil change this week and noticed that the tires were reduced to 36psi. 36psi does match the sticker on the door, and is what I have always used in my car tires. But, I keep reading about higher and higher pressures.
Read the manual.
11-29-2015, 08:55 PM
#29
I think because its quite chilly out now the temperature has dropped. it went from last week in ontario of 15-19 celsius, to now being 4 degrees or so and below zero for certain over night.
I did a rough calculation from the ideal gas law. Bought in late May temperatures around 25C/77F, temperatures now 0C/32F. difference of 45F. 45F differences in change is 8.55%. So if my tires were from 38-40 it should drop down to around 34-35. and thats not including the time from may and just losing some pressure i suppose. And once I am on the highway the PSI gets up to 31/32.
They are coming off tomorrow for winters. But the explanation you gave me makes a lot of sense.
Thanks alot. I thought I had defective tires for a bit there
Last edited by Tbrown87; 11-29-2015 at 09:03 PM.
12-01-2015, 12:20 PM
#30
Senior Member
Yes tire pressures should be checked when cold, at least once a month.
Also take into consideration that the PSI displayed on your truck computer may not be accurate (ballpark at best). There can be as much as 2-3 PSI difference against a decent tire pressure gauge.
38 PSI on my truck screen cold is actually only 35 PSI when checked with a quality tire gauge.
Also take into consideration that the PSI displayed on your truck computer may not be accurate (ballpark at best). There can be as much as 2-3 PSI difference against a decent tire pressure gauge.
38 PSI on my truck screen cold is actually only 35 PSI when checked with a quality tire gauge.