FYI: How to Check Your Tire Pressure

[TimberWolf2018]

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[Anthony]

As we said, the required pressure will vary by original equipment tire provided. Mine says 30psi (again, I've got the 17" Hankooks) a different tire will require different pressures. I've updated the first post to make that more clear.

 

[Johnpenn]

This discussion is very interesting but brings up a couple of questions in my mind, assuming tire pressure is really this critical

Since the recommended pressures seem to be tire size and manufacturer specific for the vehicle loading. How does one decided where to set the normal pressures when changing to a different tire size or manufacturer?

The second question is, should I just trust the accuracy of the TPMS system readings when I decide what pressure to use? I don't have my new Ranger yet but a couple of days ago, I was adjusting pressures on my other vehicles with my Viair 400P. I tried several gages including the Viair and the various gage readings differ by about 5 PSI. Using the Viair gage to set my Malibu tires, the TPMS gave me three different numbers among the four tires and they varied about 4 PSI highest to lowest. Which one to believe?

I worked in quality assurance for a long time and always had to be aware of accuracy and repeatability of various measuring instruments. Seemingly simple things can actually be pretty complicated sometimes. Maybe there's a tire pressure setting course somewhere that I can attend that takes this all into account. LOL

 

[VAMike]

This discussion is very interesting but brings up a couple of questions in my mind, assuming tire pressure is really this critical

Since the recommended pressures seem to be tire size and manufacturer specific for the vehicle loading. How does one decided where to set the normal pressures when changing to a different tire size or manufacturer?

Tire width is a big factor, as it changes the size of the contact patch. (Note that the highest-pressure standard tires listed so far are also the narrowest.) Also sidewall flex: the LT tires generally have stiffer sidewalls which you don't want to flex as much as offroad tires because they'll get too hot and fail. If you change the tire diameter you're adding more sidewall and may need more air to keep them from flexing too much. Some tire manufacturers will provide a recommended value for a particular vehicle (though the ranger is probably too new for this), otherwise you could try a chalk test https://www.intercotire.com/using_chalk_method_determining_psi. I'd probably start at the manufacturer pressure based on width and come up a bit for a larger diameter tire.

 

[Johnpenn]

Tire width is a big factor, as it changes the size of the contact patch. (Note that the highest-pressure standard tires listed so far are also the narrowest.) Also sidewall flex: the LT tires generally have stiffer sidewalls which you don't want to flex as much as offroad tires because they'll get too hot and fail. If you change the tire diameter you're adding more sidewall and may need more air to keep them from flexing too much. Some tire manufacturers will provide a recommended value for a particular vehicle (though the ranger is probably too new for this), otherwise you could try a chalk test https://www.intercotire.com/using_chalk_method_determining_psi. I'd probably start at the manufacturer pressure based on width and come up a bit for a larger diameter tire.

Interesting article. A little difficult to do so I hope the tire manufacturers do the work for me before I decided to change tires. I guess the Ford recommendations for the various tires supplied with the Ranger would be a good starting point for the experiment. Thanks.

 

[MT19RANGER]

This discussion is very interesting but brings up a couple of questions in my mind, assuming tire pressure is really this critical

Since the recommended pressures seem to be tire size and manufacturer specific for the vehicle loading. How does one decided where to set the normal pressures when changing to a different tire size or manufacturer?

The second question is, should I just trust the accuracy of the TPMS system readings when I decide what pressure to use? I don't have my new Ranger yet but a couple of days ago, I was adjusting pressures on my other vehicles with my Viair 400P. I tried several gages including the Viair and the various gage readings differ by about 5 PSI. Using the Viair gage to set my Malibu tires, the TPMS gave me three different numbers among the four tires and they varied about 4 PSI highest to lowest. Which one to believe?

I worked in quality assurance for a long time and always had to be aware of accuracy and repeatability of various measuring instruments. Seemingly simple things can actually be pretty complicated sometimes. Maybe there's a tire pressure setting course somewhere that I can attend that takes this all into account. LOL

2nd ?:

WARNING: The tire pressure
monitoring system is not a substitute for
manually checking tire pressures. You
should periodically check tire pressures
using a pressure gauge. Failure to
correctly maintain tire pressures could
increase the risk of tire failure, loss of
control, vehicle rollover and personal
injury.

 

[Stevie Gee]

2nd ?:

WARNING: The tire pressure
monitoring system is not a substitute for
manually checking tire pressures. You
should periodically check tire pressures
using a pressure gauge. Failure to
correctly maintain tire pressures could
increase the risk of tire failure, loss of
control, vehicle rollover and personal
injury.

Exactly, and glad u mention this. I’ve always checked mine once a week. Tires are the most important parts of a vehicle, and on CA freeways at 90 mph 5 days a week, COLD check pressure does change!

 

[Johnpenn]

2nd ?:

WARNING: The tire pressure
monitoring system is not a substitute for
manually checking tire pressures. You
should periodically check tire pressures
using a pressure gauge. Failure to
correctly maintain tire pressures could
increase the risk of tire failure, loss of
control, vehicle rollover and personal
injury.

Thanks Ford, that's comforting. I guess it's a good thing I use a separate gage too. Now all I need is to find one that's more accurate.

I just downloaded the manual. Might as well start reading it while I impatiently await the arrival of my Ranger. Probably another 8 weeks or so.

 

[MT19RANGER]

Exactly, and glad u mention this. I’ve always checked mine once a week. Tires are the most important parts of a vehicle, and on CA freeways at 90 mph 5 days a week, COLD check pressure does change!

It was so much easier in the old days, when I worked with new employees and certain warning li

Thanks Ford, that's comforting. I guess it's a good thing I use a separate gage too. Now all I need is to find one that's more accurate.

I just downloaded the manual. Might as well start reading it while I impatiently await the arrival of my Ranger. Probably another 8 weeks or so.

Version 3 of the manual is the most current.

 

[MT19RANGER]

Thanks Ford, that's comforting. I guess it's a good thing I use a separate gage too. Now all I need is to find one that's more accurate.

I just downloaded the manual. Might as well start reading it while I impatiently await the arrival of my Ranger. Probably another 8 weeks or so.

GMC 2500HD manual states: "The TPMS does not replace normal monthly tire maintenance. Maintain the correct tire pressures."
So I'm thinking just like any other electronic device or system it can fail. A person needs to check and inspect things manually instead of relying on systems.

Employees come to me and say " I don't know why the oil light is on" and I go well have you checked the oil level, they go, well no. And I go that's why the light is on. It's an "idiot light" as we used to call them, you idiot. You are responsible to check the oil on a regular basis. Same goes w/ tires. Don't just drive them till you have a problem.

 

[VAMike]

In practice the tpms is pretty accurate. They add a disclaimer so you can't sue if it breaks. But really, most people don't calibrate or maintain their pressure gauge so I'm not convinced they'd be more accurate. The ones at the gas station are pretty much guaranteed to be wrong.

 

[Johnpenn]

I agree; have you found an accurate one?

I have always kept a mechanical tire gage in my cars. I've had TPMS sensors fail on the interstate in two vehicles. With the Corvette it was one of those oh crap moments. I better get off the road now or I'll be losing a $300 run-flat. Replacing the bad sensor wasn't exactly cheap either but I got tired of having to reset the warning.

 

[THLONE]

GMC 2500HD manual states: "The TPMS does not replace normal monthly tire maintenance. Maintain the correct tire pressures."
So I'm thinking just like any other electronic device or system it can fail. A person needs to check and inspect things manually instead of relying on systems.

Employees come to me and say " I don't know why the oil light is on" and I go well have you checked the oil level, they go, well no. And I go that's why the light is on. It's an "idiot light" as we used to call them, you idiot. You are responsible to check the oil on a regular basis. Same goes w/ tires. Don't just drive them till you have a problem.

Those idiots are an integral part of the economy. LOL

 

[chasvs]

I have the 17" Hankooks. What tires do you have? Also, look at the driver's door panel sticker of the truck as well for cold tire pressures. I would not trust the app to tell you what pressure it should be at.

Yeah, the App says very clearly NOT to use it as a Tire Pressure Guage!

 

[rwjrn]

When I got my truck home I was initially confused because the recommended psi on the door said 30 and my tires were reading 47. I thought maybe I had different tires or something because I couldn't imagine the dealership wouldn't do something as basic as checking the tire pressure and making sure it was reasonably close. 17 pounds over on every tire seemed like something had to be wrong with the recommended psi. Fortunately there is this forum and I read how a lot of trucks were coming in overinflated. It doesn't do much for my confidence in Ford's production quality control or my dealer's pre sale inspection .

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