Tire Pressure: Who's Right?

[jbcrane]

Just realized I never circled back with the new ARB gauge when it arrived. Low and behold - it matches the TPMS on dash. I guess the first was just a bad unit or something? Who knows. Done and done. What I do know is I have an accurate digital gauge now and can move on to obsess over something else... let's see, what'll it be next?

Sponsored

 

[Old Jeeper]

That's great that they have good CS.

My point about them was that their products are Chinese sourced and their products are the same as many other brands found on Amazon. Their main facility is a tiny office in a commercial strip unit. Their secondary "R&D facility" in Colorado, I couldn't find.

If you go to Amazon and just search for tire pressure gauges, you will get dozens of virtually the same product under different branding. Basically, they select products from a manufacturer's catalog, configure it within the manufacture's offerings, and get their name printed on the dial that makes them different than the others. I believe this business model is a situation where the small company pays for brand labeling and order distribution services from a large manufacturer/importer and the small company does the marketing.

Somewhere there's a large warehouse full of these pressure gauges, marked in all the different brands, and an ordering/distribution services office full of "customer service agents" for all the different contracting businesses. This business model isn't specific to tire pressure gauges, but it is prevalent in off-shore manufacturing, particularly China produced goods.

LOL I knew you engineer just by your postings. FYI if you been Jeeping a long time especially the Rock Crawling crowd you will find its loaded with engineers. I used to lead runs in Moab and it would be the 7+ runs only and I would get engineers from all over the US meet me in Moab...good on ya brother.


Lets talk Air Pressure aka PSI.

Unless things have changed the ECM still compensates for Altitude. The very early TJs did not. I discovered this on my first trip to Moab from Dallas when I got my '03 Rubicon (delivered in Aug 2002). By the time I arrived in Moab the engine was running horribly. I had a guess it was due to Altitude. The solution was a hard reboot of the ECM which cleared all the tables and only left the machine code. Do that and instantly it runs better and after about 25 start-stops it ran like a new beast.

Now we segue into PSI, Accuracy etc. For many years we did not have anything but a hand-bicycle pump and no psi gauges on the ranch in spite of tractors, ranch trucks and personal cars etc. So one day my dad told me to go put some air in the tractor tire as they had done down over the winter months. Dad, how much, we do not have PSI gauges. Dad says come with me. We get out to the barn and he shows me what he did before he had gauges, in the 1920s. He cut a notch on the outer edge of the tire and it was over the letter G in Goodyear. Where he cut was where the tread met the sidewall and as he let out air the V changed positions. Dad said I look to see if that V has moved up/down in relation to the others.

Then I asked dad, how do we know how much air to put in the tires if we don't have a gauge? Son, you don't need a gauge, I have never owned one almost no one did because they were expensive. Dad went to show me...

What he showed me was how the Tire Mfg arrive at the optimal psi for the tire. Contact patch Test. Simple, drive thru a thin patch of water or a dusty road or the old stand-by chalk test. What you are looking for is a full contact patch vs the road. This takes into account the weight of the vehicle. Drive-thru dust or water whatever that will leave a mark, but not so deep as to get on the sidewalls and look at every tire to find the wet spot meets dry.

For you folk running non-OEM tires the sticker on the door jam means nothing, you need to view your contact pach; Here is a pic of my Jeep with BFG KM2s 37x12:50x17. The question was and is, HOW MUCH psi do I run? Actually, it makes no difference, your goal is to view the contact patch that will tell you the PSI. Note the dust on my tire and the slight bulge at the base of the KM2, as you can tell it look lke a properly inflated tire.

The next pic is a visual of an improper contact patch on my F 450 Dually . The PSI was 90 by the dealer and I adjusted it down to 70 psi in order to achieve a full contact patch. IF you do not have a full contact patch you are either driving on the sidewalls or towards the center of the tire.

Lastly: Accuracy. I chose to use the TPMS as the correct psi. So I adjust my tire at the valve stem to = the TPMS so the TPMS is accurate to +/- .5, good 'nuff for me.

There is a reason why I am able to extract amazing SAFE miles out of my tires vs everyone else.

I hope you have learned something, I sure did back on a ranch as a 14-year-old kid getting knowledge that went back to the 1920s that is valid today!

On my Jeep in the pick, the red one to the right lower corner the psi all the way around was:

16 psi. NOTE: My Jeep Rubicon has been weight adjusted for rock crawling, it weighed +/- 25 lbs at every corner...one of the secrets of HARD CORE Engineers who Rock Crawl seriously.