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The TPMS in my Jeep was telling me my tires were inflated at 36 psi. This seemed weird since the compressor I used at the filling station said 33. I finally got around to checking it out a couple of nights ago.

I grabbed the Currie EZ-Tire Deflator I got from Quadratec and headed out to the garage. 31 psi all around, though it also seemed like there was a bit of an air leak in the deflator. So I said screw it. Let's assume the TPMS is accurate. I'll let some air out and see how it goes. I decided to try just deflating 2psi. No big deal, right? So I hop into the Jeep and go for a ride. TPMS now says I'm at 29 psi. Huh? Well, maybe I am at 29 psi. Maybe the deflator was right after all. The tires felt very squishy so I knew I wanted to put more air in.

I pulled into a gas station, fed the compressor some quarters, and got started. Well, this fancy machine says I'm currently running at 25 psi. Um. What? Okay. Well I'm going to put 4 psi into the tires and see what happens. Surely if the TPMS currently says 29 psi then it'll say 33 psi after that, right? Wrong. Now it's 34 on two of them and 35 on two of them.

How the heck am I supposed to know what my real tire pressure is when four different gauges give me four different numbers?

Note: If it helps, these are aftermarket wheels with aftermarket TPMS. I also haven't recalibrated tire size yet (procal is on its way to me this week) but I'm not sure that matters for tire pressure.
 

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Spend a few good bucks on a quality gauge. You can't trust the ones at the pumps. i'd trust your TPMS more than anything, but sometimes it takes time to get the correct reading. You can get nice digital gauges with a calibration feature and they are pretty accurate. You can spend anywhere from 20 to 30 bucks for a good one. Make sure it has the Cal or Zero option.
 

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Spend a few good bucks on a quality gauge. You can't trust the ones at the pumps. i'd trust your TPMS more than anything, but sometimes it takes time to get the correct reading. You can get nice digital gauges with a calibration feature and they are pretty accurate. You can spend anywhere from 20 to 30 bucks for a good one. Make sure it has the Cal or Zero option.
Thanks for not mocking me over this one. I've been mocking myself enough for all of us as I feel ridiculous. Do you have a preferred brand or model that you find particularly accurate? I'd thought the Currie would be pretty good.
 

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Thanks for not mocking me over this one. I've been mocking myself enough for all of us as I feel ridiculous. Do you have a preferred brand or model that you find particularly accurate? I'd thought the Currie would be pretty good.
I recently bought one that's meant for commercial use and it's nice and rugged, but I think it was about 80 bucks. The one I used before was a slime digital gauge. It's shaped like an oval and the hose wraps around it. It is very accurate and think it was like 15 or 20 bucks.
 

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i'd trust your TPMS more than anything
this is kinda funny, i have the factory tpms and they read 6 psi lower then anything else i have. there's a little variance from guage to guage but 5 different guages read 30-32 psi while tpms read 24 psi. i have to keep the tpms set to 22 psi to keep the low tire warning from going off all the time.
 

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I have a very accurate tire pressure gauge and set my tire pressure to 30 PSI. My TPMS always matches exactly so mine seem to be pretty spot on (they are factory TPMS). Keep in mind that when you drive, your tires heat up which raises the tire pressure. Also, ambient temperature will have an effect on your tire pressure too.

Try to get access to a gauge that is trustworthy and compare to your TPMS.
 

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Tire pressure will and can fluctuate as much as 5 pounds in a tire under certain conditions and loads. Too, tire gages are not calibrated so it is a crap shoot on what you get taking a reading say, at the local air pump situation where the gages are hammered against the payment etc.

Purchase a reasonable cost gage in the pressure range of your tires. Say you are suppose to run 35 PSI so buy a gage that only goes to say 60psi.

Learn the difference in readings from your gage and the sensors.

Better yet remember to only take pressures when the tires are COLD. What is cold? First thing in the morning before you drive or after the tires have sat in the shade for three hours.
 

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Tire pressure will and can fluctuate as much as 5 pounds in a tire under certain conditions and loads. Too, tire gages are not calibrated so it is a crap shoot on what you get taking a reading say, at the local air pump situation where the gages are hammered against the payment etc.

Purchase a reasonable cost gage in the pressure range of your tires. Say you are suppose to run 35 PSI so buy a gage that only goes to say 60psi.

Learn the difference in readings from your gage and the sensors.

Better yet remember to only take pressures when the tires are COLD. What is cold? First thing in the morning before you drive or after the tires have sat in the shade for three hours.
X2. When you get the Procal lower your threshold. You'll drive yourself nuts with the JK TPMS system. The threshold set when they go off from the factory is too high. The winter is the worst. That's when all the TPMS' go off due to cold weather tire pressures.
 

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Set my TPMS to zero, it's annoying.

Bought an accurate tire pressure gauge from Summit for $15 after going through the same thing.

Tried 3 different tire gauges after airing down, got 3 different numbers.

We all had the typical pen stick style. I'm guessing they either don't work well at low psi or they just don't work well at all. I was shooting for 12-14 lbs. No idea what we really had.

Summit gauge is accurate enough for Jeep tires. Works surprisingly well at low pressure. 1 to 10 psi was spot on.

Tested it at work on a digital calibrated air pressure regulator.
Started at 1 psi and slowly went up to 55 comparing the two.

Summit gauge read about 1/2 a psi high above 25 psi.

Linky:

http://www.summitracing.com/parts/sum-900006/overview/
 

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Tire explosions. Nitrogen is an inert gas therefore beneficial for aircraft and racing tires which undergo high temperature and drastic pressure changes. Waste of money in our Jeeps if you ask me.

Completely. Unless it's free you're wasting money on a street vehicle. Besides, most commercial N2 generators top out at 95-98% purity, which is not very pure.
 

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Completely. Unless it's free you're wasting money on a street vehicle. Besides, most commercial N2 generators top out at 95-98% purity, which is not very pure.
Yeah, I went through this argument with my father in law. He was freaking out because his tires were low and they came nitro filled from the dealer. I had to explain to him that it was just a marketing scheme to get you to spend more money and he didn't want to believe it. He agreed to let me top them off only because I have a dental air compressor and I told him the air was as pure as it will get....LMAO. It's true, a dental compressor will give you super clean air, but has nothing to do with nitrogen. I then told him that air is about 78% nitro gen and another argument started. Jeez!!!
 

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Don't always trust the tpms. The sensors in each wheel have batteries, and when they start to fail they can give false readings. Nitrogen is a waste of money. Everyone that comes into my shop doesn't like it they are always filling and checking there pressures just like normal air. Just get a good guage and your set.
 

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I don't think you should expecting tire pressure gauge accuracy to be the same. There are standards (N.I.S.T.) establish the tolerance of measuring instruments.

Having said that. I don't think there is much inspections going on the test all of the foreign manufactured tire gauges to see that they are within industry standards.
 

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I don't think you should expecting tire pressure gauge accuracy to be the same. There are standards (N.I.S.T.) establish the tolerance of measuring instruments.

Having said that. I don't think there is much inspections going on the test all of the foreign manufactured tire gauges to see that they are within industry standards.
You need to spend some money for an accurate gauge. I have a Longacre digital racing tire pressure gauge that is accurate to 0.3%. I bought it a few years ago when I tracked my Camaro and had to constantly monitor tire pressures when doing road courses to create historical data to get the best grip on the track.

I laugh when someone says I spent $30 and bought an accurate tire gauge. But realistically for regular driving it's good enough.
 

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You need to spend some money for an accurate gauge. I have a Longacre digital racing tire pressure gauge that is accurate to 0.3%. I bought it a few years ago when I tracked my Camaro and had to constantly monitor tire pressures when doing road courses to create historical data to get the best grip on the track.

I laugh when someone says I spent $30 and bought an accurate tire gauge. But realistically for regular driving it's good enough.
If you will read my post again, I was replying to a quote about the accuracy of two different tire gauges being the same. I'm content that the tire gauge I use is correct.
 
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