cole328

Gents - I am normally an old school "tire pressure gauge" kind of guy, but at the dealership today, the service guy told me that the better, more accurate method is to use the TPC mode on the computer, and to adjust against the "+" 1 and "0" indications. I tried to read the OM, but must admit, it was poorly written. he was trying to explain that rather than rely on the gauge, use this function as the computer will tell you, based on your driving style, temperature outside, etc., how many pounds more of air to add He said this may not necessarily jive with the indicated pressure on the air gauge. Any interpretations from the collective borg?

Thanks

jnx

Do not rely on the TPMS. Get a good gauge and use that. You will come to hate the TPMS.

Edgy01

I happened to love the TPMS. It's my first clue that I have an issue with a tire. It's far more precise than I am with a gauge.

axhoaxho

Does anyone know if it is correct that the TPMS sensor is sensing the air pressure inside the tire and as the temperature inside the tire (because the sensor is located inside the tire)?

If so, will it contribute to the reading differences between the TPMS and our tire guages (because the tire guages measure air came out of the tire valve, that cools down a little when passing through the valve, thus the temperature affects the psi)?

Could it also mean that both the TPMS and the tire guages are accurate, but just they are measuring the air in different places (inside the tire vs air coming out through the valve?)

Thanks for any insights

With best regards,

Edgy01

You're reading far too mch into it. Some of the TPMS set ups have been found to be off a bit while the key element here is not so much absolute accuracy, but the discovery of a DELTA pressure. If you are accustomed (as I am) to always seeing 33 (F) and 39 (R) when cold/cool and watch it proceed to 36 and 42 or more hot when one of them starts to deviate I know there will soon be an issue. I can't emphasize enough how perceiving that delta in temperature (other than a minor difference due to more sun on the south side of the car when heading due East or West will show a higher number in the day).

jnx

I am happy for you. I can use a gauge without any difficulty, and again the TPMS is a PITA.

rfedele

+1, it works from a consistency std pt.

mostolf

Can anyone recommend a good (smallish) tire gauge? TIA!

jnx

I use one from Griots, although it's not small. There are many available, you could do a search and see what others are using.

cole328

I agree with you guys on the use of the TPMS to help with deviations Question tho: Is it better to use the screen that shows teh actual pressures of each tire, so that you can see trends, or the screen that shows the "0", and "+1", which the dealer indicated was the better one, as this screen took into account driving style, air temp, etc., and might actually suggest that depending on stype of driving, one front tire may needs to be 2-3 pounds higher (or lower) than the other he described it almost like a smart "brain" that could make adjustments

I found this confusing, as unless you are DE'ing a car, I have always found that my car handled best with uniform tire pressures (i.e., 39R in both tires and 33F in both tires) Thanks

Cole

cole328

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p-cardriver

I searched for a while and found a wide range in the sensitivity/tolerances of tire gauges. I wouldn't buy one that didn't have accuracy available, preferably in the packaging. Many were +/- over a pound!

Get what you are comfortable using (I have digital for readability, some say stay away from digital) and is accurate. I carry an old pencil style in my pen holder (glove box) as a backup, but keep the more accurate one in the car usually too. I think I bought mine at Tirerack, couldn't find anything accurate locally.

I also found accurate ones for anywhere from about $12 to over $100 - depending on style and features and seller.

p-cardriver

cascade

I am still dealing with the paranoia of not having a spare tire on board, so I keep a regular eye on the TPMS pressures for indication of a leak (have had two nail/screws punctures in three months). It is a very good early warning system from in this regard. I also keep a radio shack electronic gauge in the glovebox, more from habit than anything else. Old dog, new tricks, etc.

jhbrennan

Whether the air is hot or cold will determine the pressure/volume of air in the enlcosed tire (hotter = more volume and higher pressure) - I seriously doubt the few mm's that the air travels through the valve will make a difference in temperature or pressure...but I'm not an engineer and have forgotten most of my physics. As others have said, I don't rely on TPMS for accurate tire pressures (I use my trusty gauge) just differential changes.

GSIRM3

I think the reason the TPMS does not always agree with a good tire gauge is because the TPMS measures psi (converted to a psig value by car's computer), and the gauge is measuring psig. Variations in atmospheric pressure will effect the psi reading relative to the psig. At sea level, the TPMS and a gauge might differ by 2psi, but measure the same at 5,000 feet.