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Discussion Starter #1
Just went round my wheels lowering the pressure from 38 to 35 to see if there is any difference between the two pressure in terms of MPG.

I used a normal mechanical pressure gauge of the sort you just push on to the valve and the pressure indicator shoots out the end to show what your pressure is.

I set all 4 tyres to exactly 35 with the gauge. Turned the car on and looked at the tyre pressure monitor and it is showing all the pressures lower than the mechanical gauge.

3 of them were 34.2 and the fourth was 33.8.

So which of these two measurements do you think is likely to be the most accurate? I wonder if there is somewhere you can go to get a calibrated pressure reading?

Any thoughts anyone?

 

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The Antara ones are very sensitive. I use a digital gauge but still had a slight variation in pressure.

Btw just in case anyone try's it the Antara only polls or updates the pressures every few minutes so don't bother trying to use it inflate your tyres or you will be waiting a while on it showing the actual pressure.

Edited by: Grumps
 

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Discussion Starter #3
Grumps said:
The Antara ones are very sensitive. I use a digital gauge but still had a slight variation in pressure.

Btw just in case any try's it the Antara only polls or updates the pressures every few minutes so don't bother trying to use it inflate your tyres or you will be waiting a while on it showing the actual pressure.
OK, thanks for that. I'll nip out and have another look at the pressure reading after I've had my tea.
 

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My god what did you have a 9 course meal and coffee and chocs for afters
 

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Discussion Starter #5
Checked the pressure again this morning and it's still the same.
The tyre pressure gauge shows all tyres at 35 when cold.

The monitoring system shows these figures

Front left - 33.1
Front right - 32.5
Rear left - 33.1
Rear right - 34.2

There is still the same difference between the gauge and the car when the tyres are hot. The psi is about 3 psi higher when hot.

Had a word with the dealer and the workshop guy said he would expect the car to vary from the gauge by about 1 to 1.5 psi. He said I should probably take the gauge as being the most accurate.

Well as 3 of these reading are more than 1.5 psi low, I've booked the car in on Monday morning to have things checked. We will compare my tyre gauge with his tyre gauge and see whether it's the car or my gauge which is wrong.
 

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Discussion Starter #6
smino said:
My god what did you have a 9 course meal and coffee and chocs for afters
No, that was the day before.


Being as it was Thursday, it was Cow Pie day.
 

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As Grumps said, the mechanical guages aren't very accurate compared to the digital and even they can go wrong.
As you've said Inchy you did it whilst cold and again that can depend on the outside temperature. ]
 

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Took me 2 days of fiddling around with mine to get them all at 35psi on the onboard computer, when cold before driving. (That was usinga Digital Pressure Checker).I`ve noticed that especially when driving on t` Motorway, the in-car display can read as high as 39/40psi after a few miles. Just took this as normal, as all pressures were as near as doesn`t matter back to 35psi again the following day before moving off.
 

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Discussion Starter #9
Dilligaf said:
As Grumps said, the mechanical guages aren't very accurate compared to the digital and even they can go wrong.
As you've said Inchy you did it whilst cold and again that can depend on the outside temperature. ]
I'm not sure how big an effect the ambient temperature has on the measured PSI. I know the owner's manual says to take tyre pressure reading when the tyres are cold.

I don't really mind which measurement is right. My main concern is the in car measurement is showing as low as 32.5 when the mechanical gauge is showing 35. To me, if the mechanical gauge is correct,that much of a difference is telling me the sensor is faulty, and it's best to get the dealer to look at it.

I'll report back on Monday after I've been to the dealer.
 

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Discussion Starter #10
Isaac Hunt said:
Took me 2 days of fiddling around with mine to get them all at 35psi on the onboard computer, when cold before driving. (That was usinga Digital Pressure Checker).I`ve noticed that especially when driving on t` Motorway, the in-car display can read as high as 39/40psi after a few miles. Just took this as normal, as all pressures were as near as doesn`t matter back to 35psi again the following day before moving off.
Are you saying when the on board indicator is showing 35 psi, that your digital meter is also showing 35 psi?

I've measure my tyres when hot, and they tend to show about 3 PSI more than when cold.

I just need to know whether my gauge or the car is right here. I don't don't want to be driving around on under-inflated tyres..
 

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Hi Inchy,
Sorry if what I posted was confusing. The On Board Display "eventually" matched upperfectly with my Digital Tyre Pressure Gauge, which is also a Tyre Inflator as well. Problem I had, was that it took a few minutes each timefor the Computer to catch up with the increase or decrease in Pressures as I was fiddling about with the tyres, so it took a long time to get everything to tally up exactly. I reckon the on board display is pretty much smack on, so no need to worry. Being afinicky git, I wanted all of my tyre pressuresto read exactly the same, with no variation at all across all four. I was however a little surprised when in the middle of a high speed 100 mile motorway trip,I checked to see what thetyre pressures were showing, and my on board display said between 39 & 40psi all round. I thought that was a big increase from the original 35psi I had set them at. WhenI checked next morning before driving off, they were all back at 35psi again, with no more than 0.1psi difference between any of them. I had previously tried the 38psi "Eco" Setting, but found it far too harda ride for my taste, and couldn`t see any difference at all in Fuel Consumption, especially given that most of my driving is around town, or at best on A & B roads, with only an occasional Motorway jaunt.
 

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Isaac Hunt said:
Hi Inchy, 
Sorry if what I posted was confusing. The On Board Display "eventually" matched up perfectly with my Digital Tyre Pressure Gauge, which is also a Tyre Inflator as well. Problem I had, was that it took a few minutes each time for the Computer to catch up with the increase or decrease in Pressures as I was fiddling about with the tyres, so it took a long time to get everything to tally up exactly. I reckon the on board display is pretty much smack on, so no need to worry. Being a finicky git, I wanted all of my tyre pressures to read exactly the same, with no variation at all across all four. I was however a little surprised when in the middle of a high speed 100 mile motorway trip, I checked to see what the tyre pressures were showing, and my on board display said between 39 & 40psi all round. I thought that was a big increase from the original 35psi I had set them at. When I checked next morning before driving off, they were all back at 35psi again, with no more than 0.1psi difference between any of them. I had previously tried the 38psi "Eco" Setting, but found it far too hard a ride for my taste, and couldn`t see any difference at all in Fuel Consumption, especially given that most of my driving is around town, or at best on A & B roads, with only an occasional Motorway jaunt.
Exactly what I thought
 

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Discussion Starter #13
Took the car into the dealer yesterday to have them check out the tyre pressure monitoring system.
It seems the variance I was getting between my pressure gauge and the system was due to not driving the car for long enough before checking the system readings.

When the guy checked my tyres after I drove about 15 miles to the garage, the system and the gauge were closer, but still not exactly the same. But this time, it was within 1 to 1.5 PSI, which is supposed to be about as good as it gets.

The main thing I'm happy about is my mechanical pressure gauge is accurate. It matched exactly a manual gauge the mechanic had, so I know I can rely on it to tell me the right pressure.

I was rummaging through a bits and pieces box this morning and found a digital tyre pressure gauge. Can't remember buying it, but I'll give that a try when I get a couple of new batteries for it.
 
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