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[Bo Bo]

I used one of those digital tyre pumps at a local garage a couple of weeks ago & put in 32PSI all round & decided to check them this morning on my way to work at a different garage but still a digital one.

31 in rears, OK understandable but 33 in the fronts, how's more air got in there  :-/

Guess it's a calibration thing....

[Jimbob]

Pressure varies with both altitude and temperature.

IIFC that is why they fill tyres with nitrogen in some (hot) countries

[Bo Bo]

Hhmm well the garages are less than half a mile apart so don't think altitude comes into it, similar temp & distance travelled....

[Admin]

Just because a gauge has a digital display does not make it accurate.
I suspect it is as you say, calibration is maybe not the best...

[Markjay]

Pressure varies with both altitude and temperature.

IIFC that is why they fill tyres with nitrogen in some (hot) countries

Nitrogen is used because for some reason it does not escape through the rubber so the tyres do not loose pressure.

I am sure we have a chemical engineer somewhere among our members who will provide the scientific explanation  (e.g. smaller atoms / molecules etc...)

[Markjay]

As for digital gauges, I have no problem reading the mechanical ones, and I try to avoid things that need batteries where possible...

[Kevin Wood]

Nitrogen is also dry, so you don't end up with water vapour in the tyre. Water vapour can cause much greater pressure increases with temperature than nitrogen alone. In a racing environment where tyre pressures must be accurately controlled at extreme temperatures nitrogen is a must.

My local tyre fitters will fill tyres with nitrogen if you ask them to. I've never bothered because there's no way I'd notice the difference.

Kevin

[Tony H]

Pressure varies with both altitude and temperature.

IIFC that is why they fill tyres with nitrogen in some (hot) countries

Nitrogen is used because for some reason it does not escape through the rubber so the tyres do not loose pressure.

I am sure we have a chemical engineer somewhere among our members who will provide the scientific explanation  (e.g. smaller atoms / molecules etc...)

Thats correct

[Taxi_Driver]

I used one of those digital tyre pumps at a local garage a couple of weeks ago & put in 32PSI all round & decided to check them this morning on my way to work at a different garage but still a digital one.

31 in rears, OK understandable but 33 in the fronts, how's more air got in there  :-/

Guess it's a calibration thing....

Could also be explained by different tyre temperatures.....i think your suppose to check the pressures with cold tyres......tho dont think the garage will be too impressed if you park your car next to air line and say i'll be back in the morning when the tyres have cooled down  

[miggy]

Dont rate digital gauges, cannot beat the mechanical ones, digital readout on my air pump never reads the same as my mechanical one.

 

[Bo Bo]

Nitrogen is also dry, so you don't end up with water vapour in the tyre. Water vapour can cause much greater pressure increases with temperature than nitrogen alone. In a racing environment where tyre pressures must be accurately controlled at extreme temperatures nitrogen is a must.

My local tyre fitters will fill tyres with nitrogen if you ask them to. I've never bothered because there's no way I'd notice the difference.

Kevin

Interesting & yet I guess 75% ish of the air we put in tyres is Nitrogen....

[DaveL]

Dont rate digital gauges, cannot beat the mechanical ones, digital readout on my air pump never reads the same as my mechanical one.

 

imho mechanical gauges get bumped and thumped and eventually the mechanical parts tend to wear. Therefore going out of acurracy. The digital gauges, on the other hand, can be self calibrating before use. I am not talking about the ones at a garage forecourt, although i believe that they have to be within a certain accurracy.

Do any other members have a preferrance? :-?
 8-)
DaveL

[Taxi_Driver]

Do any other members have a preferrance? :-?
 8-)
DaveL

I prefer digital readouts on any guage/measuring device.....not because its more accurate (that depends on how well its been built and calibrated) but because it reduces user error on reading the value.

[Chopsdad]

I've got 2 digital guages and they vary 1-2 PSI.

When I challenged local garage that their digital guage was out, they explained that it is regularly serviced within tolerances and my guage must be wrong  

How can a £5 guage from Woolies be wrong  :-/

Cheek