A Cautionary WARNING

[Guest]

I have a compressor for pumping my tyres up but was not sure about the accuracy of the digital gauge (it's one of those RAC jobbies). So, last time I was at Sainsburys in Shrewsbury, I used their free set up to pump the tyres up to the correct pressure as I was going on a longer journey than usual and wanted to maximise the MPG. I set the pressure at 33, then 32 but I was a little concerned that it took a while to get the front and rear's up to their usual pressures but thought that perhaps the pump was struggling -it had recently been off-limits due to a fault, but was now working (in a fashion).

 After having driven up the road to Dobbies roundabout, I knew something was wrong, as they felt a little too hard. Back at home I used my untrustworthy -now the opposite- digital tyre pressure gauge (hand-held gadget, not the RAC pumper-upper) and was shocked to find the fronts at 47psi and the rears at 46. So, it seems the issue with Sainsburys compressor is not fixed, as each tyre was over by 14psi.

  So, the cautionary tale here is do not trust these (fuel) garage air pumps as they can be so out of calibration they are dangerous.

[FROSTYBALLS]

Forecourt tyre inflation equipment should be regularly re-calibrated, but checking this is the responsibility of local trading standards. Few trading standards do actually check this is so, as very few have the resources to carry out regular checks.

Best bet is to take your own tyre pressure gauge and use that in conjunction with the forecourt equipment.

[sparrow2]

One possible other reason to check your tyre pressures at home is it does say in the owner's manual that you should do it when the tyres are cold. They cannot be cold if you have driven to the garage! A warm tyre will give a higher pressure reading.

I check them at home and I have identified another minor issue. In my drive in the morning when the sun is out it shines on just one tyre and I have found that makes about 1psi difference to the pressure! So I only check them when the sun is not shining on the tyres too.

[Guest]

On 1/21/2017 at 3:05 PM, FROSTYBALLS said:

Forecourt tyre inflation equipment should be regularly re-calibrated, but checking this is the responsibility of local trading standards. Few trading standards do actually check this is so, as very few have the resources to carry out regular checks.

Best bet is to take your own tyre pressure gauge and use that in conjunction with the forecourt equipment.

True, and as it is so small, fitting in many places, easy to carry about too, and a good idea. I had left it in the bag for the pump at home, lesson learned.

[Guest]

4 hours ago, sparrow2 said:

One possible other reason to check your tyre pressures at home is it does say in the owner's manual that you should do it when the tyres are cold. They cannot be cold if you have driven to the garage! A warm tyre will give a higher pressure reading.

I check them at home and I have identified another minor issue. In my drive in the morning when the sun is out it shines on just one tyre and I have found that makes about 1psi difference to the pressure! So I only check them when the sun is not shining on the tyres too.

Yep, I agree, they cannot be cold if I have driven to the garage, which is why I only use the garage forecourt tyre pumpy uppy thingies when we have been shopping and the tyres have cooled down. Can't say I have ever noticed the difference due to the sun heating the tyre, but I see your point. When I worked in Saudi it was a little difficult to avoid the sun, I wonder what effect that had on pressures?

[craggle]

Temperature will only account for one or two psi in a tyre, not the 14psi difference you saw. 

What I need is a tyre pressure that has a very small range like 0-25psi. I ride a big wheeled, Fat Bike and the tyre pressure on that can be as low as 5psi but t's hard to find an accurate gauge that low. My Cobra kit car only runs at 20psi tyre pressures too and you can get a number of different pressures with different gauges on them.

Craig.

[Soeley]

35 minutes ago, craggle said:

Temperature will only account for one or two psi in a tyre, not the 14psi difference you saw. 

What I need is a tyre pressure that has a very small range like 0-25psi. I ride a big wheeled, Fat Bike and the tyre pressure on that can be as low as 5psi but t's hard to find an accurate gauge that low. My Cobra kit car only runs at 20psi tyre pressures too and you can get a number of different pressures with different gauges on them.

Craig.

I bought one of these GAUGES when I got my iQ 5 years ago, had to change the Battery once in it. Craig it goes down to 5 psi, don't know about the accuracy down at that level though?