Tyre Pressure - Very different readings at different supermarkets

pinkteapot

Moved house recently (well, August), went to check the tyres at the air machine at Tesco last night. Previously we had used the one at Morrisons in our old town for two years.

Pressures should be front 32 and rear 28. For the couple of years at Morrisons I checked every month or two and occasionally they would be 1 PSI off and need a bit of pumping.

Last night at Tesco, the machine decided that all the tyres were 5 PSI under what they should be and pumped them up accordingly.

Not entirely sure whether Morrisons' machine was wrong and I've been driving around under-inflated for two years, or whether Tesco is wrong and I'm now over-inflated.

Being girly about such things, there's no chance they're now pumped up to the point where they'll burst on the motorway at the weekend, right?

vikingaero

On some tyres you can get a huge drop in pressure which coincides with the cold weather. If you've left it since August before checking then a small amount of leakage and a temperature drop could account for the difference. Most manufacturers tell you to check the pressures when the tyres are cold - cold could mean 15C cold or some manufacturers recommend checking them at 0C. I go for 0C and adjust upwards. So if it's 8C outside I pump in one extra psi.

You really need to buy a tyre pressure gauge and not rely on supermarket pumps.

Ebe_Scrooge

All garage tyre gauges are notoriously inaccurate. The best thing to do is buy yourself a pressure gauge - it'll only be a couple of quid. Garage gauges are fine as a guide, but don't rely on them being accurate.

Don't worry about your tyres bursting, you'd need far more than a few PSI to do that. But it is worth making sure they're correct, as incorrect inflation can increase tyre wear and increase fuel consumption. Don't get into a lather over it, but probably worth picking up a gauge at the weekend.

pinkteapot

Hmmm I had one from Halfords and it gave different readings every time I used it (and I mean a few times in the space of ten minute) so I decided they weren't as good as the supermarket ones.

Saw a thread on here today recommending pressure gauges - will look at those.

andygb

Buy a good gauge, this came out top in a test

http://www.autoexpress.co.uk/products/products/66834/race_x_professional_tyre_gauge.html


Check tyre pressures weekly, and buy a decent pump. Always take pressure readings when cold, at the start of a journey, because a quick blast on the motorway, with some heavy braking can make a big difference.

Hammyman

Buy a cheap low rent gauge and you'll get what you pay for. Also the supermarket ones aren't exactly accurate either but the digital ones are more accurate than those on the end of the hose which spend their lives being dropped on the floor.

pinkteapot

It wasn't that cheap - £9.99 from Halfords. In fact it was the one below - maybe mine was just faulty:
http://www.autoexpress.co.uk/products/products/66842/halfords_digital_tyre_pressure_gauge.html

I do always check the tyres cold. The supermarkets I've used for the last few years are within about half a mile of home on slow roads.

Supermarket ones were both those with a digital readout on the main unit. In fact they looked like exactly the same machine which is why I was slightly surprised that they read so differently.

I have only checked the pressures every 1-3 months in the past (car only gets used at weekends) and it's never been more than 2PSI down on where it should be; usually they're still fine or only 1PSI under.

roddydogs

Yes but when you take the TP with that gauge (or any one) by the time you've got a good reading, at least 2lb psi has escaped.. Liked the 0c advise, ill wait till the temp is freezing till I take TPs..not.

andygb

roddydogs wrote: »

Yes but when you take the TP with that gauge (or any one) by the time you've got a good reading, at least 2lb psi has escaped.. Liked the 0c advise, ill wait till the temp is freezing till I take TPs..not.

I have never lost 2lb pressure with any of the dial gauges which I have used, I would say it is less than half a pound. I used to inflate them 1lb over, and then test them twice. You could easily use 2lb taking a pump adaptor off if it is a bit sticky though!;)

Hotspur

The mechanical metal pencil type gauges are robust and the most accurate in my experience and also cheapest but, not always the easiest to read.

Tyres should always be checked when cold/ambient temp rather than after travelling a long distance. A couple of miles to the garage shouldn't matter much.

In the past, having tested many garage gauges over several years I can say that they are often accurate when new but take a lot of customer abuse so soon go out of calibration. I always use a pencil gauge to check now.

H