Tyre Pressure Dropping

Phonesis

Phonesis

Phonesis

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Recently got a 2005 Suzuki Swift and all is good. It's my first car so still learning things and recently boosted the PSI of all 4 tyres at a local petrol station using one of those 50p tyre inflation pumps.

Front tyres were both 33 PSI and rear 30 PSI as per the manufacturer's guidelines.

Couple weeks passed and I decided to use the pump again (same one) just to see if the PSI had dropped. The pump detected the rear tyres were about 28 PSI, one of the fronts was around 30 and the other 25.

Is this normal to see PSI drops like this so soon after adding air? I only drive about 20 miles a week on average.
 
No but then I wouldn't really trust one of those pumps to be accurate either, especially if you're checking the pressures while warm.

Pick up a gauge from halfords or somewhere and check them at home when they're stone cold, if you still see drops then you've got a slow puncture or a leaky valve.
 
Were the tyre temps the same - was one with cold tyres, one with warm tyres after a run - can make a difference?
 
Could be: Slow puncture, poorly fitted, tyre temperature, aliens, any number of other reasons.

Invest in a tyre pressure gauge or pump so you can check it yourself every week or so to keep an eye on it. My car came with a 12v compressor that I can plug into the cigarette lighter to check/adjust it, dead convenient.
 
Think the tyres were a fair bit colder on second check (had been driving for about 10 mins).

Yeah sounds like I need to pick up a gauge. Will grab one and keep an eye on it.

What's the best way to inflate tyres then? I take it these petrol station pumps are not the best way?
 
Phonesis said:
Think the tyres were a fair bit colder on second check (had been driving for about 10 mins).

Yeah sounds like I need to pick up a gauge. Will grab one and keep an eye on it.

What's the best way to inflate tyres then? I take it these petrol station pumps are not the best way?
Click to expand...

Best way is getting a 12v portable one and you can do it yourself on the go then for free. Something generic like this one, then you can test your pressures etc while at home, without temperature getting in the way of reading.

http://www.amazon.co.uk/12-Volt-Digital-Inflator-Compressor-Built/dp/B000Q4UBMW
 
Tyre temperature has a big impact on pressure. On a cold day, say <5 degrees C, you might see a pressure difference of 5 PSI on cold (ambient temperature) tyres vs. warmed up at 18 degrees C.

Chances are that if you're seeing all pressures drop around the same amount it's just temperatures to blame.

As others have said, get an accurate gauge and measure them under the same circumstances/conditions to check.
 
Thanks all, have learnt something and it makes sense regarding temperature. Just didn't cross my mind. Will get a gauge and maybe one of those 12v pumps.

Out of interest, what sort of benefit is there to having the PSI at the recommended level? Better handling/fuel economy? Is it illegal to drive under the recommended PSI?
 
Better handling, better fuel economy, better tyre life but no there's no specific law about keeping your tyres at a sensible PSI although they may be able to shoe horn it in under another offence if you happen to have an accident while driving on a seriously deflated tyre.
 
Stringy said:
Could be: Slow puncture, poorly fitted, tyre temperature, aliens, any number of other reasons.

Invest in a tyre pressure gauge or pump so you can check it yourself every week or so to keep an eye on it. My car came with a 12v compressor that I can plug into the cigarette lighter to check/adjust it, dead convenient.
Click to expand...

+1 had the same, kept bugging me until i took it to my dealer who found a nail in the front causing the loss every other week. Replaced under Warranty. Would advise the OP to follow the slow puncture route...
 
nam said:
+1 had the same, kept bugging me until i took it to my dealer who found a nail in the front causing the loss every other week. Replaced under Warranty. Would advise the OP to follow the slow puncture route...
Click to expand...

If all the tyres are losing pressure, which I think from the first post they are, then it's more likely to be temperature related than having a slow puncture in all of the wheels.
 
I check my Tyres every two weeks and the fronts are 29 PSI and 36 PSI rear, I checked them last week and the rear right was down to 33.5 PSI according to my digital pressure gauge which was unusual so I pumped it up to 36 PSI.

Thought I may have a slow puncture so I checked again today and it’s still 36 PSI. Phew!
 
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