I am tyred of this

[OFSO]

This morning the car informed me that one tire pressure was low. Checked, front right was 1.8 bar so shot off to filling station, put in 2.5 bar. Back in car, as expected alarm gone, all tires ok.

This afternoon down to the tire depot to see friendly owner. Whipped off tire, no sign of damage so put it in tank, no bubbles. Pronounced it perfect. Checked all other tires with his (certified) gauge, all up to pressure.

I would suspect a faulty alarm system except tire pressure was low and pumping the tire up cleared the alarm.

Mystery.

[4mastacker]

I switched my car's tyre pressure warning thingy off as it was such a distraction and giving false warnings after I had to have tyre replaced. Nowt wrong with the pressures just the difference in circumference due to the deeper tread on the new tyre.

[CharlieOneSix]

....I would suspect a faulty alarm system except tire pressure was low and pumping the tire up cleared the alarm.....

A neighbour kept losing pressure from one wheel. It turn out to be corrosion of the alloy wheel at the rim and the tyre wasn't quite seating properly. He had it dressed out and the problem disappeared.

[Sisemen]

...and it turns out that the American spelling of the word to describe what a car has four of which touch the road is the correct way. It should be “tire” and not “tyre”. It derives from the phrase “attire a wheel”. It seems that tire was in use in the UK until at least the mid 1920s when, for some unaccountable reason, the generally accepted spelling became tyre.

Not a lot of people know that!

[OFSO]

For the last months, during which time I filled the tires with air, the daytime air temperature was around 30°c. This morning it was 12°c. Let me say I do NOT think in any shape or form that this was responsible but could some physicist, scientist, professor of gas technology, or simply wise-ass-know-it-all post here the coefficient of air expansion with temperature ?

Boyles Law ?

[Groundgripper]

As a member of the lattermost of your three categories of correspondent I would offer:

https://www.quora.com/What-is-the-therm ... ent-of-air

and leave the stage to those amongst us who (claim to) know what they are talking about.

Where's F3 when you need him?

GG

[ian16th]

the difference in circumference due to the deeper tread on the new tyre.

This problem can upset the computer controlled 4 wheel drive systems, such Audi Quatro and Mazda6 MPS.

With a set of half worn tyres, a blow out can cost you a full set of 4 tyres.

I had ordered a Mazda6 MPS when I learnt of this, and changed my order to a FWD model.

[Fox3WheresMyBanana]

Speak of the Devil...

It is Charles's Law you need: pressure proportional to absolute temperature (for constant volume, which a car tyre pretty much is).

Ballpark figure: Your pressure needed changes 1% for every 3 degrees Celsius. Or another way is it changes by 0.1 bar for every 12 degrees Celsius if the normal pressure is 2.5 bar. All measured cold.
In old money, change by 1 PSI for every 10 degrees Fahrenheit.

Most important: Buy a decent tyre gauge - all the cheap ones are very variable.

My leaky tyres are almost always due to corroded rims.

It is also a good idea to find out the pressure needed if your tyres are warm. How warm tyres get depends a lot on individual circumstances, so check your tyre pressures cold, then check them again immediately after your usual drive. You will probably find it's only 0.1 bar more.

Other good stuff:
Know your aquaplaning speed - in mph this is 8.6x square root of pressure in PSI, so for 2.5 bar (typical for cars) it is 52 mph/83 kph Drive at 45 mph max on very wet roads and you should avoid aquaplaning, assuming your grip is good. This works!

90% of tyre blowouts happen in the last 10% of wear. I always get mine changed 2mm before the minimum.

More details:
Absolute temperature is measured from -273.15 Celsius, in Kelvin (K, 1K = 1 degree Celsius in magnitude) so 15 degrees Celsius is 288K

[llondel]

Ideal gas law is PV=nRT, so for a fixed mass of gas, PV/T is constant. Note that T is in Kelvin, so it's gone from 303K down to 285K. If you assume the volume stays constant, that's a 6% drop in pressure if I've done my sums correctly.

[TheGreenGoblin]

Ideal gas law is PV=nRT, so for a fixed mass of gas, PV/T is constant. Note that T is in Kelvin, so it's gone from 303K down to 285K. If you assume the volume stays constant, that's a 6% drop in pressure if I've done my sums correctly.

All of which is enough to Boyle one's blood!

[unifoxos]

As said by C16 and F3, corrosion on the rims is favourite - my Jeep will intermittently lose loads of pressure from the Front offside tyre, but the loss only occurs when a certain spot on the wheel is at the bottom, distorting the tyre enough for the leak to show. It won't show up in a water tank. Same happened previously on SWMBO's Chev. Tyre off, wheel rim cleaned up and tyre back on will sort it.

I have also known intermittent loss when a sharp item is in the tyre, but only loses air when it's at the bottom and not sitting freely in its own puncture hole. But you would spot this on a good inspection.

[izod tester]

I had a similar tyre pressure warning on the lh rear tyre on my Mazda CX5. The tyre dealer I use could not find a leak, but the tyre would deflate slowly over 3 weeks or so until the warning would recur and the tyre pressure was 4 psi low. After a year, and several checks, the slow puncture finally showed up in the bubble tank and a small screw removed. Tyre plugged and has given no more problems.

[ian16th]

I had a similar tyre pressure warning on the lh rear tyre on my Mazda CX5. The tyre dealer I use could not find a leak, but the tyre would deflate slowly over 3 weeks or so until the warning would recur and the tyre pressure was 4 psi low. After a year, and several checks, the slow puncture finally showed up in the bubble tank and a small screw removed. Tyre plugged and has given no more problems.

As a former resident of The Forrest, I think that your CX5 might be the ideal vehicle for the area.

Do you have a 4WD version with the 2.5l motor? Such a vehicle would make it easy to get up Harrow Hill in Jan/Feb!

I'm looking forward to the CX30, as I find the CX5 too big and the CX3 too small for my current needs. I await the local announcement, engine choices, and pricing. If Mazda SA get it right, I might prise open the wallet.

[Hydromet]

How robust are tires these days? My RAV 4 recently had its first puncture at 140,000 km. while driving on a rough dirt road. It's had a mix of city & country driving. I seem to remember punctures were much more frequent.

When I commuted by pushbike, punctures always seemed to occur when it was raining. Is there a reason for this, or is it just my selective memory? Kevlar belted bike tyres made a huge difference, but I was amazed at the amount of small glass splinters, short lengths of wire etc that they collected.

[ian16th]

More troubles with potholes than debris.

I have totally unsuitable low profile tyres.

[Ex-Ascot]

The prime cause of punctures in the bush here is small trees that have broken or been pushed leaving a very sharp spear like protrusion. Sometimes below the surface of the sand. Jacking up a vehicle in deep sand is an entertainment.

The safari camp managers here up river have bought a new used motor for themselves. It is a massive black Hilux. It is so high off the ground you need a step ladder to get into it. 5 completely different tyres. I questioned the legality and was told that this is
Africa.

[Fox3WheresMyBanana]

All my punctures and leaks here (4) have been short screws, nails or staples. All appear to be from electrical work. I suspect this is from stuff falling off trucks that are hauling it to the waste centres for disposal. it may be from the detritus left in the bed bouncing out on the way back.