club.liberty.asn.au

I can't find the thread/post that someone posted earlier, about service stations' tyre pressure gauges being inaccurate...

I've just checked with the national forecourt manager here at work (Coles Express/Shell) and I've been told that our stores all get calibrated at least annually. He hasn't heard any issues with major variances; however if you feel they are wrong, please mention it to the staff member inside and they'll raise a problem to get a contractor to calibrate it.

Visited a Shell Petrol Station and pumped my tyres to 39psi (front) and 38psi (rear). Had my electronic gauge with me and double checked the settings, they were correct at the time.

Morning after (cold start) before driving out, I checked again. Tyres pressures had all decreased in value. Front's were 35psi and rears were 34psi.

It might be that they were correct at the time (@ petrol station) however I'd been driving so that might be the reason behind the difference. Been told best time to check and tell if they are all 100% correct is first thing when the tyres are still cold.... not when you have been driving.

u and your random questions.

In my experience the inaccuracies are due to the fault of the clasps that hold the nozzle onto the valve, and allow leakage when the machine is pumping the air in.. so the reading constantly moves. The servo's I've been to where the clasp grips on firmly, the readings have been fine, and double checked with my pressure gauge

Trieu, yours would have been the difference between hot and cold tyre pressures.

tangcla wrote:Trieu, yours would have been the difference between hot and cold tyre pressures.

Spot on. I prefer to fill my tyres when cold, at home. 35psi cold equates to 39psi hot with my tyres. That's a 4psi increase cold -> hot. This is what you should aim for (the 4psi increase that is). It's known as the Pirelli principle from memory.



Cheers,
Deucer.