I managed to pick up a slow puncture in one of my rears this weekend so I took it round to the local tyre fitters. They were able to fix the puncture which they guarantee to be as good as new and it only cost me

 

did he measure them with a separate gauge, or the gauge attached to the airhose ?

 

It doesn't make any sense does it. IME those digital things are spot on or obviously defective. There is no in between. You hadn't got one or more tyres in the sun and others in the shade after a frosty night when you checked the pressure I take it. After he'd altered the pressure what did your gauge say?

 

Ask if his pressure gauges are calibrated and how often. I use a 10 quid digi gauge as well and checked that against a recently calibrated aircraft pressure gauge. My 10 quidder was 0.5 psi out, not bad.

 

That doesn't make any sense? What's it being digital got to with it being accurate? It has to convert from an analogue sensor to the digital display so if the AD converter is out (which it will be) then it'll be inaccurate.

Think about the digital speedo in the S, that's not accurate.

 

The big issue here, is at what temperature you determine cold to be..
In the UK there is about between now, and six months ago, there is almost a 20C temperature difference in the amibient air..

That equates to about a 9% difference in temperature (using Kelvin, which is how the gas laws work, it's physics and confuse me the first few times through it), which gives a difference in pressures.

If you measure at "cold" now, you will have a 9% higher tyre pressure when it reaches working temperatures (using a rough 35C "normal" use) than if you inflated to the same pressure on a summer morning..

I know that the we're only talking differences over the weekend, but ambient temperature has quite a big part to play in this.. especially if you've driven to somewhere to get the pressures checked.

I know this doesn't help, but may explain..

 

And you of ALL people should have known this microbe!!!


(microbe's name is Kelvin for those who don't know)

 

[QUOTE=microbe,Dec 13 2004, 08:42 PM] I managed to pick up a slow puncture in one of my rears this weekend so I took it round to the local tyre fitters. They were able to fix the puncture which they guarantee to be as good as new and it only cost me

 

surely it shouldn't make a difference if the guy who checked it has calibrated his gauge? if he reads one tyre at 36 and another at 30, they were not both at the same pressure (irrespective of if that is 32, 34 or 36psi). which is what Microbe (kelvin ) is saying they were shortly before.

My guess is that the fronts were warmer than the rears and were not as cold as they were when they were originally inflated to a indicated 32psi.

 

I use a Karting guage, cost