I inflated them about two weeks ago to 35psi(well according to the machine).

 

Now 3 tires are around 34psi and seems to be steady there and the other around 31.5psi. In other words 3 tires seem to lose around 1psi , would that be when you take the hose out of the valve when using the machine?

 

So I thought if I inflated them to 36 then they would settle at 35 in a few days. I'm probably way off on my thinking here though.

Ambient temperature will affect tyre pressure.

 

You are getting excited over an insignificant difference on an everyday basic road-going vehicle.

1 hour ago, MicMac said:

Ambient temperature will affect tyre pressure.

 

You are getting excited over an insignificant difference on an everyday basic road-going vehicle.

 

Too much time on their hands during lock-down eh Mac...... Lol.

A 7.5° change in temperature will result in that difference, the ambient temperatures have swung much more than that in the last 2 weeks, the OP speaks of using the machine so I assume he was driving the vehicle for the first inflation which will have further heated the tyres.

 

Given that the "machines" normally have to be paid for I am guessing that the subsequent check was done at home, even with the same guage you would be lucky to see the same reading 10 minutes apart let alone 2 weeks.

4 hours ago, Aj77 said:

I inflated them about two weeks ago to 35psi(well according to the machine).

 

Now 3 tires are around 34psi and seems to be steady there and the other around 31.5psi. In other words 3 tires seem to lose around 1psi , would that be when you take the hose out of the valve when using the machine?

 

So I thought if I inflated them to 36 then they would settle at 35 in a few days. I'm probably way off on my thinking here though.

 

If you are losing more than 1psi each month, then that tyre has a slow leak. This is usually caused by a corroded rim where the rim meets the tyre bead, so that air escapes at this point. Of course, a slow leak can also be caused by a foreign object such as a nail penetrating the tyre.

Edited 11 September, 20205 yr by Carlston

My slow leak was corrosion on the valve seat / seal...

 

Ask the fitter to make sure it was cleaned before he fitted a new one.

7 hours ago, Aj77 said:

I inflated them about two weeks ago to 35psi(well according to the machine).

 

Now 3 tires are around 34psi and seems to be steady there and the other around 31.5psi. In other words 3 tires seem to lose around 1psi , would that be when you take the hose out of the valve when using the machine?

 

So I thought if I inflated them to 36 then they would settle at 35 in a few days. I'm probably way off on my thinking here though.

This bit suggests to me you did the pressures at a petrol station? If you had been driving for a while beforehand then when you topped up the pressures the tyres would be warmer, causing higher pressure. The 1-2psi drop is probably just cold vs "hot" pressures.
(also, I use 36 front 44 rear on my combi, fully laden pressures, good for economy too, and the slow leaks in both N/S tyres)

Edited 11 September, 20205 yr by robt100

You don’t state what car you have or tyre fitment.

 

36 would be on the higher side for something with a low profile tyre for example 

Optimum pressure will vary for individual tyre specs, the guide on the fuel filler cap flap is only that and is for the factory supplied tyres.

 

Obviously fitting different tyres with say a softer sidewall, loading the car, the weather and type of driving will all be factors.

 

Use the guide for your vehicle and experiment +/- 10%.