Tyre pressure weirdness

[Le_Fromage_Grande]

I've had a new tyre out on the back wheel of my GSXS, so far so good, got it home and checked the pressure, 25psi, should be 42psi, no idea why the shop set it to 25, so I pumped it up to 42 and thought I'll check it to see if it goes down, so last night at 22:30 it was 41, this morning at 07:30 it was 42.5, tonight at 18:00 it was 39.5, the bike hasn't been ridden.
Could the pressure go up with lower temperatures?
Could it be the tyre mildly expanding as it gets warm lowering the pressure?

[KungFooBob]

What gauge you using?

I had a digital one that was all over the shop when the battery started to go flat.

[Le_Fromage_Grande]

It's an old digital Halfords one of unknown vintage, that was another thought. I might have one of those slider things somewhere.

But tonight's 39.5 I checked 4 times (it's now down to 39 because I checked so many times)

[KungFooBob]

Split it open and it probably takes a CR2032 or similar.

[wull]

It’s your bikes way of telling you that 42 psi is too high.

[Le_Fromage_Grande]

It’s your bikes way of telling you that 42 psi is too high.

It's what Suzuki recomend, personally I think 35 would be about right

[wull]

What tyres are fitted? Those are the bike manufacturers recommended pressures which have been the case for about 400 years, forget about them. I always have a look at what the recommendations are for the tyres that are fitted, and then fine tune it.

[wull]

with that being said if it works then go with it, if it ain’t broke don’t fix it.

[Skub]

Temperature will definitely impact on psi readings. I prefer one of those Halfraud's pen type tester. They are simple and more reliable imo.

[Le_Fromage_Grande]

Pretty sure it's temperature related, it's cooled down here and it's up by 1.5 psi.

[Dodgy69]

How's the fluctuation compare to other tyre. ?

[Le_Fromage_Grande]

How's the fluctuation compare to other tyre. ?

Dunno, the front is impossible to get at with my pressure guage.

[Mr. Dazzle]

Pretty sure it's temperature related, it's cooled down here and it's up by 1.5 psi.

That is the reverse of what you'd expect, unless something very odd is going on.

Or the temperature is effecting your gauge!

[Le_Fromage_Grande]

Pretty sure it's temperature related, it's cooled down here and it's up by 1.5 psi.

That is the reverse of what you'd expect, unless something very odd is going on.

Or the temperature is effecting your gauge!

Is it though, the tyre is changing temperature because the outside air temperature is changing, meaning the tyre is expanding when warm, lowering the pressure of the air inside and contracting when cold , raising the pressure, this is different to when you ride on a tyre, when I assume the air inside gets got and expands quicker than the tyre, but I'm not sure of my logic on this one.

Or as you say the temperature effects the guage or the way I'm measuring it.

[wull]

What tyres do you have fitted

[Le_Fromage_Grande]

What tyres do you have fitted

Pirelli Angel STs.

[The Spin Doctor]

Pretty sure it's temperature related, it's cooled down here and it's up by 1.5 psi.

That is the reverse of what you'd expect, unless something very odd is going on.

Or the temperature is effecting your gauge!

Is it though, the tyre is changing temperature because the outside air temperature is changing, meaning the tyre is expanding when warm, lowering the pressure of the air inside and contracting when cold , raising the pressure, this is different to when you ride on a tyre, when I assume the air inside gets got and expands quicker than the tyre, but I'm not sure of my logic on this one.

Or as you say the temperature effects the guage or the way I'm measuring it.

Nope, the static tyre itself won't expand when warm - at least, not that I have ever heard - but the air inside it will, which means the pressure goes up. Not by much, mind. Across a typical 10c night to 20c day, my calculations (Gay-Lussac's Gas Law) suggest that the variation would be around 1.5 PSI.

[Count Steer]

Coefficient of thermal expansion of air is way higher than rubber. I'd try another gauge.

[Mr. Dazzle]

The tyre itself will expand, s'just that the air inside it will expand alot more.

I'd be more inclined to believe the temperature effects the battery voltage in the sensor or something like that.

How good are cheapo sensors anyway?

[Le_Fromage_Grande]

I did say it was weird, it probably is the guage, that would make more sense, it's not exactly a scientific instrument.

But it is interesting from a perspective of those people who say they can feel the difference in 0.5 psi tyre pressure, I know I can't feel the difference 5 psi makes.