Latex tube pressure loss

Decided this morning it was time to put the summer tyres back on the Cube, a pair of 700x28 GP4000S IIs bought and used last summer, along with the pair of Vittoria 25-28mm latex tubes fitted with these tyres last year.
At ~0830, I inflated them to ~95PSI front and ~100PSI rear.
Just thought I'd check the pressures at ~1715, before thinking about getting changed for an early evening ride, to find the front has dropped to ~80PSI and the rear to ~70PSI! :shock:
I was aware of this pressure drop last summer, albeit not to this extent, often inflating to similar ~95/100 front/rear (when I was ~78Kg rather than ~81.5Kg currently) to allow for ~10PSI drop over a ~3-hour ride.
In contrast, I've been using cheapy Valvert 25-32mm butyl tubes with "28mm" GP 4 Seasons (that measure ~29mm wide) at ~90/95PSI since around early November and they barely drop any pressure between bi-weekly checks with the same track pump.
Now "28mm" GP4000S IIs measure ~31mm in the real world... Is this extra volume stretching the Vittoria tubes so they diffuse air even quicker, or is it more likely I have a micro-punctures (didn't need to use levers to install today, but did last year IIRC)?
I guess I could test the diffusion theory by using the 4 Seasons with the latex tubes, but was keen to feel the ~20W (going on https://www.bicyclerollingresistance.com/ ) reduction in rolling resistance... I need all the help I can get after a ~13% drop in my 20mins power after my early March to early May lurgy!
At ~0830, I inflated them to ~95PSI front and ~100PSI rear.
Just thought I'd check the pressures at ~1715, before thinking about getting changed for an early evening ride, to find the front has dropped to ~80PSI and the rear to ~70PSI! :shock:
I was aware of this pressure drop last summer, albeit not to this extent, often inflating to similar ~95/100 front/rear (when I was ~78Kg rather than ~81.5Kg currently) to allow for ~10PSI drop over a ~3-hour ride.
In contrast, I've been using cheapy Valvert 25-32mm butyl tubes with "28mm" GP 4 Seasons (that measure ~29mm wide) at ~90/95PSI since around early November and they barely drop any pressure between bi-weekly checks with the same track pump.
Now "28mm" GP4000S IIs measure ~31mm in the real world... Is this extra volume stretching the Vittoria tubes so they diffuse air even quicker, or is it more likely I have a micro-punctures (didn't need to use levers to install today, but did last year IIRC)?
I guess I could test the diffusion theory by using the 4 Seasons with the latex tubes, but was keen to feel the ~20W (going on https://www.bicyclerollingresistance.com/ ) reduction in rolling resistance... I need all the help I can get after a ~13% drop in my 20mins power after my early March to early May lurgy!


================
2020 Voodoo Marasa
2017 Cube Attain GTC Pro Disc 2016
2016 Voodoo Wazoo
2020 Voodoo Marasa
2017 Cube Attain GTC Pro Disc 2016
2016 Voodoo Wazoo
0
Posts
#normalforlatex
I am not sure. You have no chance.
Marin Palisades Trail 91 and 06
Scott CR1 SL 12
Cannondale Synapse Adventure 15 & 16 Di2
Scott Foil 18
you can try larger diameter tubes, might slow it a bit, but they'll still lose pressure
The Valvert tubes they replaced are ~150g compared to the latex ones being ~75g each, will see how things go over the next few days or so... Beginning to remember getting a bit peeved with this pressure loss last year and contemplating ditching the Vittorias.
2020 Voodoo Marasa
2017 Cube Attain GTC Pro Disc 2016
2016 Voodoo Wazoo
I used to think the loss of pressure was a good thing for long races. Start on the high side when you’re fresh, then the loss of pressure would give a bit more comfort as the ride went on. On 21mm tyres everything helped