I started using latex tubes one week ago (reasons: rolling resistance and better feeling).
Yesterday I measured a pressure loss of around 0.3 bar (~5 psi) in 5 hours. Should I start with a higher pressure so that the average over the ride is close to the optimal pressure? What pressure do you run for longer rides?
I’m concerned that the pressure will drop too much during longer rides (7-8 hours). Is latex unsuitable for this?
Excuse my beginner question. Google only gave half answers.
C.1psi drop per hour isn’t anything to worry about. Latex tubes are absolutely suitable for long rides (the rolling resistance savings just mean it won’t be quite as long as it would have been on butyl 
)
Just err on the side of a couple more psi when topping it up first thing. This is exactly what they used to do with tubulars at Paris Roubaix - run a marginally higher pressure for the start which is on tarmac, so they hit the ideal pressure for the last ~150km where all the cobbles are.
Don’t worry about being Uber precise on pressure, just round it up a touch before a long day in the saddle.
I thought that I would lose all my RR savings and that would slow me down a lot. 
Thanks 
Outside of races and PR attempts I run my latex tubes 5-10 psi lower than recommended. I’ll take comfort over RR any day. A nice plush ride is a fun ride. And most definitely worth an extra minute or three over the course of a four hour ride.
The SIlca tyre pressure calculator actually recommends the same pressures for latex as for Tubeless tyres, so they can be surprisingly low.
No, you can choose the “tire type” - the ones with latex are a bit higher.
I doubt you’ll notice 7-8psi. On standard butyl tubes I’ve got to lose circa 30psi + before I notice they are sluggish, and I have to loose around 50psi on tubeless. I suspect that latex will be similar. Lol the longest I’ve been racing on them is 2hours and I doubt the slugishness at the end of a 50miles TT was anything to do with a loss of 2psi 
That’s why I asked.
Doing everything but speed is not improving (or not in an understandable way - too many variables).
Silca has said (based on testing by themselves and others) that going lower than the optimum pressure is a smaller penalty than going higher. Based on that, I don’t bother worrying about pressure loss on longer rides. I think Josh has said on his podcast that the pros would go test the leak rates, and then set their pressures so that they are optimal at the critical section of the course.
Last, if you are worried about a 7-8 hour ride, then I bet you are stopping to refuel. You could top your air up at a stop!
We usually only do a stop of 15 minutes or so to eat, talk and chill a bit. I could top up with my hand pump, but maybe too much of a hassle. 
I use latex tubes as well but, don’t worry about the drop. Something to experiment with perhaps is using a little latex based sealant. I don’t do this but, iiRC it will help with the psi loss. I don’t use sealant as everything comes with a cost. Sealant in my climate dries very quickly and I think would just be more of a hassle than anything. JMO
If you are truly worried about pressure loss you might check out the new thermoplastic polyurethane tubes.
I have one of them (Aerothan) lying around. I heard stories about sudden air loss on puncture. May going to try out anyway.
LOL really? That’s more than 40% of the total pressure I run on the road.
Run latex for years and never worried about it. The silca recommendations seems spot on.
When I still used Butyl tubes on the road bike I’d usually pump to 80-90psi and leave them for weeks at below 50-60psi I’d perceive them sluggish (whether they actually were though ). So its about 40% too With tubeless its only when the pressure is between 20-40psi I start to perceive that they might be sluggish and they only start at 80psi so its more than 50% 
Ah, I’m running 70psi on 700x28 tires and butyl tubes on the road. So losing 30psi puts me well below your 50psi threshold (which is about the same for me - 50psi feels squishy, and much less and I snake bite on every bad pothole).
Gravel is tubeless, 700x40 and 35-40psi. I check that every ride because much less pressure feels pretty sketchy.
Ive 700x42mm tubeless on the gravel bike and run them at 25-28psi. I am more particular about topping them up though.
So generations of racers back in the day with their tubulars finished long races with their tires damn near flat? I don’t think that was ever a thing (?)
Joe
I have latex on my 64 wheels and race butyl on 36. Pumping latex before every single ride is boring at the very least. Read this test results, on Conti Race28 Light you will lose like 1W. And really, spending for inner tube at the price of decent tire?