About a month ago I purchased a Foss tube for my 36er and noticed that the tire pressure seemed to decrease slightly day by day(like 5psi a day). But now I am noticing a large difference in pressure. I left the uni out in my garage last night at 60psi and checked it this morning and it was a 35psi. I have heard of foss tubes leaking a bit because of the different material but this seems unusual.
indeed. They lose a little, but not that much. Slow leak. Use water in a sink to find it, slow leaks are pretty hard to find without bubbles.
And yet for me, I just bought a replacement tube because I figure after 3 years, mine which has been trouble-free probably will need replacement soon!
Did you inflate the tyre right before it started leaking at this increased rate?
In the best case you just have to disassemble the valve and clean it.
Tube? That’s so 1990’s
lol, how much sealant does one need for a 36er? I’ve been using a 29er tube, and can’t imagine it’d be less weight than that.
I lose almost exactly 1 psi per day on the Foss tube in my 36er. That’s normal for the Foss tubes, and you may be running at a higher pressure than I do. I run at 52 PSI on my Nightfox. You could have a very slow leak, but it’s almost not worth it to do anything about it. Just pump it up before each ride. I think most of us that use Foss tubes do that anyways.
It’s doubtful, but the schrader valve could be loose. You might get a valve tool for $2, if you don’t already have one, and check it to make sure it’s tight, or you could smear soapy water over the valve to make sure it’s not leaking. If it blows a bubble, it’s leaking. That’s an easy thing to do without needing tools or disassembling anything.
Sounds like it’s fine, though. If it were me, I’d probably do nothing.
25 psi in one night is not a normal loss of pressure… that’s fast enough that you couldn’t make a day ride without having to pump it up.
My bad. Didn’t read the post carefully, and I hate it when people do that! Sorry! Yeah, 25 is bad. Certainly a leak.
no worries. Yea, I’ve noticed I lose even more air out of the 29er tube than the foss tube, but no nowhere near that level.
New formula
I Just bought one from UDC US and I noticed two things:
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may be some dust blocked in the valve as I had on a mountain bike some years ago while riding without valve cap
I had tried the foss tube in my 36, but I didn’t like putting air in the tube so often. Currently trying out using a 32 inch(Kent/Walmart) tube to reduce the weight to about half of the standard 36 inch tube. 476 std36 vs 264 walmart32 grams.
Had a hard time getting the tire on with the 32. Like a 29 inch tube, the smaller tube gets in the way of allowing the tire to seat deep in the rim when mounting. But, like the 29 inch tube, the fix is to add some air to the tube so that it expands away from the rim when mounting the tire.
I’ve ridden two days now and like it. Can not yet report on how well pressure is maintained. When I checked today, found a few psi lower, but also found the air valve was not seated tightly and was definitely leaking a bit. I’ll check the pressure again in a few days now that the valve is tight.
Update on using the 32" tube in the 36" wheel… It’s been 4 days and 15miles since I topped off the pressure at 40psi. Still at 40psi! 
Those 32" look cheap in Walmart! Could be a good 36er alternative, how are they for getting on? 29ers look like too much of a faff, but a 32 might make it easier and cut some weight off…
Shame I can’t seem to get them here in the UK though. I guess UDC UK just ships their 32" with a 29er tube?