Hi, I have a nimbus oracle 36er. Every couple of months the tyre goes slightly flat. I have just taken tube out, can’t find an air leak anywhere???
I have just tried to put a brand new, standard black rubber tube in, bought from unicycle.com but the valve stem does not fit through rim. Has anyone else had this problem?
Many thanks for any feedback 
The Foss tube is far nicer to ride than a standard rubber tube, but it does let air through over a period of time. You just need to top it up from time to time.
Yep, foss tubes need filling more often than rubber ones. It’s an annoyance but then the weight difference between the 2 types in a 36er is distinctly noticeable while riding…
Hello there, my 36" foss tubes leaked from the very beginning.
It tooks me several attempts to find the problem, it was a leak where the valve stem is inserted in the tube…
My 2 cents is to use a 29 standard tube, same weight as the Foss, zero maintenaince, zero problem, zero leaks. 
Cheers
Experienced the same thing. Just recently switched, noticed I was having a harder time with a known ride. Didn’t think anything of it. Next time I noticed how low I was and remembered having heard about foss tubes having a slow leak. Filled it back up and everything was back to normal.