Help needed why a dual tube trials rim ?

Got myself a kuberg freerider and it comes with a 3.00 14" rear tyre the rim has 2 innertubes one is standard shrauder valve and the other is slightly oversized with different pitch threads can anyone tell me what this is about I can not find anything on it or have I seen it before.

Just a mean to let you ride after a flat. Not the best way IMO, but double tube is not so unusual. It was more frequent on trial and dirt motorcycles 25-30 years ago. Today, most dirt and trial riders are riding tubeless with foam insert. The appeared on enduro bikes 25 years ago, now improved and common for MX, trial and other disciplins. Lately, they became popular in MTB cycling, competitions especially.

Top man, I just looked at my second tube and its just a blank plug so it's running single tube at moment, the rear hub has a 7 bolt pattern for the sprocket and I want to use a oset sprocket to go kart adapter so I might aswell source a complete wheel and save myself the trouble of lacing and truing.
I won't be running as low psi as trails i'll he using it more for technical climbing than rock hopping.

Probably a silly question but Is the blank tube a rim lock for holding the tire against the rim?

captain387 said:

Probably a silly question but Is the blank tube a rim lock for holding the tire against the rim?

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Could be I've not pulled it apart yet to see the inner workings, it's only a silly question if I'm not a silly person but I'm so it very well may be a rim lock of some sort never come across it but don't ride the discipline to have seen it either.