I believe that the old HD brand 18'' mag wheels require tubes... I have an 18'' rear mag wheel on my 1978 XLH, and the original owners manual that came with the bike says that it requires a tube (both the wheel and manual are original to the bike). I have heard of people running tubeless tires on the old HD mags, but I have no personal experience with it and my 1978 owners manual explicitly says to use a tube... so I do. It was (and its) required that tubeless rims say "tubeless" on them somewhere... but the old HD mags do NOT. It wasn't until 1982 that the HD mags started to have the word "TUBELESS" cast into them... but by 1982 the MoCo was no longer making rear 18'' wheels. Maybe Gusanito has some advice on this. Gusanito, do you run a tube in your 18'' rear mag??