Tire Concerns: Is there a inner tube for a 225 55r18 rim?
I have some 18" reverse offset rims. The rubber on the inside of the rim is not sealing because it is too close to the bead of the tire. Is there a inner tube that I can use rather than having to put new rubber seal on each of the rims?
The description you've given doesn't give me a clear picture of exactly what is causing the problem so I am not comfortable in suggesting a solution.
What I can tell you is that with the trend to using tubeless tires continuing, the available of inner tubes is getting less and less every day and finding a specific tube for a certain tire size is unlikely. On the other hand, most tubes, but their nature, can fit a number of different tire sizes because they have a certain amount of stretch built in, so if you get a tube which is fairly close it may work satisfactorily.
The trick is to choose a size which is not so large that it will buckle or fold when it is placed inside your tire, or so small that it will stretch excessively and be too thin to give a good result.
The best thing to do is to locate a business which specializes in or has a lot of experience in tubes. One of those, I believe, is Ken Jones Tires, who I believe you can locate doing an internet search and they may be able to advise you what you could try.