gem rdoc <gem name> --no-ri --overwrite
Then you can remove only ri of the gem, and leave the gem itself. I don't see we need any other way around for this.
This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review
Do you think I didn't understand the question? The question was "How can I remove the ri and rdoc of installed gems?" :)
You asked the OP to try something, which sounds like a guess, and hence a comment. If you are sure of what you are writing in your answer, I don't see why you'll use such words.