$ rvm install 2.4.1

$ rvm list

$ rvm 2.0.0

$ rvm --default use 2.4.1

$ rvm 2.4.1
$ gem install rails -v 5.1.1

$ rvm gemset create rails511 rails501
Gemset 'rails511' created.
Gemset 'rails501' created.

$ rvm 2.4.1@rails511
$ gem install rails -v 5.1.1

$ rvm 2.4.1@rails501
$ gem install rails -v 5.0.1

$ rvm 2.4.1@rails511 ; rails --version

Rails 5.1.1

$ rvm 2.4.1@rails501 ; rails --version

Rails 5.0.1

$ rvm use 2.4.1@rails501 --default