why ???zsh: command not found: rails

$gem install rails -n /home/steven/.rvm/gems/ruby-1.9.2-p318/bin -l

Successfully installed rails-3.2.2
1 gem installed
Installing ri documentation for rails-3.2.2...
Installing RDoc documentation for rails-3.2.2...

$rvm use 1.9.2

$ rails -v
zsh: command not found: rails