Laravel validation rules for related checkboxes

In my form I have a couple checkboxes and i want at least one of them (or both) to be checked before submitting my form. My input checkboxes are named car and bike. In my controller i am validating my request

$this->validate($request, [
            'content'=> 'required',
            'title' => 'required',
            'car | bike' => 'required', //this is not correct.
        ]);

What i couldn't figure is the statement that allows me to do the validation above