选项1

来自Bootstrap文档(http://getbootstrap.com/components/#navbar)

Depending on the content in your navbar,you might need to change the point at which your navbar switches between collapsed and horizontal mode. Customize the @grid-float-breakpoint variable or add your own media query.

选项2

如果您不想要自定义Bootstrap构建,则可以使用CSS媒体查询.例如,这里设置断点为1280像素：

@media (max-width: 1280px) {
    .navbar-header {
        float: none;
    }
    .navbar-toggle {
        display: block;
    }
    .navbar-collapse {
        border-top: 1px solid transparent;
        Box-shadow: inset 0 1px 0 rgba(255,255,0.1);
    }
    .navbar-collapse.collapse {
        display: none!important;
    }
    .navbar-nav {
        float: none!important;
        margin: 7.5px -15px;
    }
    .navbar-nav>li {
        float: none;
    }
    .navbar-nav>li>a {
        padding-top: 10px;
        padding-bottom: 10px;
    }
}

http://www.bootply.com/98488

Bootstrap 3.1的更新

3.1中的导航栏已更改,因此覆盖断点的CSS不同于3.0.这将阻止导航栏显示然后在3.1中突然崩溃
http://www.bootply.com/120604