Hide ribbon on custom page via code

I would like to hide ribbon on my custom forms (so users cannot use the default save function...). I used the following code in Page_Load event in SharePoint 2010. It did the job.

//hide ribbon 

SPRibbon ribbon = SPRibbon.GetCurrent(Page);

ribbon.CommandUIVisible = false;

Now I am working in SharePoint 2013. These codes seems unable to hide the ribbon?

I will appreicate your help.