Winrar compression

Hi, I was wondering how can I obtain the best compression with winrars for ISO files?

I downloaded a couple PS2 games that was in RAR format. When unrar, the file size triples that of the rar file. How can I compress it and other games/ISO file back into RAR format to decrease the file size?

I tried setting the method of cmpression to "best" but the file size came out to be bigger than that of the ISO...

Generally best is just that althoough it depends on what your compressing and much it can...