In API v1.1, the Twitter docs now tell you to âmodify the URLâ rather than make another request to get the URL for a different image size. So basically, like @pete_klein said, take the profile_image_url from a previous API call (like get friends) and do a string replacement for ânormalâ to âbiggerâ or ânormalâ to ââ to get larger profile images.
It feels a little sneaky, but so long as the conventions donât change itâs one less API call for Twitterâs servers to respond to, and one less API call for your client to make.