dired-compress-file-suffixes is a variable defined in `dired-aux.el'.
Its value is shown below.

Control changes in file name suffixes for compression and uncompression.
Each element specifies one transformation rule, and has the form:
The rule applies when the old file name matches REGEXP.
The new file name is computed by deleting the part that matches REGEXP
(as well as anything after that), then adding NEW-SUFFIX in its place.
If PROGRAM is non-nil, the rule is an uncompression rule,
and uncompression is done by running PROGRAM.
Otherwise, the rule is a compression rule, and compression is done with gzip.


(("\\.gz\\'" "" "gunzip") ("\\.tgz\\'" ".tar" "gunzip") ("\\.Z\\'" "" "uncompress") ("\\.z\\'" "" "gunzip") ("\\.dz\\'" "" "dictunzip") ("\\.tbz\\'" ".tar" "bunzip2") ("\\.bz2\\'" "" "bunzip2") ("\\.xz\\'" "" "unxz") ("\\.tar\\'" ".tgz" nil))