I have not
used clonezilla, but...
Sounds like what you're making is a physical clone...every bit on every sector of the drive. Still, one would think a smart
compression program might do a better job than reducing 80GB to 55GB...esp if every unused sector was formatted or overwritten with zeros or something.
Does clonezilla not offer a logical clone capability? (or if it plans to do so, it may simply not be functional yet...I've seen some utilities actually claim functions only to find that a claimed function is still not yet actually implemented...just planned for the future)
If it doesn't, you might try HDclone...the self-booting
version for an arbitrary system, or there is also a version that runs an separate app under Windows
but STILL lets you clone a drive regardless of the OS used on the drive to be cloned (e.g. you can clone a Linux drive that is connected to a Windows system just for the purposes of making the backup).
The free version
of HDclone may not let you do what you want, but I'd wager one of the paid versions would.
edit to add:
BTW, just to let you know, I've used the freeware
version of HDclone to successfully clone an entire drive to another drive of equal or greater size...I realize but that's not what you're looking for but I'm just saying the freeware part of the functionality has been rock-solid, suggesting the rest of the claimed
functionality (e.g. the "Smart" function under the "Professional" version) might be decent as well.
And the HDclone website says this, which seems like it might help you determine if your disk can be backed up in a given mode without spending any money up front
Note- Please use the Free Edition to find out if a certain PC system and its mass storage media are supported. The Free Edition shows all supported and recognized drives, but some of them may only be usable with one of the higher editions.