53MB? That is only the program then.
The 2GB SD was (in the past) recommended to have enough room for all content, based on the full Europe content. These days and with all bells and whistles, a 4GB is needed. A 2GB is too small, just.
Although less than 2GB may be enough, depending on your needs (maps/POI/speedcam/...) and devices capabilities (DEM/3D features/..). Of course, also dependable on where (internal memory or SD) you store everything. Thus a 128MB can be sufficient in some cases, for program and minimal content.
On one of my old devices (which I don't have anymore), I set up a full iGO8.3.5 with only the content I (in fact my son) really needed and I did this on a 512MB SD. There was still room for more. But with the restriction of the available space that rested on the SD. There was no room left for e.g. the German map (I think that one is 248 MB), but plenty for Vatican City
.
Also I do think it's best not to fill up the SD for 100% but leave some space for the devices needs. You may delete some useless files from time to time (logs, history, crash txt ;) , ....)