With the new format and resolution of preview thumbnails stored in the AutoCAD 2013 DWG files, we wanted to benchmark the influence of thumbnail settings to the overall size of DWG files. The thumbnail size is controlled by the THUMBSIZE variable - it specifies the pixel resolution of PNG previews stored inside the DWG files.
DWG file size is also influenced by the incremental save mechanism so first of all we needed to set ISAVEPERCENT to 0. Our initial tests brought strange results - some DWG files were influenced by THUMBSIZE setting but some were not. With the help of Autodesk support (thanks!) we located the problem - the new, higher THUMBSIZE values are applied only on 3D drawings.
We measured a single DWG file (a small, simple 3D DWG) - incremented the THUMBNAIL variable from 0 to 8 and repeatedly saved (SAVEAS) the drawing under individual names (always with the Update thumbnail option), plus added a version with THUMBSAVE off (without any thumbnail):
The DWG file size is more than doubled with the highest THUMBSIZE setting but the influence in real-world drawings will be less dramatical. But in any case do not increase the THUMBSIZE setting if you have no good reason to store hi-res thumbnails (up to 2560x2560 pixels).
This is the comparison table of DWG file sizes depending on THUMBSIZE values (on a sample DWG file):
More information in the CAD Forum Tip #8754