Is there a limit as to the biggest size SD card that can be used in these cars? So far, I've used 2GB without problems, but wondering if I could go to 4GB or even 8GB.

...you are limited to only 512 folder/files per card. You can drop more on the SD, but the system will only recognize the first 512.

Also, you can't use "SDHC" type cards.

It may be a waste of money to get anything larger than 2GB or 4GB SD cards, assuming your first 512 track sizes don't exceed the cards total capacity.

Make sense?

Thank you very much for your help. FWIW, I rip my MP3 files at the highest rate of 320 Kbps. This yields an average of 10MB per normal duration song.