Rendered MP3's are 32bit ?

Whenever I render an MP3 in WL the file is 32bit. This is a problem because 32bit MP3 files seem to be incompatible with a web app I am using. So, how do I save a 16bit MP3, and why is WL rendering a 16bit WAV to a 32bit MP£ anyway ?

There is no 16 bit or 32 bit mp3 format. The mp3 is fully independent from this.

However, you might see that WaveLab decode a files in 32 bit. But this is independent from the mp3 contents itself.

I think your problem is elsewhere. Maybe you use VBR while you should use CBR, or the inverse. Try this.
You can also try the Fraunhofer encoder vs the Lame encoder.