LARTC - Jan 2007 - HTB burst howto ?

Hello

First of all  : Happy new year !

Does anyone can explain me or give me resource of how can I setup burst
on  HTB classes ...
I''ve got a 20Mb of bandwith with burst to ~  24Mb

I haven''t understand well how to cburst , burst parameters (calculate
values) !
Seems that If I don''t specify these parameters  the bandwith is shapped
to 20Mb without any burst ?

I''ve found this discussion
http://mailman.ds9a.nl/pipermail/lartc/2001q4/001972.html

Does anyone can light me ?
Regards

Sébastien