Rudimentary matters around American measures of speed (5)

'speed' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'rudimentary matters around american measures' is the wordplay.
'rudimentary matters' becomes 'bu' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'around' is an insertion indicator.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'measures' becomes 'Ds' (D is an example).
'bu' placed around 'a' is 'bau'.
'bau'+'ds'='BAUDS'

'of' is the link.

Can you help me to learn more?