I just wonder how much of my bandwidth is consumed by my mic when i'm chatting online during races...
Virtually nothing, microphones were fine on dial-up connections years ago. Generally, most games use less than 50mb an hour in bandwith, which is lower than 14kb/s. Talking on the microphone will use less than 11kb/s, it's only a very low and basic sound quality/bitrate, and the frequency range is strangled too.
Say you were gaming with a number of people and chatting along:
Gaming (14kb/s) + talking (11kb/s) = 25kb/s
25kb/s X 60 seconds = 1.5mb per minute
1.5mb X 60 mintues = 90mb per hour
90mb X 6 hours = 540mb per day
540mb X 7 days = 3.78Gb per week or
540mb X 30days = 16.2Gb per month
That's with some pretty heavy gaming hours/sessions. There's nothing to worry about. This is based off the general consesus that most games use an average of 40mb per hour without microhpones, so I was being generous by calculating it up to 50mb an hour.