You're confusing two different moving violations here: exceeding posted speed limit and failure to keep right. (AKA impeding traffic; the exact term varies from

You're confusing two different moving violations here: exceeding posted speed limit and failure to keep right. (AKA impeding traffic; the exact term varies from state to state. Also, I'm assuming American traffic law here.) If the speed limit is 65, the flow of traffic is at 80, and you drive 65 in the left lane - you are failing to keep as far right as practicable, because you're moving slower than the flow of traffic in other than the rightmost lane. If you're going 80, you are still speeding, but you're not failing to keep right. Yes, it's unlikely you'll be pulled over, but you are committing a moving violation nonetheless. If you're going 65 and you're in the rightmost lane, there is no violation even though you're travelling slower than the flow of traffic. Posted speed limits are still do-not-exceed values; the requirement to keep as far right as practicable is a completely separate issue.