I guess the "average speed" really doesn't mean much to me because depending on the "reason" for the bike ride the speed could change dramatically.
:moo:
We know that Elizabeth often cycled to Lake Avenue according to Mr Carpenter, so there's no reason to assume that when she cycled to Lake Avenue on July 13 she had any reason for cycling there other than the usual recreational ride. It sounds like the only difference between the trip on July 13 and any other trip she made was that Lyric was with her.
What happened after she and Lyric reached the Arbutus end of Lake Avenue (where Elizabeth usually turned around) is what interests me as this is where the routine was broken. Instead of looping back, it appears that the children continued on to the lake trail.