Jack from Wolgarston High School gave this a lot of thought, here are some more ideas about the bike tracks :
We know that there's an important difference between a back wheel and a front wheel : the front wheel can point in any direction, just turn the handle bar, but the back wheel always points exactly forward towards the front wheel, or more exactly, towards the point where the front wheel has contact with the ground.
So we could test to see if a track could have been made by that back wheel :
From the track being tested draw out a line that seems to be the wheel's direction at that point, and then continue that direction line until it hits the other track - that's where the front wheel would have needed to be.
Do that for lots of points along the 'tested back wheel track', and if that was a genuine back wheel track the distance along any of those direction lines to the front wheel contact point would be a constant length.
That's because, although the front wheel can turn the contact point with the ground is the same however you angle the handle bar.
If the line first tested is unsuccessful the other track ought to be the back wheel, but it's a good idea to do the test and check !
The straight line from a point on the back wheel track which shows the direction of the back wheel at that point is called the 'tangent'.