While David was riding his bike around the circular cul-de-sac by his house, he wondered if the constant circular motion was having any effect on his tires. What would be the best way for David to investigate this?

I would measure the depth of the tread in the middle and on each side of the tread of the tyres, and then measure again after riding around for a while. Riding in a circle is likely to wear the tread down more on one edge than the other.