It’s supposed to make it more difficult for autonomous targeting systems to recognize the aircraft:

https://www.twz.com/air/russia-covering-its-aircraft-in-tires-is-about-befuddling-image-matching-seekers-u-s-military-confirms

This stems from the times when Ukraine used Drones to drop shells/grenades on the planes close to the contact line. The tires are for the planes are what the cope cages were for armored vehicles.

I thought it was a ghetto way of hoping a dropped grenade from a drone might bounce off.