Kinesin-1 is a nanoscale molecular motor that walks towards the fast growing (plus) ends of microtubules, hauling molecular cargo to specific reaction sites in cells. Kinesin-driven transport is central to the self-organisation of eukaryotic cells and shows great promise as a tool for nano-engineering1,2. Recent work hints that kinesin may also play a role in modulating the stability of its microtubule track, both in vitro3-5 and in vivo6, but results are conflicting7-9 and mechanisms are unclear. Here we report a new dimension to the kinesin-microtubule interaction, whereby strong-state (ATP-bound and apo) kinesin-1 motor domains inhibit the shrinkage of dynamic microtubules by up to 2 orders of magnitude and expand their lattice spacing by ∼1.6%. Our data reveal an unexpected new mechanism by which the mechanochemical cycles of kinesin and tubulin interlock, allowing motile kinesins to influence the structure, stability and mechanics of their microtubule track.