  This paper describes the effect of PYTHIA8 tunes on event simulation of
$e^+e^-$ collisions with center-of-mass (CM) energies of 380 GeV and 3 TeV at
the proposed CLIC collider. Event shapes, such as thrust, thrust major, thrust
minor, oblateness, as well as particle multiplicities have been analyzed and
relative differences with respect to the default PYTHIA8 tune were determined.
The effect of tunes on top-mass reconstruction in the resolved and boosted
regimes was analyzed. No statistically significant variation for reconstructed
top masses using invariant masses of three jets was found for events with a CM
energy of 380 GeV. For the fully boosted top reconstruction at a CM energy of 3
TeV, a significant shift in reconstructed top mass of about 700 MeV for the
"Montull" tune was observed. This shift correlates with an increase in particle
multiplicity compared to all other PYTHIA8 tunes.
