Tractor or Car?

In the event of no fuel, which one is easier to push? Or conversely, while pushing with the same constant force which of the two is likely to have a higher acceleration as it begins to move?

In cars, all four wheels have same size. In tractors, the front two wheels are smaller than rear two wheels.

Assumptions:

• $r_{\text{car}} = r_0$
• $r_{\text{tractor-front}} = \epsilon r_0$
• $r_{\text{tractor-back}} = \sqrt{(2-\epsilon^2)}r_0$
• $\epsilon = \frac 1{\sqrt 2}$
• Mass of tractor without wheels = Mass of car without wheels = $m_0$
• Mass of a wheel is proportional to the square of its radius $m_{\text{wheel}} = k r_{\text{wheel}}^2$
• Coefficient of rolling & static friction between any wheel and the road is $\mu = 0.5$