anyway,. after looking at the data, if you want to have the least variables possible you would need to consider all proper cars as being at least 1/3rd the weight since the coefficient of friction of ordinary tires on SAND is 0.3 (the number gets better with better road material, but lets just go with worst case). next you take an average of the radius of the all the tires and divide the weight again by that number. so if it has 4 20-inch wheels, that is 10 inch radius meaning divide the weight by 10. for a 3000lbs car step one 1/3rd it = 1000, step 2, 20 inch wheels = 1/10th = 100 lbs. and then x2 for "getting it moving" = 200lbs. so if you can push 200 lbs you can move a 3000 lbs car.

on the high end a regular tire on a proper surface like concrete gives us a coefficient of 0.01, which would result in something being considered only 1/100th the weight for the purposes of pushing it, before accounting for wheel size. which can let a regular person push something like 10000 lbs easily.