[OXO cube]

A length of piano wire is cheap and easy to feed under cars and move back/forth.

...or 3D print a simple ground clearance scrutineering block.  Here's one I just drew up in the last few minutes with 1.5mm ground clearance (it could be any distance)

made this a couple years ago , its not super accurate due to the 0.4 nozzle i used , but its near enough
i use it in conjunction with my setup block , works well , free STL for you 3DP guys :)

ride height guage.stl Size: 311.7 KB  Downloads: 0