You cannot measure the trueness of a wheel via the tire because the tire is rubber with high and low points depending on how the tire is seated and inflated. If you would like to measure the trueness of the rim, you need to remove the tire before doing a spin test.
Also, please note that the key to fixing a wobbly wheel is adjusting the spoke(s) on the correct side of the wheel. Note that the spokes have nut-like devices at the rim called nipples. When viewed from above, nipples are turned clockwise with the spoke wrench to tighten spoke tension and counterclockwise to loosen it.
Please see the video below on how to fix a wobbly bike or how to true a wheel:
Truing Wheels | Crankset Sprocket positioning | Gas Cap Gasket | F-Zero Motorized Bike (see segment video at 9 minutes and 49 seconds)
https://www.youtube.com/watch?v=V3NND07tETc