The similar triangles approach works as far as the math goes...but I can't see how you can get the car on there evenly. The angle at the ground, no matter how small (unless we're talking a really long 2x4, but then I doubt you'd get a good reading), would still create uneven weight distribution over that wheel as the whole car sits slightly at an angle. Maybe I'm just not seeing something...and now I'll spend the day at classes thinking about solutions...great creativity by the way.