Couldn't it work by checking that crankshaft speed increases remarkably without any corresponding increase in wheel speed? I don't know how racetrack drivers d

Couldn't it work by checking that crankshaft speed increases remarkably without any corresponding increase in wheel speed? I don't know how racetrack drivers do this, but when I downshift, the crankshaft has some opportunity to fall a little while I get the gearbox in neutral and engage the clutch again. Then the crankshaft speed rises to 4000 rpm or more.