How to reliably sample a sensor during the rotation of a wheel in a car?
An active inductive proximity sensor can detect the passing of the aluminium spokes: -



It produces a high frequency magnetic field and detects the eddy currents induced in conductive objects in its path. One thing to watch out for is operating frequency - if you require high resolution to precisely detect the spoke and judge the "correct" position then operating at higher frequencies is necessary. In effect the oscillator frequency can be regarded as sampling the eddy current disturbance so you'll want plenty of cycles of AC for each spoke that passes.

I use them on aero engine tests looking at blade wobbles on the turbines.

A similar solution might be a capacitance probe - the tip of the probe is excited with an AC source and the amplitude changes as a spoke passes by: -