a
$Y = \frac{{F/S}}{{\Delta L/L}} \Rightarrow \Delta L = \frac{{FL}}{{SY}}$
$\therefore L\alpha \Delta T = \frac{{FL}}{{SY}}$ $\left[ {\Delta L = L\alpha \Delta T} \right]$
$\therefore F = SY\alpha \Delta T$
$\therefore $ The ring is pressing the wheel from both sides,
$\therefore {F_{net}} = 2F = 2YS\alpha \Delta T$