Does changing the diameter of a wire affect the TCR of a wire?
Changing the diameter of a wire does not effect the TCR of a wire. However the TCR is not necessarily linear. The TCR at a high temperature could be higher or lower than it is at room temperature. Of course a change in diameter will change the resistivity. Using a larger wire to make a resistor of the same value will mean that the temperature will not increase as much for a given power dissipation because there is more surface area available to transfer heat our of the wire.