Tourqing alum rims

The torque is dependent on the size of the lug. The numbers below are the typical guide line numbers to use for dry threads, lubed threads will be less.

7/16 in. 70 - 80
1/2 in. 75 - 85
9/16 in. 135 - 145

The torque value doesn't change because of the wheel material and a properly torqued lug nut combination will not loosen because of a normal temperature changes. When torqued properly the force clamping the wheel on is much greater than the force generated by different expansion rates of different materials so nothing moves and nothing loosens up, if it did then aluminum head iron block engines would always requiring re-torquing.

Not torquing your lug nuts can result in warping of the drum or rotor. This is because the uneven clamping of the wheel to the hub/axle will cause uneven stresses in the drum/rotor that manifests it self as warpage when they get hot then cool down. This phenomena is such a concern in aluminum headed engines that even a torque wrench is not accurate enough to provide even clamong and torque to yield bolts are used thus elminating the inaccuracies of a torque wrench.