Disc brake pads - steel vs aluminium back plate
Some Tektro calipers use a magnet to retain and position the brake pad. The magnet is part of the caliper piston so the pad backing material would have to be steel.Most hydraulic brake pistons are aluminum to reduce weight and resist corrosion.If your pistons are aluminum I would use the aluminum pads due to the possible corrosion caused by the disimilar metals (steelpad against an aluminum piston).