[SV650rules]

Front discs get a lot more cooling air than the rear does. All disc brakes drag a bit, there is nothing to pull the pads back except a bit of flex in the seals. With drum brakes there were big springs to pull shoes away from drum, with discs all you are doing is releasing pressure - if the disc is perfectly flat and true there is nothing to push the pads away (if discs are not true the bumps will knock the pistons back, but not good for braking). As long as you can comfortably touch and hold the discs they are below 50deg C - not enough to damage anything - are your rear wheel bearings OK, is the heat coming from them ? Can you get rear wheel off the ground and spin it and listen for noise ?