Batman also wouldn't kill him for even trying to lift parts, the man never killed anyone. If Jason could lift all the tires, then it would be enough to pay for Mom's rehab treatment. There would be even enough left over for them to finally get away from Gotham.
Wait, is he really considering robbing Batman? Nah, even Jason wouldn't do something that risky and he half way believes it too. Until he wakes up in the middle of the night, covered in a cold sweat. Still shaking from his nightmares, he begins to come up with the perfect plan.