If don't paint the whole tire (the part that contacts the ground shouldn't be painted)
this stuff works pretty well. I've used it to touch up whitewalls before that had been gouged and it lasted for months with no issues at highway speeds.
You won't be able to paint the whole tire with a spray can and get the results you want, but a product designed for the job will do pretty well. Just like any paintjob, the prepwork is almost more important than the application.