Powell said he struggled to loosen the lug bolts, but that's when he saw a man pull up in front of his car.
As the stranger got out of his vehicle, Powell noticed he had an artificial leg.
The man who stopped, Anthony Maggert, lost his leg in Afghanistan when he was a civilian employee.
Maggert said he recognized Powell and wanted to help him.
Once the tire was changed, Powell said they both "hurriedly headed off to appointments at Walter Reed."
"Thanks, Anthony. You touched my soul and reminded me about what this country is all about and why it is so great. Let's stop screaming at each other. Let's just take care of each other. You made my day," Powell wrote in a Facebook post.
Powell added that he initially did not get Maggert's information but later Wednesday night, he received this message from his roadside hero:
"Gen. Powell, I hope I never forget today because I'll never forget reading your books. You were always an inspiration, a leader and statesman. After 33 years in the military you were the giant whose shoulders we stood upon to carry the torch to light the way and now it is tomorrow's generation that must do the same. Anthony Maggert."