I would say it's a little too hot at 173 deg... but that could have been from running it for more than 5 or 6 min. I generally try to run my practices just as I would race. I try to keep my brushed motors at around 150 degrees... if you are pushing 170, you will probably burn up brushes quickly and then damage might be done to the comm as well...
Also consider your tires too.. Where you getting the correct traction too?
Just some things to thing about..