Is it brushed or brushless? I'm guessing it's brushed, and the stock Tamiya TEU-101BK is supposedly 60A, and I wouldn't go much more than a 23T motor on one of those, so I'd guess an 18T motor would be within its capabilities. I'm afraid I don't know that much about brushed ESC ratings, though most ESC ratings are pretty much made up anyway.
If it's brushless, and accurately rated (which it doesn't sound like it is) it should probably do down to a 6.5T motor.
__________________
|