Ive had 2 fire eels, and 1 tire track eel, all around the same size but the tire track 2X as thick. The tire track would swim around the tank looking for the fire eels and biting them and beating them up, it only lasted 2 days before i took out the tire track. Didnt work for me but good luck.
they get around the same size 36''-40'' max most say they won't get over 2 feet in captivity but people n this site have spiny eels we'll over 2 feet but tire tracks tend to get a little bigger
most likely if they end up not likeing each other it will be when there older
For me it works. My fire eels is about 10 inches and the tire track is about 4 inches..both in a 55 gallon, i've never seen aggression. In fact they are close friends, i've kept them together for about a 4 months now..you can try it out, i hope it works out for you.