The Rainhill Gang
There's so much untapped characterization potential for the locomotives of the Rainhill Trials, or as @northbritishatlantic and I have dubbed them, the "Rainhill Gang."
Like imagine this: Stephenson's Rocket, Sans Pareil, Novelty, Perseverance, and Cycloped. Bitter rivals, because:
"Someone's winning this thing, and it's going to be me!"-Stephenson's Rocket
"It'll be me, actually. I am without equal, after all."- Sans Pareil
"What about me? I could win too!"- Novelty
"Barley and I could take you all on easily."- Cycloped
"I could snag the first place, if I wanted."- Perseverance
And then after the Rainhill Trials, everyone's utterly exhausted, there are no hard feelings toward Stephenson's Rocket, who has won. And then the five become firm friends ever since.