The Transformers: Evolutions

A line of alternate-universe Transformers comics published by IDW. The first story arc, Hearts of Steel, puts forth a reality where the Transformers awakened in industrial revolution-era USA; Optimus Prime and others become steam locomotives, while Megatron is a giant wheeled cannon instead of a pistol. Or... tank. Or jet plane, or race car, or two headed dragon... eh, you get the idea.

From Teletraan I: The Transformers Wiki, a Wikia wiki.