As the plot becomes heavier the characters become less profound. (moviereviewworld.com)
The characters themselves have unique stats, where heavier characters are faster but accelerate more slowly and lighter characters aren't as fast but accelerate more quickly. (entertainmentbuddha.com)
Some tweaking would need to occur on this track to make sure heavy characters didn't immediately have a disadvantage due to their increased weight and decreased acceleration but I think it's feasible. (gamerassaultweekly.com)