Yes, generally speaking, Mario Kart drivers are broken into 3 main types:
- Lightweight Peach, Yoshi and Toad - They have the fastest acceleration but the lowest top speed. Toad is slightly lighter than Yoshi or Peach, but the difference is so small it's not really noticeable.
- Middleweight Mario, Luigi - The only differences between the middleweights and the heavyweights are that they're lighter and also have quicker acceleration when going on dirt, mud etc.
- Heavyweight D.K., Wario & Bowser - They have the slowest acceleration and the highest speed. In Battlemode you can make an opponent lose a balloon by ramming them at high speed.
Source: Mario Kart Central (Link has since gone down). See also Keanu's answer on a previous question for more information.