In Mario Kart 64, are there weight classes or does each character have a different weight?

There are three weight classes:

• Light weight: Toad, Princess Peach, Yoshi
• Medium weight: Mario, Luigi
• Heavy weight: Bowser, Wario, Donkey Kong

Heavy weight karts will take a long time to accelerate, but they have the highest top speed. Also, when a heavy kart collides with a lighter kart, that light kart will sometimes spin out.

Light weight karts have a high acceleration, so they can get going quicker after a complete stop, but they have the lowest top speed.

Medium weight karts are a good balance of the two - medium acceleration and medium top speed.

In mario kart 64, lightweights actually have both the fastest acceleration and highest top speed. Middleweights have the lowest acceleration, and share the same top speed as the heavyweights. The other differences between weight classes are things like speed loss during a turn, handling, and determining who spins out during a collision, which is also the only difference among characters of the same weight class. The data is demonstrated in this video.

It could be argued that in the race modes (grand prix and vs) top speed and acceleration are by far the most important characteristics, making the lightweights superior. However in battle mode these traits are less important.

Lightest to heaviest: Toad, Peach, Yoshi, Mario, Luigi, Wario, DK, Bowser. You learn this when you play battle mode a lot.

Also, if Peach and Toad ram into each other Toad will get affected. Simularily if Bowser rams into DK, DK gets injured.