The fun thing about ride-on mowers is that they're only slow because only a small portion of its power (2-3hp usually) actually goes to the wheels. But if remove the blades and install an aftermarket drivetrain, you get to use all 15-20hp, which doesn't sound like much until you realize that it weighs ~180kg. So now you have this ridiculously fast go kart for ~$450 that can do 90km/h+