Possible Clues:

• Tilt to one side
• Be able to circle lough and lean over to one side
• Sway at high speed
• What speeding cars do around turns
• Drive like a drunk
• It's for transport, even if you turn it over
• List quickly?
• Can one drive it, even if it were to overturn?
• Swerve motor, even losing velocity
• It's OK for transport, even if you keel it over