chassis vs wheel arch

chassis

noun
  • The base frame of a motor vehicle. 

  • A woman's buttocks. 

  • A base frame, or movable railway, along which the carriage of a mounted gun moves backward and forward. 

  • A frame or housing containing electrical or mechanical equipment, such as on a computer. 

wheel arch

noun
  • The shaped part of the bodywork of a car or other vehicle that allows the wheel to be accessed, and in the case of front wheels, enable them to be steered. 

How often have the words chassis and wheel arch occurred in a corpus of books? (source: Google Ngram Viewer )