running gear

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The working parts of an automobile, locomotive, or other vehicle.

from The Century Dictionary.

• noun The wheels and axles of a vehicle, and their attachments, as distinguished from the body; all the working parts of a locomotive.
• noun Same as running rigging. See rigging.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun automotive The wheels, suspension, steering, powertrain and usually the chassis of a motor vehicle.