page_title: Axle
section_title: Structural features and design
hierarchical_section_title: Axle / Structural features and design
caption_attribution_description: 0_Series_Shinkansen_Wheel Tokyo Japan
context_page_description: An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle is supported. In the latter case, a bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes, especially on bicycles, the latter type axle is referred to as a spindle.
context_section_description: A straight axle is a single rigid shaft connecting a wheel on the left side of the vehicle to a wheel on the right side.  The axis of rotation fixed by the axle is common to both wheels.  Such a design can keep the wheel positions steady under heavy stress, and can therefore support heavy loads.  Straight axles are used on trains (that is, locomotives and railway wagons), for the rear axles of commercial trucks, and on heavy duty off-road vehicles.  The axle can optionally be protected and further reinforced by enclosing the length of the axle in a housing.
  In split-axle designs, the wheel on each side is attached to a separate shaft. Modern passenger cars have split drive axles. In some designs, this allows independent suspension of the left and right wheels, and therefore a smoother ride. Even when the suspension is not independent, split axles permit the use of a differential, allowing the left and right drive wheels to be driven at different speeds as the automobile turns, improving traction and extending tire life.
  A tandem axle is a group of two or more axles situated close together.  Truck designs use such a configuration to provide a greater weight capacity than a single axle.  Semi trailers usually have a tandem axle at the rear.
  Axles are typically made from SAE grade 41xx steel or SAE grade 10xx steel.  SAE grade 41xx steel is commonly known as "chrome-molybdenum steel" (or "chrome-moly") while SAE grade 10xx steel is known as "carbon steel".  The primary differences between the two are that chrome-moly steel is significantly more resistant to bending or breaking, and is very difficult to weld with tools normally found outside a professional welding shop.
caption: 0 Series Shinkansen wheel used on Japanese high-speed bullet trains
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