Rail vehicle wheel set size measuring instrument and method for determining optimal turning amount

The invention discloses a rail vehicle wheel set size measuring instrument which comprises a body, a module slide guide rail arranged at the front part of the body, a motor driver coaxially connectedto the module slide guide rail, a laser displacement sensor fixed to the module slide guide rail, a grating scale which is parallelly arranged on the module slide guide rail, a ranging sensor arrangedat the back part of the body, a positioning rod arranged at the lower part of the body, an electromagnet arranged at the lower part of the body, and a power supply which is arranged in the machine and supplies power to the measuring instrument. The measuring instrument of the invention is based on the principle of laser triangulation, and the non-contact high-precision measurement of parameters such as a wheel tread shape, a rim thickness, a rim height, a qR value, a wheel wear amount, a wheel diameter and a wheel set inner distance can be achieved. The present invention also provides a method of determining an optima