Speedway NZ rules require the anchoring point for seat belts to be no more than 250mm from the back of the seat or from the guide, see rules S4-2-9 and S4-4-8.
You can see on the picture below of an Open Wheel vehicle how this measurement is obtained.
This then ensures the belts are not too long, as any extra length would add to the stretch of the webbing in a sudden stop, therefore causing more forward movement of the driver.
Also the alignment of the belt through the seat must be clear and should go from the shoulder (or top of Head and Neck device if used) to the mount or guide without touching the seat. For some seats it may be necessary to cross the belts to achieve adequate seat clearance and this is an acceptable mounting practice as shown in the picture B below. Of course the anchor points on the bottom bar should have a locator device fitted so the belts cannot slide sideways away from their optimum position.
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