Seatback Strength in Cars

I don't have a formula per se' but perhaps you could do some investigation.

The average westerner is 110kg, approximately 170 cm tall. Although there are quite a few who tip the scales over 160kg. It would be reasonable to assume that your seat would need to survive being sat in by a person on the larger size.

In an accident, Newtons laws of physics are well applied. Its the reaction movement which breaks seat backs. That is, the returning movement of the body after the impact in the case of frontal collision.

In the case of the vehicle being rear ended, then its the force of the inertial mass of the person multiplied by the mass/velocity of the impacting vehicle.

If you want some examples of well constructed seats, look to Volvo, Saab, Mercedes Benz. Then compare them to Kia, Proton, and just about anything out of China. They will look similar but its the quality of the fittings and materials that make the difference.

Hope that helps

Perry