Does anyone know the required strength of the mounting points of a car seat? I'm working on a new sliding mechanism and don't want to damage the integrity of the seat mounting. "Child seats" have rather poisoned the search results for this.

No points for "don't do it" or "buy one in" - what I'm building simply isn't available - a 2-3' track extension into the rear of the vehicle. The extension is only while the vehicle is stationary so it's really down to the material which will probably be a little weaker than the thick, folded steel of the regular runners. I'm just looking for a baseline I can work from.


  • $\begingroup$ You need to meet the standards for crash and impact loadings, fore, aft and sideways... in the UK you could start with the Construction and Use regulations, won’t be the only source... $\endgroup$
    – Solar Mike
    Mar 22, 2020 at 11:26
  • $\begingroup$ are the seat belts attached to the seat as well? I would think that the requirements are vastly different between seat belt attachment and seat attachment $\endgroup$
    – Ack
    Mar 22, 2020 at 17:56
  • 1
    $\begingroup$ fbtrial.com/wp-content/uploads/2015/11/… is a good pace to start at least. $\endgroup$
    – Tiger Guy
    Mar 22, 2020 at 18:00
  • $\begingroup$ @Ack - yes, they do so the force of the impact will, indeed, be transferred. However, the calculations are simplified by the fact that the extended section won't be used while the vehicle is in motion - they are purely to use the seat as a work chair while stopped and to move them out of the way to utilize the cab for sleeping. I'm not too worried about liability since I can remove them if I sell the vehicle but I don't want to make it ridiculously unsafe and flimsy. Checking out the links now. $\endgroup$
    – Mike
    Mar 23, 2020 at 8:09

2 Answers 2


In the US there are codes and standards covering hundreds of pages of coded as to type and materials and standard tests. And codes for even the huge testing machines.

Basically it's a huge liability can of worms.

There are codes on chemistry, fire resisting, structural strength, alergy tests, bolts and weld, you name it, etc.

You can start the search from :

49 CFR § 571.209 - Standard No. 209; Seat belt assemblies.

There are many hyperlinks on the code that you should check.

You also need to consult with a specialised attorney.

Here is the link. 49CFR


Going from the seat belt papers, the highest figure mentioned is 46,000N which is kind of helpful in that it gives me a starting point on raw materials but not manufactured solutions.

I think I may have to modify my design to bypass the problem completely. A hefty, steel latch on either side of the seat transferring the force from the base to the seat mounts (both known to be within spec) should mean that whatever changes I put in between do not become the weakest link in the assembly.

Thanks for your help.

[Edit:] I've discovered a work-around. Unwin rails (aka L-Track) is the stuff they put in the back of ambulances so is certified for collisions. They also lock by simply dropping a washer into the required position so 4 linear actuators will do the trick. In addition, a relatively simple linkage will allow them to fold down when not in use. enter image description here Now I'm trying to figure out whether 3mm, T6 aluminium C channel can take a 300lb load without tearing at the bolt holes, if not I may have to go with steel.

  • 1
    $\begingroup$ This sounds like an excellent decision, easier too probably $\endgroup$
    – Ack
    Mar 23, 2020 at 18:05

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