I have one in the master bath.

 

John,

The seat base subs look good but don't the violate the put a jack under it and see what happens idea?

 

Only if the seat - or the floor - deforms.

In the case of a floor, it will, no question. Probably the seat too, although I'm guessing there will be some lessening of that because the load follows a more complex path and is spread over more and differing structures.

As I said, I am mulling over updates.

 

John, don't underestimate the benefit to your design. Keep in mind that the floor pan can be compromised something other than pull from the sub. It could see an underside impact, collapse upward in a heavy side impact, etc. So when bolting to the floor you need to consider primary (sub-pull) and the secondary mentioned above. It may very well need to be twice as strong as the seat to outperform your set-up. I guess what I'm saying is that even if both failed the jack test, I'd rather have your set-up because it only sees sub loading.

The only reason I don't like mounting to the seats is typical the mounting methods aren't designed for it and if those fail then the entire driver restraint system is compromised.

 

I see it this way too. John's design is very complex as I certainly can't calculate the load so I would be a dumby and just try to break it with tools to see what happened but that would be expensive and only one datapoint. Seats would need to be anchored much better and designed much more stout IMO than even the untrashield recomendation of 8 mounting places to the cage if I was using the seat as an integral driver restraint. You see if you can mount the sub to the seat you can also mount the shoulders and the laps to the seat for a very clean set-up, none of which would pass tech in the typical tin-top I am afraid. In fact while in a case by case basis John's sub design is probably fine I think he fails tech although I doubt the inspectors look for much more than a "date stamp".

 

Once we're successful at getting harnesses mounted to seats we can start looking at ejector seats. That would be cool.

 

Yeah man just rig them to the airbag sensors. I'll start working on it!

 

There seems to be something missing in this discussion that is an important consideration when thinking about load distribution. While the sub strap(s) may experience the same load as the shoulder harness, the question is over what area is the load distributed? Using a single mounting point reinforced by a 4" square plate is much different than a single bolt and 1" diameter washer.

I understand the rationale for mounting sub straps to the seat (JH configuration) or the seat mounts (Chrisp), but there will still be a load placed on the floor pan via the bolts that hold the seat rails in place. I am not saying their approach is wrong - it's just that the analysis doesn't stop with where the strap(s) are mounted. John's mounting is complex because their are two areas that can deform - the seat and floor plan. I would prefer Chrisp's set up provided his seat is mounted to the floor and well reinforced along those mounting points.

Shroth offers excellent instructions on proper mounting of 6pt harnesses" http://www.schrothracing.com/docs/Co...structions.pdf

 

You are right. It was kind of a given that the seat is mounted well. Amazingly I see many really good cages many done by DIY'ER's but what I rarely see are seat anchors tied into or integral with the cage. That is really the best way so that if you get a unibody deformation the seat stays inside the capsule of the cage. It is really bad if the unibody collapses and takes the seat via floorpan with it only to have the driver hit by the cage.

 

This is true, but...

You need to factor further. Speaking of flat panels like a floor, especially loaded at an obtuse angle, the amount of backing is irrelevant to me. Using a flat floor in any event is not sufficient in my estimation.

The only effective difference with a 1" or 4" backing of a bolt is that the 1" will tear through the sheetmetal sooner. However, the distance that both mount points travel under a deforming load (short of failure) will be similar over a large portion of the deformation. The SHAPE of the deformation will be different, but the distance will not be different enough to matter, I'd wager.

Only when the surface area contained by a flat panel mount reinforcement begins to activate a structural component - like a center tunnel, inner rocker panel, roll cage tube, etc. - will it begin to gain significant enough strength to make a substantive difference in travel. In other words, you would need a plate that was thick/strong and/or large enough to activate one of these structural members before it would interest me as a valid reinforcement for a sub mount.

My rule of thumb is no unreinforced sub mounts in floor pans. Of course that makes for a lot of work, but... that's what I do.

 

Oh... I don't underestimate it at all;

You raise some outstanding points, and those are all factors that go/went into my decision. Another is keeping the sub belts the same for vastly different size drivers, which is something normal narrow rules don't account for very well.