Installed Seat & Harness Install (Seat / Harness install part 3)

It took a lot of trying-and-discovering-shit-it-doesn't-work to make the seat mounts. The harness install is much more straightforward and acceptable. Before installing, read the SFI and manufacturer warning on your harness. If you bought your harness used, which I don't recommend doing, go on the SFI foundation website and your manufacturer's website and read online versions of the guidelines. This is important and your life depends on it!

I used all stock mounting holes so there was no need to drill anything. This is possible on my year Miata because the right seat belt receiver bolts onto the transmission tunnel. This hole exists on all NA Miatas but on later models it might not be threaded.

I bolted in my sub and hip belts onto the stock mounting holes along with the stock seat belts so I can use the stock seat belt on the street. On the left side of the driver's side, loop the belt through the left harness slot so you can do this, or remove the stock seat belt altogether if you don't drive your car on the street.

No install is perfect, and here are my concerns of this install.

1. On my hard dog roll bar, the harness bar is a bit low. With the mount I made for the seat, the harness bar is about 1.5" lower than the shoulder harness slots on the Sparco sprint seat. This is barely acceptable. The harness mounting point should be on the same level or up to 10 degrees higher, and at most, -5 degrees lower. The solution would be to bypass the harness bar and bolt on to the rear deck using backing plates.

2. The sub strap is connected to the left seat belt mounting point. I hope the sub-strap hole on this seat is strong to keep the sub strap in line in the case of an impact. The sub strap, ideally would be mounted behind the sub strap hole on the floor under the seat or behind the seat. Instead, the strap on my setup goes to the side.

3. The hip belt angle works nice at my seating position. It looks like its at 45 - 50 degrees. Check out the picture with reference to the seat rails for reference.

On sedans race cars, some people mount all of the belts at the rearmost part of the race car to minimize any harsh angles and let the bolt-in tabs work at a more perfect angle. I don't recommend this because using really long belts or fully extended belts will result in too much stretching in the moment of an impact.















Final notes
I went on a test drive. This is my first experience in a race seat in a production car. Amazing! I felt very much connected to the car. The feedback received was very detailed. I won't talk about streetability here since that is not the focus of my blog, but it blocks rear view and hard to climb in and out of the car. Also, if you are road racing, you really should get a removable steering wheel.

I could not use any washers on the seat-tube mounting bolts. Also, the bolts were cut so that the thread length was only about 2.5 times the bolt head. I don't know if that is enough, but its slightly shorter than the stock bolts that screw into the stock seat. Also, the rectangular shape of the tube and the fact that the mount is four pieces makes me question how well it will take a side impact. For these reasons, it is my opinion that this is not safe enough for a road-racing application. Whether it is okay for track days, you decide.

Copyright 2009, 2010 (c) by Jerry Lee.