(Updated below in Bold Face).
Yes, I am reusing some of the SRF pics from earlier for this discussion.
Here is the shoulder harness and the fiberglass seat from the earlier blog entry. It happens to be an SRF, but it could be one of any number of types of formula car or sports racer; I've seen similar problematic harness mounts in a number of different types of cars.
Now what is the issue here? It's the spacing of the shoulder harness mount points behind the seat. The standard mount points in an SRF are 8" center-to-center; in some Formula Cars and Sports Racers it's even larger (I've measured 10" in some.) The General Competition Rules have for many years called for 4" to 6" center-to-center (see figure 1, page 80, 2007 GCR).
On top of this, for drivers using a HANS device, the HANS Owners Manual
explicitly calls for no more than 3" inside-to-inside. There is a small amount of math that's good to do here; if we are using 3" wide belts (the conventional type) with a HANS then 3"+1.5"+1.5" yields 6" center-to-center which matches exactly the widest spacing permitted by the GCR. If we're using 2" wide belts (permitted only with a HANS), then we get 3"+1"+1", so we have 5" max center-to-center when using 2" wide belts with a HANS.
If we go back up to the picture and look at it, we see that the car is equipped with the 2" HANS only belts, but is using the 8" mount points the SRF came with. This leads to 6" spacing inside-to-inside, 3" more than the HANS owners manual calls for. The driver may have problems with the belts slipping off in this set up; it is not in conformance with the GCR or with the HANS owners manual, although it is in conformance with the car shipped by SCCA Enterprises.
This installation represents one that will work well with a HANS. The belts are an appropriate distance apart, laying flat as they come forward through the seat, they will not bunch up and will drop naturally over the HANS "horse collar". This particular SRF has had the new kit installed that allows better spaced mounting of the shoulder harnesses.
This seat/harness setup is an intermediate step; this car is still using the 8" spaced mount points, but the Butler seat is pulling the straps closer together. This driver will probably not have problems with his shoulder harness and a HANS, although the bunching of the webbing at the outside ends of the slots is slightly troubling (See the discussion of this installation in the earlier SRF Seats posting.)
Drivers are trying various other things with the HANS. Some are using harnesses with the extra sternum latch up near the top of the chest; unfortunately, these are not actually legal harnesses in the SCCA (2007 GCR 9.3.18.D page 78 requires a SINGLE common release point for the lap and shoulder harnesses.) At the NARRCOffs one driver showed me a friction material applied to the top side of the HANS "horse collar" to assist in keeping the shoulder belt from sliding off. I am uncertain how well this will actually work.