Legality of adding 4-Point harness to middle seat position?

Knurled wrote: The DOT legal harnesses use a more idiotproof latch than the camlock or latch and link arrangement, and one of the shoulder straps is designed to stretch more than the other so that your body can rotate forward, which keeps you from submarining. (Is also how the 3-point belts work)

That's not how modern 3 points work (or any 3 point?). Remember 3 points are a single belt that has a pivot point across your hip. Hips are the strongest bone you've got. When the slack rapidly get's taken out and the mechanism locks your hips are cinched down and your upper body has the ability to move forward more (so not all that energy is dissipated at the pivot point of your neck). Ideally you are then hitting an airbag that hurts like a bitch but dissipates even more energy.

Those seatbelt locks are considered pretty unsafe for that reason, keeps you in tighter, but pretty unsafe in a high speed collision if the belt isn't allowed to gradually slow you down as they are designed. But hey, everyone is going to make their own decisions and decide their own risk factor.

accordionfolder wrote:

Knurled wrote: The DOT legal harnesses use a more idiotproof latch than the camlock or latch and link arrangement, and one of the shoulder straps is designed to stretch more than the other so that your body can rotate forward, which keeps you from submarining. (Is also how the 3-point belts work)

That's not how modern 3 points work (or any 3 point?). Remember 3 points are a single belt that has a pivot point across your hip. Hips are the strongest bone you've got. When the slack rapidly get's taken out and the mechanism locks your hips are cinched down and your upper body has the ability to move forward more (so not all that energy is dissipated at the pivot point of your neck). Ideally you are then hitting an airbag that hurts like a bitch but dissipates even more energy.

3-points existed long before airbags did. (Yes, I know about the '74 GMs)

A lot of 3-points had/have separate lap and shoulder belts, even the non-motorized ones that a lot of cars were infected with in the 80s and early 90s. Separate reels for the lap and the shoulder.

(And I know that lap belts are supposed to go across the pelvis, but I've never been in a car where they actually did. They always ride up really high.)

In reply to Knurled:

What modern 3 point has separate shoulder/lap section? I wasn't aware that was still considered valid with the "smart" tensioners that very based on impact speed, etc.

To the other point: Yeah, 3 points have been around a fair bit longer than airbags, and are "supplementary," hence the "ideally."

Regardless, the VAST majority of modern 3 points don't have a "stretchier" chest section. They're a single belt.

accordionfolder wrote: I still can't fathom why anyone here thinks a 4 point harness is safer than a 3 point belt?

I don't think anyone has said that.

The comparison is between the existing lap (only) belt and a race harness.

I have a '95 F150 Supercab now. My plan was to get another Bronco (I'm very familiar with this gen Ford).

It's the retrofit plan or buy an Expedition or Suburban. I'm not psyched about the wheelbase. But E36 M3 happens!

accordionfolder wrote: Regardless, the VAST majority of modern 3 points don't have a "stretchier" chest section. They're a single belt.

I was speaking of 4-point DOT rated harnesses. They get around not having a sub strap to stabilize the harness by having one shoulder belt have a weak point in it, allowing the upper torso to come forward and rotate a bit, keeping the body's mass behind the lap belts instead of sliding under.

Which (separate statement) is the way 3-points keep you from sliding under the lap belt, the unsupported shoulder rotates forward.

From experience, the way this torques the upper back can hurt like hell for a while afterwards.

In reply to Knurled:

I misunderstood this line to imply that the 3 point belt itself was somehow stretchier at the top: "which keeps you from submarining. (Is also how the 3-point belts work)" Gotcha now, we're on the same page.