Seat Belts

[donfaber]

So, the retractable part of my seat belt doesn't work any more (79B) - how about some good suggestions for replacement seat belts for this car?

[Bill Young]

Don, I receintly installed seat belts from Victoria British in the MG Warrior project. They went in pretty easily and I did like the adjustment for the pendelum so that the locking mechanism would work in any installation. They're not cheap, but well engineered and look pretty good. http://www.victoriabritish.com/icatalog/mg/full.aspx?Page=86

[crashbash]

I put 4 point harnesses in all cars. Less than $100.00.   Better than air bags!

[Moderator]

David just had to go and mention four point harnesses... That opens a can of worms!

Three-point OEM seat belts are mainly designed for collisions where occupants will be thrown forward (e.g. head on collisions). The design anticipates that in an accident the driver's torso will fold over the lap belt, and thus counteract  any tendency for the abdomen to slide UNDER the belt. If the abdomen slides under the lapbelt, the driver is likely to be severely injured. At least In North America, race cars normally have either five or six point harnesses - they have straps that go between your legs to keep your abdomen from moving forward in an accident. Most four point harnesses don't have any such "anti-submarining" feature, and therefore some people feel they're very dangerous.

It's arguable whether three-point harnesses make the most sense for our sportscars. Are our cars like racecars? Racers may be statistically more likely to be involved in a rollover accident or even to be t-boned compared to the public at large. It's not THAT common for racers to drive straight into something stationary, and it's rare for them to drive into oncoming traffic. I have argued in the past that I feel safer in a four point harness in my MG because I'm more worried about sliding off the edge of the road than I am about running into anything head on...

From an OEM perspective, three-point systems have two other huge advantages. The design doesn't need to be adjusted (much) for users of various size. Adjustment is generally within the limits of an automatic retractor. Also, the design is relatively comfortable. Perhaps people are more likely to use it.

If you're considering taking Dave's advice and fitting four-point harnesses, I'd recommend considering the points Schroth Racing makes regarding their design, and specifically lap belt width and "anti-submarining" features.  (Schroth Engineering makes four-point harnesses with a unique anti-submarining feature!)

Read about them here: http://www.schrothracing.com/main/Engineering

One more important point about four, five, and six point harnesses: it's quite important that the shoulder straps be mounted at approximately shoulder height. If the belts angle appreciably downward to an attachment point, your spine will be compressed and probably damaged in the event of a head-on collision.

[Moderator]

I forgot to include these two photos...

Dave Burstyn's MGB:


Ken Biermann's MGB:

[rficalora]

So, Curtis, what about 5 or 6 point?  Maybe a bit more inconvenient, but wouldn't that'd address the "submarining" concern?  Are there camlocks that leave the left shoulder, lap, & bottom belts connected so you lock/unlock the two sides?

[Moderator]

5 or 6 point is awesome - no submarining, so long as you buckle-up - but you need a seat that's set up for the extra strap(s).

If you squint at this photo, you can see that there's a slit for the crotch strap:


Here you don't have to squint:

[rficalora]

I like the idea of 5 or 6 point belts.  Have you seen any seats that'd be appropriate for daily use, fit, & have the slot?

[Bill Young]

Rob, it's not too difficult to modify a seat for the crotch strap. I did it with the Nissan Pulsar seat on the driver's side in my Midget. I just cut a hole in the seat pan and used some protective plastic edging on the metal, then cut a notch in the seat foam and sewed a sleeve into the seat bottom cover to reach down through the pan. Just make sure you make the cut large enough to pass the latch hardware or mounting plate through. In the photo you can see the red crotch belt sticking up through the seat bottom.

[BlownMGB-V8]

What is the anti-submarine feature of those 4-way belt systems? Is it just that they are using 2" webbing?

Jim

[Moderator]

As I understand it (and as explained and illustrated on their website) the inboard of the two shoulder straps has a segment of webbing that's made differently and that's engineered to stretch a pre-engineered amount in the event of a head-on accident so that the torso will fold over the lap belt enough to prevent submarining, but apparently it doesn't let the user fling anywhere near as far forward and around as a three-point's shoulder strap.

[Moderator]

Rob asked: "Have you seen any seats that'd be appropriate for daily use, fit, & have the slot?"

I want to see and sit in this company's seats in person... they seem to meet the criteria and they look period correct for our cars, but they're pricey.  http://www.exoticcarseats.com/

[Bill Young]

Jim, I read their site also and the method they use isn't clear. I'm only guessing but they mention an energy converter in one shoulder strap and I'm thinking that they are allowing some forward movement of the upper body before the belts tension to position the person in a way that they will pull on the lap belt instead of sliding down as you would if the upper body is held back against the seat.

[classic conversions]

Curtis is right on.  You can have the correct seat and belts, but if they are not correctly installed they become useless and more prone to hurt you than safe/minimize and injury. Also harnesses have an exparation date

Seats need to be bolted in 5 places four in the bottom with good support and brackets made of specific carbon steel and thickness, not your MGB standard bolts, a fifth bolt behind the seat attached to the roll bar and the list goes on. Curtis touched all of points very well.

I would suggest that Curtis do an article in this topic of safety

[Moderator]

ASM stands for Anti-SubMarining. It's an extra flap of material sewn into the inboard shoulder belt that prevents you from sliding underneath the lap belt. In a 4 point harness made by some other company, the two shoulder straps restrain your upper body equally. They keep your chest from moving forward. However, this also pulls up on the lap belt and allows your accelerating pelvis to slide under the lap belt and cause serious damage to your stomach and intestines. With ASM, one of the shoulder belts will elongate at a different rate which will force your pelvis down into the seat cushion. Upon rebound, you will be placed back in an upright position with the belt correctly placed over your body.

Here's a movie, with crash test dummies filmed by high speed cameras:  http://www.schrothracing.com/docs/SchrothASMII.wmv