I read somewhere that it would be dangerous to attach seatbelts to the frame. They stated that in case of a severe accident, the body could come seperated from the frame (or partially) and the Seat belt would tighten. I Don`t know this was from experience or just a story. I Made me think tough.
“shoulder belt or belts should form a 90 degree angle, to the spinal column”
In a perfect world, maybe. But we aren’t redesigning the ots from scratch so if you want seat belts and aren’t doing a bespoke roll bar with the lateral bar height perfectly matched to your individual height . . . there must be some compromises ;-).
Close to 90 degrees…
Just NOT over the shoulder, than back down to the floor.
A source of good positioning data…especiaaly for street-legal Formula cars…
I let it go first time Paul, but cant after an emphasised second time.
I totally disagree.
A ‘sash seat belt’ which is what we are talking about, must not be ‘close to 90 degrees’ as in a front accident - and work out the geometry - that will produce unacceptable vertical loads through your shoulders onto your spinal column. Not desirable to say the least.
Go and have a look at any modern car with optimum located seat belt ‘upper’ anchorages designed into the structure from the start. They are all mounted above and outside the shoulder, so the sash locates across the shoulder and chest to restrain the torso from going forward, without loading the shoulder and the spinal column.
AS before, in Australia, all this geometry for seat belt anchorages (and thus the seat belts in a static and active condition) is spelt out in Australian Design Rule (ADR) 5, and ADR 5 is compatible with the International ECE Regulation (the number escapes my memory cells). USA has a different regulation, but again it will be consistent based on many many years now of a lot of science and evaluation regarding seat belt design.
But my earlier point is that XK120/140 OTS (the original question) were not designed/built to provide optimum seat belt anchorage locations at all, let alone optimum upper sash anchorage points - and indeed there is no structure in an XK120/140 OTS at all within the range of suitable upper-sash locations. You either fit seat belts wherever you like - and feel good in ignorance of the science - or do a bit of research into how you can maximise structure and location of all three anchorage points. The bottom two are relatively easy, and indeed I personally cannot see any problem at all mounting reinforcing brackets/anchorages onto the chassis frame. If the body moves significantly on chassis in a crash, then the seat belts are not going to help much anyway. You can fit a major structure, such as a full width roll bar, as you often see with club racing cars, albeit most club racing cars don’t fit road legal seatbelts but instead fit full racing harnesses (in Australia - racing harnesses are not road use legal), and indeed in non-road use racing cars - anything goes re anchorage points, as you are trying to protect against a totally different environment/exposure. Have a look at a modern Formula 1 car re what they now do for driver protection - and is mandatory FIA requirement, but totally impractical/impossible/unsuitable for even a modern road car. Horses for Courses.
Personally I think a soundly designed/installed Lap-Belt arrangement can be relatively easily achieved in an XK120/140 OTS, if the anchorage points are structurally sound (ie - not through wood or non-reinforced sheet metal), but short of adding a full width roll bar, structurally secured/triangulated to the chassis, I cant see any practical way of an optimum upper sash mounting, so anything less will be a compromise of greater/lesser extent. But try to avoid anything mounted at or below shoulder height, where the belt bears on top of the shoulder, as in event of a front crash, load will be applied to the spinal column.
You can fit special high backed seats that have a high-mounted/above shoulder guide for a belt, that effectively changes the loading geometry for an anchorage mounted at or below shoulder height. This may be a preferable solution than a full width roll bar, or maybe you just accept the ‘feel good’ aspect of ‘something is better than nothing’ and accept that if you have a major accident beyond the protection of a lap-belt only, then it probably wont matter anyway. Indeed there has been accidents where an un-belted driver/passenger thrown out of car, has survived less injured than if they had remained belted-in-car.
If you ever get the chance to view/witness a full front on, or offset front crash test (Controlled test for Regulation compliance), where $M manikins are seated in the drivers and passenger seats, with all manner of calibrated instruments measuring all the forces experienced by the manikins; its a sobering experience. There is a lot of medical data now that can predict death and injuries based on measured forces to these manikins.
Roger
When I had my 1951 Mk VII registered in Victoria there was a complicated regime
Older than a certain age , no belts required , but the MK VII required front seat belts for the outer seats, which I made lap sash , but may have only required lap. But there was a number of variations depending on year of manufacture, something which may not always be clear on old cars.
Different regs also applied between whether the car was being sold/ re-registered or still on its original ownership/ registration. Basically if it was still on the original ownership from prior to seat belt regs, you could leave it that way.
Ed,
I am only going to put the 120 on club plates but changes to the system mean you need a roadworthy certificate, not just the old way of the club doing an assesment.
I checked with Vic Roads and they only require this and proof of ownership to re register it fully, so it is up to the mechanic inspecting it to say it is roadworthy.
The link below to the vehicle standards for seatbelt requirements which is current.
VSI21 (1).pdf (631.2 KB)
To make things easy on myself I will remove the seatbelts before the inspection so there can’t be any discussion about mounts,etc. The information sheet only says if belts are fitted they “recommend” they are retained. I will be fitting lap belts which are fully compliant after the inspection. New carpet will hide any prior evidence😒.
As far as seatbelt mount reinforcing plates there is a sqmm requirement under Australian Design Rules of 3750 sq mm and one site I looked at had plates for sale 50mmx75mmx3mm thick with a welded nut for $5 each. You could use round, square or rectangular, whatever works best.
Hope this helps anyone looking at mounting plate sizes.
Matt (Not Matthew, only used by my mother when I was in trouble 
)
We agree: Let me restate, more clearly than I did, the geometry.
The shoulder belt should not be MORE than a 90-degree angle, wrt to the spinal column, in a seated position.
Most street cars do indeed have a flatter position, and in a car like an XK, even an EType, with no real B post to affix it to, the angle is going to be neccessarily greater than a flatter position.
SCCA and all other racing sanctioning bodies disallow shoulder belt mounts, that put the belts in a position of holding you DOWN in the seat: the belt is to hold you BACK.
What I stated, if not clearly—and it is indeed backed up by science—is the shoulder belt(s) main job is to mainly restrain the torso from forward acceleration.
Hope that clears things up!
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Wiggles, Right you are. It’s hard to believe but I’ve seen people do that (eg not use a high mounted shoulder loop).
IMHO, there’s nothing wrong with fitting race belts into a classic car as long as common sense is applied. Race belts are typically 3” wide (HANS devices now use mainly 2” shoulder straps). These have very little give/stretch. Therefore, I would only use them as a lap belt.
The problem with roll bars are that they place very strong steel poles near your head. In an accident you head may come into contact with these bars. Therefore A roll bar can increase the danger of injury when used inappropriately on street cars. Once a roll bar is in the XK120, you should ideally always wear a Snell or FIA rated helmet, and use SFI approved padding on the roll bar.
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All true, and in the absence of a roll bar, only three-point belts should be used.
Nick_53_XK120_OTS you may not wish to re-live the head-on you had in your XK120 but I would be keen to learn more about it in terms of your back. I note Roger Payne’s advice re spinal damage through compression in an impact. However I am having difficulty reconciling this advice with Nick’s practical experience. I totally get why the legislators make the rules and want only to do what is safest.
I have been researching better protection in my XK120 OTS since having lap belts mounted during a recent restoration. The thought of my and my son’s heads smashing forward in a frontal impact is concerning.
I rather stupidly recently purchased a Sabelt 3 point harness with clips (instead of mounting bolts) before doing any research. Once I set about installing it, I then started the research. Yes very stupid in hindsight but inexperienced me thought fitting better belts seemed straightforward enough.
For the shoulder straps: I had already drilled a mounting hole for the 7/16 eyelet, to screw into a 60mm by 80mm spreader plate (professionally made, purchased from a race car parts supplier), behind the seat, but due to the length of the shoulder belts, as far back as possible on the horizontal panel under the rear cowl, just in front of the narrow vertical panel to which the boot lid hinges are mounted. There is very little strength in this sheet metal I know, but I figured it might be better than no torso restraint at all. I figured that in a heavy impact, the metalwork around where the shoulder belts are mounted might distort relatively gradually (obviously we’re talking milliseconds in a crash) under the forces from the shoulder belts – wreck the car but reduce injury to the occupants.
My concern is that my shoulders sit around 100 mm above the seat back, so the shoulder belts do angle down towards the eyelet mounting.
I appreciate that the belts would have to be unclipped at the change of seasons to allow the roof to come up to provide some insulation from our Canberra winters! The car does not venture out in the rain.
I’m prepared to walk away from the 3 point harness and stick with only the lap belts.
I don’t want to to make mileage out of this, but only a month ago, a local friend of mine had a low speed (fortunately) head on collision into a tree after blacking out at wheel - in his XK140 roadster.
He has bruising across the chest from the seat-belt sash which is no big deal, but unfortunately he has a period of major recovery to get through from spinal injuries he sustained, caused exactly they way I said was the major risk. He had a lap-sash seat belt installed with the sash over his shoulder, and mounted behind/below shoulder-height. So the momentum going forward, caused the seat belt sash to compress and twist his spine through his right-shoulder. (a RHD XK140).
Both my friend and the XK140 are repairable and should recover 100%, but I suspect the XK140 will be first.
Dave ring me if you want more details - as you probably know I am in Canberra also.
Thanks Roger, really appreciate the quick reply. The belts will be going on Gumtree!
… which should NEVER be done.
Now you have me worried, My 74 TR6 has factory fitted belts where the sash mounting point is well below shoulder height.
It’s good to be worried: the angle wrt your spine should not be more than 100 degrees.
in my 1960s near head on in XK120 OTS, …my car at about 35…the other at about 45 in a turn …I had 3 in lap competition belts of the day, with the double shoulder belts…the shoulder belts to bolts in the side curtain tray…which was reinforced with metal plate, and large washers…it all kept me alive and only injury was cut to chin from the rather close steering wheel. No back injury, no neck whiplash, How it did it, who knows. But it did. Impact took enine off mounts, blew both front tires, car bent back to the doors…BTW in rock/mtn climb ropes…there is built in stretch to limit the load on a climbers body via the harness. the amount of stretch depends on the amount of rope that is out…in the system from belay to climber…more rope = more stretch…called a fall factor. Ropes can be rated for 3 falls or 7 or whatever but it depends on the fall factor as to how much the rope stretches over its length. There may be some sense to that…tho if in a car…stretch whether metal or belt…if it creates enough to cause a hard impact of body parts to car parts…not good…but the Hans Device does similar work to mitiate brain movement within the skull. SCCA has a lot on belt install specs…but race cars are constructed to accommodate.
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That is not the purpose of the HANS device: it is to limit forward and downward acceleration of the head, in a frontal impact, that can break the neck, such as a basilar skull fracture.
That is what killed Dale Earnhardt.
True…the main purpose is to allow the head to move…but not to the point of basal skull/spine injury…but it does not end with that as a byproduct of this is that the deceleration force is mitigated in part because the device is not hard attached to the car, . the main purpose of a climbers rope is so that he does not make a crater in the ground…but the rope stretch that is built in is also important. It is not only that the device stops head movement at a certain point:
The restraint provided by the HANS device reduces neck tension by 81 percent, shear by 72 percent, and the total neck load by 78 percent. The head experiences a tolerable 62 g. Because the driver’s head and neck motion is now in synch with his torso’s movement, chest g-forces rise slightly, though chest compression is reduced. (Car and Driver Jan 2012)…
All true, but the brain still accelerates/decelerates within the cranial cavity.
The HANS device may well keep the deceleration lower, but it does not stop it.
Back to the topic: shoulder belts, to be in optimal placement for rollover accidents, should not be at a greater angle, wrt the spine, than 100 degrees. 90 is better, but difficult to attain in most street cars.
Also, were I ever to go back racing, not only would I wear a HANS, I would also utilize a chest clasp: Neil Bonnet died because of not having one.
Roger, not knowing any details of the case you describe: His injuries are not proof that he would’ve been better off without the sash belt.
Without knowing how low the sash anchor was relative to his shoulder and how tall the person was, we don’t know how far it was from optimal. I have seen many sash anchors on classic cars set into the floor behind the front seat, giving a practically VERTICAL orientation! That is hugely different than an anchor in the windscreen tray, which is essentially flush with the top of the seat back (and the seat back will ultimately limit the amount of downward movement of the sash belt). If you are not very tall, this orientation might be an excellent fit for you. My shoulders are about 50-60mm above the seat back. I believe, without proof, that this is better than not having the third belt.
Finally, a sash belt mounted at even +10 degrees off the shoulder could compress your spine as your torso moves forward because that forward movement reduces the relative angle. The belt is there to help trade off torso injuries against head injuries. Up to you to decide which is more important.
My point is don’t condemn a sash belt without looking at the particulars of the situation.
And I would recommend against using 3” racing-style belts of fixed length in a street car because they could be designed with much less stretch than belts for road use. This is why I use a belt where the sash is controlled by an inertial reel mounted in the stiffest part of the side screen tray (with appropriately large backing plate. I gave it a very stout pull and believe this mounting to be strong enough to prevent a head into windscreen occurrence at slow to moderate speed crashes. Yet the belt and reel allow some movement which should reduce the peak forces in a crash. In a biggy I’m sure all hell
will break loose and I’ll be a goner, but otherwise I think my car is safer with the 3-Point belt.
FWIW, my spouse and kids are all short enough that their shoulders are not significantly above the back of the seat, so for them downward compression is more limited.
John
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