Technical Three Point Seat belts

I plan to put in 3 point seat belts in place of the lap belts I have now. Since I have a roll bar I can use bottom roll bar mounting bolt for the Inertia/recoil mount and a exhaust clamp for the top mount, either a SS typical U-bolt style or would a band style (https://www.amazon.com/Roadformer-E...prefix=exhaust+pipe+clamp,aps,96&sr=8-13&th=1) be strong enough?

 

Muffler clamps are for mufflers not seat belts. I would weld a substantial tab to the roll bar and attach the top mount to that. Make sure you install the tab at the correct height in relationship to the seat.

 

***uming I'm using this right...
Impact Force Calculator - Calculate the impact force in a collision (gigacalculator.com)

A 200lb person travelling at 30mph experience a stop over a total distance of 1yd (seems somewhat resonable for how much a car can crumple) makes a max force of 17.8kN, we'll round that off to 1.7 metric tons or 3500lb.

Would you hang your entire 3500lb car from one of those clamps?
This was at low 30mph, higher speed means bigger forces.

 

weld on a tab and use a 7/16" bolt, perhaps?

 

The bottom roll bar mounting bolt would probably be OK for the recoil mount, since both are bolted to the floor pan. But I would rather see the upper mount be in the door post, or body structure rather than hose clamped to a bolted in roll bar.

I have serious doubts that clamp pictured would have the capacity to keep the belt mount attached to the roll bar in a crash, then there is the fact the seat isn't attached to the bar.

If the seat base was attached to the roll bar, and the belt mounting bracket was welded to the roll bar, maybe that would p*** for me.

If the seat and the roll bar are not attached to each other, there is a possibility the bar and the seat may move in different directions in a crash. There are reasons you do not bolt a seat belt to the frame on a car, but you bolt it to the floor pan beside the seat.

All that said, a 3 point belt that won't pull free of the vehicle in a crash, is probably a lot safer then just a lap belt. My opinion is worth as much as you paid for it.

 

This is what I am looking at (https://www.ebay.com/itm/2320457663...pCzmqJDIJJiBjf5Kcfs52q2OA=|tkp:Bk9SR7C3jLXhYA) local business.

 

Useful calculator, thanks!

There are a number of factors which determine whether that clamp would be suitable for the job, and what it's meant for isn't one of them. Valid factors would include the cross-sectional area of the strap and the tensile strength of the material. The ad Seb linked to gives a cross-sectional area of .0875 square inches, but it doesn't mention a material grade. Adjusting a typical stainless tensile strength value for impact and a safety factor suggests a working figure of around 26 000psi, which means that the clamp would practically be good for about 2275lbs in the proposed application.

@G-son rightly points out that his calculated figure of 3500lbs ***umes a very low speed. It nevertheless makes no sense to design for a tensile strength vastly greater than that of the seat belt which is to be attached to the clamp. That is known: seat belt webbing is rated at around 5000lbs, though it might carry somewhat more in actual fact. It points to the clamp being at best less than half as strong as it should be.

So: this muffler clamp would be wholly inadequate for the proposed purpose, but a different, heavier muffler clamp might be perfectly suitable.

 

Go look at Wesco's site. They cater to the race car crowd too.
https://www.wescoperformance.com/seatbelts.html

 

What does N.H.R.A. want for belt mounting points with a roll bar? That would be the "gold standard" for how a seat belt should be mounted. I would look at the specs for what they want of stock bodied cars that run just fast enough where they are required. 10.00 et. I believe.
They might be for a 5 point belt, but it will still point you in the right direction.

 

If you're willing to spend $230 on your belt why would you go with a cheap exhaust clamp to hold it? Weld a tab to the roll cage and be safe. Might as well keep just a lap belt if the top is secured with that clamp.

 

If this is race car, the roll cage should be NHRA approved and five point belts already installed, its mandatory. If this is just a bolt in cage never to be raced, it could be as easy as drilling a hole through the tube and bolting the upper mount to it, this would be far stronger then a u-bolt type mount, but neither of which will p*** any type of tech inspections. I would bet any type of tab mount would get looked at pretty hard as well.
Post some pictures of the area, the upper body mount would be the best bet, it would spread the load out along the the whole upper structure leaving the cage as is.
An easier option would be to use four or five point belts bolted to the floor, run the shoulder belts over the cage cross bar and down to the floor.
https://www.wescoperformance.com/3lap3shinwra.html
https://www.summitracing.com/parts/csu-44001b

 

Know that by law, Race Type harnesses (which typically have to be re-webbed or replaced every few years) are illegal on the roads in the US. Maybe no one will ever check or question them. Meanwhile, you can use 60 year old junkyard belts forever on the streets. I just went through this on my latest project, spent 45 minutes in the boneyard 'til I found a set I like (Dodge Dakota back seat) and I got them for $25.

 

Uh....which law? and when installed in what car? Sounds like a blanket statement that might not fit all situations.

 

The law that says arms aren't long enough to reach dashboard?

 

Shoulder harnesses save you, lap belts insure a pretty corpse. With a lap you are still gonna hit the steering wheel

 

Best angle I could find. I did try shoulder harness but quickly found out I couldn't reach the ing switch when buckled in. Only reason for the roll bar was because of gl*** body parts, not ET. I have to measure the relationship of B pillar roll bar and seat. Seat maybe too far back for B pillar, Roll bar maybe wide enough to keep belt away from neck when buckled.

 

NO DOT approval tag. The kit car guys fight that one a lot. Even though the car has a 4 point harness that can p*** tech at any drag strip in the country and p*** land speed tech forr the cl*** the car would run in including having do***entation that the webbing is up to date it won't p*** inspection for highway beause it doesn't have the DOT tag.

 

From where I sit it looks like having the mount point on that roll bar might be a good way to snap your neck with the belt, meaning that the position is going to put the point where the belt crosses the seat inboard of the seam that is 2 inches or more in. It won't go across your shoulder and chest it will go around you neck and cross your chest at a steep angle.

The proper place is on the door post at the correct height using the plate provided in the kit and having it securely fastened.

 

You live in Ct call or look up Juliano's in Ellington on their website they have a bunch of ways to set up your seat belts with good safe hardware, if your gonna do something safety related do it right

 

So....that might apply to a car that's subject to a state inspection? But not my cars, since I live in Arizona....we don't have that safety inspection foolishness here. The guy who brought it up, made it sound like you can't drive a car in the US without having a DOT approved seat belt in the car.

 

Isn't it federal like sealed beams?

 

if you have a roll bar there should be a cross brace behind front seat(s). then you should utilize that bar to install 4 point seat belts, not 3 point. there are some aftermarket cross braces available for cars without roll bar.

 

Like I said in previous post: with a 4 pt I can't reach the Ing switch...

 

sounds like you need to build a console, or?, that places ignition switch to a place that you can reach - easier to do than repairing your body in an accident with improper safety equipment

 

Post 6, 16, 18. I hate to get into the B pillar as I really don't think there is that much material there but if all that know insist there is then thats it. Was in Juliano's web site last week but couldn't find any thing other than a PU truck install that had factory B pillar mount; was looking for some install like in mid fiftys cars.

 

The AC knobs are there..

 

your life

 

I was kidding.. Post #18 looks like what I will do.

 

You won't find info on how shoulder belts were installed in cars in the 50's because that didn't start until the late 60's. Most of the time those belts attached to the roof above the quarter window or rear door.

Do it simple and just weld a tab to the roll bar.

 

Sheesh.. Post #18