What would be the injury without a seatbelt?

Perhaps the best improvement would be to get everyone to wear them and next, get people off their phones while driving.

@Solar Mike 1 Without a seat belt it generally a guaranteed fatality somewhere between 25 - 40 MPH.

No, I had a head on without a belt, but I bent the steering wherl as I kept my arms locked.

I’m voting to close this question because it is a design question, not maintenace or repair.

@Solar Mike Modifying a vehicle is not on topic here? And were you suggesting that seat belts don't need to be worn?

Are you saying that you would like to increase the load limiter so that in a crash your body is subject to more forces by the seatbelt?

As for modifying, most car modders can get access to rolling roads to evaluate power changes or Tapley meters. But access to crash test dummies and high speed recording equipment is a different game.

@Solar Mike What was the comment about being in an accident without a seat belt and bending the steering wheel about about?

@HandyHowie yes that is exactly what I want to do. I would rather either die from internal injuries or recover than have severe brain and neck injuries that I may not die from. My body can handle a higher seat belt force than the average sized person.

You quoted a 50mph crash, I quoted another. Both are valid as singular occurrences but you need to understand statistics - evaluate the thousands, even millions, of crashes over years to see the results of your proposed changes.

Is your car the Kia Rio or the "older car"? Doesn't it have airbags? How will you adapt the belts in a way that on one journey a light and frail person is "safe" and on another journey a heavy and rugged person is safe when using the same belt? If it is for you only, the driver, I would not suggest (or advise) tampering with the belt, but to remove it and replace it with a fixed belt with 2 shoulder straps (like the Unwin belt based on a parachute harness my father installed in our first car in 1960, before they became law).

... but I don't see how you can expect anyone to advise you on how to tamper with a safety device. How many attempts do you have to 'get it right'?

Another thought about tampering with a most crucial safety devise: you may not be the only one to drive this vehicle. You may be putting someone else's life on the line. What about reselling the vehicle. You are not just taking a risk on your life, but others as well.

@AlexCannon, you may want to consider that the car companies know something you don't. There's been thousands of crash tests and study of real world accidents, if they have their belts configured in a certain way it's for a good reason.

When you have removed the load limiter and spent time in hospital with broken ribs and punctured lungs caused by your seat belt, you might want to change your mind about load limiters. Just saying. Your skull is a lot harder to break than your chest. Peer-reviewed papers have reported up to 85% reduction in injuries in real-world crashes, when load limiters are installed.

@alephzero The NHTSA did a study showing a 12.9% reduction in deaths where load limiters are installed. What study are your referring to? NHTSA is here: crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/811835

It was a paper about injuries not deaths, and it was a study of road accidents in France (Renault were one of the first manufacturers to introduce load limiters). Sample size was about 350 crashes with, and 350 without limiters. BTW do you realize how high seat belt loads on your chest are without load limiters? You are talking numbers like 1500 pounds or more. I would say even if you avoided chest injuries in a high speed crash without a limiter, you would most likely have a broken neck (which could leave you as a quadriplegic for the rest of your life, if that's your preferred outcome).

@GdD For a Volvo I would trust them. Guess what? The Volvo XC90 does fine in a 50 MPH 40% crash and their load limiter seems to spool out less! I trust the other companies to do no more than to make their car look good in a specific crash test. Is one test at 50 MPH too much to ask from the other car companies?

It seems absurd to me that random internet people will be able to give you advice to improve the safety of your car more than the auto manufacturer has already done. No, you should NOT attempt to adjust or modify the restraint systems in your vehicle. If you are concerned that yours is unsafe, get rid of it and buy another one that has the sort of safety rating you are looking for. Some manufacturer advertise their safety qualities.

@Weather Vane Install a 5 point harness and racing seats to go along with it? I actually like this idea. The car is a full size car that is in between the Kia and the older car in terms of front end strength. It has enough crumple room to where it can do as well as the Kia without load limiters, and I believe the IIHS tested version didn't have load limiters but the newer revision of the car does.

@jwh20 I can't afford a Volvo, and no other car maker tests their cars in 50 MPH crash tests that I know of. Have to make do with what I have. The older version of this Toyota doesn't have load limiters and it does all right. I'll handle the engineering side of adjusting the load limiter and you can tell me how to modify it and what parts can be swapped out!