between rebuilding my cousins dirt car last winter and caging my s10 this year, ive noticed something both interesting and potentially dangerous with how people are mounting these.
according to harness manufactures as well as the nhra rule book there are specific criteria for the mount location of the shoulder belts that state to have them within a few inches of horizontal with top of shoulder(not going to state specifics due to variations between places of reference) to reduce chance of increased spinal compression and serious injury/death from being mounted too low/too severe of an angle, or too high where it wouldnt hold you in as well.
i noticed when looking at both a tech article in circle track mag, as well as a lot of modified, sportsmans, street stocks, etc(most of which are professionally built chassis) that almost all of them have the belts coming almost straight down at 60-90 degrees to ensure the belts hold you in, however they are completely disregarding the spinal compression issue.
this leads me to believe that many in the racing industry are completely ignoring the safety precautions of the manufactures of the belts they are using. ive seen cars barrel roll and flip end over end in the air during dirt races…would be a shame to see someone not able to climb out due to a builders inferior design.
i know theres alot of guys building their own cars on here, be sure to pay attention to what youre doing. im still really suprised with how many big name builders arent…
^ That’s what I thought. But the seat back can act as the bar(?). If the Bar is at the same height as the seat holes what does it add other than a longer belt?
In that first pic with the “Scary” belts as long as your shoulders are below the belts holes you will be fine. The belt will only pull the seat down…no?
Now, if the Seat is a POS then it won’t withstand the impact. Obviously, the bar is more rigid. But, my question is from a Spinal Tap prespective…does adding a secondary bar at the same height of the seat holes provide any compression benefit?
Makes sense. So, don’t use your seatback for your harness bar. Mounting point is irrelevent provided your bar is at the right height and the belt uses the bar for tension.
In other words, that “SCARY” picture is just dumb because there is no bar. The belts can mount there but you need a bar at shoulder height. In fact, that is probably the best place to mount them as those are existing seat belt holes…assuming that is what was used (Although they look just “clipped” in the back belt buckle). But, a bar is needed to be safe.
Let’s assume that a car in a crash goes from 65mph to 0mph in .5 seconds… With a 200lb person, that’s an acceleration of 5220N
Lets assume that the belts are mounted at a 45 degree angle going over the seat… That means the vertical portion of the the load of your body is 3691N or 891 lbs… Do you really think a thin CF seat shell is going to withstand that kind of load???
^ I assume you are asking me. No, I agree that the seat will not withstand that load. You need the bar to withstand the tension caused by the harness under load. The seat just contains you and directs it into the harness.
nick, not as common knowledge as you would think. i would say a solid 75% of the cars at ransomville have improper shoulder belt location.
nhra rulebook says 1-4" off horizontal of shoulder perpendicular to body line / spine. must be wrapped to rollbar or frame or otherwise attached to frame using 1/4" plate. if you go to the guidelines by manufactures they state within 30 degrees above to 5 degrees below horizontoal of shoulder perpendicular to body line / spine.
keep in mind the further back the belts are the less effective they are in keeping you in place. mounting them further out to keep correct angle would not be proper, but locating mounting point closer to achieve correct angle is better.
Race belts have some stretch to them under impact.
A short distance to the harness bar will stretch less than a belt bolted down in the trunk. Too much stretch may allow a shoulder to get free from underneath the belt. The less amount of movement the better.
Simpson Race Products has also tested and uses polyester. As a result of their testing, they have published some rather amazing stats. One of the most impressive is that at 2,500 pounds of force, nylon belts will elongate (stretch) 15-17 percent their normal length. The elongation on polyester at the same amount of force is only 7-9 percent. Further, the nylon webbing has a tendency to absorb water, and when it gets wet it loses some of its strength, approximately 12 percent. However, Simpson’s testing concluded that belts made primarily of polyester webbing lost no strength when exposed to water. This is the reason that Simpson is currently manufacturing two different sets of polyester belts, the most popular being the platinum-style safety belt.
