The Science of Seat Belt Installation

The Science
of Seat Belt
Installation
Evolution of Seat Belt Testing
 Early 1950’s - simple static testing
 Late 1950’s - dynamic testing added
 Initial values set to represent an average mid sized car:
 80’s and 90’s – static and dynamic testing of components and
racing belt assemblies by FIA and SFI
 Impact speed ~30 mph / Deceleration peak at ~28g / Deformation 16”
 Sled testing today is approaching real world
∆V > 40 mph
Deceleration peaks up to 75g
Deformation ~41”
requirements on restraint performance have been almost doubled over
the years
 Done in conjunction with HNR and seat development – SAFETY CELL

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Here’s 31mph on the track!
SCHROTH TEST 17589
F-type restraint
Test Date: 2001-10-25
Anti-Sub Strap routed backwards
No HANS
Hybrid II Dummy, 31 mph impact speed
Sled deceleration - 28 g max.
Complete 6-point competition belt properly installed – NO HANS!
At the peak load point note that the shoulder and back are
8 to 10” off of the seat back & note the neck extension.
IRL car with no HANS 31pmh/28g
Steering wheel becomes part of restraint!
Webbing Technology
 Webbing must provide:
 Strength capabilities
 Load spreading capabilities
 Energy conversion
capabilities (controlled
elongation)
 Durability against use and
UV exposure
Webbing – Polyester vs. Nylon
Advantages of
Polyester Webbing
over Nylon Webbing
 (Battery) Acid resistance
 Multiple times higher UV-resistance
 Polyester webbing starts taking the load sooner and stretches
more evenly under higher loads with less “rubber band effect”
 Water, moisture, and humidity does not change performance
 Polyester provides better color fastening
 Nylon’s surface is more slippery, easing adjustment but also
risking micro slip in restraints (less need to retighten belts)
Webbing Wear and Inspection
• Webbing should not show any signs of unusual wear.
Frayed edge – rubbing on belt housing or
other parts – MUST BE REPLACED
Belt that had be elongated in an
incident – MUST BE REPLACED
Caught in the door latch. Webbing is cut –
MUST BE REPLACED
Webbing simply worn out from too much
movement through adjuster – REPLACE
2” Lap Belts – Superior Fit
Why 2 inch Lap Belts?
2” rides below the pelvic crest
3” Rides over the top
of the pelvic crest
The red 2” belt on the left
rides cleanly below the
crest at the top of the
pelvis. The full width of
the webbing is supported
over the pelvis
The 3” blue belt on the
right is already well over
the top of the pelvis
making slippage more
likely and decreasing the
comfort of the lap belt.
You are in effect
tightening the belt to the
small crest at the top.
2” Lap Belts – Superior Fit
 2” webbing is milled to provide same strength
and elongation as 3” webbing
 Better load spreading over its pressure surface
due to higher transversal stiffness
 Optimum fit into the crest between upper thighs
and pelvis – up to 2” tighter thus better pelvic
restraint reducing submarining
 Faster loading of the lap belt reduces the loads
on the chest
 Smaller and lighter hardware and adjusters
 Less interference with seat openings for laps
and shoulders allowing proper routing
 Easier to adjust
3" lap-strap
2" lap-strap
40mph – 40g Sled Test
No chest or neck loads
until the pelvis has
stopped moving.
No neck loads until the
chest has stopped
moving.
Initial position
Pelvis stopped – start chest load
The more that the
pelvis and lower body
is allowed to move, the
greater the subsequent
loads will be on the
chest and even greater
loads on the neck…
Force=Mass*Acceleration
Chest stopped – peak neck load
Rebound starting
Advantages of 6-Point over 5-Point Belts

Load transfer from shoulder belts into crotch
straps is critical for good restraining results

5-point restraints


The crotch strap routed forward

Higher rate of sternum injuries by chest
deflection found (see publications from Dr.
Melvin and others)
6-point T-bar restraint

provides good load transfer

T-bar size must be a certain width to provide the
necessary separation

Increased load requirements result in lager,
bulkier T-bars

T-bar is likely to stick into upper thighs

T-bar makes it more difficult to wear the buckle
low (pelvic straps are raised, supporting
tendency of submarining)

Prevents the addition of a 7th or 9th point substrap
Comparison of Chest Compression
6-point v. 5 point belts
30 mph - 31 G
10
0
-10
0
100
200
300
-20
400
500
600
5-point
6-point
-30
-40
-50
-60
Time, msec
The chart shows that, under the same
dynamic loads, the 5-point belt results in
nearly 60mm of chest compression where
the 6-point belt results in only 20mm of
compression. This significantly reduces
the likelihood of a sternum injury.
NASCAR has not had a single sternum
injury (common with 5-point belts) since
they have mandated 6-point belts.
Belt Dating– Homologated Restraints
SFI – 16.1& 16.5
2 years from month and year
punched. Belts are punched 3
months forward when shipped to
dealers to allow for “shelf life”
FIA – 5 years ending
12/31 of year on label
•(C) = with 5-point anti-sub strap
•(D) = with 6-point anti-sub strap
SAFETY PRODUCTS
SAFETY PRODUCTS
not valid after
not valid after
2014
2014
FIA C-129.T/98
FIA D-130.T/98
FIA D-136.T/98
Made in Germany
Made in Germany
How Harnessbelts Differ
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Mounting points – 3,4,5,6,7,8, or 9!
Locking – latch link vs. CAM lock
Weight – lightest/smallest hardware
Snap-on, bolt-on, wrap-in
Positioning of adjusters
Webbing materials – nylon vs. polyester
Webbing widths – 2”vs. 3” lap
Configuration of shoulder belts – 2”, 3”, double
Configuration and routing of sub straps
Sebastian Bourdais in
the new 2007 Elan
Champ car chassis
Latch Link Style Belts
Typical Latch Link Configurations
LL IIIH- T6
LL IIIV-T7
LL III-V6
Latch Link belts come with either sfi 16.5 or 16.1 certification
tags. All of the available sub-strap options are pictured above.
Adjusters for any belt can be left side, right side, both sides, pulldown, or pull-up.
Junior Belt
The LatchLink “Jr” belt
uses 2” webbing for both
lap and shoulder belts.
Our “Jr” belt is tested to
the same higher loads
required by sfi for the 3”
belts.
Cam Lock Type Belt Configurations
Competition belts from 4 to 9 points
2
Formula IIH-7
2
3
3
Profi II-6
1
7
2
4
8
3
4
1
1
4
Profi II-6Y
6
5
6
7
5
6
5
“9th Point” would be an additional forward facing crotch belt between points 6
and 6 BUT this is only possible with Formula and Hybrid style belts.
Typical 6-Point Sub Belt Options
Formula
Hybrid
T-Bar
V Style
*Only Formula and Hybrid belts can be
used in 7 or 9 point configurations!
Profi II – New SL88 Lap Adjuster
2 Inch Lap Belt with Pull-Down Adjusters at Buckle – T-Bar
SFI 16.5 and FIA – The Ultimate in Ease of Adjustment!
Competition
Harnessbelt
Installation Guide
Proper Positioning and Routing Angles of Belts
The geometry for harnessbelts
is the same regardless of the
type of vehicle - marine, aircraft,
or land vehicle.
There are only two hard parts of
the body that can sustain the
belt loads that you can find in a
vehicular incident – the pelvis
and the collar bone!
Using the ribs, abdomen, or
other body parts will result in
serious injury.
Proper Positioning and Routing Angles of Belts
 Must pass over hard body partscollar bone & pelvis
 All belts should be as short as
possible
 Different belt designs with
different crotch belt options
require different mounting points
 The lap belt should be positioned
with the CAM lock two inches
below the belly button and the
lap belt riding just below the
crest of the pelvic bone.
General Belt Installation Guidelines
 Webbing must lie flat as it passes through the shoulder
and lap belt openings in the seat
 Webbing must not be “loaded” on either the top or bottom
edges of the belt openings
 Webbing should not be folded over on the sides or edges of
any of the seat openings (when the belt is properly tightened)
 Webbing must not ride against any seat mounting
hardware or exposed plastic or metal edges that could
cut or abrade the webbing
 3-bar adjusters must be as close to the harnessbar or
end fitting as possible
Selection of Belt Design Criteria
Know what you need - before you buy!
 Lap belt attachment options- bolt, snap, or wrap or a
combination
 Sizes of pre-existing bolt holes in chassis
 Lap belt adjustment options- pull-up or pull-down
 Positioning of adjuster and mounting hardware in
relation to your specific seat
 Belt use - multiple drivers? different sizes?
 Study your car carefully or work with an established
supplier- expert in your car
 Check FIA & SFI dates before accepting “new” belts
Competition Installation
Shoulder Belts
Competition Harnessbelt – NASCAR Dynamic Test
70g Test - HANS Double Shoulder Belt for NASCAR at Delphi
Proper Positioning and Routing of Shoulder Belts
 Shoulder openings must clear top of shoulder
and the NHR with clear path to the harnessbar
or mounting point(s)
 Shoulder belts should be as short as possible
 Angle from the top of the shoulder (HNR) back
to the mounting point should be 0º to -20º with
-10º being optimum and -30º the maximum –
NEVER at an upward angle
 Ensure no interference either up, down, or
side to side on the shoulder openings in the
seat
 If the shoulder belt mounting points are
further than 18” from the back of the seat, the
tail straps should be crossed
 Distance between the shoulder belts can be
calculated with the formula on the following
page
Shoulder Belt Separation Calculation at Mount
•Maximum distance inside edge to inside edge of 5” to 7”
•Ideal shoulder mount positioning – Y = Z - (X * 0,50)
(If “Y” is negative – cross shoulders)
Shoulder Belt Latches
Figure 1
Figure 2
 Some manufacturers have shoulder belt latches that
are left and right specific!!

Figure 1 shows the correct orientation with the latches
angled inward – latches in Green

Figure 2 shows the WRONG orientation
“3” to 2” Shoulder Belts – HNR Specific
3” to 2” shoulder belts are the standard used by
most professional drivers using a HANS® device.
Can be used with other HRN (Head and Neck
Restraints) such as the Hybrid series, R3,
and Defender systems
Reduces interference with seat back
openings
Optimum fit over the HNR with no overhang
Greater driver comfort and feeling of
security as the belt rides within the outside
lip of the HNR
From a performance view – there is no
significant difference between a 2” shoulder
belts or 3” shoulder belt in an incident
HANS ® Double (Over-Under) Shoulder Belt
 “Sandwiches” the HANS between the
lower 3” body belt and the upper 2”
HANS® belt

Separate pull-down adjuster for the
upper 2” HANS belt

Standard 3” pull-down adjuster
tightens both belts at the same time

Single release maintained
 NASCAR testing has shown a 50%
improvement in the already great
performance of the HANS®
 Recommend by NASCAR and IRL to their
drivers as the optimum belt solution
Typical Shoulder NASCAR Double Shoulder Belt
This is an example of the
NASCAR “Hendrick”
carbon fiber seat in use
by many of the Sprint
Cup teams. All lap,
shoulder, and crotch
belts are mounting within
the seat itself.
•
Pictured here are the
mounts for the HANS
double shoulder belts
(over/under belts) that is
now popular with
NASCAR and IRL drivers.
The HANS in sandwiched
between the lower 3”
body belt and the upper
2” HANS belt.
Jeff Gordon’s SCHROTH Double Belt installation – #24 Car
Double Shoulder Belt Installation Guidelines
Where possible there should be a 2-2.5”
separation between the lower body belt and the
upper HANS belt. Be sure that the lower belt
does not prevent the HANS from resting
completely down over the top of the shoulder.
Typical formula car setup or NASCAR carbon
seat with shoulder belts mounted internal to the
seat. Similar to the Jeff Gordon setup on the
previous slide.
In cases where there is only one harnessbar, both
belts may be installed to the same bar. Follow the
“xyz formula” to determine if the HANS shoulder
belts need to be crossed. Alternatively, a harness
bracket as pictured in the next slide may be added
to a harnessbar.
Adjustable Height Harness Mount Bracket
 Use for mounting the Double Shoulder
belts as pictured at top right or to
create a better angle on a standard
shoulder belt where a harnessbar is too
high or too low
 Must be welded by a Certified Welder to
the rear of the harness bar
 Only available for 1.75” & 1.5” tubing
 4 adjustable mounting positions
 Can be welded up or down to provide up
to 2” of adjustment in the position of
the shoulder belt mounting point
 Tested to FIA load standards
Proper Wrap of 3-Bar Adjuster
Only one bar of the 3 bar
adjuster should be visible if the
wrap is completed correctly.
If wrapping in 3” webbing into a
mounting bracket with a 1.75-2”
slot, be sure to evenly fold in
edges of the webbing to the
inside of the bracket.
 3-Bar Adjuster must be as close as possible to the
harnessbar or mounting bracket
 Be sure to get the final locking loop
 Leave 4” of webbing after the final loop of the wrap
extending beyond the adjuster
3-Bar Wrap Mount Ends … what’s the worry?
… the 3-bar Slide will slide!
When properly wraped
AND positioned next to
the bar – slipage is
nearly eliminated.
5
K raft [N ]
10.000
5.000
0
0
50
100
150
Weg [mm]
8
15.000
K r a ft [N ]
The video shows how a
properly wraped 3-bar
slide adjuster that is
NOT positioned
immediately next to the
bar, as it should be
(pictured below) – takes
the initial load but then
begins to slip.
10.000
5.000
0
0
50
100
Weg [mm]
Shoulder Belt Positioning
 Rear downward angle from 0º to max 20º
 Harness guide bar at shoulder height if low mounts
 Crossed tail straps on belts mounted 18+” behind seat
 Guides or padding to restrict sideward movement at mounts
 Peak loads of 3,500lbs per mounting point
Typical Shoulder Belt Installation Problems
BAD INSTALL EXAMPLE!
 Rear tail straps should
be crossed. 18+ back
from seat
 3-bar adjuster is not up
against the harnessbar
– large visible loop
 No guides or padding to
prevent the shoulders
from sliding side to side
THIS WAS A
“PROFESSIONAL “ RACE
INSTALLATION!
Typical Shoulder Belt Installation Problems
3-bar adjuster is tight to
the bar but look at what
bar they used!
Huge loop and
wrong wrap.
The webbing is binding in the seat
opening. The 3 bar adjuster is wrapped
wrong. Hardware is resting on the
shoulder – inside the seat!!! WOW
Typical Shoulder Belt Installation Problems
 With a structural
harnessbar as it appears to
be in this car, the belts
would be better wrapped
around the bar with the 3bar adjuster.
 The 3-bar adjusters here
are missing the final wrap.
 The 3-bar adjuster is too
far away from the bolt in
bracket – it should ride up
right next to it.
•
Typical Shoulder Belt Installation Problems
 The right side shoulder belt
anchor bracket is not
mounted in plane
 Webbing is not folded
under properly in the
mounting brackets
 One 3-bar adjuster in to the
inside of the seat
 The visible 3-bar adjuster
does not have the final
wrap
 3-bar adjusters are too far
from the mounting
brackets
Typical Shoulder Belt Installation Problems
 Shoulder belts eye bolts
should be positioned
vertically to allow belts to lie
flat over shoulder.
 3-bar adjusters are not
properly wrapped
 3-bar adjuster should not be
to the inside of the drivers
seat. Adjuster should be
located directly in front of the
snap-on bracket.
 Excess webbing should be
rolled and zip tied at the
mount or cut (4” outside the
adjuster) and edge sealed with
a lighter.
•
Competition Installation
Lap Belts
Proper Positioning and Routing of Lap Belts
 Lap belt should be as short as possible riding over the pelvis at an
angle of 60º to 80º
 Mounts should be as close as possible to the sides of the seat
(maximum 20º to 25º) but never less than the width of the seat (i.e..
behind the seat)
 Inline adjusters and mounting brackets must not be in contact with
seat openings (a pull-up lap belt adjuster sitting just outside the seat opening could
get caught and cause the adjuster to release tension on the lap belt)
Proper Positioning and Routing of Lap Belts
 Make sure the webbing is not riding on or
over any seat mounting hardware such as
side plates or mounting bolts (see Figure 1)
Figure 1
 Bolt on lap belts must swivel at mounting
point to allow the hardware to be loaded “in
plane” (see Figure 2)

Use machined “pivot sleeves” when possible to
ensure rotation.

Alternative is to use Red LockTite and leave nut just
barely loose enough for pivot of mounting bracket
 Never modify hardware by enlarging bolt
holes or “trimming” for clearance
 Never mix hardware from different
manufacturers – especially hardware that is
used in any wrap attachment
Figure 2
Loading of Lap Belt Mounting Hardware
 Load all lap belt hardware in plane with a direct load path between the cam
lock or latch link and the mounting point
 most hardened steel mounting hardware will take a load of 8,000lbs
pulled in plane but less then 4,000lbs if pulled at a 90º angle
 Webbing must not be allowed to load at one edge of a bracket. Webbing
pulled evenly over the full width of a mounting bracket will takes loads in
excess of 7,000lbs. When an edge is loaded, this load can be less than
3,000lbs. – always allow the lap belt to pivot
Lap Belt “Snap-On” Considerations
 Eyebolts must be mounted securely
either using factory DOT mounting points
or a proper backing plate with welded nut
 Eyebolts should be positioned so that
when the snap-on mounting bracket is
connected and the lap belt is tightened –
the bracket is free to move fore and aft
(this generally means that the hole of the
eyebolt hole is facing the front of the car)
 Snap-on bracket should be connected
with the release flap on the on the lower
side and secured with a cotter pin or wire
through the small hole in the release flap
Release flap – lock with cotter pin
Optimum Lapbelt Mounting
Pictured at right is the
Hendrick NASCAR carbon
seat with the SCHROTH B40
bolt-on bracket mounted. The
B40 bracket is installed with
the S64 pivot sleeve.
The Hendrick seat has all belt
points (shoulders, laps, and
subs) mounted internal to the
seat itself.
Note that the lap belt has
multiple attachment points to
ensure proper fitment over
the pelvis.
Mounting all belts internal to
the seat allows for the
shortest possible lap,
shoulder, and sub straps.
Typical Lap Belt Installation Problems
WRONG
 Eyebolt is facing the wrong direction –
should be turned 90º
 The snap-on bracket is attached with
the release flap on the up side and
there is no cotter pin for locking
WRONG
 Since the eyebolt is improperly
positioned the webbing is “loaded” on
one edge of the inline adjuster
 Too far from the seat
CORRECT
 All of these problems are solved with
the installation at the bottom
CORRECT
Typical Lap Belt Installation Problems
Does this look ok?
Typical Lap Belt Installation Problems
Under the lap
belt on the
previous slide
sits this “knife”
waiting to cut
the belt!
 Webbing must not be restricted by seat
mounting brackets and/or mounting bolts
 Do not mount lap belts to the seat
mounting side plates by drilling holes in
the side plates. If lap belt mounting holes
are not provided by the side plate
manufacturer, they must not be drilled
 Webbing must not be folded or “corded” in
the seat opening when the belt is in use
 Be sure any exposed edges of opening or
bars are smooth to protect from webbing
abrasion.
Typical Lap Belt Installation Problems
The pull-up lap belt adjuster is getting
caught up on the outside edge of the lap
belt opening.
 There is slack in the belt between the
mounting point to the chassis and the
adjuster getting hung up on the seat
 In an impact, the load will cause the
adjuster to open and the remaining
webbing will be released through the
adjuster
 Additional loads will be created if the
adjuster comes through the seat
opening to take up the slack to the
mounting point
pe
Typical Lap Belt Installation Problems
VIEW DOWN FROM TOP
 Lap belt goes back at
about a 30º angle rather
then the recommended
• 60º to 80º - likely to
cause injury to liver and
kidneys in a crash
 This setup will allow
significant submarining
and will increase the
loads to the crotch belt
likely causing a groin
injury as well
Typical Lap Belt Installation Problems
VIEW DOWN FROM TOP
 Lap belt bolt on bracket
is angled to the front
causing the webbing in
the bracket to bunch up
and edge load
 The wrap on the 3-bar
adjuster has not been
completed. The final
locking loop is missing.
Competition Installation
Sub-Straps
Sub Strap Installation
 The purpose of the sub-strap is to maintain the proper position of
the lap belt with the cam lock (or latch link) centered 1” to 2”
below the belly -button regardless of how tightly the shoulder
belts are worn
 Proper backing plates must be used on all bolt points other than
factory DOT mounting points (most fender washers are not
sufficient)
 Sub-straps can see typical loads of 800lb to 1,200lb with peaks
of 2,400lb in cases where the lap belt is either mounted
improperly or worn to loose
 Sub-straps mounted at other then the recommended angles may
result in significantly higher loads on the sub-straps and
proportionately higher loads on the chest and neck
 Improperly routed sub-straps may cause groin injuries
 Sub-Strap “hole” in seat bottom should be approximately 10” to
12” forward from the inside seat back
5 Point – Belt Mounting Positions

Sub-strap should follow the
plane of the shoulder belt
down the chest directly to the
mounting point or up to 20º
forward

The sub strap must pass
directly through an opening in
the seat and must not be routed
around the front of the seat

The opening in the seat bottom
for the sub strap should
between 11” and 13” from the
inside back of the seat - forward

Cross bars under the seat may
be use to mount sub straps
providing they are designed to
bear the load of at least 1,800lbs

These guidelines also apply for
an additional 7th point as part of
a Formula or Hybrid-Restraint
6-Point T-Bar/V-Strap Mounting Positions

For standard FIA shell type seats
draw a perpendicular through the
center of the sub-slot in the seat
and measure an angle rearward
20º (generally 2” to 3”). From the
center line create two separate
mounting points 2” to 3” left and
right of center

Drill holes through the floor and
use SCHROTH backing plates with
welded nut to install bolts or
eyebolts – floor structure with
plate must be able to take a
minimum load of 1,800lbs at each
point

A properly positioned cross bars
under the seat may be used to
mount sub straps providing it is
designed to bear the minimum of
an 1,800lb load

7th point sub-strap can not be
added to the T-Bar or V-Strap
6-Point/7-Point Formula/Hybrid Style Mounting
Seat
bottom
ramp

Designed for single seat Formula
style cars where the drivers seat is
one with the chassis – typically with a
bead type insert – and where there is
some sort of “seat bottom ramp”
helping to restrict forward movement

Lap belt and sub strap mounts are at
or near the same locations OR substrap may be mounted just under or
behind the each buttock slightly aft of
the lap belt

Driver sits directly on the sub-straps
with them wrapping around their
inner thigh

Adding a “7th point” – mounted
similar to a traditional 5th point - will
improve the performance of the belt,
especially in rollovers

Not recommended for FIA type and
aluminum seats where the sub-straps
go through a single sub hole
7th point
6-Point Hybrid-Restraint™

The Hybrid-Restraint™ sub straps
may be routed following either the
guidelines of the T-Bar or the
Formula style belts

Optional 7th point sub-strap may
be used when following the
“Formula Style” sub strap routing

Drill holes through the floor and
use SCHROTH backing plates with
welded nut to install bolts or
eyebolts – floor structure with
plate must be able to take a
minimum load of 1,800lbs at each
point

A properly positioned cross bars
under the seat may be used to
mount sub straps providing it is
designed to bear the minimum of
an 1,800lb load
Optional 7th Point
Belts – Seats – Nets – HNR – ONE SYSTEM!
•
Belts – Seats – Nets – HNR – ONE SYSTEM!
SCHROTH - SAFETY THROUGH TECHNOLOGY
AND HE WALKED AWAY!!