harness belts 101

2 inch seat belt graphic 1 1.jpg


Harness belts attach you to the internal safety structure (cell) of your vehicle. The belts are attached to your full or half roll cage. Your torso can no longer move independently - as it does with the standard 3 point seat belt. The standard 3 point belt system is designed to let you move, but locks in the event of a crash. Your body will move until caught by the airbags.

When installing harnesses follow the manufactures installation instructions precisely - deviations from the angles can cause serious injuries.

makes sense that the 3” belt is stronger so better - wrong…

  1. Historically correct - sort of. The belts and the webbing material evolved from various industries, such as the military and shipping. Carl Schroth devised his seat belt for more personal reasons. He was an avid rally driver and devised a way to secure his co-driver with straps - so he could read the maps.

  2. Seemed to make sense that the wider the webbing material the stronger the strap was. Plus the 3” belt does have the added advantage of covering larger areas of the body for greater containment. However the harnesses design, science and technology has evolved along with the material used to weave the webbing. In addition crash statistics, both visual and data driven have resulted in new safety products such as the frontal head restraints (Hans.)

  3. For example, it is now understood that the 3” lap belt can do more harm than the 2”. This is because it is too wide to fit into the ‘hip pocket’ that’s created when a driver sits. The 3” sits on top of the hip bone (the Iliac crest) and in the event of a crash can move (usually) upwards doing damage to unprotected soft tissue. The 2” belts gets closer to the body and allows the driver to fully tightened the belt - for greater hip containment.

  4. The 3” lap belt is more inclined to fold, so potentially inflicting greater damage to body by cutting into the body’s soft tissue. NASCAR does not allow 3” lap belts, neither does the latest FIA homologation sanction them. 3” shoulder belts are allowed except FIA now stipulates 2” shoulder belts when worn with a frontal head restraint device.

  5. Harness belts should never sit over the waist, especially 4 pt. belts. The lower the belt the better it helps prevent ‘submarining’ - where the drivers slips under and out of the harness. There’s a reason why most sanctioning bodies require, at minimum, a 5 pt. harness.

graphic 2 inch v 3 inch belts 1 1.jpg

nylon verses polyester

There’s a good reason why FIA harnesses are tagged for 5 years and SFI have a 2 year expiration date.

FIA requires polyester, SFI stills allows nylon. Nylon does not match Polyester’s strength and longevity. After UV exposure new Nylon loses 52% of its strength - breaking at 5,069lb. New Polyester loses 23% - breaking at 8,056lb. (SFI’s minimum requirement is 6,300lb.)

Polyester’s elasticity is also superior. Nylon’s elasticity (that is the ability to resume its normal shape after being stretched or compressed) drops dramatically after 2 years. For polyester this occurs after 5 years.

Note many SFI manufacturers do now use polyester, but not all. SFI continues to tag for only 2 years for safety - and budget considerations. Nylon is cheaper, but more importantly SFI wants to keep all racers safe. Therefore they set their standards based on the worse case scenario - that you are racing hard, every weekend, year round in an open cockpit, in all weather conditions - AND that you do not take care of your harnesses. Forcing you to change your harness every 2 years keeps you safer.

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A myriad of choices from multiple manufacturers, but each manufacturer has to pass identical safety tests quantified from only two sanctioning bodies - the FIA or SFI. The tests are performed at appropriate, licensed facilities.

FIA 8853-2016 Recently introduced and after 2023 all FIA belts will have been manufactured to this standard. The harness has to withstand forces of up to 70Gs, from multiple angles and more.

SFI 16.1 The harness must not break under 6,300lbs

SF2 16.2 A youth harness (lower) rating

SFI 16.5 The harness must not break under 7,000lbs. Designed for the rigors of off-roading