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The argument of whether or not aftermarket harnesses are safe to use in a street-driven car has always been a tumultuous topic. Is it legal? Will it mess with factory safety equipment? Do I need a roll cage? There’s a lot to it, with plenty of negatives balancing out some pretty pronounced positives. If you’re considering installing a harness, we have some advice to present, mostly erring on the side of why not to. Here are some things to keep in mind if you’re thinking about upping your retention game. 

Why It’s a Consideration

If you’ve ever considered putting a four-, five-, or six-point harness or harnesses in your car, you’ve most likely come to this decision because you want more retention. A harness firmly holding you down in the seat allows you to focus more on performance driving; the lateral g-forces aren’t making you brace your knee on the door card, press firmly into the dead pedal, lean into long sweepers, etc. This is prevalent in spirited street driving, but way more so on track. With the added comfort and retention, you can focus, zone in, and start dropping lap times.

Though, replacing a worn factory belt might also be a consideration. If you’re in a position where your factory three-point belt is very worn and most likely not going to do its job in the event of a crash, it’s often cheaper to buy a harness than an OEM replacement. There are a lot of super inexpensive four-point harnesses out there, and if extra straps mean more safety, why not? But there are several safety and legal factors to consider.

This Mini race car is an example of where harnesses are the most at-home. Image: BMW/Mini USA

Why It’s a Bad Idea

Just because there are more straps on a belt doesn’t mean it’s safer. OEM seat belts are tested extensively for their longevity and effectiveness, and they’re designed to stay safe for the vehicle’s entire lifespan. Sure, they sometimes do wear out and need replacing, but they’re not considered a normal wear item. The cheap harnesses that you’ll find on eBay, Amazon, etc., are not strenuously tested like OEM belts, or any belt that’s DOT-, FIA-, or SFI-approved. You should also make sure the belts you’re considering buying don’t have fake DOT, FIA, or SFI tags on them. When replacing a normal, factory three-point belt, source it directly from the automaker.

Then there are the legal ramifications. Only four-point harnesses that are DOT-approved, such as Schroth Rallye and Takata Drift (which is essentially a re-branded Schroth product) should be considered for street-driven cars. However, there is a long list of requirements to ensure they’re mounted up correctly and safely, as detailed extensively by Schroth. Schroth also makes DOT-legal harnesses that are specially designed for certain cars, and those are in the same category as their Rallye belts.

What makes them legal is their push-button release and Anti-Submarine (ASM) loop (more on that in a bit), but only if they’re installed in addition to the OEM three-point belts.

A car that’s definitely setup for harness use: the Porsche 911 RSR. Image: Porsche USA

Why It’s a Worse Idea

Three-point belts are engineered to disallow the body from getting crushed in an upright seating position and to prevent submarining, which is when the body slides under the waist belt in a head-on collision. Seats will flex and contort under extreme forces to prevent these as well, but generally, a three-point will allow the body to fold forward, thus increasing head clearance and preventing submarining. The ASM loop on Schroth and Takata belts breaks open under extreme g-force and allows the body to do the same.

Cheap harnesses don’t do this, and also don’t provide enough initial restraint in the first place due to being of cheap/poor quality.

OEM belts are designed to stretch out to a certain regulated point and slow down the body under extreme g-forces. Then, they allow it to be cushioned in reassuring comfort by the supplemental restraint system, aka the airbags. In modern cars, they’re also designed to tighten via the pre-tensioners if need be, but it all depends on the kind of collision that’s happening within the given fraction of a second. This is also why I’m not a fan of aftermarket steering wheels in street-driven cars that were originally equipped with airbags, but that’s a blog for another day.

A non-ASM four-, five-, or six-point harness will potentially hold the body in too well, by either not allowing enough movement, causing you to get crushed if you don’t have added rollover protection, or truly, hold the body in too well. What I mean by this is that it puts too much strain on the neck and head and could lead to the brutal killer of many race car drivers, the basal skull fracture. I’ll hyperlink the basal skull fracture’s description because thinking about it makes me really queasy. After all, it’s why the Hans device was invented.

As far as preventing submarining goes with five- and six-point belts, these put a sturdy piece of harness right in front of the crotch. Certain sub belt designs are better at not crushing this region of the body than others; some route this piece, or these pieces (if it’s a 6-point), around the crotch. Yeah… I’d save that for when it’s actually required in wheel-to-wheel racing.

Again, another car where harnesses definitely belong: a TCR Hyundai Veloster N Image: Hyundai USA

If You Still Aren’t Detracted

If you’re game for DOT-approved four-point belts, they are great for retention on track and help provide a better connection to the chassis. Street driving, however, makes them huge pains in the neck (pun definitely intended). They restrict movement for checking blind spots, going through drive-thrus is annoying, and you might not be able to reach certain controls when fully belted in. If you’re thinking, “ah, well, I’ll just run them loose,” that actually completely negates their effectiveness, so fuhgeddaboudit.

There are certain DOT harnesses that are easy to detach for street driving, and DOT-approved ones are fine in general, but they make life harder. Like anything performance-driving-equipment-for-the-street-oriented, it’s always a balancing act.

There’s also a lot of engineering and regulatory consideration to, well, take into consideration, such as mounting angles, seat design, mounting points, and more. Are they being run with an FIA-approved seat that won’t break under pressure? Are they contacting the harness holes before they’re contacting your shoulders? They shouldn’t; they should always contact your shoulders first, at the correct angle. Is the camlock or buckle sitting right on your waist and not up high on your belly button? Does your local track day organization or company even allow them in a non-caged car? There’s a lot to think about and plan for.

If all this sounds like too much, or you aren’t sure, stick with OEM seat belts that are in good condition. You don’t want to be inconvenienced, crushed, or suffer a basal skull fracture,  potentially all the same day. Speaking of neck protection, the Simpson Hybrid S, while a bit pricey, help fill in the gaps of protecting your neck in the event of an incident on track while wearing three- (that’s right, they work with OEM), four-, five-, or six-point belts.

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