5th member of seat belts

[Duke66]

Hi All,
What is the recommended fastening point of the crotch strap part of the seat belts?
Through the aluminum is not adequate is it?
Why does FFR not have a predrilled hole through steel plate to bolt it to?
Would it be best to have a hole in bottom of seat cushion to route strap through?
What have others done?
Thanks in advance for answers.
Dave

[edwardb]

Absolutely has to be in the steel seat pan. Not the aluminum. No set position because there are multiple seat possibilities. With the standard fixed Roadster seats, the only experience I've had, you can bolt right at the front of the seat pan and fits OK. Little more complicated if you have seat sliders, but still should work. For other seats, you'll need to hear from those who've used them. Just don't leave that belt out as unfortunately (my opinion) some have done. Install it and use it. An essential part of the safety of the 5-point harness.

[BEAR-AvHistory]

Agree. The 5th strap is sometimes called a submarine strap. This is true for cars with a extreme reline seat position. In our cars with the very upright seat it performs a different primary function.

When you put the belts on the lap belts get taken up first so they are low on your hips. Then the shoulder belts are pulled tight. The 5th strap when adjusted correctly will prevent the shoulder belts from pulling the lap belts up off your hips to the soft tissue of your stomach.

When the car is finally good to go adjust the 5th belt so it preforms its proper function. The belt will hold its adjustment but is good to reset it if anything in the seating position changes.

[JohnK]

I know that many here have installed the 5th strap on the roadster coming around the front of the seat, and I agree that it's definitely better than nothing. However, I'll point out that Simpson specifically warn in their instruction to not install the strap in that manner, and that it needs to come down through a hole in the seat and anchor behind the driver. If you don't want to modify the seat to put a strap hole in it, another option is to use a system that doesn't rely on a 5th strap to accomplish the anti-sub function.

[silver_pilate]

I just drilled for my 5th straps last night. I have the vintage bit/tall seats, and I drilled through the metal seat pan in the floor just back from the front edge of the seat and centered on the seat. The strap will come up over the front of the seat to the latch.

I know it's not ideal or per manufacturer's guidelines, but then again, it's also perhaps a different application. In a racing car with a more laid-back seating position, the anti-submarine strap really does help keep you from sliding under the lap belt (thus keeping the lab belt form sliding up relative to your body and into your organs/ribs). In our cars, with an upright position, a frontal collision is going to cause us to bend forward at the waist. This will push into the shoulder straps which will then pull the lap belt up into organs and ribs. The 5th strap, even if installed like I have it, should help reduce that to some degree by keeping the lap belt down a bit more.

--Nathan

[Avalanche325]

I agree with everyone else. Through the steel. Keeps the lap belt low.

FFR probably figures that you have the required skills to drill a hole while you are building a car. :-)

[Duke66]

That's funny Avalanche...I guess we've all drilled one or two holes throughout the building process...lol
And I never really thought about different location depending on style of seats.
If a guy puts a hole through the seat the strap is more difficult to adjust for length as well. But the skinnier you are the further back in the seat you sit / further the lap belt is from the front of the seat... lots of variables

[John4337]

I agree with everyone else. Through the steel. Keeps the lap belt low.

FFR probably figures that you have the required skills to drill a hole while you are building a car. :-)

You drilled a hole? I thought a big hammer was enough.... ;-)

I agree. I had mine thru the steel until I switched the schroth 4 point harnesses

John

[Mustang Man]

Not a fan of five-point restraints without the belt coming up through a seat slot as close to the body as possible. Otherwise it is not doing its job and holding you and the belt in the proper location. The best alternative is a four-point with anti-submarine technology built in. The only one I am aware of, and what I use in my cars, is the Schroth with ASM. I have their Rallye 4 ASM 4-point in my Mustang, and in the FFR Mk3 we built I use their Profi II ASM FE camlock with push button (not the twist lock). The camlocks makes it easy for anyone to assemble the belt when they get in (versus the latch link/duckbill) and the ASM means no crotch strap is required. The Profi uses a comfortable 2-inch lap belt with 3-inch shoulder belts.

https://www.schrothracing.com/products/profi

HTH...
Mark