PSA: Use load-spreading washers, please
 

The driver is OK. This did not happen during an event that I worked, but happened immediately beforehand and I had the chance to see the failure myself. I wouldn't usually take and share post-crash pictures, but no one was limiting access to the wreck and plenty of non-affiliated people were snapping pics, so there's nothing in these pics that isn't somewhere else on the interwebs.

What I know: a Mustang rolled several times coming down the Corkscrew at Laguna Seca. The seat was bolted through these sliders and the bolts holding the seat to the sliders ripped through during the crash.

You can see in the first picture that the rails are held to the mounts using socket head cap screws, without backing washers. The seat was held to the other half of the rails in the same manner. It's an understandable mistake - because of the slider design, there is very little room for a fastener, let alone a load-spreading washer. I actually don't know anything about the slider - whether it's stock, a name-brand, or some cheap piece of junk. If there wasn't room for the right fastener (or fastener + washer), this rail should not have been used.

Please, if you can't put a washer on a critical connection, have a good, solid think about what that could mean.


https://cimg9.ibsrv.net/gimg/www.mia...3b6fa066cf.jpg
See the problem(s)?
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Enhance ... enhance.

Yikes.

Guessing it was this one posted a few days ago on facebook.....when I saw it I was wondering why that seat moved around so much...to me it looked like it moved around way to much before the crash as well...

Bolts were loose, that seat should not wobble like that. Presumably that would contribute to the failure of the sliders.

Amazes me the number of people who drive fast in shirtsleeves.

Sliders. Are. For. The. Street.

race. Cars. Have. Fixed. Seats.

it probably wasn’t loose. They’re like that out of the box, believe me I’ve installed dozens. You hard mount a seat for the biggest driver, use pour ins for smaller drivers.

Washer wont do it, if you wanted to make this strong, I’d slice some solid bar stock lengthwise, take a 2” section, cross drill it, and use that as a “washer”.

I take your point Curly, and don't disagree.

However my car (dual-duty) and my (now-defunct) racecar both had/have sliders, the factory ones - there is and was no 'slop' in them. I appreciate it may be different in different applications, and FWIW I am rather on the smaller size than the larger. If that was slop in the slider, as opposed to loose mounting bolts, well it shouldn't have made any difference - either should have been a big red flashing light for the intrepid pilote.

I hope said pilot got out of it OK, we have just had someone here shunt a GT3 with loose belts, very bad outcome, he survived but had serious injuries and faces a protracted recovery. The dynamics would have been similar, but the velocity probably greater. https://www.speedcafe.com/2022/08/31...fing-swear-it/

IME pour seats in a sedan (not a formula car) really only work if you've got a fairly small difference in driver heights. If one driver is a foot taller than the other you need a slider.

--Ian

To be fair I’ve got pour-ins on the mind and maybe not the best option for everyone. My main beef is with the aftermarket sparco or recaro sliders. Pretty hard to fuck it up on a Miata, you either fit or you don’t. As always, they’re always the answer.

My buddy was there when this happened, he showed me the car and the bolts. The washers distribute the pulling force around a greater area of the mounting platform. Washers increase the load area by approx. 2x id say. That means if proper washers were used the seat would be twice as strong. Being that the seat tore out with half the area that washer would give that would leave us with a safety factor of < 2. Thats not enough for me. I am going to make new seat brackets. I now feel uncomfortable with how my exige seats are mounted.

For my racecar, I went with a 3" x 12" steel plate 1/8 thick, welded to the floor on either side of the seat. Then six 1/4" steel tabs welded to that, with six 1/2" grade 8 bolts connecting to the seat.

you should feel incredible uncomfortable with any lotus parts bolted to your car.

id be curious to know how long ago that seat was installed, and if the bolts were tight that whole time. Rocking back and forth on a loose bolt or small surface area could have fatigued the slider metal.

Possibly, I would have imagined the driver to immediately tighten any loose bolts though. Its instinct to do so. But my goodness that seat is moving in the video clip. Structurally wise what happened is it looks like when the back of the car hit the barrier the drivers back pushed on the back of the seat creating a large enough moment force on the entire seat assembly to pull the front bolts out of the sliders which then that allowed the bolts in the back to sheer through the slider metal. Could be fatigued steel from loose bolts, that steel looks awfully thin to me. One possibility I thought maybe how the steal kind of tapers in(upward) on the slider. Maybe the bolt the assembler used had its edges on the tapered portion rather than the flat portion so tightening it down could have unshaped the metal weakening it or even started cutting through the metal. To think of it, it doesn't even look like assembler could have used a washer, if they did the washer probably would have been pressing on the caved portion of the seat rails, so when they tighten it they would just started bending the slider metal.

Incorrect, it's your instinct to do so. Mine as well. But not everyone's. There's some scary shit going around on track these days. I saw a race seat spaced up with a piece of 2x4 once. This was on an instructors car.

Those sliders inherently have some slop to them. I check all the seats after every race, but you really need to have a 2nd person jiggling the seat while you climb under it and inspect with a flash light to see if it's just rail, or a bolt has come loose. This isn't a rarity btw, the bolts come loose more than you'd think.

I went through a lot of trouble to keep the Stock NB sliders when I installed the Corbeau-for-Lotus seats in my NB. When using factory seat belts, the inside connection runs through the slider assembly, which is specifically constructed to handle the forces involved. Aftermarket sliders will not.