It's on my list to add a back mount to my seat (caged car, Racetech seat that doesn't require back mounting, but has threadsert provisions for it), but want to be 100% sure I'm not monkeying with the seat position any more before I do it. In the meanwhile, buddy hit tire wall in very nearly identical car (cages are essentially identical, chassis's are both E46, but his sedan, mine coupe) and his seat shifted down and back essentially in the direction of the initial hit (passenger rear quarter, then it slapped the whole passenger side against the tires, then bounced back out towards the track). Seat was not braced to cage in the back and it had me wondering, is that little bit of flex potentially good? I mean it took force to bend the side mounts the little bit they bent/twisted and if the back had been held secure, wouldn't that force have instead been transferred to my buddy? That a totally wrong way of thinking about it? Can my analysis of the above be true, but that specific scenario be the exception, not the rule that a back mount would be protecting against?
Thanks for any thoughts.
The initial shift might be good for inertia reasons (reduced initial impact to your body) but the problem becomes that you are now loose in your belts and improperly restrained when the follow up hits come. The risk is you might flail around more and come into contact with things that aren't good for your frail human body to contact. In an extreme case you might come out of the belts partially. I'm not a race car safety engineer though just a total layman, but a race car crash is seldom one hit and done. You're going fast enough that there's continued travel and hits against the wall, other cars, roll overs, etc.
In reply to dculberson :
I'd buy that. Hadn't thought about the belts loosening since the seat creates space when it moved back. Thanks!
In reply to Spearfishin :
Belts will stretch in a hard impact more than you probably think. The more secure the seat, the less belt-stretch, in most cases.
Yeah everyone is on track here. There may be some atypical benefit from flex is very specific scenarios, but that's really only for the first order effects.
That said, modern FIA rated seats are really, really good. But they also really benefit from proper belt mounting (shoulder angles, etc.).
Oh, I forgot to mention - make sure you're not creating a spear with your seat back brace. Spreader plates are good. Flailing around is better than a steel tube to the spine.
dculberson said:
Oh, I forgot to mention - make sure you're not creating a spear with your seat back brace. Spreader plates are good. Flailing around is better than a steel tube to the spine.
I'd likely be using on the Racetech mounts...which to my eye look a little like repurposed side mounts.
Regardless of any out of date "the seats are supposed to collapse" BS from the street car side keeping the driver in a fixed position so that the restraints can do their job and the crash structure of the car can do its job is always the best. All seats should be rigidly braced to the harness bar or main hoop.
Treat it the same as a floor plate at least 6x6 steel .125 thick affixed to the seat back if the seat manufacturer has provisions, follow their mounting recommendations if not. Tube should be at least 1.25x.095 steel.
Spearfishin said:
buddy hit tire wall in very nearly identical car (cages are essentially identical, chassis's are both E46, but his sedan, mine coupe) and his seat shifted down and back essentially in the direction of the initial hit (passenger rear quarter, then it slapped the whole passenger side against the tires, then bounced back out towards the track).
Thanks for any thoughts.
so... how exactly do you know the seat did what you described?
kinda sounds like it was not properly mounted or a knock off that wasn't built to fia specs.
Another option is to have something solid attached to the harness bar that minimizes the gap between seat and cage. This is especially useful when multiple drivers of various statures drive the same car.
Furthest back has the seat just about touching this "brace". Furthest forward should only be 2 or 3 inches away.
amg_rx7 (Forum Supporter) said:
Spearfishin said:
buddy hit tire wall in very nearly identical car (cages are essentially identical, chassis's are both E46, but his sedan, mine coupe) and his seat shifted down and back essentially in the direction of the initial hit (passenger rear quarter, then it slapped the whole passenger side against the tires, then bounced back out towards the track).
Thanks for any thoughts.
so... how exactly do you know the seat did what you described?
kinda sounds like it was not properly mounted or a knock off that wasn't built to fia specs.
Seat is an OMP mounted on (I think, going from memory) Racetech steel side mounts bolted to BimmerWorld "cribbage board" floor mounts. All the bolts are tight in their holes, far as I can see. And you can visually see the the seat is down and back. It's leaning. Looks like the side mount plates are what gave, but didn't take it out yet to confirm.
go rally spec and never go back
