Diabolis

Hi Jim,

I asked both of my cage builders (at different shops) and both of them said the same thing - 99% of the time they use 1.75" x 0.120" DOM steel tubing for sports / GT cars. It is compliant with all sanctioning body regulations in North America (CASC, SCCA, NASA, IMSA, BMW & PCA Club Racing, etc.) and easy to work with. Both of them now also use TIG welding exclusively for race cars (one of them uses MIG for movie stunt cars as the crashes occur at lower speeds). Neither one normally uses chromoly (alloy steel) when they are building custom cages or tube chassis as it apparently needs to be properly heat treated both before and after welding to relieve stress and avoid cold cracking, but both of them are able to do it.

The only rule book I have easy access to is CASC-OR (my local racing regulatory body - part of ASN Canada FIA) and they do allow alloy steel (SAE 4125 & 4130) cages but also don't recommend them due to said difficulties with welding and need to normalize the tubing to relive stress. For cars over 2500 lbs, the minimum alloy steel tubing thickness is 1.50" x 0.095" or 1.75" x 0.095". For comparison, minimum tubing thickness for DOM steel is 1.50" x 0.120" and ERW steel - which CASC allows in vintage classes but most other sanctioning bodies don't - is 1.75" x 0.120".

When it comes to cages, seats, restraints and other safety equipment, one of the most knowledgeable guys I've spoken with is Ken Myers of I/O Port Racing in California (I bought seat back braces and some other miscellaneous stuff from him). He's a safety tech inspector for NASA so he has seen a lot of ***** and races a 944 himself. He's always happy to chat and I'm sure he wouldn't mind if you called his office. I found an FAQ on his web site about the roll bars and roll cage kits they sell that mentions the different types of steel at https://www.ioportracing.com/faq/rollbar.htm that also answers some of your questions. Also found this about MIG vs. TIG welding at Grassroots Morosports: https://grassrootsmotorsports.com/ar...ig-versus-tig/.

In short, what these guys are telling you about their cage makes sense.

Cheers,
Doug

BLKROKT

That’s amazing Doug. Thank you for sharing your depth of knowledge (and connections) with the community as always. This is a great place to get started and I feel more comfortable already.

Got some light weekend reading to do lol. And the Ken Myers connection, can I use your name or just call him direct? (hopefully I can give him at least a little business in the process - he’s out here too, so I’ll probably meet him sooner or later anyway) The NASA guys (I’m a member of course) are always so willing to go out of their way to help, everywhere I’ve been with them, and that’s what’s so great about the org.

Diabolis

Hi Jim,

Anytime Sir. As for Ken Myers, I highly doubt that he knows me by name... but if you told him "the guy from Canada that picked your brain for an hour on seat back rebound characteristics in the event of a crash and possible secondary cervical injuries in composite vs. aluminum seats with and without seat back bracing", he may remember better. He really is a great guy and has a wealth of knowledge that he doesn't mind sharing. If you are putting a race seat in the C63 and a cage, I would highly recommend that you consider getting one of Ken's seat back braces for it.

BLKROKT

Well shoot, that sounds like an important oversight on my part. Oops. MBNRG is sure to chime in anytime now about the horrible injuries I’m bound to suffer from. Here’s what’s going in:
- 4-point StudioRSR gusseted chromoly roll bar with harness bar and mounts/brackets to add a 6-point section later this year
- 2 Sparco Evo 2 seats with Planted seat mount, side mounts and Sparco sliders
- 2 Sparco 6-Point HANS - 3"/2" Steel Harness
- HANS

Car is gutted now. I’d like to get reinforcement plates welded in, but honestly not sure I’ll be able to do it in this phase, it may have to wait until late summer. I know it’s not the best idea, but it’s where I’m at on it. At that point I’ll just get the cage and everything welded in in one shot.

I guess my most basic question is, how do I need to secure the seat backs to the cage? Seat back brace, or is this something else altogether?

Sliders are going in because my street driving position is pretty different from my track driving one. Is this a bad idea?

Thanks as always

Crya

iTrader: (1)

Awesome excited to see your progress. You all have waaaaay more track experience and expertise, but when I was researching going Spec E30 racing, everything I was reading from those guys was that sliders were a "no no", I suspect simply because it's a potential added failure point?

BLKROKT

Yeah that’s what I’ve heard too. But if I can have it slide for street use, then lock it in place to the cage for track use, problem mitigated right?

Why would Sparco even sell sliders for their “racing seats” if they weren’t robust enough to handle the demands?

And plenty of OE manufactured “track cars” with cages have sliders as well (think GT2 RS).

I think it it has something to do with the addition of a cage and harnesses makes it a supremely bad idea, but forgot the salient points from that. I’m sure Doug will remind/scold me in due time and change my mind. Besides, it’s really just my recline that is significantly different on street, and that’s 2 bolts for adjustment. The distance that the sliders would provide (maybe 4” difference) isn’t so much that I can’t just adapt. And I no longer will have to access the rear seats because there are none.

See, I talked myself out of sliders. Thanks Crya! (they are heavy anyway)

Diabolis

DISCLAIMER - THE OPINIONS EXPRESSED HERE ARE MY OWN AND DO NOT CONSTITUTE ADVICE ON DRIVER SAFETY. I KNOW NOTHING ABOUT DRIVER SAFETY AND EVERYTHING I SAY HERE IS PURE CONJECTURE AND POSSIBLY A LIE. IN FACT, YOU COULD BE INJURED OR KILLED JUST BY READING THIS POST, SO DO NOT CONTINUE READING IF YOU DO NOT AGREE TO THIS.

Having the seat on sliders and/or there being any distance between the seat back and the roll bar cross member where the shoulder belts are fastened, and a seat back brace IMHO should go together hand in hand. That was the gist of my previously mentioned long conversation with Ken.

In case of a frontal impact, your body hurls forward and all the energy is absorbed by the harness (the seat and mount play no part). The harness will reduce the deceleration rate of the INITIAL impact as the weave is actually made to have some give and will permanently stretch in the process of slowing down your body.

In case of a rear impact, your body pushes against the seat back. Depending on the construction of said seat, how and where it is mounted / supported, the strength of the mounting and finally the distance from the seat back to the roll bar cross member, a number of different things may happen.

If the seat back is rigid and fixed in place (for example supported by the cage cross member), there is minimal to no give in the seat itself and your entire torso and head are subjected to a single, high deceleration akin to you being slammed down on your back, but at least your head and your back are already in contact with the seat and the load is evenly spread. The SFI and thus most (if not all) North American race sanctioning bodies allow this. The FIA and most European sanctioning bodies do not. Single seater formula cars in NA (like F2000 / Formula Ford for example) don't even have a seat - you are literally sitting on the bare floor and leaning back against the bare steel tank (if you are on the smaller side they may give you a cushion or two to bring you up and/or forward, but the only way I could squeeze into a Van Diemen DP08 was on the bare floor and tank).

If the seat back is not supported and the seat back can travel backwards, there are several things to consider, First, the weight of your body multiplied by the deceleration rate is now transferred to the seat and seat mount, so if we're dealing with a 200lb driver and 20g's of deceleration, that would be 4000lbs (neglecting any additional forces arising out of the seat back acting as a lever on the bottom). While the seat itself may be able to withstand this without breaking, the seat mount - and sliders in particular as they are usually the weakest part of the mount - would likely give way and the seat would get ripped out from the floor, hence the "sliders are a no-no" opinion that very likely has its origins from European marquee HPDE events or club races.

Second, as is the case with FIA approved composite seats, the seat back is designed to flex in order to minimize the deceleration rate experienced in a rear impact. While this slows you down more gently, the downside is that the seat stores this energy and then recoils, relaunching you forward against the harness. Now, if the HANS device and the harness do their jobs properly and this is the ONLY impact, the safety equipment has worked as designed and exposed you to the lowest possible deceleration rates under the circumstances.

However, the harness is now permanently stretched by some 10-15% and from this point on has no ability to dissipate any more energy while your torso is essentially loose. Should there be a SECONDARY impact and/or another seat recoil, things get very ugly. This is where the FIA and the SFI and in general the two schools of thought tend to disagree. The FIA thinks that it may be better to have your torso decelerate once in each direction at a lower rate but leave you essentially unprotected after the initial impact, while the SFI thinks that a seat back that doesn't deflect and will subject your back to a higher initial deceleration rate in case of a rear crash but which will then not launch you forward against the harness (in the direction in which your neck is more likely to snap) and will furthermore also leave the harness unstretched and still able to absorb a secondary (frontal) impact may be preferable.

My strictly personal view is that the second scenario may be preferable to the first, so the backs on the seats in both cars I drive are braced. The seat back won't snap and it won't launch me forward if I hit something going backwards or get rear-ended, but the initial deceleration that my back would be subjected to will be greater than if the seat back was unbraced and flexible.

So - again IMHO - having sliders is not an issue if they are of decent quality if the seat back is braced. If there is 4" of room behind the seat back and the cage cross member, that is an issue regardless of whether you have sliders or not as the seat back has tons of room to travel and will then either recoil and hurl you forward with all that energy or possibly even snap (think Ari Vatanen in the 1985 Argentina rally). CASC and ChumpCar require that the seat back be no further than 30mm or 1.5" respectively away from the rear cross member if it is unsupported regardless of whether you have a FIA or SFI seat. Some folks don't like seat back braces because they are afraid of the support brace punching through the seat back and hitting them directly in the spine, but IMHO that is preventable (you could put a steel plate against the back of the seat for example). As for the seats themselves, I have an aluminum Kirkey in the Vette and a Sparco Evo II in the Civic. Both have sliders (my wife has taken an interest in HPDE and now also tracks the Vette with increased frequency, and there are four of us that race the Civic) and both have seat back braces. The back of the Kirkey is bolted to the brace, which also prevents it from deflecting from side to side (I had no idea just how much the seat was flexing in the corners until I did that - the difference was huge). The Evo II is not physically attached to the back brace as you can't drill a composite seat without compromising its structural integrity and it does flex laterally, but with me in it and pushing back hard on purpose with my shoulders against the seat back I can make it touch the padding material on the plate on the brace.

If I was the only driver in either car, I would get rid of the sliders because that would drop the seat another 10mm lower, not because I'd be concerned with the sliders letting go - that's a moot point if the seat back is braced.

BLKROKT

GREAT info as always Doug, thank you. I checked out Ken’s back braces, and as soon as I have the rollbar in and can determine if I can get the back of the seat on it or not, I’ll be ordering one if needed. I like the clamp-on brace he makes, and I’ll just have to attach a larger plate and padding to it so that it can sit against the back of the composite Evo 2 and distribute any forces evenly (and minimize the possibility of it punching through my chest, from my back, which does sound like a bad day). The increased back deceleration doesn’t bother me, afterall most racing series seats are fixed and braced, so it makes perfect sense to keep the seat in place and prevent the head accel/decelerations above all else.

I will keep the sliders in then for adjustability, which is considered “ok” if I have the seat back properly braced if I’m reading the above correctly.

Now the next question is for street driving. 6-point harnesses aren’t safe obviously unless I’m driving around out there with helmet, HANS and brace all on. Clearly not optimal. So that means I should be keeping the stock 3-point seatbelt hardware on the car for street use also. Is that right?

Thanks for the education here, very helpful (it would have almost been easier to have stayed ignorant on all of this and kept the OE hardware/seats/etc, but this should be safer if I get it setup right, lighter too even with the rollbar)

Diabolis

Anytime. Re sliders and back brace - you only need to consider getting one if the back of the seat at your track driving position is far enough from the cage that it bending backwards could result in serious recoil or seat / mount failure. If the back of the seat is only 1" away from the cage, I wouldn't worry about it at all. And yes, if the rearward motion of the seat back in case of an impact is limited by the brace or cage itself, it (the brace or cage) will be subjected to most of the force exerted by the inertia your torso, so having the seat mounted on sliders becomes less of a concern as they wouldn't be subjected to nearly as much force.

Yes, keep the stock seat belts in place and operational for street driving. A 5- or 6-point harness is outright dangerous without a HANS device because it is designed to firmly hold your torso in place and you're much more likely to sustain a serious cervical injury even in a minor collision as your chest won't be able to move at all (the way it does with a 3-point seat belt) but your head is unrestrained and will snap forward. Furthermore, I am not sure what the law in the US is but a racing harness is illegal for street use here in Canada. I have both in the vette for exactly that reason. If you ever get a passenger on the track and they don't have a HANS device, have them use the OEM seat belt, not the harness. They will presumably have a helmet on which will protect their head from a possible impact with the cage, but a harness without a HANS is a big no-no from a safety perspective.

BLKROKT

Awesome thanks for getting me (us) on the right path here! Will update on progress. Seeing the pig empty has me inspired to do some more weight saving this weekend... wonder how much the door panels and interior trim all weigh....

Diabolis

ceesixthree

Option to fit coupe

BLKROKT

Went over to Studio RSR today to take a look around and see the progress on my cage. They’re working on all sorts of cool stuff, just finished an exoskeleton Lambo which was unveiled today and had a 996 slant nose and widebody conversion there which looked sweet. The guys are all track lunatics, and had their various cars there as well. They definitely know what they’re doing, smaller shop but true enthusiasts. Also open to other projects - we’re going to do the aluminum roof and 6-point extension over next winter. Good to meet people in person, and they gave me some additional ideas I’m going to work on while the car is stripped out.

Cage is still about 4 weeks away from being complete as the crazy Lambo build took more time than expected, and it’s just an 8 person crew with only a couple of fabricators for cage type stuff. Had them modify the order to add extra gussetting around the tube intersections, otherwise it should be done in less than a month.


Check out that Lambo here. Bonkers.

Crya

iTrader: (1)

Now that is sweet. Since you’re full race car. What about swapping lexan or whatever the material is for all the glass? Waste or legit?

BLKROKT

I still want it to be a nice place to sit in and stay somewhat streetable for road trips etc. I don’t ever see it becoming a trailer queen. Keeping carpet, probably the rear trim, glass windows, dash, speakers and sub, door panels, etc. Once this stage is done I should be just under 3750#. After the next round I should get to 3500# which has always been the goal. And the car will still look fairly nice inside and be fine to drive on the street. Have some more things on the outside to optimize - some heat shielding to remove, lighter wheels, remove the secondary air pump (need a cooler to go there), etc. At 3500# and 500whp it’ll be lots of fun and won’t eat consumables and break weird stuff like it does now and that’s the point.

Jasonoff

Interested in hearing about the experience. This is the cage I was thinking of ordering and installing in a parking lot across the boarder (you know... so it's easier to claim...) if I just don't have something custom done.

Diabolis

Good to hear Jim. Keep us updated please!

BLKROKT

Quick update. Studio RSR missed the first “6 week” build deadline due to that stupid Lambo build. They then missed their second “promised” deadline of last Wednesday with no reason given whatsoever. They have until the end of this week to produce a cage before I ask for my money back because I’m out of patience. 3 months is not acceptable. Car has been torn apart for months waiting only for this cage to be finished. Will keep everyone posted.

Crya

iTrader: (1)

Well that's a bunch of crap. Knowing your MO surely you were speaking to them on the phone. If so, did they "care"? I mean how do they offer no explanation? Must be good to have a business model where customer satisfaction isn't part of the equation. I wanted to see about a harness bar for sedans but doesn't sound promising. Good luck man.

BLKROKT

I’m told that they’re getting it back from powdercoat on Friday. Delays were due to something about the town shutting them down temporarily for permits or something. We will see...

Delays are fine, but first impressions are important. If you say 6 weeks, I expect 6 weeks. Should have told me 12 weeks and been pleasantly surprised if less.

Jasonoff

Hummmmmm, maybe I should scratch this item off the list.

BLKROKT

We’ll see, shít happens. I still hope I’m picking up a beautiful red cage early next week and all this was just a minor hiccup.

mr747

JUst got a custom one built if they dont come through

Jasonoff

This one saves the huge pain in the dick it is to paint it.

BLKROKT

Week 12. No cage. Was told on Wed that it had just been dropped off to powdercoat and would be done Thu or Fri. Wait... I thought it was supposed to get back from powdercoat last Fri?

Just got off the phone with the owner. He’ll hand deliver it to me tomorrow. I hope.