Serious rollbar/cage in a streetcar question

I am very aware of, and agree with all of the “no rollcage in a street car” arguements.  So no need to warn me anymore about the danger.  My question is how to do it with the minimum impact on safety.

I have a 2000 MR2 spyder with no roll over protection other than the windshield frame.  I would like to add a custom rollbar behind the stock seats.  I want to know what everyone thinks needs to be the proper setback from my head in the stock seats and 3-point belts.  This is just a fun backroads car, not a racecar.  Would 12 inches be enough?  I will remove the roof if necessary:)

I would also like to add some doorbars to tighten up the chassis and I don’t know what would be the maximum safe height for that with the stock seats and belts.  I was thinking they should be put next to the factory side impact brace built into the door.   Maybe I should weld up the doors Duke Boys Style!

Thanks,

Justin

Jah29 said:

I have a 2000 MR2 spyder with no roll over protection other than the windshield frame.  I would like to add a custom rollbar behind the stock seats.  I want to know what everyone thinks needs to be the proper setback from my head in the stock seats and 3-point belts.  This is just a fun backroads car, not a racecar.  Would 12 inches be enough?  I will remove the roof if necessary:)

I think 12 inches is probably excessive.  Look at pictures of Miatas out there with bolt-in roll bars -- while you will find a few people on the internet who think the standard bolt-in bars are unsafe, they've been on the market for 30-ish years at this point and we don't seem to have many reports of people with serious injuries from roll bars that are 4-6 inches behind the seat.

Roll cage in FRONT of the seat is obviously a very different story.

Personally I am not a fan of door bars in a street car.  I don't know if safety is a concern, but personally I just find that they're always taking up the space where my leg wants to be -- at least in a Miata.  Never tried one in an MR-S, but I recommend testing carefully before welding something like that in.

I'd look at building a bar that was race legal with the exception of some removable struts - like a door bar on the driver side connected with pip pins for easy access. Having a car that you had to climb over bars to get into would be a real pain.

On an MR2, I don't know how close to legal you can get - you might get in touch with someone that actually has raced one or run in serious solo competition, as they may have tips.

One issue for you on the legality of a bar in that car might be the same one I had with one of my race cars - a fairly swift 'roll-off' from roof level at the back behind the driver. In my case I had to argue with the tech boys that my bar was as close to the roof as possible, and that it couldn't be any higher unless one punched through the roof , so either my car was unraceable in stock body configuration (but then the factory had run them at Le Mans.... ) or the height at the rearmost location possible had to be allowed.

IMHO the things to worry most about on the street are the things you have the least control over:  side impact and rear impact.

The problem with door bars on the street is you have very little protection in a side impact.   A race seat/harnesses will keep you planted, and the seat is usually high enough to offer some hip protection.  Stock seat/belts + door bar + side impact = the potential for lots of broken structure.  And I'm not talking about the car.

A rear impact with a roll bar will often result in a head injury, as the stock seats/belts don't do a great job from keeping your body from sliding rearward/upward and impacting the bar.  Miatas are about a worse case scenario because of how close to your head the bar needs to be to fit under the top.  Lots of discussion about it on the Miata forums, but as far as I know, only two actual posters received serious head injuries from such a collision.  Maybe the fear is overblown... maybe the others are dead... I don't know.  Getting the bar as far away from your head as you can is the best practice.

Watch some crash dummy videos, and pay close attention to how much the bodies move at impact... it's pretty eye opening.

I have a full cage/seats/harness in our NA Miata, and it does get street driven, if only to the gas station and the occasional C&C.  It still makes me nervous.  Every time.

It sounds like you want what's in the Elise - a roll hoop behind the seats. It is behind the head rest and higher up, so zero concern about contacting it, and it passed whatever little testing Lotus and the government did. Probably just a broomstick test, haha. 

cyow5 said:

It sounds like you want what's in the Elise - a roll hoop behind the seats. It is behind the head rest and higher up, so zero concern about contacting it, and it passed whatever little testing Lotus and the government did. Probably just a broomstick test, haha. 

Yes, I am kinda trying to replicate an elise.   My interest in door bars is to gain some chassis stiffness like the lotus gets with it's high door sills.  maybe I should just replicate that car and put a bar in 3 inches above the current sills and cut a slot in the door.

I definitely prefer moving the bar further back rather than a little back and a lot up.

thanks
 

Rodan said:

IMHO the things to worry most about on the street are the things you have the least control over:  side impact and rear impact.

good perspective!  I am very risk adverse when driving, but have never thought about it in those terms.  Thanks.

Are you open to moving to a race seat and harness at the same time as the roll bar installation? Street cars and race cars have safety systems that work on different principles, and it's generally a bad idea to mix and match pieces of each system. 

The main difference in principle is whether or not the driver's body is able to move around in an impact. So realistically the rollbar alone is fine as long as it's outside of attainable reach. Fixed back seat does make a lot of things easier though - bar can be closer, leg containment makes adding door bars less of a safety risk, lower driving position makes the rollbar more effective and/or not need to be as tall.

Tom Suddard said:

Are you open to moving to a race seat and harness at the same time as the roll bar installation? Street cars and race cars have safety systems that work on different principles, and it's generally a bad idea to mix and match pieces of each system. 

On track I definitely would, but this only a street car.  Willing to do a race seat, but not a full harness.  I think a 3- point is much safer than a harness without a head/neck restraint.  I am not  going to be wearing a helmet and a hans on the street:) 

MR2 spyder has no rollover protection whatsoever behind the driver, so I think it needs a rollbar.  Most non-oem systems I have seen on any car don't look so safe for 3 point belts.

Thanks, justin

dps214 said:

The main difference in principle is whether or not the driver's body is able to move around in an impact. So realistically the rollbar alone is fine as long as it's outside of attainable reach. Fixed back seat does make a lot of things easier though - bar can be closer, leg containment makes adding door bars less of a safety risk, lower driving position makes the rollbar more effective and/or not need to be as tall.

I think you are right.  The stock leather seats are really slippery.  Some basic race seats with only thigh and hip support might be the best way for me to feel comfortable and actually be safe adding some bars to the car, even if I put them pretty far away. 
 

Is there any consesus on the safety of a bucket seat with oem seatbelts and airbags?  I know porsche and bmw have used recaro pole positions in many cars, but I don't think any of those models have made it stateside.  Are they unlikely to test well in the USA crash test protocol?

thanks

Any reason you wouldn't just do the Hard Dog? http://bethania-garage.com/spyder.htm

It's high enough and back enough that there are few issues. Much more room than the normal Miata roll-bar

If it's just a street car, and not going on track, I'm really not sure I'd put a roll bar in it. The odds of rolling it over are way lower than the odds of getting rear-ended, and any bar that's usable on the street with a stock seat and belt would provide marginal protection in a roll and increase the risk of injury in the more likely scenarios.

I have a Triumph Spitfire street car, and a roll bar in the attic for it. Unless I start doing track days and install a seat and harness, they'll never meet. It's a super dangerous car to roll, but getting rear-ended by a Minivan in traffic is way more likely. 

Rodan said:

IMHO the things to worry most about on the street are the things you have the least control over:  side impact and rear impact.

The problem with door bars on the street is you have very little protection in a side impact.   A race seat/harnesses will keep you planted, and the seat is usually high enough to offer some hip protection.  Stock seat/belts + door bar + side impact = the potential for lots of broken structure.  And I'm not talking about the car.

A rear impact with a roll bar will often result in a head injury, as the stock seats/belts don't do a great job from keeping your body from sliding  Lots of discussion about it on the Miata forums, but as far as I know, only two actual posters received serious head injuries from such a collision.  Maybe the fear is overblown... maybe the others are dead... I don't know.

The issue I have with this is fear and lack of data. We only have anecdotal stories about the effectiveness or the danger of roll bars/cages in street cars. People keep saying things like you just did: "will often result." But is there data to back up the claim that it's a real "often" occurrence?

For every story of a serious head injury, I can come up with one where a life was saved by the roll cage after, say, a trip off an embankment (for example, my buddy was driving his ex-IMSA RS Mazda RX3 on the PCH and come around a corner to find a large rock in the road, and in trying to avoid it went off the embankment. Not a straight panel left on the car, but he only got a little beat up). We need real data on if people are getting banged up right and left due to adding a roll bar/cage and I don't think we're ever going to get any. So until then, it's all just speculation on what could happen. Nothing wrong with that, until it's couched as a certainty.

My anecdotal story: I spent 5 years with a street driven V8 RX7 with an Autopower 6 point roll cage in it (and padding). Never once bonked my head on it, not even getting in and out. But even though the side bars were quite low and generally out of the way, it WAS more of a PITA to get in and out of the car with the cage in there.

In reply to Chris_V :

Before this thread swirls too much further toward the bottom of the bowl, would you mind to qualify your anecdotes with the type of seat and harnesses in those cars relative to the OP's situation?

Safety equipment is a system, and all that....as previously mentioned

I dunno, I wonder if this is one of those cases where you take a cue from racing...

and turn the roll protection predominately north-south, with a lower 'shoulder hoop(s)' to support the blade from buckling under side loads, and lots of foam to smooth the shape and reduce head-metal deceleration/jerk/snap/crackle/pop.  Foam is effectively the predominant protection in a helmet, after all.... and the door window frame, and the seat... and, and.

what's the head deceleration specification that people design to?  while they are different systems, they all start with that root goal;  and if you know that, you can design your own system.

gumby said:

In reply to Chris_V :

Before this thread swirls too much further toward the bottom of the bowl, would you mind to qualify your anecdotes with the type of seat and harnesses in those cars relative to the OP's situation?

Safety equipment is a system, and all that....as previously mentioned

My question, and I guess I didn't couch it properly, was simple: what data (not assumptions) do we have that safety devices (not necessarily sytems, per se, but even then...) ARE causing injury, vs merely causing the possibility of injury in certian specific situations? Because we can "what if" any situation to make things worse no matter what side of the aisle you land on. Saying that a roll bar "will often cause" more injury requires data to back up that statement. Do we have data on street car crashes that back that up and not just anecdotal stories? Quantity, frequency, etc. If we had that, it would be great to have on hand for threads like this not only on this site, but other sites.

 Funny, as I think about/read through this, I'm reminded of a guy who posted that he's been rear ended twice in a Miata and swore the roll bar prevented the cabin from being crushed in further.  I do not recall him saying he had head impacts with the bar, nor do I recall what bar he used, except that they were 4pt attachment.  He did post pics, I think of both cars. 

Mine has the hard dog 2pt, so I do wonder sometimes. 

In reply to Jah29 :

If you want a cage, the best thing to do is follow SCCA .GCR.  For a roll bar, there are a number of companies that make bars that you can reference.  Basic rules, make sure your head can't move backwards.  Will need forward support to handle load in case of use.  Use the SCCA GCR for rollbar diameter and wall thickness.

Haven't read the articles and comment about no roll bar is a street car.  If the car is strictly street and has rolll over protection, then yes.  If you are tracking your car and exceed 120 mph, our family recommendation has been a roll bar. 

sleepyhead the buffalo said:

I dunno, I wonder if this is one of those cases where you take a cue from racing...

and turn the roll protection predominately north-south, with a lower 'shoulder hoop(s)' to support the blade from buckling under side loads, and lots of foam to smooth the shape and reduce head-metal deceleration/jerk/snap/crackle/pop.  Foam is effectively the predominant protection in a helmet, after all.... and the door window frame, and the seat... and, and.

what's the head deceleration specification that people design to?  while they are different systems, they all start with that root goal;  and if you know that, you can design your own system.

Yeah, that looks fantastic!  I was looking at stuff like that before I remembered I don't know anything about carbon fiber or fiberglass.  If I win the powerball I promise you I will be buying an autoclave and watching some youtube videos:)

seriously though, some sort of north south solution is probably where I am heading.

I have been hit 6 times in the last 7 years sitting still at a stop light, so I am very concerned about rear collisions and rollbar location.  Tom has almost talked me out of a rollbar, but if I can figure out a good solution I will make one.