Hi guys. Honda tech RR is where I always come for up to date saftey information, so I thought id make a thread. Sorry that this topic has been duplicated to hell, but better safe than sorry right?

my car is a late model nissan 240sx so you guys may not have much direct experience with one, but the same basic stuff applies. I would imagine the cage build would be similar to a preplude.

As you may have assumed from current trends, the cars current primary use is *ahem* (drifting). eep . sorry, haha, I want to switch to roadracing when money allows, please keep reading.

Right now I have a kirk racing rollbar that I will be modifying slightly as well as building a front cage section onto. the kirk racing bar includes the main hoop, harnessbar, diagonal, secondary diagonal from drivers head to passenger rear leg, and obviously the rear legs. I will be adding a halo, door bars, and A pillar bars to the existing setup. Also I will be adding a rear strut tower base, and be relocating the downbars to the strut towers (the kirk downbars bolt to the wheel tubs; i dont trust it)

To further complicate things, I would prefer the door bars to be more unobtrusive while maintaining acceptible side impact protection. What would you guys suggest as a good design for this? The main designs I have been looking at are a low sitting supergt style gusseted X, or a simplified nascar style bar (the rules are pretty open). The passenger side will be using a single diagonal. I have an aerosport as500 (shell dimensions identical to recaro spg racer) so the door bars can cut up relativley high before they start to interfere with anything, but, I am not sure if this would be high enough up to provide ample protection. Additionally, the car needs to retain oem crash bars and glass, So the only extra room I can pick up is in the door skin. Mainly, I dont want to be smashing my elbows into stuff with the rapid steering inputs and such.

Lastly, regarding the rear downbars, would it be structurally sound to mount them directly to the rear strut bar without any further bracing, or would it be triangulated better if they went to the actual rear strut tower metal? here is a picture of a prepared 240sx that I have been looking at for ideas.



thanks for any oppinions or comments guys!

 

I'm sure others will chime in, but here's my $0.02...
The rear supports should attach to whatever metal is thickest - most good cages attempt to tie the shock tower to the "frame rail" using a 3-D mounting plate. The braces should mount directly to the plate, not the rear strut-tower brace, though I've seen both.

Use good "NASCAR" bars, like in the picture. I'd a third bar down low, behind the rocker/sill (running straight from bottom of main hoop to bottom of front leg) and tie it up to the two that intrude into the door cavity.

If you're the only driver (not using sliding rails), I'd also build out the cage so that it supports the seat. At minumum, reinforce the floor-pan.

Be sure to check rules for whichever group you want to join - they all differ slightly.

 

just for reference here is the other design i was looking at


to reiterate, the cage rules are very open (basically it must connect to the chassis at 6 points and cant go through the firewall is about it)

what advantages would the nascar bars offer over the X design above? also i dont want this to sound argumentative, im just trying to educate myself.

 

I think the ideal behind the X is they transfer load (from an impact) into the main and front hoops better than standard NASCAR bars. I think, I'm no expert. Just imagine pushing on the center of the X vs the middle of the NASCAR bars - what would happen to the bars?

That second cage has lots of gusseting, which is good. It also appears to be tied into the A-pillar, which is fine if allowed. Most club racing classes don't, drifting might.

If you do a search in the forum, you should find plenty of threads with pictures and discussion.

 

Be careful asking rambling questions - you could get rambling answers.

First, as I understand it with regards to drift risks and hence safety - the risk of high impact is lower for many of those events than RR usually is. Even if drifting on a road course - there isn't anyone helping you leave the course usually. I may be very wrong but I think of drift cages as primarily for structural regidity and secondarily for safety (mostly as it relates to things other than the main hoop, because roll over is more a concern than intrustion. RR cages are primarily concerned with safety - usually can only design for safety, structure is an ancillary benefit that the rules don't care if you achieve or not.) Not a judgement an observation, which could be right or wrong. So if you are in events that even require a roll bar or cage they may permit a cage that when you go to get a log book for road racing would not be permitted.

I recommend two things in this regard if you are building now with wheel 2 wheel road racing in mind for the future:

1. Look at SCCA's GCR and NASA's CCR for cage requirements.

2. Look at logbooked road race cars for examples. (Can find at least 1 240SX example at almost any SCCA and most NASA races.)

Trying to answer the specific question I can gleen from your initial post:

Door bar design priorities:

1. Prevent intrustion.
2. Allow exit.
3. Comfort.

Quick, rapid or any way you want to describe steering inputs are the same for road racing as they are for drifting - their purpose is control and control is achieved by smoothness - flailing should never be the result. The smoother you get, the better you will get in either sport.

Where is intrusion most likely? From just above and just below your competitors' bumpers IMO. That should be the focus of your intrusion prevention, from there a line from just above your feet to just above your shoulder is the next place to add to it.

"NASCAR" bars which likely no one here has ever seen the proprietary requirements for, give space for both exit and driver comfort, most in use probably wouldn't pass whatever NASCARS actual requirements are. Properly designed they can be just as safe as what some say is the only safe way (straight bars from main to front hoop).

There is quite a bit of flexibility balance your priorities.

Main hoop supports:

Mount them to the car - not to the strut bar. Consider the directions forces will take when the supports come into play. The supports are going to put shear forces on the ends of the strut bar - most strut bars and their attachments are not designed for shear forces. Near the strut tower tops make the most sense for the 240SX.

Also anytime you have multiple tubes coming to the same location - align them such that their centerlines all intersect at the same imaginary point. In this case somewhere in the middle of your strut.

On the diagnol bar I would bring it much closer to the corner than in the picture posted. The purpose of this bar is to prevent lateral distortion. NASA requires it at the corner or on the horizonal within 12" of the corner - SCCA doesn't have the same exacting language but their example shows at the corner.

Just some thoughts. I have two 240SX's with roll cages sitting in my garage currently - one stripped to the shell on a rotisserie.

 

thanks very much for all the info

Id like to make it clear that my main point for installing saftey equipment is, in fact, saftey, haha. I have absolutley no intention of building this cage with rigidity being the first priority. This thing needs to keep me alive when im face down in a K rail, not help my car handle better.

regarding the door bars - So nascar style door bars are generally less protective than a standard X? They are only in use because they take advantage of the door skin cavity, is that correct? Im not necissarily partial to either design and if the X is "better" than the nascar style bars, that would save me some money.

Would you happen to have pictures of either of your 240s? very curious

 

If X bars were safer than Nascar bars, then I don't think SCCA and NASA would be thinking of making them a requirement for the future.

 

Some feel an X or even parallel straight bars from main to front hoop prevent intrusion better.

Many "NASCAR" style bars were designed in a way that clearly focused on either additional space or merely to take advantage of door gutting rules (some classes you can't gut unless you are using NASCAR bars). Many of these examples are provided in support of the above position.

I have seen very well designed NASCAR bars that in my own belief would be as good at preventing intrustion as straight bars. I am not an engineer, though I do have an undestanding of compression, tension and shear forces and have slept at a Holiday Inn before.

Far and away it is easier to design door protection to prevent intrusion with straight tubes than to do so equally well with "NASCAR" style tubes - but I wouldn't say it couldn't be done (because I have seen it done) nor that one is better than the other. A poor design though will always be a poor design.

I don't have any pictures specifically of the cages.

Pictures I do have can be found here:

http://gallery.chargedperforma...s.php

 

The only place I have seen them required is in the driver side of SCCA club Touring cars.

What I think is unfortunate and what I think they need to do anytime they require NASCAR bars or even to permit NASCAR bars as an option is to require that they be designed to act primarily in compression and not in shear as most NASCAR bars are installed in club cars (including my own )

The "safety" of NASCAR bars largely come from the design being changed from intrustion putting the door bars in primarily shear at their joints to putting them primarily in compression. None of the other organizations metion or focus on the key thing that actually does and would make NASCAR bars safer than straight tubes.

 

Keep in mind that NASCAR rules are proprietary so I have yet to see what their actual door bar requirements are - and have not met anyone that does.

Most people focus on it is two bars with trusses that intrude into the door cavity. SCCA only requires one in their glossary definition of "NASCAR" type. NASA requires two but no trusses. (NASA actually requires to NASCAR spec in addition to their basic description, but NASCAR spec is not available to any of us club racers...)

When I look at actual NASCAR door bars they all have one thing in common - they designed in a way that forces intruding on the bars in the door area will transfer at least half their force in compession on the joints at the main and front hoop and no more than half the force would act in shear. This should be the focus of any NASCAR door bar rules.

Here is a good example of the design I am talking about on an S2000

 

cool thanks for all the replies. deffinitley giving me somthing to think about

 

Here is a pictures of the shell to become the next race car. (Click on Picture to go to the gallery.)



I did not build the cage, it came in the car.