Roll bar angle:

[Glen]

If you take time to look at pictures in the programs, rule books and the photographs on this web site you will see every kind of roll bar, the different angles and shapes you can imagine. Look in the build diaries for a few more ideas. The original drawings shown in the rule books are the same as NHRA's rule book.

As far as the lakester that had the roll bar torn off Like JD I was there and timing the car when it went out of control and crashed. The cage shoulder bar was .049 wall tubing and being a old drag race car most of the chassis was modified to run as a lakester. It also had rear suspension. There were several meetings with the board of SCTA and several chassis builders to discuss the failure and how to come up with a fix to correct and assure the new builds would include the upgrades.  The drag race chassis were later banned due to the thin wall tubing frames. SCTA changed the material requirements and wall thickness to this type of vehicle.

There have been no other roll bar failures of this type since that incident. There have been some cracked welds and some bending on cages due to impact but the heavier wall thickness and the corner braces along with the helmet retention straps have made the difference in additional protection for the drivers.



 

[Rex Schimmer]

I completely agree with Pork Pie as to the design of a proper tube junction. My reference is a guy named Omar W.  Boldgett that wrote several books on weldment design back in the 60s and his term for this is "eccentricity" . A good tube joint or node has the center line of all of the tubes intersecting at one point. This provides the higest strength and stiffness. The people that at really good at tube structure design and fabrication are the off road guys doing the big trucks.

Rex

[John Burk]

Rex

In your opinion Is maximum strength synonyms with maximum crash survivability .

John

[Gwillard]

I completely agree with Pork Pie as to the design of a proper tube junction. My reference is a guy named Omar W.  Boldgett that wrote several books on weldment design back in the 60s and his term for this is "eccentricity" . A good tube joint or node has the center line of all of the tubes intersecting at one point. This provides the higest strength and stiffness. The people that at really good at tube structure design and fabrication are the off road guys doing the big trucks.

Rex

I agree with Rex. One of my most prized books is a first-printing copy of "Design of Welded Structures". Only 5000 were made in the first run back in '66. Another is a copy of Blodgett's "Design of Weldments" that is signed by Mr Blodgett. Both are very good resources and should be on every fabricators shelf.
One other that is a good reference as well is the AWS (American Welding Society) Welding Handbook, eighth edition, volume 2, "Welding Processes". It covers almost all welding processes from oxy-fuel welding to electron beam welding. If you look for this one be sure to get the exact edition and volume, as the newer edition have two volumes covering processes and are much more expensive.
All three of these books are available through online bookstores.

[maguromic]

PorkPie,  Is the point which tube is continuous and which tube is cut and joined? If so, I see the point and I agree.  The front hoop should be the continuous bar and the front upper tube the spliced in joint. Thanks for the impute.  Tony

[PorkPie]

PorkPie,  Is the point which tube is continuous and which tube is cut and joined? If so, I see the point and I agree.  The front hoop should be the continuous bar and the front upper tube the spliced in joint. Thanks for the impute.  Tony

Yeap

[hotschue]

SFI has rollbar/chassis specs. and designs available for different applications.  I assume if SFI  puts it out there, it's backed up by engineering reports.  I acquired a copy of the cage illustration that best fits my particular build.  My local chassis shop purchased the master guide which is several hundred pages.  He was kind enough to photo copy two designs which fit my application.  When I get to the point of finalizing the cage I'm going to give Joe Timney, Delaware Chassis a call, he familiar with lsr, let him take a look and recommend.....

Udo

[SPARKY]

Well, well, well, new hoop is tacked with a 35 degree lay back,  put fire suit on, hans and helment---we can get in and out but we are tight, tight, tight---lol will have to re think the steering---

  any suggestions on a small gear box with a fairly high ratio?

[sheribuchta]

http://www.landracing.com/forum/index.php/topic,4872.0.html                          willie buchta

[interested bystander]

Do NOT assume that the SFI Specs are backed up by engineering reports.

If so, they have NEVER been made public.

This whole topic has opened up a large can of worms with much seat of pants speculating, etc etc.

Pork Pie's diagrams were enlightening. I did not see what form of motorsports they came from - not USA Drag Racing, sadly.

Any forward bar angle over 30 degrees would make Street Roadster ingress, egress extremely difficult.

More important IMHOP is CONTAINMENT of the driver's head in the structure (and the rest of his/her torso).

Fore/aft mid-point bracing, whose importance has in more recent years been recognized as VERY essential, should probably be paid more attention to enforcement/wise.

I've used up my 25 cents.  

[Rex Schimmer]

In reply to John Burk's question:
Rex

In your opinion Is maximum strength synonyms with maximum crash survivability .

John


I would say in the case of Land Speed racing maximum strength is what we are looking for and crash survivability needs to be provided by the safety equipment now being mandated and used. I know that there are many people that believe you want to have a structure that folds and adsorbs crash loads, my question is how do you know what the loads are and how do you calculate how to design a structure that will fold up to adsorb these loads?? I would think it is best to design a structure that carries all of the loads in tension and compression, and that each tube joint is designed to transfer load most efficiently into other tubes in the joint. This is what a well designed joint or node does. Back in the day of the Indy roadsters, they were so strong and rigid that when they crashed hard the car could be fixed and back at the track the next day but the driver was either in the hospital or morgue! but they did not have the type of safety equipment we have today, Hans devices, much better helmets, certified protective foams etc. Certainly high G loads can be fatal but so can having the roll cage collapse and having your head crushed! Brad Kesoloski came close a couple of weeks ago to proving this at Atlanta.

Rex

[maguromic]

Pork Pie's diagrams were enlightening. I did not see what form of motorsports they came from - not USA Drag Racing, sadly.

That’s one of the first drawings of our rear engine roadster cage area.  It’s a work in progress and in the next few weeks I will post the completed drawing along with some screen shots of the FEA runs on my build site. Tony

[desotoman]

In reply to John Burk's question:
Rex

In your opinion Is maximum strength synonyms with maximum crash survivability .

John


I would say in the case of Land Speed racing maximum strength is what we are looking for and crash survivability needs to be provided by the safety equipment now being mandated and used. I know that there are many people that believe you want to have a structure that folds and adsorbs crash loads, my question is how do you know what the loads are and how do you calculate how to design a structure that will fold up to adsorb these loads?? I would think it is best to design a structure that carries all of the loads in tension and compression, and that each tube joint is designed to transfer load most efficiently into other tubes in the joint. This is what a well designed joint or node does. Back in the day of the Indy roadsters, they were so strong and rigid that when they crashed hard the car could be fixed and back at the track the next day but the driver was either in the hospital or morgue! but they did not have the type of safety equipment we have today, Hans devices, much better helmets, certified protective foams etc. Certainly high G loads can be fatal but so can having the roll cage collapse and having your head crushed! Brad Kesoloski came close a couple of weeks ago to proving this at Atlanta.

Rex

Rex,

I have to play the devil's advocate here. With the majority of us being old farts (driving) do you really think we have a chance in a car as you described above even with modern Safety equipment? Personally I don't. JMO

Tom G.

[tedgram]

In LSR we shouldn't have to worry about impacting anything (high G forces). Guardrails, Trees, big rocks other cars, ect.. Mainly worry about rolling and sliding on your roof if you have one. Your cage should be strong enough to support the weight of the car and keep the driver secure inside. Roadsters have to have bars that can withstand the extra stress of sliding friction from the track surface directly on the bars themselves. Sheet metal roofs slide nicely I've had that experience.

[Gwillard]

In LSR we shouldn't have to worry about impacting anything (high G forces). Guardrails, Trees, big rocks other cars, ect.. Mainly worry about rolling and sliding on your roof if you have one. Your cage should be strong enough to support the weight of the car and keep the driver secure inside. Roadsters have to have bars that can withstand the extra stress of sliding friction from the track surface directly on the bars themselves. Sheet metal roofs slide nicely I've had that experience.

Don't underestimate the damage that can be sustained from impacting the ground during a flip or roll.