Topic: Front legs and Back stays gray area

To any Tech Inspector

I need some advice on building a Lemons cage for my Miata. This is my first cage build so I am trying my best to get it right the first time. I have read and reread the rules but I believe I have found a gray area that I would like some clarification on.

Front Legs coming down from halo hoop
Currently the legs are one tube with a 50 degree bend in them. At the bend they are slightly angel outward towards the A pillar. this gives the vertical section of the tube a slight angle inward before it meets the spreader plate. The angle inward is not very much less than 10 degrees for sure. I dont see this as against the rules anywhere but I want an second opinion while it is still tacked.

Back Stays angle
Due to the OEM fuel filler tube and small size of the miata I can only make the back stays a 55 degrees off horizontal a steeper angle than the required 45 degree. The spreader plates will be welded right next to the upper shock mount but I am having trouble getting any closer to 45 degrees. Does 55 degrees seem acceptable if the spreader plate location is satisfactory?

Secondly it is unclear if the back stays need to be parallel to the center line of the vehicle (as viewed from the top on the vehicle) or I can angle them to meet the main hoop where the halo hoop meets the main hoop. I believe it would be a stronger design to have a slight angle and have them meet the main hoop at the same location as the halo hoop. Drawn in blue on the below picture link vs parallel to the vehicle center line drawn in red.

Pictures will follow


Thanks for all the help
Mike

Re: Front legs and Back stays gray area

Pictures of front legs and cage in general
https://goo.gl/photos/bXM8ddbXpBjjjenz6

Sketch for parallel angle of back stays
https://goo.gl/photos/6ikjFD3VrTKectzy8

Re: Front legs and Back stays gray area

The rear stays do NOT have to be parallel to each other or to the long axis of the car.  That was one critique we received when our cage was judged at tech--the rear stays were inboard of where the halo meets the main hoop.  Ideally, they should all three meet and be in line.  On our ZX3 that would have meant a spreader plate on the front of the rear wheel housings.

Re: Front legs and Back stays gray area

Disclaimer:  I'm not a tech inspector.
But, I have built a few cages and fixed a lot of cages.

I'm having trouble visualizing your front legs question.  Since you say they have a single bend in them, you "should" be ok.  A bit of angle to make room for welding to the spreader is ok.  Anything that looks like a back bend, or adds an inward bending moment during impact is what you have to avoid.

The back stay angle is as close to 45 degrees as possible.  Some cars just can't do that and still have a reasonable rear hoop and spreader plate location.  Your first priority is a good spreader plate location.  Curves, arches and reinforced areas of the car body are your best bet.  Often that means using the rear wheel arches. 
A bit of inward angle to meet up with the halo tube location is ok.  I've done that on all my cages - the ability to translate an impact load straight from the halo to the backstays is good.  An offset from the halo to the backstays will cause a bending force in the rear hoop.  I like to discourage bending the steel cage I'm sitting in...

Apparently my name is really "Craigers".  Who knew?
We might be yellow, but at least we are slow
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5 (edited by VKZ24 2017-05-25 11:42 AM)

Re: Front legs and Back stays gray area

What size is your tubing?  It may be an optical illusion, but it looks like 1.75", which is way overkill on a car as lightweight as a Miata.

Captain
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Re: Front legs and Back stays gray area

VKZ24 wrote:

What size is your tubing?  It may be an optical illusion, but it looks like 1.75", which is way overkill on a car as lightweight as a Miata.


I would always try and use 1.75x.095 its stronger than 1.5 and you gain almost no weight from it.  if a 1/4" makes the cage too tight to the driver you didnt have enough room anyways

959 Toyota Tercel   6x Lemons loser

New England Area roll cages send me an email I'm in Central MA

Re: Front legs and Back stays gray area

Ah - I see the photos now.  The front legs look ok.  The slight inward bend isn't a big deal.  Plenty of cars have passed like that.

I am a bit concerned about the clean up on the tubes where you are planning to weld.  It looks like they were cleaned up with a grinder, which is a bad thing.  The general rule is to not grind into the roll cage tubes at all.  If you need to clean up the mill scale for welding, use a light hand sanding or some kind of welding safe solvent.  I can't tell from the pictures if the grinding is significant, but I've seen cages failed due to grinder marks.

I use 1.75x.120 tube on our Hondas.  Overkill for the rules?  Yep.  Do I feel better when on track with a 70's LTD who is faster than they have any right to be?  Yep.

Apparently my name is really "Craigers".  Who knew?
We might be yellow, but at least we are slow
I'm a WINNER!

Re: Front legs and Back stays gray area

While it may pass tech, personally, I'd like the front bars to be a bit further forward -- more in line with the a-pillar. Where will your dash bar and door bars go?

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Re: Front legs and Back stays gray area

Thanks everyone for the replies

Yes i am using 1.75" 0.120 wall DOM - I figure this is my life and I would rather have the thickest strongest material to make my cage protecting me.

So it seems like the conclusion is the blue mount for the back stays is the best option and the 55 degrees is ok since the spreader plates will be in a good loaction. Also the inward bend in the front legs is ok.

Thanks for the comment on the clean up of the tube. I have been using a flap disk just being very careful to remove the least amount of material possible. The marks of the tubes are from the flap disk but they are not deep. I like the idea of a solvent do you have any suggestions on what solvent to use? I am using TIG so the base metal has to be very clean and I have only had good results by grinding both base metals.

As far as moving the front legs forward. Since I already have spreader plates there i am going to keep the current legs. I am planning to add another bar in front for the front legs connecting the firewall next to the clutch pedal. Does this seem like a good option to address the concern of the legs not being far enough forward?

As for driver door bars I am planning NASCAR style bars. A total of three continuous bars 1 straight bar by the sill and two more with two 45 degree bends to give some room for the driver to get in and out. all three of these bars will be connected with 6-8 small tubes. For passenger I have not decided yet but I'm thinking I may go with an X style made up of two continuous tubes and possibly a third by the sill.

Re: Front legs and Back stays gray area

You are in luck!  The head of Lemons tech has built Miata cages and is really helpful.  He is even selling one here http://forums.24hoursoflemons.com/viewt … p?id=34829.  It is always a good idea to contact him with questions and send pictures of what's going on.  Plus use the search too for Miata Cages and you'll find some examples.  Google Miata Lemons Roll Cage and more come up https://www.google.com/search?q=miata+L … p;dpr=1.09

It looks like you have a good plan and are smart to ask questions.  Lots of good ideas can be found here.  The only thing I would question is the potential grinding marks, that might draw some questions.  I also use 1.75 regardless of car weight, my only fear in Lemons is someone getting hurt in or by one of my cars.  Other than that it's all fun.  Not sure where you're from, but I would suggest finding a local team with experience.  Odds are there is someone with a lot of Lemons experience within an hour of where you live.  Pay them in beer to look at your car and give ideas.

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Re: Front legs and Back stays gray area

http://www.empireabrasives.com/2-quick- … t-removal/

I use these to clean up when i will be welding,  does not remove base material just sort of polishes the steel at the ends.  Works perfect

959 Toyota Tercel   6x Lemons loser

New England Area roll cages send me an email I'm in Central MA

Re: Front legs and Back stays gray area

mblake30 wrote:

Thanks for the comment on the clean up of the tube. I have been using a flap disk just being very careful to remove the least amount of material possible. The marks of the tubes are from the flap disk but they are not deep. I like the idea of a solvent do you have any suggestions on what solvent to use? I am using TIG so the base metal has to be very clean and I have only had good results by grinding both base metals.

I weld MIG (flux, gas and dual) and have best results with carb cleaner to clean up the metals.  Might not work as well for TIG.  I knew a guy who would use paint thinner - not sure the type.  Read the warning labels on paint thinner since some of them produce nasty byproducts when exposed to welding.  Never, ever, use brake cleaner.  Most brake cleaners make phosgene gas when exposed to UV.  Phosgene is a bad way to go and once you smell it you've already had 4 times the threshold limit.

Apparently my name is really "Craigers".  Who knew?
We might be yellow, but at least we are slow
I'm a WINNER!

Re: Front legs and Back stays gray area

I use denatured alcohol and fine-grit sandpaper to clean off oil and milling scale - it works surprisingly well. You can make an entire hoop/beam weldable and paintable in a couple minutes or so. Grab a paper towel, soak it in alcohol, wrap it around the tube, rub, then use sandpaper till it's shiny, then a fresh alcoholy paper towel until your tube is clean. It might not be THE fastest way, but it's clean, easy, doesn't smell bad, and won't kill/blind/maim you.

Although make sure not to throw those soaked paper towels on the floor after doing this, right before welding, because that's how your ass catches fire.

Not that I did it.

Nope, never happened.

K Car Stalker

Re: Front legs and Back stays gray area

Apparently Sasha likes to take the long and through approach to "cleaning his tube"

Chris from 3 Pedal Mafia

Re: Front legs and Back stays gray area

If any of your drivers are over 5'10" the cage will be too low.   Overall, the fab work is good, bit the cage is low and small.

Gosh, my business card says 'Tech Tyrant'

Re: Front legs and Back stays gray area

Thanks for the comments

@ Evil Genius

What are the rules about bump outs in the floor to lower the seat? I didn't read anything in the rules prohibiting bump outs.

I am 5"11 and I just make it under the 2" rule. The seat I have is a 20 degree layback so that helps a lot.  I was planning on adding a bar connecting the main hoop to the halo hoop following the centerline of the car. That may get another 1/2 inch. Does the 2 inch rule have to be measured by the main hoop? or can it be measured by this supporting bar I am going to add.

I have added the back stays, diagonal main hoop support and dash bar so I would like to fix it rather than cut it all out and redo it. Is there another method that could recommend to fix current setup?

Re: Front legs and Back stays gray area

mblake30 wrote:

I am 5"11 and I just make it under the 2" rule. The seat I have is a 20 degree layback so that helps a lot.  I was planning on adding a bar connecting the main hoop to the halo hoop following the centerline of the car. That may get another 1/2 inch. Does the 2 inch rule have to be measured by the main hoop? or can it be measured by this supporting bar I am going to add.

This is legal, and if you put bends in the bar you can gain even more clearance.  Some teams with hard tops even put this bar above the roof.

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Re: Front legs and Back stays gray area

So the reason the cage is relatively low and small is because I stayed within the boundaries of the soft top. The main hoop is literally touching the soft top all the way around. See pic link below
https://goo.gl/photos/cX5trPnkLLWojz7n6

I would like to keep the soft top in place so I can rally this car across the country. To get more room to get below the 2 inch rule I want to bump out the floor like the below example. Is this legal in Lemons? if not then Ill have to cut everything out and not have a top at all.
https://goo.gl/photos/J15fNVXkkrS77t6V6