• From: Sunbury Ohio
  • Registered: 2009-09-06
  • Posts: 92

Topic: 2" helmet clearance clarification

Hello all. Before I trouble Evil Genius directly via email, I want to clarify the 2" helmeted driver rule. Cage is tacked in, but before we fully weld I want to ensure we're on the same page with the rule. Car is 1994 Lincoln Mark VIII. Using stock seat mounting locations with Corbeau seat and slider. Shortest driver is 5' 6", tallest is 6". Slider set so as not to allow the seat to extend more than 5" from the harness bar per rules. Main hoop  provides plenty of clearance for the 2" rule. We are using left/right down tubes connected to each other at the windshield/roof line. At that point, the top of the connecting bar isn't 2" over the driver's helmet. If you draw a string from the top of the connector bar, over the driver to the top of the main hoop, and a string from the left downbar to the right downbar over the driver's head, we properly exceed the 2" of clearance over the driver's helmet. That's our understanding of the area contained by the cage. Other posts have said "imagine a box welded to the outside of the cage, and the helmet must be 2" from any of the box" which I think is the same idea. I just wanted to make sure this is the correct idea - string from bar top to bar top. If you drew a string from the top of the windshield connecting bar parallel to the rear of the car, you wouldn't get the 2" -- only if you draw it bar to bar (because the main hoop is higher than the windshield).

Is that clear enough of a question? Thanks to all for the help. Decision made which affects the above question - we are trying to use the stock seat location with a slider. We have also left the sunroof in, however this doesn't impact the issue which is the front connector - rear hoop left plenty of room even with the sunroof mechanicals.

Cage built having read each and every rule 100+ times, fabricated/bent by professional cage shop in Dayton, Ohio, being welded in by us. Adding dash bar and anti-bow bar as recommended. We are trying very hard to have hit every rule as written AND INTENDED and adding the extras for good measure!

IOE Fall Gingerman 2018 1994 Lincoln Mark VIII
  • jmas
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  • Registered: 2016-08-30
  • Posts: 58

Re: 2" helmet clearance clarification

I probably know less details of the rule than you do.  But we had the same problem, only worse in a smaller prelude with a cage that was built to be lower than the factory sunroof brackets.  We ended up scraping the factory seat slide on Friday before the race at the track, we mounted the race seat directly to the floor and brackets to the rocker and tunnel.  We used foam pads to adjust for different driver sizes.  Also for tall drivers we found a wedge shaped foam pad behind the lower back had the same affect as reclining a factory seat.  by getting the taller driver's position to be slightly reclined it can get top of the helmet a lot lower.

  • Hamsa9
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  • From: Our National Capital
  • Registered: 2012-11-03
  • Posts: 239

Re: 2" helmet clearance clarification

To measure from the outside of the protected area, one gets into lying strings over cages and measuring.  Since there are several ways one could lay strings, measure the internal clearance.

Get a four to five foot section of 1/2" dowel. Have each driver adjust seat and sit in car.  Position the dowel across the A-pillars, behind the windshield and run the dowel rearward, horizontally along the underside of the A-pillar bars & halo.   With each driver in and their seat adjusted the dowel should clear the space over their head between the helmet and the roll cage.  If the dowel clears the space, your drivers are well and good inside of the enclosed space (and their was no strings, measuring, or interpreting)

Do this with all of the drivers, as each positions the seat differently and if the seat slides on an angle, that can impact the clearance more than the reduction in height.  If any of your drivers are close, sometimes you can squeak out a little more protected/enclosed space by adding a shallow-bowed dorsal bar longitudinally in the middle of the halo.  Think of it like a NASCAR bar for above the driver's head.

I'll try to remember to take pics when I get home tonight.

FWIW,

Hamsa

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His nerves of metal and his blood oil.
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His least bidding, and lo, he's away.
  • BoB
  • BoB
  • Lemons Staff Stalker
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  • From: Elmhurst, IL
  • Registered: 2009-05-01
  • Posts: 4,206

Re: 2" helmet clearance clarification

I've always gone by the broom handle measuring. Put something running along the top of the cage.  Put in your driver whose head is the highest  while sitting (not always the tallest person since some people have long legs, some people have long torsos) with their helmet on.  Measure from the top of their helmet straight up to the bottom of what you are laying over the top of the cage.  This simulates your car on the roof and where things will crush till it hits the cage.

If it doesn't work you can put a bent bar on the top of the cage to raise the height .

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  • From: Tustin, CA
  • Registered: 2010-12-30
  • Posts: 3,275

Re: 2" helmet clearance clarification

The theoretical test they apply is if a broomstick was set on top of the cage, would your helmet be 2" below that?  Whether the broomstick is set front/rear, side/side or diagonal, the top of the helmet with the driver in the seat needs to be "2 below the stick.  Something to note here is that there is no rule preventing the seat from being more than 5" from the harness bar.  It says you need to use a seatback brace if the seatback brace is more than 6" from the seatback.  I suppose that if push comes to shove, there is nothing that says the harness bar must be in the same plane as the main hoop and couldn't be an extra hoop added on that is rolled forward towards the seatback outside of the main hoop plane but that doesn't seem like something you should need to do.  Adjustable seatback braces are commercially available.  Also note that you can mount your seat bracket with the front angled higher than the rear.  This lets your 6' driver sit lower with the seat slid back for leg room, then as you move the seat forward the seat is also moved upwards so your shorter drivers can see over the dash.

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  • From: NH
  • Registered: 2010-01-20
  • Posts: 3,299

Re: 2" helmet clearance clarification

Mostly covered, but yes. it's 2" inside the outer bounding box of the cage. There are ways to play with this, like adding a bar along the center of the roof that bends up to touch the roof skin. Then you can lay your string over that center bar when you spread it across.


What they're basically getting at is that if you car goes rolling, there is some amount of stretch in the belts that will allow you to move upward. If you are not low enough inside the cage you will find yourself smashing your head into the roof which is now essentially the ground. This is bad, you don't want this.

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  • From: Sunbury Ohio
  • Registered: 2009-09-06
  • Posts: 92

Re: 2" helmet clearance clarification

Thanks all. With those answers I'm comfortable that we are good!

IOE Fall Gingerman 2018 1994 Lincoln Mark VIII
  • Registered: 2016-02-15
  • Posts: 25

Re: 2" helmet clearance clarification

We are looking at adding the "dorsal bar" to accommodate a tall driver, I was wondering if there might be an advantage to doing a pair of dorsals would be better - seems like this would provide even more clearance for the driver. Looks like someone was adding a dorsal in the RIdge wrapup video at about 2:31

Thanks, Monty

  • From: SF BayArea/Land of Enchantment
  • Registered: 2012-01-22
  • Posts: 903

Re: 2" helmet clearance clarification

montyq wrote:

Looks like someone was adding a dorsal in the RIdge wrapup video at about 2:31
Thanks, Monty

That is correct....That was being done on Sunday morning,while there was a race going on.......

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