• bilcoh
  • Ripened Lemon
  • Offline
  • From: Seattle
  • Registered: 2018-07-02
  • Posts: 164

Topic: Modifying existing roll cage

Hello LeMoners:

On a car with an existing roll cage, we might need to gain a little more space for the driver's left arm.  Can we cut out the door bars, grind off the old welds at the main hoop and left main bar (see figure 1.C of "How not to fail Lemons Tech" for current cage style) and weld in new bars with the proper outward bends? 

Just wanting to make sure modifying a cage isn't verboten for some metallurgical reason I don't understand.

Also, would like to add gussets and the other mods recommended (dash bar, etc).  On the gussets, is there a recommended material thickness?

Thanks in advance.

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

Re: Modifying existing roll cage

You can cut and replace, but you're better to leave stubs than to grind it flush. If you try to grind down to the main hoop you're likely to fail tech for modifying the wall thickness of the main hoop.

Put together a plan for what you want to do and email it to HQ/Pagel and work through it with them to make sure they're on board with what you're doing.


Flat out adding bars you're ok, because you're just adding to an existing cage, not cutting and grinding.

20+ Time Loser FutilityMotorsport
Abandoned E36 Build
2008 Saab 9-5Aero Wagon
Retired - 1989 Dodge Daytona Shelby 2011-2015 "Lifetime Award for Lack of Achievement" IOE, 3X I got screwed, Organizer's Choice
  • Registered: 2015-05-13
  • Posts: 122

Re: Modifying existing roll cage

I am assuming you only need an inch or two on the driver left side. Before cutting I would take a look at possibly moving the seat to the right. Another thing to look at is replacing the door bar padding with the very high density (solid looking rather than foam appearance) padding. It is a lot thinner but it is also pretty expensive.

If you do decide to cut out and replace, I echo TheEngineer warnings plus ...  You can't weld the new bar where you leave the cutout stubs. The new bars can't have an S in them and the top and bottom door bars must be a minimum of 7.5 inches apart at both ends. A lot of people seem to miss that the 7.5 inches is a minimum distance between the bars.

  • Registered: 2011-10-14
  • Posts: 4,167

Re: Modifying existing roll cage

moparfan wrote:

I am assuming you only need an inch or two on the driver left side. Before cutting I would take a look at possibly moving the seat to the right.

We offset AND angled the Saturn seat where the rear was an inch more inboard than the front.  It gained that elbow clearance an literally no one noticed until we pointed it out to them.

  • Spank
  • Utter Madman
  • Offline
  • From: Escondido, CA
  • Registered: 2009-06-10
  • Posts: 5,863

Re: Modifying existing roll cage

moparfan wrote:

If you do decide to cut out and replace, I echo TheEngineer warnings plus ...  You can't weld the new bar where you leave the cutout stubs. The new bars can't have an S in them and the top and bottom door bars must be a minimum of 7.5 inches apart at both ends.

Not trying to start an argument, just posting that S bends in DOOR BARS are NOT expressly prohibited in Lemons. I believe there is another series (NASA?) that counsels against them, but Lemons as yet has made no official statement.

S bends in the A-pillar downbars (to get around a dash without cutting it, for example) are definitely a no-no.

Spank's Website

  • Registered: 2009-07-19
  • Posts: 1,585

Re: Modifying existing roll cage

When we did that, we left the stubs of the old bars, and just beveled the cut edges a bit  with an angle grinder to keep from cutting ourselves. It's passed tech multiple times since then.

Everybody grab your brooms, it's shenanigans!
  • VKZ24
  • VKZ24
  • Lemons Staff Stalker
  • Offline
  • From: Wilson, NC
  • Registered: 2009-05-20
  • Posts: 1,839

Re: Modifying existing roll cage

Spank wrote:

Not trying to start an argument, just posting that S bends in DOOR BARS are NOT expressly prohibited in Lemons.

Correct, but they should be prohibited IMO.  If an S-bend is unacceptable in the A-pillars (because it creates a weak point) it should be unacceptable in the door bars as well.

Captain
Team Super Westerfield Bros.
'93 Acura Integra - No VTEC Yo!

VKZ24's Website

  • Registered: 2014-11-04
  • Posts: 274

Re: Modifying existing roll cage

OnkelUdo wrote:
moparfan wrote:

I am assuming you only need an inch or two on the driver left side. Before cutting I would take a look at possibly moving the seat to the right.

We offset AND angled the Saturn seat where the rear was an inch more inboard than the front.  It gained that elbow clearance an literally no one noticed until we pointed it out to them.

I will second this. We had to add a door bar and nobody had a bender at the track, so the seat got moved about 3/4" inboard. No problems whatsoever.

Owner of the Knights Templar Neon
A&D of middling proportions
  • From: Newport News, VA
  • Registered: 2015-12-23
  • Posts: 620

Re: Modifying existing roll cage

VKZ24 wrote:
Spank wrote:

Not trying to start an argument, just posting that S bends in DOOR BARS are NOT expressly prohibited in Lemons.

Correct, but they should be prohibited IMO.  If an S-bend is unacceptable in the A-pillars (because it creates a weak point) it should be unacceptable in the door bars as well.

I'm not an engineer, but I would guess the reason is the direction of compressive forces. In the A-pillar the S-bend becomes the place the bar folds.

In the door bar, the S-bend distributes force to the A-pillar and the main hoop. Probably better than straight bars, but not as good as a two-bend door bar.

That guy