should I add a diagonal brace? (street car) - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 20 Old 10-01-2009, 12:21 AM Thread Starter
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should I add a diagonal brace? (street car)

I'm in the middle of a complete tear down and rebuild of my 89 GT. I just installed a 6 point roll bar that I bought as a kit from Wolfe Racecraft a while back and now I'm wondering if I should add in a diagonal brace. My car is going to be a street car, but I'm building it with open track days in mind. I don't plan on road racing competitively, just for fun. My question is whether or not I should bother adding a diagonal brace to the main hoop? Will it make that much of a difference to be worth the hassle? What would you do?

Thanks guys,
Allan


89 GT - Brought it down to the bare shell, rebuilding it the right way.

Last edited by bleeatch; 10-01-2009 at 11:31 AM.
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post #2 of 20 Old 10-01-2009, 01:11 AM
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Do you still have a backseat that you expect people, especially children, to ride in? If "yes", then uninstall the cage. Street cars don't need cages. Cars that are taken to a few lapping sessions per year do fine with a good set of sub-frame connectors (no one's head can split like a ripe watermelon against a sub-frame connector during an accident).

If "no", I suggest reading this thread. You'll learn more about cage design reading it than you could dream possible.
http://forums.corner-carvers.com/showthread.php?t=27556

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post #3 of 20 Old 10-01-2009, 02:36 AM Thread Starter
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Thanks for the link, and no, I wont have a back seat.

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post #4 of 20 Old 10-01-2009, 09:43 AM
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1. Don't run a cage on the street. It's a track-only car, that's OK, but cages and unprotected heads don't mix.
2. Install the diagonal. It keep;s the main hoop from folding up in a rollover. I'm surprised Wolfe (or any other cage or cage kit fabricator,) doesn't do this on every cage they build. That and harness bars are mandatory.

-- Robert King
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post #5 of 20 Old 10-01-2009, 12:10 PM Thread Starter
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Thanks for your input!

It has a harness bar, just no diagonal bar and its technically just a roll bar, not a cage. I just realized I called it a cage originally, sorry for any confusion. It's just your average 6 point. I wanted the roll bar not just for safety reasons, but also because the car will have a 550-600hp 408, and I wanted to stiffen up the chassis more. Plus, I want to be able to run down the 1/4 mile faster than 10.99 with out getting kicked out. I guess I'm just wondering if should I add the diagonal brace and seep its benefits since I've gone this far already, or if its not really worth the hassle.

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post #6 of 20 Old 10-01-2009, 12:18 PM
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it is definataley worth it... it will add both structural rigidity and roll strength...

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post #7 of 20 Old 10-01-2009, 02:54 PM
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Quote:
Originally Posted by bleeatch View Post
Thanks for your input!

It has a harness bar, just no diagonal bar and its technically just a roll bar, not a cage. I just realized I called it a cage originally, sorry for any confusion. It's just your average 6 point.
Doesn't matter. The main hoop should ALWAYS be triangulated with a diagonal brace, and ideally, that brace should be one piece of steel. that means cutting out the harness bar and re-doing it after the diagonal has been installed.

(Some rule sets allow the diagonal to be two pieces as long as the two pieces line up with each other. I'm not a big fan of that. I'd rather have a one piece diagonal and a two-piece harness bar.


Quote:
I wanted the roll bar not just for safety reasons, but also because the car will have a 550-600hp 408, and I wanted to stiffen up the chassis more.
A 4-point roll bar won't do much to stiffen the chassis, with or without a diagonal. (And a roll bar without the rear stringers is worthless.)

Quote:
Plus, I want to be able to run down the 1/4 mile faster than 10.99 with out getting kicked out.
that's strictly a rules issue and may or may not have anything to do with safety. I've seen plenty of legal cages that aren't safe. And I've seen plenth of safe cages that aren't legal, too.

Quote:
I guess I'm just wondering if should I add the diagonal brace and seep its benefits since I've gone this far already, or if its not really worth the hassle.
Add it -- period. A hoop without a diagonal is unsafe.

-- Robert King
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Instructor, NASA Texas Region
Instructor, TWS Perf. Driving School
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post #8 of 20 Old 12-03-2009, 06:53 PM Thread Starter
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Bringing this thread back because I finally had time to work on adding a diagonal brace and already ran into an issue. Wolfe Racecraft bends their main hoop so that the top half of the hoop slighty leans forward as seen in the picture below. (This picture is from their website, its not my car)



This obviously causes an issue when trying to add a diagonal brace. If I try to add a straight bar, only half of the tubing passes through the horizontal brace since it has to lean forward slightly to meet where the top of the main hoop is. My other option is to use two bars for the diagonal brace. One from the the bottom passenger side to the middle(ish) of the horizontal brace and another one that continues from horizontal brace up to the top of the main hoop on the drivers side. This second bar would have to be slightly angled forward. Its kind of hard to explain what I mean, so forgive me if none of that makes sense. I made quick drawing to show what Im talking about.

The gray represents the main hoop (also shows where the rear and door braces come off), the black circle in the middle is the horizontal brace, the black circle at the top is the top of the main hoop where it runs horizontal, and the red is the diagonal brace


Which is the best way to go about this? Again, the car will be weekend cruiser that also sees open track, HPDE and probably some auto crossing events.

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Last edited by bleeatch; 12-05-2009 at 01:14 PM.
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post #9 of 20 Old 12-03-2009, 08:48 PM
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Quote:
Originally Posted by bleeatch View Post
Bringing this thread back because I finally had time to work on adding a diagonal brace and already ran into an issue. Wolfe Racecraft bends their main hoop so that the top half of the hoop slighty leans forward as seen in the picture below...
If it were my car, I'd replace the whole thing rather than trying to make what you have work.

-- Robert King
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Instructor, NASA Texas Region
Instructor, TWS Perf. Driving School
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post #10 of 20 Old 12-03-2009, 09:16 PM Thread Starter
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Are either of the ways I drew unsafe? I realize its not ideal, but is it that bad/wrong?


89 GT - Brought it down to the bare shell, rebuilding it the right way.

Last edited by bleeatch; 12-03-2009 at 09:33 PM.
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post #11 of 20 Old 12-03-2009, 10:43 PM
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Originally Posted by bleeatch View Post
Are either of the ways I drew unsafe? I realize its not ideal, but is it that bad/wrong?
The main hoop of a roll bar/cage should be in a SINGLE plane Yours is not. I wouldn't trust my life to that even if it did have a diagonal.. What was Wolfe thinking?!?

There are several problems with that roll bar that I can see.

-- Robert King
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post #12 of 20 Old 12-03-2009, 11:12 PM
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I also don't like the bend in the main hoop. It gives the bar a place to fold over if you get in a serious wreck. It surprises me from Wolfe, as they usually make high quality parts (even if they are geared toward going straight).

If I had to pick from what you have shown, then I would go with the 1-piece straight diagonal as it will add more strength. The 1-piece diagonal would help to keep the hoop from folding at the harness bar, while the 2-piece diagonal would not. As a bonus (if you can call it that) you would not have to completely cut the harness bar. You could just cut a "C" shaped notch out where the diagonal passes through and then weld the harness bar to the diagonal.

I am in agreement with Robert though, if possible get a different rollbar. More than just the weakening of the main hoop due to the bend, it looks like that bend puts the hoop right over the top of your head. It does not look safe to me, especially without a helmet on while cruising the streets.

--Vince

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post #13 of 20 Old 12-04-2009, 08:49 AM
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You are going to have to bend the crossbar or ride the steering wheel. I have had to do it before also. It is not ideal for sure but sometimes you have to work with what you have. I have seen quite a few cages fail at the bends but it will be stronger then what you have now. BTW I also own a wolfe cage (full cage). I like it for what it is. Very unobtrusive and adds some safety. It was a good compromise for my needs.
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post #14 of 20 Old 12-04-2009, 09:22 AM
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The top of the hoop is "in front of" the seat backs? That doesn't look safe at all unless you have a helmet.
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post #15 of 20 Old 12-04-2009, 01:05 PM
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OK, here's just some of the problems I see with that roll bar:
  1. The main hoop is non-planar, as we've been discussing.
  2. It's tough to tell in that photo, but it appears that there are no tubes running from the top of the main hoop rearward. That leaves the upper hoop unsupported.
  3. The door bars are the only thing supporting the main hoop, and thy are BENT too!
  4. The main hoop ends up above the driver's head, leaving no room for a hlemet for many drivers. Plus, any diagonal installed would have to run from the passenger-side to the driver's side, which is not recommended (and illegal in almost all road racing series.)
  5. The forward location of the hoop interferes with a harness brace, too. This means the brace will have to run BEHIND the main hoop, which is technically OK, but not recommended.
  6. It's hard to tell in the photo, but it appears that the main hoop attaches to the floor pan in front of the rear seat bulkhead. The main hoop should be tied very strongly into the rear seat bulkhead itself (many do no because it means you can't reinstall the rear seat,) or to the rocker panels (or both). I'll bet this bar suffers from the same vulnerability as the blue S197 Mustang that flipped and pancaked itself at Hallett a few months ago.
  7. The "door bars" are pretty much useless in a side-impact. NASA no longer allows this design in American Iron, CMC and likely in other racing series too.

Get rid of that bar.

-- Robert King
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post #16 of 20 Old 12-05-2009, 11:20 AM
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But it's such a pretty shade of purple!
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post #17 of 20 Old 12-05-2009, 12:03 PM
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I'm quite roll cage safety ignorant, but even that bar makes me go It certainly looks more of a "show bar" with the emphasis being on following body line/door opening.
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post #18 of 20 Old 12-05-2009, 12:23 PM
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Quote:
Originally Posted by gt40mkII View Post
It's tough to tell in that photo, but it appears that there are no tubes running from the top of the main hoop rearward. That leaves the upper hoop unsupported.
Robert,
He stated earlier that it is a 6-point rollbar, so it should have the rear struts.


bleeatch,
I am sure this is not what you want to hear, but IMO you should remove that bar. The more I look at those pictures, the more that I am concerned for your (and any passenger's) safety. Personally, I would not ride in that car. I would not even drive it around the block as it is right now. There is too high of a risk that any front seat passenger could smash their head open on the main hoop.

If you really like the bar and you want to "save" it then I would suggest that you move the entire hoop 6"-12" rearward. Instead of the hoop landing just in front of the door opening it should land right in front of or on the rear seat shelf. Also, I would add a 1-piece straight diagonal bar from the LH top corner to the RH bottom corner.


--Vince

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+ Tremec 3550, D&D shifter, 3.73:1 gears, & TrueTrac differential
+ EVM watts & 3-link, Homemade LCA's, & Koni SA's
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post #19 of 20 Old 12-05-2009, 01:01 PM
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Just for curiosity sake, does any one have a pic of the cage being mounted to the rear seat? I always thought they where installed right in front of the rear seat on a 6x6 plate.

Charlie R
1992 GT | AutoX / Weekend Cruiser
Killing them with 10 inches of body roll
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post #20 of 20 Old 03-26-2010, 02:47 AM
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Quote:
Originally Posted by sprayin50 View Post
Just for curiosity sake, does any one have a pic of the cage being mounted to the rear seat? I always thought they where installed right in front of the rear seat on a 6x6 plate.
Sorry to bring up a dead thread but I just saw this. I think I have pictures as to what you are wanting to see. Sorry Im too new and it wont let me post or link pictures. If anyone wants to see the pics let me know and I can send you a link so you can post them up. Thanks.
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