SFC design?
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Teching In
Joined: Aug 2002
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From: Flower Mound TX.
SFC design? What is the difference in SFC styles and what are the pro's and con's?? For example there is the double diamond/SLP design and there is the G2/BMR/Global West design? I DO NOT have T-tops or a convertible and I am trying to make a decession on what SFC's to buy. I guess the first thing I need to decide is what design. I haven't decided yet if I am lowering the car yet since I like to drag more then auto-x. If the straight bar type is better for what ever reason why does G2 sell a cross brace to bolt on to their SFC's? Are they trying to cover both design ideals? Any help will be appreciated..
TECH Fanatic
Joined: Nov 2001
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From: Mi./Al.
Re: SFC design? Man 24 hours and no replys, <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> I thought I'd wait and see what everyone had to say but I guess there's no takers. From my e-mails too you I think I've made it clear which ones I think are the best and why.
Let me see if I can't get this post going, the best SFC are Spectacle Solutions or the SLP bolt-on's...the weld-on type suck. <img border="0" title="" alt="[Razz]" src="gr_tounge.gif" /> There, that should get things going and if not then we all know for sure which SFC is the best.
Al
Let me see if I can't get this post going, the best SFC are Spectacle Solutions or the SLP bolt-on's...the weld-on type suck. <img border="0" title="" alt="[Razz]" src="gr_tounge.gif" /> There, that should get things going and if not then we all know for sure which SFC is the best.
Al
Staging Lane
Joined: Jul 2002
Posts: 64
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From: Wolverine Lake, MI
Re: SFC design? OK, I'll give you my opinion on this since noone else is speaking up.
The 2 point connection "straight" bars are a good improvement over stock. Try to get round bars, not boxed. Round bars are better in torsion and you'll normally have better ground clearance with round bars anyway.
However, bars like the SLP and KBDD are the next step up. Triangulation is always good, and you'll find that most race car tube frames use triangulation to make the frames more resistant to bending and torsion.
The next step up from them is the LG X brace option, but it's an expensive step. This connects both bars to each other directly. They have a 25% off sale right now, so that combo would be about $300 I believe. At that price I think it's a worthwhile upgrade over the KBDD, but at $400 . . . Hmm.
The 2 point connection "straight" bars are a good improvement over stock. Try to get round bars, not boxed. Round bars are better in torsion and you'll normally have better ground clearance with round bars anyway.
However, bars like the SLP and KBDD are the next step up. Triangulation is always good, and you'll find that most race car tube frames use triangulation to make the frames more resistant to bending and torsion.
The next step up from them is the LG X brace option, but it's an expensive step. This connects both bars to each other directly. They have a 25% off sale right now, so that combo would be about $300 I believe. At that price I think it's a worthwhile upgrade over the KBDD, but at $400 . . . Hmm.
On The Tree
Joined: Nov 2001
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From: San Jose,CA
Re: SFC design? Round bars are not better in torsion. Square or boxed steel is stronger to resist torsion.
If round was, you would have skyscrapers built out of tubular steel wouldn't you?
You can have round tubing stiff enough to emulate smaller boxed steel per given weight,
but it has to be big enough in diameter.
That is why Global West uses huge 2" tubing in their connectors.
The triangle is one of the strongest shapes, go with an SLP or KBDD connector for maximum stiffness.
If you are worried about weight, then Global west is your next choice.
If round was, you would have skyscrapers built out of tubular steel wouldn't you?
You can have round tubing stiff enough to emulate smaller boxed steel per given weight,
but it has to be big enough in diameter.
That is why Global West uses huge 2" tubing in their connectors.
The triangle is one of the strongest shapes, go with an SLP or KBDD connector for maximum stiffness.
If you are worried about weight, then Global west is your next choice.
Re: SFC design? I had my subframe connectors installed by a shop that builds tube frame Autox cars from scratch. he looked at all the designs, GW/LG, SLP/KB, BMR. His review was that the best avail was the GW/LG tubular design. The KB/SLP triangulated design would be stronger in some directions on force, but those forces would not be present in this application. So all that extra metal is doing nothing but adding weight to the car. Also the center tie in to the tunnel brace does nothing.
The BMR square tube was close to the GW tube design, but was too heavy with no extra strength and hung down too low.
Also if they are not welded in properly all SFC are worthless. you might as well just put 20 lbs of metal in the trunk.
I am not saying the GW design is perfect, mine needed some minor bending and trimming to fit correctly.
The BMR square tube was close to the GW tube design, but was too heavy with no extra strength and hung down too low.
Also if they are not welded in properly all SFC are worthless. you might as well just put 20 lbs of metal in the trunk.
I am not saying the GW design is perfect, mine needed some minor bending and trimming to fit correctly.
Staging Lane
Joined: Jul 2002
Posts: 64
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From: Wolverine Lake, MI
Re: SFC design? Steve C,
Well, it turns out you're right. I pulled out an old college textbook and ran through some numbers. Round bars are not better in torsion for the same area as rectangular bars. Round bars are better in bending. The overall best choice seems to be rectangular bars though. Their benefits in torsion outweigh the round bar's gains in bending. I just can't run a rectangular bar easily because they hang down too low.
Bill, I would disagree that the triangulated sfcs are made for loads that do not exist in our application. A tie-in to the tunnel brace bolts would have to help in torsion. Granted, the tunnel brace bolting point may flex enough to lessen this benefit, but I'd find it hard to believe the gain is nonexistent. However, that's why I think the LG X brace is the best choice. It takes the tunnel brace bolting location out of the picture.
Well, it turns out you're right. I pulled out an old college textbook and ran through some numbers. Round bars are not better in torsion for the same area as rectangular bars. Round bars are better in bending. The overall best choice seems to be rectangular bars though. Their benefits in torsion outweigh the round bar's gains in bending. I just can't run a rectangular bar easily because they hang down too low.
Bill, I would disagree that the triangulated sfcs are made for loads that do not exist in our application. A tie-in to the tunnel brace bolts would have to help in torsion. Granted, the tunnel brace bolting point may flex enough to lessen this benefit, but I'd find it hard to believe the gain is nonexistent. However, that's why I think the LG X brace is the best choice. It takes the tunnel brace bolting location out of the picture.
Re: SFC design? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 94bird:
Well, it turns out you're right. I pulled out an old college textbook and ran through some numbers. Round bars are not better in torsion for the same area as rectangular bars. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">True, but misleading. For a given overall area the square tube is more resistant to twisting. However, the box is also heavier. If you look at the torsional rigidity per unit weight then round tube is more efficient. It does however end up larger in diameter.
For example (I'm assuming thin-walled tube and axial torsion here):
A 2" square box section of 0.125" wall thickness weighs the same as a 2.4" diameter round tube of the same wall thickness per unit length. This same round tube would have almost a 34% greater polar moment of inertia (i.e. resistance to twisting), but it would be 20% larger in diameter. So it really becomes a balance between size, weight, and rigidity.
Well, it turns out you're right. I pulled out an old college textbook and ran through some numbers. Round bars are not better in torsion for the same area as rectangular bars. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">True, but misleading. For a given overall area the square tube is more resistant to twisting. However, the box is also heavier. If you look at the torsional rigidity per unit weight then round tube is more efficient. It does however end up larger in diameter.
For example (I'm assuming thin-walled tube and axial torsion here):
A 2" square box section of 0.125" wall thickness weighs the same as a 2.4" diameter round tube of the same wall thickness per unit length. This same round tube would have almost a 34% greater polar moment of inertia (i.e. resistance to twisting), but it would be 20% larger in diameter. So it really becomes a balance between size, weight, and rigidity.
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Staging Lane
Joined: Jul 2002
Posts: 64
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From: Wolverine Lake, MI
Re: SFC design? Steve,
The V and X braces are on LG's website, and for the same price. I would assume he carries both.
Fulton1,
My calcs were based on solid material. That's a good point about these SFCs being made out of tubing and hollow boxed material. I knew there was some reason I had kept it in my head to use round tubing for torsional loads since my college days. I guess my memory got rusty since I'm more of a testing engineer now, than a design engineer.
<small>[ August 22, 2002, 03:59 PM: Message edited by: 94bird ]</small>
The V and X braces are on LG's website, and for the same price. I would assume he carries both.
Fulton1,
My calcs were based on solid material. That's a good point about these SFCs being made out of tubing and hollow boxed material. I knew there was some reason I had kept it in my head to use round tubing for torsional loads since my college days. I guess my memory got rusty since I'm more of a testing engineer now, than a design engineer.
<small>[ August 22, 2002, 03:59 PM: Message edited by: 94bird ]</small>
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Verdad Gallardo Re: SFC design? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"> I guess my memory got rusty since I'm more of a testing engineer now, than a design engineer. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yeah, I know the feeling <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
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Joined: Nov 2001
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From: Houston, TX
Re: SFC design? Must resist being an engineering nerd.....must not..... OK....just a little. For bending the more area of material you have from the center line, the better because higher moment of inertia allows you lower stresses because of the formaule stress=Mc/I. As for bending the stress = Tr/J where J is polar moment of inertia, and generally as someone else pointed out the round tubing will have highest polar moment of inertia per area.....OK...I will stop now.
TECH Apprentice
Joined: Nov 2001
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From: Ottawa
Re: SFC design? If you are going to add a torque arm (a big plus if you drag) then you may want to shy away from the "diamond" style SFCs, as many people I have talked to had problems fitting their torque arms in with the diamond SFCs alread in place.
TECH Apprentice
Joined: Jun 2002
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From: Richmond, Va.
Re: SFC design? i have the global west sfc, and i'm very satisfied with them. excellent fit, and they do not hang low. you have to look underneath the car to see them. i got mine from thunder racing for $189.
On The Tree
Joined: Nov 2001
Posts: 106
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From: San Jose,CA
Re: SFC design? 94 bird, I don't think LG makes that x brace anymore, they now incorporate a v-shape tie-in to the tunnel brace.
I do agree with bill that the KBDD is a little heavier (36lbs vs 24lbs for GW) but structurally there is an advantage.
Think of it this way, the Kenny browns tie into 10 points on the car. That includes 4 frame rails, 2 rocker panels and 4 bolt-in points (tunnel brace).
Have you ever built a shed or wall for a house?
Picture a wood rectangle (2x4" beams x4) with a piece of plywood sheet over it
Now step onto the plywood and walk across it, you'll find near the middle that the plywood starts to sag (some jumping may be required but it may still do it)
Now take off the plywood sheet and hammer in two more 2x4" beams (equadistant) in the rectangle. Put the plywood back and and walk down the middle.
Does the plywood sink or sag now?
I do agree with bill that the KBDD is a little heavier (36lbs vs 24lbs for GW) but structurally there is an advantage.
Think of it this way, the Kenny browns tie into 10 points on the car. That includes 4 frame rails, 2 rocker panels and 4 bolt-in points (tunnel brace).
Have you ever built a shed or wall for a house?
Picture a wood rectangle (2x4" beams x4) with a piece of plywood sheet over it
Now step onto the plywood and walk across it, you'll find near the middle that the plywood starts to sag (some jumping may be required but it may still do it)
Now take off the plywood sheet and hammer in two more 2x4" beams (equadistant) in the rectangle. Put the plywood back and and walk down the middle.
Does the plywood sink or sag now?