How good is the TCP X brace?

[S-Car-Go]

Does anyone have first hand experience with the TCP center section sub frame connector? Can you compare on/off conditions? Does it add any torsional rigidity? I’m getting ready to remove my GW sub frames and go custom. Local fabricator wants to do something like the TCP center, but I’m not convinced it does much to prevent twisting. Especially since this is a convertible.

 

[rbohm]

while i dont have any personal experience with them, the Xbrace does add stiffness to the chassis by preventing twisting. it does this by changing the load path through the chassis. by the way i also recommend using jacking rails welded to the inned rocker panel and tied to the subframe connectors either with tubing, or shear panels.

 

[10secgoal]

if your going a custom route, why can't he just add to your existing X brace ?

 

[jamison42166]

i cant compare TCP's x brace to other companies braces but it made a big difference in stiffness. i had mine installed and they had to run all new brake lines fuel lines and i also had to run a custom exhaust so the pipes would fit under the bracing. it also sticks down fairly low so you have to be careful with bumps.

[/IMG]

that picture is a few yrs old nevermind the nasty trans pan it was redone since then

 

[S-Car-Go]

Jamison, Did you add the x brace after installing the sub frames or at the same time? btw, no sees the trans pan when it's next to R&P and tubular control arms

10secgoal, I don't have an existing X brace. I’m just exploring options at this point.

rbohm, Even in Jamison's photo it looks like it would twist like the handle on a cork screw. If it were a true X, I think it would want to bow along the diagonal load path (unless it attached to the floor pan along the way). It's not triangulated on a vertical plane like a roll bar, firewall, etc. I'm not trying to be argumentative. I just don't get where the strength comes from and I want to learn.

Thanks all

 

[rbohm]

S, you are right the chassis will still twist a bit since you cant eliminate twisting even with a tubular chassis like you would find on a sprint cup car, or even with a carbon fiber chassis like you would find on an indy car or formula one car. what you are doing here is reducing the twist that does happen by changing the load path. the center brace acts like a torsion bar to limit chassis twisting.

with these chassis's every little bit helps, as the stiffer you can make the chassis, the softer your suspension, and thus more tunable, can be. stiffen up the chassis as much as possible, and you can run a much softer spring and tune the suspension with shocks and sway bars.

 

[jamison42166]

Jamison, Did you add the x brace after installing the sub frames or at the same time? btw, no sees the trans pan when it's next to R&P and tubular control arms

10secgoal, I don't have an existing X brace. I’m just exploring options at this point.

rbohm, Even in Jamison's photo it looks like it would twist like the handle on a cork screw. If it were a true X, I think it would want to bow along the diagonal load path (unless it attached to the floor pan along the way). It's not triangulated on a vertical plane like a roll bar, firewall, etc. I'm not trying to be argumentative. I just don't get where the strength comes from and I want to learn.

Thanks all

i bought the whole thing at one the x brace gets bolted in after the subframes are installed, ive been contemplating a gv overdrive and to do that id need to lose the xbrace. im not really sure how much strength it has either but i figure its not hurting anything either. i just thought it looked cool when i boght it lol. right now lack of funds and a severe hand injury makes a trans swap/mod impossible

heres another pic i found if it helps. good luck with whatever you decide.
jamie

 

[70vert]

I did the Tinman subframes through the convertible subfloor

S-Car-Go, what I did is to weld the Tinman subframes in a manner similar to the photo on this site:

'66 Mustang Convertible

My general theory about frame reinforcement is that it should work with the existing unibody and tie into it at as many points as possible, not seek to replace it - for example, I think the perimeter frame replacements for our subframe/unibody/subframe are crazy wastes of weight and money.

Doing the subframes this way through the convertible subfloor helps to tie the subframes into the rest of the unibody AND to the rocker panels, where your real strength is on a convertible. We pretty much can't have enough reinforcement between the rockers, subframe connectors, and floor of the car since this is where all our strength is with no roof.

I totally agree with rbohm about jacking rails or sheet metal to connect subframe to rocker panels. Don't get rid of the convertible plate since that "U" in the transmission tunnel can be a big source of strength if the top of the U is kept boxed in.

I would almost recommend something like the Tinmans as a jacking rail as well. Boxed-in frame members welded to the subframe on one side and to the rocker panels on the other and spot welded to the floor itself at a few points would be pretty interesting. I don't like the designs that have an open top and use the floor as the top of the boxed-in frame member. I just don't trust the thickness of the floor there, and you could do some spot welds to the floor to get the same effect of tie-in.

Anyway, there you go - that's my take on it. With the Tinmans, the shop that installed them was very impressed that when you jack up the driver's rear, for example, the driver's front comes right up with it. I'm very pleased with the increase in rigidity, but with a convertible, especially when I get some real power, there could be even more, so I might go with jacking rails of some sort down the road.

 

[Psydwaze]

Time for an analogy...

Think of the floor pan as a shoebox lid. What happens when you twist it? The distance between two of the opposite corners becomes shorter. Now place a diagonal brace that spans between the two opposite corners. You can't bend the box lid in that direction anymore. The main strength of the X-brace comes from fixing the distance between both sets of opposite corners. If you only add braces along two of the outside edges of the box lid (standard subframe connectors) you gain the torsional ridigitity of the connector itself, but you can still twist the box lid.

For a physical example, get a piece of paper or light cardstock, some match sticks, and some tape or glue if you're more patient. Test the ridigity of the cardstock in all three states of bracing: unbraced, two parallel edge braces, and finally with two diagonal braces.


Lino
TCP

 

[70vert]

In theory I definitely agree that an X across the center of the chassis is a great id

An "X" across the center of the chassis running with the legs running from the front of one rocker panel to the back of the other, with subframe connectors running straight through those legs or welded or bolted to the legs of the "X" would seem like a great idea, but I'm not sure about an X-brace that just bolts to the front and rear subframes. There are lots of ways to improve rigidity, but what's the best design? I'm sure the TCP X-brace helps, but there are a few issues to consider: (by the way, I've spent more money than I care to admit on TCP suspension, Wilwood brakes, KRC PS pumps, etc., so I'm definitely a fan of some of your products)

1. The OP has a convertible where much of the strength is in the rockers, and the TCP X-brace completely ignores the rockers like almost all of the subframe connectors out there. I don't think it's a bad thing to take some of the work away from the rockers, but I think it would be much better if the main structural elements were tied together.

2. An X-brace that goes below the convertible floorpan lowers ground clearance - convertibles are already challenged on this.

3. You raise a really good point about an X-brace in general limiting the travel of each of the corners, but how much does the TCP brace do this? It's not a pure "X" - is there any twist along those center tubes?

4. I think if I were to start with a clean sheet of paper, I'd build a huge "X" with boxed-in legs molded to the floor pan so they could be skip welded at a few points to the floor pan and with the subframe connectors running through the legs of the "X" to give some longitudinal rigidity and tie the front to the rear. You'd have to cut into the convertible subfloor, fit it in, and weld it to the subfloor. Driveshaft and exhaust clearance would be a problem. It would tie to the rockers at the front and back, and in the center with the convertible subfloor that runs from rocker to rocker. It would be heavy.


Convertibles are tough . . . there's no simple or easy way to reinforce them well . . .

 

[jamison42166]

BTW IIRC i dont think you cant use TCPS X BRACE in a vert, my car is a coupe, guess i should have read your original post better.

this is the one for verts:
http://www.totalcontrolproducts.com/support/sub/PKG-SFC-02_AT.jpg

 

[phutch11]

Jamison, there is a very interesting thread over on corner carvers where the poster took a very scientific approach and measured before and after torsional stiffness after installing various chassis components.
Interestingly the results run counter to most advice you hear about how to stiffen up your frame and make you car handle.

The single biggest addition to torsional stiffness was the addition of a steel rear seat divider. Next was an export brace.

As I recall, normal frame connectors helped a little, and the x connectors helped a little more, but still not much overall.

The Monte Carlo bar did nothing.

Good luck...

 

[rbohm]

Jamison, there is a very interesting thread over on corner carvers where the poster took a very scientific approach and measured before and after torsional stiffness after installing various chassis components.
Interestingly the results run counter to most advice you hear about how to stiffen up your frame and make you car handle.

The single biggest addition to torsional stiffness was the addition of a steel rear seat divider.

goes to show what a well placed shear panel will do for chassis stiffness.

Next was an export brace.

in this case a well placed gusset.

As I recall, normal frame connectors helped a little, and the x connectors helped a little more, but still not much overall.

these do more than reduce twisting, they help prevent bowing as well.

The Monte Carlo bar did nothing.

this bar while it doesnt prevent twisting, it does prevent shock tower flexing, which is why it is useful.

 

[other_shoe]

The single biggest addition to torsional stiffness was the addition of a steel rear seat divider. Next was an export brace.

I am guessing the steel trunk divider would not do much for a convertible. Right?

Also, there was a poster here (something like Mustbereal) who did a "torsional stiffness" thread and had some of the same findings.

 

[70vert]

I am guessing the steel trunk divider would not do much for a convertible. Right?

no, they already have one. You could stiffen up that trunk divider, with its open holes, by welding one of those trunk divider plates to it and make it stronger and extend it to the wheelhouse, but all that would do is to make the wheelhouse, rear subframes, and seat back move as one. It wouldn't get you the tie in to the roof that you would get on, say, a coupe with a trunk divider, but it would do something, assuming that that open trunk divider that convertibles have is a little flimsy. It might be OK as-is. Who knows?

All of the of the stiffening writeups don't pertain to convertibles. I would love to see a convertible study. It has to be a totally different approach, because you are trying to make the load path go from the shock towers through the relatively flat floor and rocker panels to the rear suspension pick up points. The firewall and rear seat divider help, because they give you some vertical resistance to the flexing front and rear and tie in the opposite side frame structure (frame rail, rockers) into the struggle, but in the end the twisting rear structure and the twisting front structure (assuming they both can be made to twist as one solid box front and rear) have to be resisted or transferred by the relatively flat floor and trans tunnel and rocker panels.

 

[S-Car-Go]

One of the "for sure" items on my list is to seam weld all the panels on the rear (seat divider, additional floor pan, etc.) Similar to what the track guys do with the shock towers. I believe Ford tried to take the twist out of these cars by adding vertical panels where they could. Along with looking at diagonal bracing, I've been toying with adding thickness to the vertical portion of the convertible floor pans. More gusseting. I think rbohm nailed it on his last post. If you looked at the car from a cut-away (fore/aft) view then it would look like an I beam on its side ][. Easy to twist, until you added shear to one or both sides. You're right 70vert, everything I've seen written is about coupes or FB which are a completely different animal. I've owned about a dozen cp/fb over the last 30 yrs but this is my first vintage convertible. Bigger learning curve than I expected. What ever I end up doing will go through the floor or at least get welded along the length.

If the diagonal dimensions lengthen when twisted, then I can see where an X brace would help, but connecting along the floor pan would be much more effective than just connecting at the corners. I don't think it helps that the brace is bowed.

 

[CochinoFilipino]

I'm thinking that closing up the bottom of the transmission tunnel might have a significant effect on torsional stiffness. Our convertibles have a nice thick plate for a small portion but I think closing it up as far as possible would be even better.

I looked around the house for a paper towel tube but could only muster up a toilet paper tube. Anyway, as a far from perfect experiment, I drove pencils through the sides of the tube at each end so I could twist it without crushing it. Then I cut out part of it length wise, leaving a small section to simulate the brace. It was much easier to twist. Removed the brace, forget about it. Taped in all sections and torsional stiffness came back.

 

[CochinoFilipino]

Another idea I have is to install some type of bracing from the cowl, right behind where the export brace attaches, to the transmission tunnel. I haven't much thought into it, but I'm thinking tubing with some sheet metal shearing. Nothing invasive, it should be able to hide behind the console. I don't even know that he firewall/cowl flexes much. But it looks as though it would.

 

[MitchGT]

I can say with certainty that the x-brace helps. I can jack up the back and the front tire lifts as well, and it doesn't sag anywhere near as much as it used to. Then again, I put in the subframe connecters and x-brace at the same time, so the improvement was from both. It doesn't weigh much or cost much, and the brace has more ground clearance than my headers, so why not do it?

 

[mxhotshot]

http://www.stangnet.com/mustang-forums/723029-torsional-rigidity-test-67-coupe.html