napacruzerc5

Just installed a Brey-Krause harness bar on my 2001 C5 coupe. SOTP feels like it added some stiffness to the chassis. Feels like it tied the B-pillars together. My imagination or does this thought have merit?

Armycop

SOTP is correct. The harness bar ties the car together somewhat. Body flex is reduced, and the car feels tighter in turns. I discovered that too with my B-K bar the first day on Waterford. Then I pitched it into the sand trap...! When I remove the harness bar, the car feels 'wiggly' again. (there's a racing term...'wiggly'..)

AU N EGL

When I put my BK bar in and with my Ultra-Shield seats with the seat backs bolted to the Harness bar, I can grab one of my seats, shake side to side and the whole car shakes.

varkwso

your whole car shakes when it sees you walk up...

BrianCunningham

The SCCA used to make you put slip fits on them so they wouldn't stiffen the chassis.

Stupid rule, but it does tell you how much they stiffen just about any car up.

Wayne O

I have a B-K harness bar and I feel it helps increase rigidity. The beefier tunnel plate also helps. I plan on installing a roll bar/cage in the near future primarily for safety but the additional benefit will be to tighten-up the car.

ptindall

I felt nothing adding one to my C5Z06. Maybe it's just me or maybe it's due to the Z06 already having the 'vert's brace right under where the bar goes.

trackboss

A harness bar may take away some nvh(noise, vibration, harshness), but I guarnatee you it does not stiffen up the chassis. Put it on a chassis jig and twist before and after. The torsional stiffness will not change. Its just along for the ride. Even a simple 4 point roll bar doesn't do anything for stiffness. Both of those items are built for installing a harness on a car without a proper cage. The roll bar adds some roll over protection. Absolutely nothing more. If anyone thinks it does they have been fooled. In order to properly stiffen a chassis a proper structure needs to connect all the critical points of the bare chassis. It has to be done with triangulation and sheer panels.

RAFTeRACER

Guarnatee or not i disagree! And what is a guarnatee? any relation to a Manatee? Many people have said their car feels stiffer with a harness bar. I know my car was stiffer with a welded in 4 pt. roll bar. Of course not the result you would get with a full cage but certainly improvement. Besides I'd certainly have more fun putting my **** in the seat and feelling the chasis than setting the car up on a jig.

trackboss

And what makes it feel more rigid?
Trust me, it doesn't do anything for chassis rigidity. I'll bet real money on it. Connecting b-pillars to themselves does nothing. The imortant parts of the chassis will still flex.

69427

I spent several months modifying a C3 frame to improve the ridiculously low production torsional stiffness value, even doing some modeling (one of the test iterations pictured below), and was amazed at what it took to stiffen things up. After each change I put 2000 ft-lbs (or pounds-feet, if you prefer) of torque on the actual frame, and measured the torsional twist. It convinced me that it takes more than one bar, or even a four point cage, to significantly stiffen up any frame.

trackboss

Simple models are great to prove things like this. I simply think many don't understand. They often confuse NVH with rigidity. A single stiffener can make a difference if done correctly. However, it is true that an entire system needs to be designed and implemented in order to produce a positive result. A simple model to prove proper design is to take four popsicle sticks and glue them at the ends to form a box. Clamp one to a table to hold the box up then push on a top corner towards the opposite side. Do another one with an additional stick glued in the middle. Then do a third one with the additional stick glued at two opposing corners to form a diagonal. One will find that the second example really doesn't do much. The third example triangulates everything and makes a noticable difference.
Another thing to point out is that if stiffening is done it must be done all the way around to work well unless there the chassis has a weak spot. If you made one end of the car extremely rigid with something like a roll bar (it would have to be a very elaborate one) then more stress would be put on all the other components (when driven hard) and possibly break something as well as reduce handling performance. Anything is only as strong as its weakest link.
Personally, I'm just passing on information that I"ve learned over the years from building real race cars and actually racing them. I don't give all my information away for free, but if I am attacked with information that is purely subjective I might as well not help anyone.

napacruzerc5

Wow. I sure didn't expect the later responses. I liked the early one better since they agreed with my SOTP analysis. I don't care!!! I'll never put in a full cage in my C5 and I'll go on believing that it feels stiffer...that too

69427

Whatever. Remember though, there's a reason they call them "laws of physics", rather than "suggestions of physics". But hey, it's a free country. Believe what you like. Some of us (I'm a design engineer) just prefer actual data.
(The above comments are not intended to sound rude. They're just my opinions. The fact that you drive your car the way it was meant to be driven (hard and fast) puts you in a rare group of Corvette owners. I respect that.)

napacruzerc5

Thanks. I'm not trying to debunk the data. I'm just happy with my SOTP feeling. And I'll enjoy my C5, stiff or not.

The Void

What are you opinions about all of the billet tunnel plates that claim to increse rigidity? You sound like you are knowedgable about the c5 frame. What would you suggest sans the harness bars and roll cages?

RedLS1GTO

You are a design engineer... ok, so am I. I honestly have never looked at any sort of analysis of a C5 Vette with or without a bar between the pillars, but the people saying that a single bar can't add torsional support are simply wrong. Why do cranes, towers, and any other similar structure have as many lattices as they do? A majority of those lattices are not load bearing in a static environment but when it goes dynamic with wind, weight, etc. different lattices start to contribute depending on the force, blah, blah, blah. Statics/Dynamics 101 which I'm sure I don't need to explain any farther.

Is a single brace going between the pillars enough to give a NOTICEABLE difference? I certainly have my doubts about that, but I'm guessing that it will certainly add something.

trackboss

triangulation is done for a reason so that cranes don't collapse. It increases dimension without adding a ton of weight as would a solid structure.
A-pillars hold the roof up and do not connect suspension pickup points. Just so we are all clear I myself have a harness bar. The only reason is to properly mount harnesses on a street vehicle that I take to the track.
I have a tunnel plate that has been sitting on my bench for almost a year. Only reason I have it is so that when I install headers (soon) I can replace my original one with the coated one I have to reduce heat in the cockpit. I got the lightest one I could find. I could have used heat insulation, but it ended up costing more and the plate is simpler as well as cleaner to install. Kinda like wrapping headers vs. coating them. The only time can see an aftermarket tunnel plate stiffening anything more so than the factory one is with a side impact and even then the outer frame rails are really only tied to the inners at the ends (with the exception of the wood floors) so the plate wouldn't be all that effective. It most likely is a NVH thing. Venders who advertise the thicker ones as adding stiffness to the chassis are fooling the customers. Suckers are out there.
Personally, if something gives you the impression that you are benefiting from it and that makes you happy then go ahead and do it. Nothing wrong with that. I just have seen so many be completely brainwashed that something works as advertised when it really doesn't.

BEZ06

Why exactly did they solidly attach the roof on the C6 Z06?

Everything I've read says that it was to add needed rigidity to the structure because of the aluminum frame.

If the roof just sits on the pillars, you're saying that it can't add any stiffness.

If the roof can add stiffness to the structure by just tying the pillars together, why can't a solid bar between them do the same?

Bob

The Void

For the record I am not trying to start a pissing contest. There are alot of 'upgrades' out there for these cars. I am just doing the research to make sure I am speeding money on results and not perception. Sometimes it feels like alot of stuff done to the cars is just keeping up with the Jones's.

I have not heard many people on here dispell the tunnel plates effectiveness and I am glad to hear a dissenting opinion. I would challenge you to post back after you install the plate with your first hand experience. I am always reading, so either way it turns out I'd like to hear the follow up.

I wonder if it is more of a game of inches. Hard to quantify all these small things but as a whole they begin to add up. Thanks again for the responses, you can never know too much.