subrame braces

[johnl]

oneoffaccord, you may just want to let this one go, i did.
why trust the millions of dollars in years of engineering, stress analysis, statistical and experimental data preformed by Honda so they could build the best race cars and street cars.

because

engineering isn't anything compared to opinions!

You make lot of assumptions about the reasons why a particular chassis may be designed in the manner in which it is for a particlar market and particular purpose. There are a lot of competing requirements for a comercial chassis structure, some of which will be anti-thetical to the goal of producing a very rigid chassis capable of providing superior handling characteristics.

For the average punter a very rigid chassis is of no real importance, they'll never push the car to the point where it will make any difference to them, and they'll never notice it. On the other hand they will want the convenience of being able to fold down the rear seat back so they can transport the annual Xmas tree home. The manufacturer's aren't going to bother building additional rigidity into the structure when their customer's will be resistant to paying the additional cost, and won't care in any case if the chassis is just that bit more responsive and better handling, it will be more important to most of their customer base that the car has adequate cup holders.

Note that for Honda's 'Type R' models that additional bracing is indeed fitted to the car, because the customers purchasing the 'sportier' variants will want better response and handling and are prepared to pay for it, up to a point. Even so, the additional stiffening is still constrained by by practical and economic considerations, some additional stiffenening is simply impractical for road usage, some adds too much cost and weight for the possibly subtle benefits that may be gained.

A full roll cage is desirable for handling etc, but impossible to live with day to day (and probably not legal in many if not most markets), so isn't offered even if it does improve chasis dynamics. Other braces may also be beneficial, but the cost starts to add up, so aren't offered. Keep in mind too that weight and it's affect on fuel economy will also be considerations, especially on a car that is already fat with sound deadening, AC, power windows, power steer, auto box (which tend to be heavy), etc etc.

Just because a chassis is designed at X stiffness for whatever range of reasons can in no way be used as evidence that increased rigidity is in some way not a good thing. Your opinion is no more just an opinion than mine is, except that you seem to think your's is backed up by the "the millions of dollars in years of engineering, stress analysis, statistical and experimental data preformed", that you in fact are not privy to and thus have no insight as to why various decisions may have been made as to how and why the chassis was designed in the way it was for a particular market.

My opinion is backed up by the commonly accepted and well understood principle that chassis stiffness is a pre-requisite for a superior handling car chassis.

[johnl]

Lift of individual wheels is much less likely to occur on cars with stiff suspension rates and low CGs (e.g. 'formula' cars and sports prototype cars with high rates of downforce), though such cars may still have a significantly different roll stiffness front to rear in order to assist IR traction.

Was watching the A1 GP race from New Zealand last night and paying particular attention to inside wheel lifting.

What I noticed was the IF actually occasionally coming off the ground at mid corner through exit (i.e. daylight under the contact patch), whereas I saw no evidence at all of IR lifting. This characteristic was evident with most cars on the track, maybe all. This was most evident on corners with some bumps, i.e. the bump would cause a momentary flash of daylight to be visible under the IF tyre (but not the OF, OR or IR).

On corners where the track was smooth you could sometimes see complete IF lift, but easily see partial IF unloading where the tyre was only contacting the track on the inner edge of the tread with no visible lateral or vertical deformation of the tyre casing, but the IR seemed well panted with visible sidewall deformation.

This might not be surprising as the car is exiting a corner under hard acceleration with a resulting strong rearward weight transfer, but the affect was also quite visible at mid corner before any hard acceleration would be possible. This strongly supports the idea of front roll stiffness being significantly higher than rear roll stiffness (in order to improve IR traction), even on stiffly suspended high downforce cars.

[19dabeast85]

Don't forget that with a full tank of gas we have an ~100lb dead weight behind the rear wheels that must create some pretty strong side forces when cornering, thus the desire to have a trunk "x-brace" to keep the trunk floor from flexing. Whether it is cost effective for daily driving is probably up to the personal benefit you feel from it.

My thought on chassis stiffness: If I have a pretty good idea that it will increase handling (using my geometry/physics knowledge along with professional research and others' experiences), and it won't significantly increase weight or decrease usability, then I go for it because I know that if I ever get into a wreck (especially those with sideways impacts) chassis/suspension braces will help keep my car from completely collapsing on me. FWIW

[GreenMadness]

i haven't been reading post longer than the persons information on the left, but 19dabeast85 i did read yours, thats exactly what you should do. Take everything you read from another person on here with a grain of salt. Use your own tools, hopefully some physics based ones to make your own judgement call and then evaluate what YOU want, and see if it seems resonable.

The OP wanted to know a simple question of a lower tie bar, most would say its a waist. But if when he got in his car, knowing he had that bar made it "Seem" more fun to drive, than who is to rain on his parade.

We are all here because we want to have fun in our CB7's... now if it comes from beating STI's in a drag.... or out cornering BMW's on a track... or just having all your friends crawl under your car and say "DAMN THAT IS PIMP"

AND that is a ture matter of opinion.

[Ronald_Type-R]

id love to have a rear x-brace like oneoff posted. my only thing is that for me to ever install it, the X part would need to be removable, with the strut bar being permanent.

[johnl]

Don't forget that with a full tank of gas we have an ~100lb dead weight behind the rear wheels that must create some pretty strong side forces when cornering, thus the desire to have a trunk "x-brace" to keep the trunk floor from flexing. Whether it is cost effective for daily driving is probably up to the personal benefit you feel from it.

On the CB7 (and I assume at least some other Accords and Civics etc) the fuel tank isn't behind the rear wheels but directly in front of them, and entirely within the wheelbase. This is nice enginnering oh Honda's part, meaning that the difference in handling between a full tank and nearly empty will be minimal compared to a tank hanging out the rear of the car. As a result a trunk mounted X brace won't do anything to lessen chassis flexure caused by the weight of fuel in the tank.

Having said that, IMO a trunk mounted X brace is one the more worthwhile braces that can be used, as it resists lateral loadings seen at the tops of the rear strut towers and at the upper suspension mounting points. A rear strut bar does this too, but only braces one tower to the other, but neither tower is triangulated to a lateraly rigid part of the chassis, which is what the X brace does. The trunk floor section of the chassis is hugely stiff laterally, much of this stiffness coming from the box sections that run longitudinally under the floor, but also simply because of it's shape acting as a stressed skin in shear loading, even though the wheel well compromises this to some degree (less than you might expect).

My thought on chassis stiffness: If I have a pretty good idea that it will increase handling (using my geometry/physics knowledge along with professional research and others' experiences), and it won't significantly increase weight or decrease usability, then I go for it because I know that if I ever get into a wreck (especially those with sideways impacts) chassis/suspension braces will help keep my car from completely collapsing on me. FWIW

You mean a trunk mounted X brace? If so then I agree (as above). My objection was to the stiffening effectiveness (or not) of the 'trunk wall brace' and 'trunk floor brace' that are simple straight bars fitted inside the trunk but at the extreme rear end of the trunk near the floor. These are simply not located in a position that will make any real difference to structural stiffness, i.e. any stiffness they may contribute is laterally in compression / tension through the bar, in an area that is already laterally rigid.

Keep in mind that for handling purposes 'stiffness' means the chassis' resistance to twisting between the axle lines, i.e. within the wheelbase. Most of this stiffness will come from that part of the structure that is physically located within the wheelbase, including that part between the strut towers at each end. This isn't to say that any part of the structure in front of or behind the axle lines will have no affect, but the further away from the axle lines the less stiffeneing affect will exist from those parts of the chassis (largely limited by the lateral stiffness of the longitudinal parts of the structure that connect the rearward or forward parts of the chassis to section within the wheelbase, and the longer these longitudinal parts are the more lateral flexure they will have).

For side impact protection, the only thing you can add that might make a difference to your safety is a side intrusion bar, that would usually be part of a full cage. Other stiffening bars that might add longitudinal stiffness (e.g. a trunk X brace, or a front subframe brace) could conceivably impair the 'crashworthiness' of the chassis due to adding too much longitudinal stiffness / strength (keeping in mind that stiffness and strength aren't necessarily the same thing). This means that the forward and rear 'crumple zones' may not work as effectively, though I'd think any real difference likely to be minimal.

You DO want the front and rear sections of the chassis to "collapse" in an accident. If they don't then more of the impact loading will be transferred directly into your body, with resulting higher likelihood of injury or death.

[johnl]

i haven't been reading post longer than the persons information on the left, but 19dabeast85 i did read yours, your
AND that is a ture matter of opinion.

So, if someone disagrees with your opinion you'll no longer bother listening to what they have to say? That says a lot.

[GreenMadness]

its not that, i said once that we are going round and round with the same words. then you tore apart what i said... still maintaining the same point.

so in an effort to get back on topic with the original poster wanting a rear lower tie bar i dropped the debate, i would love to continue in a new thread because it stimulates thinking and good information for anyone reading, but i doubted the person that was wonerding about the tie bar even visits this now that its full of info he didn't want.

[johnl]

its not that, i said once that we are going round and round with the same words. then you tore apart what i said... still maintaining the same point.

so in an effort to get back on topic with the original poster wanting a rear lower tie bar i dropped the debate, i would love to continue in a new thread because it stimulates thinking and good information for anyone reading, but i doubted the person that was wonerding about the tie bar even visits this now that its full of info he didn't want.

I don't want a fight. We do seem at least to be misunderstanding each other, or maybe it's just me misunderstanding you, but I do find deciphering what you're saying a bit difficult sometimes.

I don't agree with 'keep it simple'. If the thread heads off down a more difficult path then IMO that's fine so long as it's not really going off topic. The OP can take what's useful to himself / herself and leave the rest, but then the OP isn't the only reader and not the only one who may find a more in depth exploration of interest (or not).

[johnl]

Who ARE you? that is the last long winded, pompous post I think I can bear to read. This thread is 2yrs old, and here you come with a bunch (and I mean a bunch) of over protracted thoughts/opinions blah blah blah blah..

Well don't read it then. And who the hell do you think you are???

The age of the thread is immaterial.

You seem to think things should always have an easily digested simplistic two sentence explanation, but the world just isn't like that. My posts may often be long, but I'm not trying to 'keep it simple' for the sake of being simplistic, I'm often trying to explain fairly complex things as I understand them as clearly as I can, and this often can't be done in a few sentences without the 'explanation' being misleading due to ommission.

If I read a post that I know (or strongly suspect) to be a misunderstanding of reality, then I have every right to reply explaining my understanding to the best of my ability to anyone who cares to listen, and not to then just abandon my opinion because someone disagrees either with no argument or an argument based on faulty assumptions or interpretation of fact (and yes I am opinionated in that I have opinions, but I don't have a closed mind and am open to changing my mind when presented with a well argued contrary viewpoint).

What was posted about the rear lower subframe on a CB/CD is TRUE
it is a Stout structure, it is constructed of High Strength Steel,
I know this because I have first hand experience of trying to repair the item.
A hit from an Expedition cause almost the entire rear of the car to crush,
while the Rear suspension section of the car remained NOT ONLY square to the frame, but parallel to the ground.

I don't doubt that the structure is "stout" and strong, but strength does not necessarily equate to stiffness, which is the point I'm trying to get across to people like you (and others with more open minds) who apparently have no understanding of the difference. This is very basic engineering, and if you don't understand it then I suggest you refrain from commenting quite so stridently, your ignorance is showing.

You need to think ALOT more before u post. I grow tired of clicking
on a thread that seems intersting, and then finding that you have verbally shit all over it. I'm not starting a fight either, It's just my opinion, in a thread were only FACTS matter.

You certainly sound like you want a fight, why else the rude and personally abusive content of your post? I would suggect that it is in fact you who need to think a lot more before you post, you obviously don't understand either what you're saying nor what I say.

....I think i'll shut up now.

I think you ought to before you embarrass yourself further. Do yourself a favour and grow up.

[HenRoc]

ok and the moral of the story is...?

But aside from that, if anyone who's looking to stiffen up the chassis I would tend to think that you would want to focus on the critical sections of the car.

1. The front shock towers because as we all know, that front end of the car flexes more and more over the years because of the insane amount of weight up front.

2. Center or 'B' pillar - This where rigidity is lost over the age of the car because of all the turns and rolls the car takes over the span of it's life. There are floor braces but thats just bracing the floor. Wouldn't an owner want the bar to be a bit up higher say at the center in between the B pillars?

Unless you can make a brace such as this:

---------

/ \

Basically my little font rendered sketch shows the pillar mounted horizontally across the car with anchors at the mid section that bolt to the floor.

3. Now I don't really get the point of the upper C pillar bar but just common sense would tell you that direct behind the passengers and above their heads wouldn't really flex as much except for the rear shock towers. (Correct me if I'm wrong here)

Again it's all in the matter of physics. You can take a thin plastic film and twist it, most of the stress would be in the center of the plastic film, while it is allot different from an automobile you can get the general idea. (refer to 2)

So as I said before concentrating on the three primary sections of the car, with enough ingenuity you could probably make a perfect handler.

[johnl]

I did understand why you posted.
Now you do have a fight. The point I am trying to make is that
#1 u need to shut the fuck up
#2 I'm just as intelligent as you are, but would rather not have to scroll
through half a fucking page of what amounts to bullshit
and good showmanship, I dont know how old you are, or where the fuck you are from, but you're pissing me off.

I don't give a rat's arse what you want or what you "need", and you aren't the only reader of these forums so don't presume to speak as if your opinion of what I write is the only one that matters.

I have no idea how intelligent you may be, but you aren't displaying much evidence of it. Frankly you are incredibly rude and unecessarily abusive, which is no substitute for reasoned argument. If you don't agree with what I write then by all means feel free to put forward a thought through counter argument questioning and / or refuting my statements, but since you're attempts so far are frankly pathetic to non existant I won't be holding my breath...

The attitude in almost every post you make is "holier than thou" do you know what that means?

Your attitude seems to be an assumption that you have a superior understanding and intelligence than I do ("do you know what this means?" is a feeble attempt to question my basic intelligence) and back this up with insults but no significantly reasoned thought.

My attitude is that of someone putting forward an argument intended to clarify ideas put forward by others that are IMO misinterpretations of the reality or just plain wrong. I place my reasoning out there in an attempt to substantiate why I think this to be the case, which is far prefferable to simply disagreeing with no credible attempt at explanation as to why I think what I do.

If I disagree with something then it's hard to seem as if I'm not disagreeing, which isn't meant to imply either stupidity on the part of others or superiority on my part. You can choose to interpret this as being 'holier than thou' if you wish, I can't do anything about your misinterpretation.

All I want to see happen is for you to think about your audience. This is a Honda forum dude. We are NOT
engineering jet fighters here. the man simply wanted to know if there where sub frame braces available commercially.

You seem to have a low estimation of the intelligence of the people who read this forum. "The man" wanted to know something, others made suggestions, I put my 2c worth in (OK, so maybe it's worth a lot more than that to some people if not to you!) to explain why I think some of the products suggested were not really effective while others were. 'The man' now may or may not have a better basis for making an informed decision as to what to fit to his car.

The nature of forums such as this isn't merely to allow simple black and white answers (often conflicting) to questions particular people may have, but also to allow discussion of matters arising that may be of interest to more people than merely the original questioner. Discussion can on occassion become more theoretical to more fully explore the factors involved, and so long as the discussion doesn't veer wildy off topic then there's nothing wrong with this, it can actually be helpful to people's understanding.

With that being answered, the next question would be to the actual twisting strength of the rear and front sub frames of the vehicle, Now, Mr. Engineer, do YOU work in a body shop? Have you ever had to apply well over a metric ton of pulling force to a CB subframe? I've put well over 25,000 PSI of pull on a CB rear frame only to have my hook slide out and shatter a taillight.

The front and rear subframes are substantial and stiff members (as your experience suggests), and the rest of the structure at the front and rear ends may also be quite rigid in certain directions, but aren't nearly so rigid in others and really it's here that the problem lies.

It may well take a great deal of force to alter the plastic shape of the subframe members (especially if the 'bent' member is still attached to other structural parts of the chassis, in which case at least some of the deformation is likely not in the subframe itself), but before this point is reached a significant amount of elastic deformation will occur.

The chassis is like a metal box with a more or less open end at the rear (and similar but less so at the front between the strut towers). You can stiffen the analagous box structure up somewhat by welding in a decently rigid beam at the bottom the rear (or front) opening, but no matter how rigid this beam may be it's affect on the totality of structural stiffness can only be so much, the remaining three inadequately supported sides will still flex in torsion unless thay are adequately braced (and to the subtsantial subframe is a good place, among others).

I just would like to know where your knowledge comes from? Do you actually have real world experience, or are you just some dweeb behind a keyboard?

There you go again, unecessary rudeness as a sad substitute for argument.

To answer you're question (though you don't really deserve a reply, I don't have to justify myself to you); Years of practical experience, reading and study, and carefully applied thought. I'm not a qualified engineer, but neither it seems are you. Don't make the mistake of thinking that experience working in a body shop qualifies you to properly understand structural engineering, which isn't meant to imply that practical experience isn't a very worthwhile thing to have.

But I would like to try to make some of these braces at some point in the future....See if they make a difference.

Well I have made some of these braces and I do know from practical experience what affects what I've done to my car has on my car. This can be extrapolated to cars with a simialar basic structure. I've also built an entire space frame chassis for a sports racer and substantially modified another, and studied / thought hard on what affects of bracing / triangulation design in certain parts of the structure will have on overall chassis stiffness.

A space frame isn't a unibody construction, but the forces that act between the axle lines still need to be resisted by members arranged in stategically thought out manner to achieve adequate rigidity (stiffer is always better), and in many unibody stuctures some of these elements are often absent or compromised by other factors / requirements.

This understanding can be brought to bear when judging the likely benefit or otherwise on chassis rigidity of particular commercially available chassis stiffeneing braces on overall chassis stiffness. Some are very worthwhile, none are utterly useless, but some have minimal real affect.

[johnl]

But aside from that, if anyone who's looking to stiffen up the chassis I would tend to think that you would want to focus on the critical sections of the car.

1. The front shock towers because as we all know, that front end of the car flexes more and more over the years because of the insane amount of weight up front.

My experience and thinking suggests that the rear end is typically (with many chassis but not all) also problematic as far as stiffness is concerned, despite weight at the rear being less. The problem exists from new due to the design, and may or may not get significantly worse over time depending on the chassis.

For rigidity to lessen over time then the spot welds would need to start 'popping' or the sheet metal actually fatigue and eventually start cracking. If a particular chassis design never seems to have cracking problems in old age then this probably isn't much of an issue for that design.

2. Center or 'B' pillar - This where rigidity is lost over the age of the car because of all the turns and rolls the car takes over the span of it's life. There are floor braces but thats just bracing the floor. Wouldn't an owner want the bar to be a bit up higher say at the center in between the B pillars?

I would expect so. Such a bar would typically be part of a full cage, but on a road car such a bar might be a bit hard to live with, or even illegal in some places...

[QUOTE=Accrdkid]3. Now I don't really get the point of the upper C pillar bar but just common sense would tell you that direct behind the passengers and above their heads wouldn't really flex as much except for the rear shock towers. (Correct me if I'm wrong here)

IMO the towers are likely to be the most important part of the rear stiffening with a strut bar, but keep in mind that this only braces one tower to the other and if both towres are subject to flexure all you've done is brace a flexable part of the chassis to another flexable part (which will reduce flexure so is a good thing). For max rigidity you should triangulate the towers to a more rigid part of the chassis, or fully triangulate between the towers.

Again it's all in the matter of physics.

If you can look at something from the perspective of first principles and ask youself "what sort of forces must be involved and what will X actually do with these forces", you can answer a lot of questions for yourself.

So as I said before concentrating on the three primary sections of the car, with enough ingenuity you could probably make a perfect handler.

A rigid chassis alone won't ensure a good handling car, but within the constraints you're forced to work with you can make the best possible basis for a "perfect handler" (keeping in mind that no such thing actually exists).

[johnl]

Ahhhhhhh Touche' Sir! well played lol.
dude chill man, I like messing with people, dont get so worked up!

And the contents of your PM:

LOL damn dude. I was just checking.
in the time I've been a member here you are one of the few to display such knowledge....I just had to know,
and I wanted to do so in the most immature way possible. Thanks for humoring me.
No Hard feelings?
I feel bad, like I hope I didnt actually offend you dude.

You seem to be claiming to have been playing some sort of childish game with me. I have to wonder why you would bother. It's only a game if all the players understand it to be one. I don't understand how you can think your comments could be taken as being other than quite offensive and then imply surprise that you did piss me off. Frankly I think it more likely that you're now feeling a bit embarrassed and are attempting to cover your arse.

You now seem to be attempting an apology, which I'll accept on the basis of 'forgiven but not forgotten'.

PS I apologise for posting your PM to me, but since it was you who decided to conduct your 'game' in public rather than privately I do feel justified.

[oneoffaccord]

http://jspec.com/ekrearbars.html