Hey guys, i posted this in the fabrication forum of honda-tech, but i think alot of the people here in the RR/AX will be able to give me much better, more educated/informed feedback on my design, please have a look and let me know what you think.

Im designing a rear brace to siffen things up in my civic hatchback for track fun, while being easy to install and remove before and after the event. Let me know any thoughts you have, i plan on producing 3-4 to start with, too see if they'll sell.
Cheers

https://honda-tech.com/zerothread/1974632


Modified by Muzz at 8:18 AM 5/5/2007

 

That brace will effectively throw you out of any class most autocrossers participate in. Road racers already have a full cage. HPDE'ers really don't care about speed. i.e. your market is minuscule.

Edit: I see you're in australia, so I'm not sure how classes are formed there...best advice I can give would be to consult a rulebook.


Modified by rice r0cket at 9:54 AM 5/5/2007

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rice r0cket &raquo;</TD></TR><TR><TD CLASS="quote">That brace will effectively throw you out of any class most autocrossers participate in. Road racers already have a full cage. HPDE'ers really don't care about speed. i.e. your market is minuscule.

Modified by rice r0cket at 9:54 AM 5/5/2007</TD></TR></TABLE>

Thats correct, sorry i wasnt really clear to start with, if i were to sell these units they wouldnt be marketed toward the RR/AX crowd, as youve mentioned the market truly would be miniscule, especially here in Australia. I doubt id sell a single one.

I can see the potential buyers being much more the type of people who take their daily driver cars to the open track days here (99% of people here on the local honda site dont compete in motorsport, a very small few do, many do "track" their cars though), classes for the open days are usually based alone on engine cylinders, or displacement with turbo/nitrous bumping you into the next catagory.

The majority of cars are filled up with pillar braces and the such, with the majority of people thinking that every bit of stiffness cuts a chunk out of there laptimes. A piece like this would be a dream come true to the guys like this.

Theres also a ton of people who seem very concerned about there pride and joy's chassis being beaten and flexed around by running stiff springs/coilovers. Many feel the bracing the chassis will stop it from stressing over time and keep it from developing bad creaking noises, as it ages. Then theres the type of people that purely enjoy driving somthing a little more stiff and solid, probably why the majority of modifyied hondas here have pillar braces/tie bars/strut braces etc..
Alot of people strip the rear seats from there road cars, so i can see quite a few that would definatly look into purchasing somthing like this over the usual pillar braces etc.

Anyways im not really doing this to make money, id get a huge kick out of designing my own parts, i think a nice quality brace would be the best simple starting point. Id really enjoy the experiance, and get alot of satisfaction out of accomplishing it. Ill only make another 3-4 when i make mine up, im sure i can get rid of em over time.. Depending on how fast they sell i might make a few more for some spare cash. If it takes a while to get rid of them i wouldnt bother.

Im really just more interested in what people here think of the design. To me, with my short time studying mech. engineering it seems to me that bracing the rear in this way would increase the torsional resistance to twisting much much more than b/c pillar bars and strut braces, infact most braces at the rear short of going with a half cage.

Im hoping to get opinions from people with more experiance in this area. It seems odd that there have been millions of useless braces made, yet i have never seen any made like this which seems alot more effective in my eyes than most braces. Am i thinking wrong, and it wont be much more effective? Im thinking it will help hold the rear struts much better, and cut out quite alot of torsional flex from the b pillar back. With a bar between the struts aswell like a strut brace, flex in all 3 dimensions at the strut towers will be reduced alot..

Thoughts on the design Im here to learn.

 

All that bar is going to is slow you down with the additional weight of the bar. The rear end of the car is basically dead weight just following the front end. All that bar is doing, is making the dead weight heavier.


Edit typo



Modified by Another Drew at 4:41 PM 5/5/2007

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by http://www.importtuner.com/tech/0510...sion_products/ &raquo;</TD></TR><TR><TD CLASS="quote">

Saikyo Rear Tower Bar
Similar to the Saikyo front tower bar, the four-point rear bar is a solid, one-piece design with no moving parts or bolts. The AE86's factory design makes it difficult to stabilize and reinforce the shock towers and rear. The Saikyo four-point rear tower brace ties in both sections of the rear chassis to increase stability. We asked Taka Aono (the former SCCA Solo2 champion, and Formula Drift and Drift Association member) what the advantages are when using a rear tower brace. "A Hachiroku using a four-point tower bar and one without becomes apparent--even more so on hatchback-style vehicles sporting JDM bumpers. Those who drive through the canyons or drift with no rear tower bar have, or will encounter, what I like to call the 'ghost in the car.'" Relax folks; it's not an actual ghost. Aggressive cornering on twisty roads such as touge causes the vehicle's dome light to flicker on and off as if there were a ghost. The rear hatch moving and twisting along with the chassis causes the flickering, as the movement triggers the dome light.</TD></TR></TABLE>

I'm no engineer by any means, but I know what works with a general idea as to why.

This is the style of brace I ran in the back of my AE86 that saw alot of autocross. The AE86 is an extremely fleible vehicle. The design from Ueo tightened the rear up considerably in the case of the AE86. Of course, this bar put me in Street Modified (in our local events here and state, and some may see it on or crossing the Prepared threshold) but the benefit was a significant improvement in rear stiffness. It literally ties the strut mounts together, and triangulates to the rear bumper supports. That design allowed access to the spare tire well. I believed that if I could pull a brace from each strut top itself, and not the floor where the mounts are, it would be even better still.
This design effectively stiffens the rear floor making it resist deflection on more than just one plane as it covers more than just one axis such as your design. However, I cannot speak for the rigidness of the rear section on your application. Perhaps if you could build into your application, a process that tied to yet an additional rearward point, you would see remarkable benefits.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Another Drew &raquo;</TD></TR><TR><TD CLASS="quote">All that bar is going to so is slow you down with the additional weight of the bar. The rear end of the car is basically dead weight just following the front end. All that bar is doing is making the dead weight heavier.</TD></TR></TABLE>

I did not want to be quite so blunt as the individual is obviously young and making an effort to learn, but you did hit the nail on the head.

My advise to him might be to spend a bit more time understanding the engineering for the application and what it is going to actually do for the vehicle before you start thinking about designing a stiffing or strengthen device.

 

Just out of curiousity... if they do nothing, then why do so many manufacturers produce rear strut tower bars for FWDs?

How about the front strut? Are they worth having then?

 

why are their dozens of companies that sell pills they say will make your dick bigger?

cause people are stupid and they will waste their money on just about anything if they believe it will actually provide results.

 

A rear strut brace is a little bit different than this X bar type of suspension upgrade. I agree on a FWD vehicle the rear is just being pulled along and there is no need for rear reinforcement while going in a straight line.

On the flip side during high speed trail braking you will have rear flex between the strut towers. Tie a string between the strut towers and shoot a video camera at the string while road racing and you will see how much flex is happening. We did this with only a Autopower bolt-in cage installed and the string drooped enough to hit the floor of the car.

Our result was installing a strut bar and side to side cage enhancement. This provided a good amount of over-steer and gave back a couple of seconds per lap.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by cibola &raquo;</TD></TR><TR><TD CLASS="quote">the string drooped enough to hit the floor of the car.

gave back a couple of seconds per lap. </TD></TR></TABLE>

Drooped enough to touch the floor? Extra oversteer during corner entry gave you "couple of seconds"?

Please tell me you're exaggerating. Are you sure your chassis didn't have a major crack before you installed the bars?

EDIT: BTW, the "strut towers" aren't really strut towers. They're just shock mounts so the only loads that section sees is the vertical loads from the shocks. There are no control arms attached there, thus they're not "struts"


Modified by Another Drew at 7:51 PM 5/7/2007


Modified by Another Drew at 7:52 PM 5/7/2007

 

Yeah, that really sounds excessive. Just for kicks, I'm gonna do just that on my car, see if the string droops like that. I mean, just by physics, there'd have to be an incredible amount of flex/movement for the string to move that much. Like, the roof folding to accomodate it or something.

 

What did you tie the string to? I would assume tying to the top of the shock rod would show a good amount of movement, it mounted in a rubber bushing!

Did you tie it to, say, the top hat stud? That would be an accurate portrayal of flex back there.

 

The Civic chassis has a tremoundous ammount of flex. The whole body is held together with spot welds 3 inches apart. I did tie the string to the top of the shock where its threded and the string did touch the hump just behind the gas tank. It happened at turn 1 at pir which is a high speed dive bomb turn doing about 115-120 mph.

Nothing is cracked, nothing is bent, nothing is loose, the only thing that was bad was the rear trailing arm bushings were torn out.

 

well that test was completely skewed. You were measuring how much movement there was in the bushings. Redo the test with the string tied directly to a chassis point, not a point mounted to the chassis by rubber bushings.

That shock moves as the roads pulls/pushes the wheel. If your LCA bushings were worn, you would get even more movement. Redo this test with the string tied to the top hat mounting location, the same place the strut bar is mounted to. You will probably see a seriously limited amount of flex compared to before.

 

The design the OP linked are, well, not going to work.
Having four bars all pivoting off a central point is ok when the bars are being pulled. But at the same time they are being pulley, the perpendicular bars are being pushed, and could shove the center mounting point out of alignment, make it flex, etc. One single, solid bar would probably do a better job.
The other design, you have two bars that would be pushing and pulling at the center or another bar. The weakest part of the bar is the middle. The cross bar would flex like crazy. Going from the shock towers to the outside of the bar would be better.

But really, why not spend less money, have a main hoop, harness bar, and two rearward facing bars? A rollbar can also be tied completely to the B pillar, making it amazingly more strong.