WVRx7

So you believe that the chassis is flexing enough to change the cornering attitude?

I'm shocked that so many people believe that their beloved FD3S is a "wet noodle" utterly devoid of a proper chassis.

The upper strut bar is there solely to control maybe a 64th to a 32nd of an inch of deflection that may occur in the upper suspension towers due to heavy loading.

There is simply no way that an upper strut bar will have any effect on body roll or cornering attitude. It can't happen, the two items aren't in any way related and it is silly to believe otherwise.

If the chassis were to experience flex sufficient to trigger body roll then the fenders would be rubbing the doors, the hood would hit the windshield and the nosecone would fall off.

mibad

No way did I imply wet noodle. The car is a great handling car. I'm just saying I can tell a difference in the cornering of the car with the strut bar on. This is about mass, momentum, inertia, gravity, velocity, geometry, etc. I'm not an expert and I dont claim to be, but there plenty of people that are.

"if your outer strut tower is deflected outwards 0.20" by this 333 lb force, then you just lost 0.5° of negative camber! If it deflects 0.42" you have lost a full degree of negative camber. "

That's from this web site http://e30m3performance.com/myths/St...bar_theory.htm

Shinobi-X

Quick question though (or Damon). I believe that some people tend to refer to the FD as if it were able to produce the identical numbers it was capable of over a decade ago, but given wear and age of the chassis on some of our FDs, would it (chassis flex) then be more of an issue, where the strut bar would have noticeable effects?

WVRx7

That data is going to vary widely depending on the design of the particular automobile.

In fact, in the case of the FD, the shock is the only item that would be moved by a deflected upper strut area.

The upper control arm in the FD is connected to the frame horn. It's not an area known to deflect from suspension loading.

In the case of the E30 BMW, they use the strut as the upper control arm and yes, if you move the strut inward, then there could potentially be a loss of camber.

It's simple. The effect of the upper strut bar is largely psychological. While it does contribute to a front suspension that is stiffer when it is in place, it is highly unlikely and illogical that a driver would be able to determine its presence (in a double blind comparison on street tires)

On DOT racing tires or Slicks with a trained driver that is familiar with the car, I could absolutely believe that a difference could be detected, but that would be at suspension loads far outside the envelope the car was designed to experience in normal use.

DamonB

All that link proves is that E30 BMW's flex between the shock towers. Aren't we talking about FD's?

You may also want to spend some time studying why shock tower flex is much worse for an E30 than it is for an FD. Namely because an E30 uses the strut tower on the chassis as a locating member of the suspension and the FD does not.

adam c

iTrader: (2)

I could feel an obviously apparent difference on street tires. This was easily detectable during moderate cornering forces on the street. I can't say for sure that the difference made the car faster in corners, but I suspect it has.

DamonB

Sure. An older car with lots of miles is going to "loosen up" over time; mostly due to metal fatigue. It won't break in half but it is there and it will get worse with age. But again you'll never tell the difference on the street except for maybe squeaks and rattles; surely not handling.

If the chassis were actually moving and flexing as much as some seem to insinuate large parts of the chassis structure would be ripping off the car over the years due to metal fatigue at the weld seams.

WVRx7

I can list several engineering words too, but that doesn't mean I am applying any of them to any part of my argument.

I am FAR FROM AN EXPERT as well, but I tend to stick with logic and experience. I shared my opinion which I gleaned from 10 years of ownership of an FD. I have well over 1500 Auto X events in my past, I have done track driving schools and lapping days for 8 years and I now instruct for BMW Club, Audi Club, Mazda Drivers, Porsche Club and I also organized a Skidpad Training School where we teach handling dynamics, car control and suspension tuning.

I probably have one of the only FD3s that has spent hundreds of hours on a 150 foot diameter skidpad doing laps to tune the suspension.

I have changed my front spring rate 50lbs and been able to determine the change. I have also forgotten to replace my strut bar and I never noticed.

Your opinion has value to you and that's fine. My statements are just opinion as well, but I do have a basis for what I said.

s-thetikz

iTrader: (1)

I'm going to have to go with WVRx7 and Damon on this. Just as when your car feels like it is going slightly faster when it has a loud exhaust as compared to stock, or when your handling seems better when your seat sits lower than stock, it makes sense that when this bar bridges a void in your engine bay, linking two sides to eachother, most people will feel that it makes a big improvement. it looks like statistics are going to be the deciding factor here.

adam c

iTrader: (2)

Is it possible that the suspension on "YOUR CAR" is so stiff that a strut bar really doesn't make any difference?

My car is a 94 PEG with stock suspension. 94's have softer suspension than the 93's, and much softer thatn the R1's. I can feel a big difference with a strut bar on "MY CAR". Does my car handle better? I think it does!

I will try to do a test at my next autocross. If I go, it will be next month.

mibad

What car we are talking about is not as important as the issue of whether the strut bar will improve the vehicle dynamics and I believe that link provides considerable evidence that it does. It's not all psychological, I can't say that there is no psychological effect since I do know when it's on there. As for the double blind test, I am certain I could pass it.

Shinobi-X

I don't think it makes much sense to dismiss the fact that they are different cars...otherwise the individual in your link, would have left it as a generic observation. If suspension geometry is designed differently, then you can't expect a strut bar to behave on an M3, in the same fashion that it would an FD.

Taking a look at the final portion of the link, it states:

In conclusion, some cars spend most of their lives driving in a straight line. Such cars might experience the strut towers moving together over time. Track cars spend a lot of their time cornering at over 1G. Thus a track car might see it's strut towers spread apart over the years. Thus a strut tower bar can be under tension OR compression depending on the environment that the car is operated in.

Some people may be getting caught up on what qualifies as "the street", but I doubt most cars primarily driven on public roads are regularly cornering at forces as described above. If someone chooses to corner harder than usual, in order to simulate "track performance", then in a nutshell, it only stands to reinforce what Damon and WV are stating. Track behavior, or setups will experience more flex, and thus make the strut bar necessary, while 'normal' street driving (which wouldn't warrant the attention of the law), apparently will not. Without evidence of the contrary, other than "feel", the logic is pretty solid.

WVRx7

Your question is valid, to a point.

Unfortunately, your question is a perfect example of the complete misunderstanding of chassis dynamics at play here.

The car could have shocks and springs like concrete and it wouldn't make a bit of difference. If how stiff the suspension was made a difference then the car would be deflecting and folding up on itself simply from being parked (supporting its own weight on the suspension assembly)

The only thing that could cause deflection of the upper strut area is significant loading from the suspension. I simply believe that street tires cannot provide enough grip, for long enough periods of time to introduce measurable levels of deflection.

Even if there were measured levels of deflection of the upper strut area, I don't know how it would contribute to an erosion of handling "feel" in the FD.

One of the things that is so perfect about our cars is the upper and lower control arm front suspension. The shock is the only thing in the upper strut area and it mounts to the lower control arm in such a way that it could be moving around like a straw in a water glass on top and it wouldn't so much as notice the movement at the bottom.

OTHER CARS, like 98% of all cars manufactured today use the strut assembly as the upper control arm. Most of those vehicles can find marked improvement in rigidity from using an upper strut bar. ALL of the suspension loading is transferred straight up to the upper strut area. That simply isn't the case with the FD. We are lucky to have a REAL suspension with dynamics designed in to eliminate the kind of chassis flex that you see in traditional cars.

I am not trying to make enemies but I feel that much of this thread is a terrible disservice to the simply amazing chassis that that we have in the FD. A casual reader stumbles upon this crap and then goes on other forums telling how an Rx7 requires a $50 dollar pipe over its engine or it flexes itself to death.

DamonB

You're nuts. This discussion is particular to the FD.

Without a controlled test it's useless as you'll still only be left with your personal opinion. Without real data you'll tend to "prove" to yourself your original opinion was correct (no matter what it was to start with). I'm confident I'll be able to tell a difference in the car with and without the strut bar and I'm confident I'll prefer the car with the bar in place but I don't think I'll be able to see a difference in the numbers recorded.

adam c

iTrader: (2)

Damon,

Perhaps my original question should have been: Is the FD "better" with a strut bar? The obvious answer is YES. Of course, that question may not have provoked an entertaining discussion .

Does it handle better? That remains to be seen .

BicuspiD

FWIW I worked on a friends FD and did not put the STB back on - (I thought I'd have to take the UIM off again and wanted to save time) I wound up not having to remove the UIM again, but forgot to reinstall the STB..

Took my friend 3 days of driving until he called me and said "Wheres my STB?".. He didn't notice it instantly, and it wasn't until he actually opened the hood to check the oil on a fillup that he noticed it was gone! So take that with a grain of salt.. Big grains of salt..

jayk

This proves nothing, but at one point one of the ball joints in my r1 strut bar was loose, when I cornered even lightly you could hear it flexing up and down. It would make this kind of ticking sound as I cornered. The ends of the strut bar were bolted down tightly, just the adjustable part in the middle was not. Took me forever to figure out what it was, but when I tightened everything up the noise stopped. So there are definetly forces acting on a strut bar in even light cornering. Whether it actually affects handling I think is probably impossible to prove. Whether it makes handling "better" is probably even more impossible considering the subjective nature of the word...

mibad

That's not what my psychiatrist says. He says the physical principles of the universe apply to everything in said universe.

adam c

iTrader: (2)

If your friend drove the car easy during that time, he would not have noticed a difference.

maxcooper

My 2 cents:

* You can feel the difference between with-bar and sans-bar on street tires. Mainly beacuse impacts are more harsh with the bar installed. But it also improves feel a bit. Your hands will fatigue faster on bumpy roads with the bar installed. This is my direct personal experience. For anyone who doesn't believe this, try it and see for yourself. I am fairly certain I could pass a double-blind test.

* I doubt that the bar will improve lap times or make a street car a more capable handler in any significant way. You get more feel, but it makes the car a little stiffer (= less grip). Neither effect is large. I call it a wash.

* The BMW has a mac-strut suspension. The FD has a double-wishbone suspension. The info in the BMW article do not apply to the FD. Specifically, camber does not change from deflections of the top of the shock on the FD.

-Max

WVRx7

I would agree with this. Max is a talented and experienced driver and I would wager he could determine if the bar was installed. In other words, I respect his opinion.

Personally, my experience is different, but I normally have one on my car for a reason.

adam c

iTrader: (2)

I get no respect

jic

iTrader: (1)

just slap on the strut bar and call it a day
forget debating

mibad

You're right. I did not know that strut bars are primarily used on macpherson struts, but if I didn't stick my newbie nose where it doesn't belong I'd never learn anything. I still believe that there is a noticible difference in the (stock) car's handling with the bar off/on and I agree with WVRX7 that Max Cooper is the voice of reason here. I think Adam c is correct in in pointing out that WVRX7's racing suspension would likely not be affected by the bar.
I wasn't questioning yours or WVRX7's expertise. You guys are light years beyond me, but I have to question your AuthoriTAY when I am certain of something I experience.
Do you believe the brace is just eye candy? More importantly should adam c be flogged for asking such a loaded question?

clayne

What does a strut tower brace have to do with body roll?