STI flexible draw stiffener experience anyone?

[wparsons]

Originally Posted by norcalpb

The top chart is the 86, and the lower chart is an e46 on a track. Positive numbers mean the chassis is spreading apart, and negative means the chassis is spreading inward. The STi bar can prevent these motions, but what these graphs don’t show is when you hit a bump and part of the chassis moves up relative to the other. A stiff strut bar makes these bumps pretty brutal (looking at the Focus RS) but a bar that flexes during these kind of movements makes the ride more compliant, which can actually handle better over rough roads or imperfections on the track.

Are you suggesting that a horizontal bar is making the strut tower flex upwards less?


A bar with a pivot in the middle can also pivot when the suspension tries to push the strut towers closer together, I'd LOVE to see data like what grimspeed shows for the STI flexible braces to show how much movement there still is.



The whole point of chassis braces of any kind is to let the suspension do the work vs the chassis flex doing it.

The comment about the STI race cars using this is a bit of a moot point, their cages are already adding WAY more stiffness than any bolt on brace is. The braces like this are purely for show/marketing on the race cars.

[JIM THEO]

I don't think any aftermarket company did the same research on this chassis as Subaru nor have the same knowledge to produce focused on this frame products, yes STI products are overpriced but they are designed for this specific car to work in combination and together!

[gpvecchi]

I have the STi steering rack bushes, they are not so difficult to fit. It's very easy to remove the steering rack and press them in.

[norcalpb]

Originally Posted by wparsons

Are you suggesting that a horizontal bar is making the strut tower flex upwards less?


A bar with a pivot in the middle can also pivot when the suspension tries to push the strut towers closer together, I'd LOVE to see data like what grimspeed shows for the STI flexible braces to show how much movement there still is.



The whole point of chassis braces of any kind is to let the suspension do the work vs the chassis flex doing it.

The comment about the STI race cars using this is a bit of a moot point, their cages are already adding WAY more stiffness than any bolt on brace is. The braces like this are purely for show/marketing on the race cars.

Yes a horizontal bar will do its best to prevent vertical flex, but if it does it transfers all that shock to the other side of the car. Have a passenger in the car and a vertical bar will make nvh even worse but you are keeping the chassis in line which makes the suspension work better.

I have the controversial opinion that too much chassis stiffness can add discomfort even though it is letting the suspension geometry work in the most ideal conditions. I consider the V bars as part of the frame because I’d never run an 86 without them, so having slack in the chassis can add comfort.

[leevanf]

Originally Posted by norcalpb

Yes a horizontal bar will do its best to prevent vertical flex, but if it does it transfers all that shock to the other side of the car. Have a passenger in the car and a vertical bar will make nvh even worse but you are keeping the chassis in line which makes the suspension work better.



I have the controversial opinion that too much chassis stiffness can add discomfort even though it is letting the suspension geometry work in the most ideal conditions. I consider the V bars as part of the frame because I’d never run an 86 without them, so having slack in the chassis can add comfort.

Which is i think the intention if this STI “flexible” tower bar. It provides rigidity from horizontal flex, while the joint at the center prevents the shocks from right or left to transfer to the other side of the car thereby improving chassis rigidity during turns, while minimizing the side to side shock transfer.


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[leevanf]

Originally Posted by wparsons

Are you suggesting that a horizontal bar is making the strut tower flex upwards less?


A bar with a pivot in the middle can also pivot when the suspension tries to push the strut towers closer together, I'd LOVE to see data like what grimspeed shows for the STI flexible braces to show how much movement there still is.



The whole point of chassis braces of any kind is to let the suspension do the work vs the chassis flex doing it.

The comment about the STI race cars using this is a bit of a moot point, their cages are already adding WAY more stiffness than any bolt on brace is. The braces like this are purely for show/marketing on the race cars.

I think we can all agree that bracing and stiffness is not an absolute number, but a relative one depending on how much one considers is high in reference to a total car/chassis/mods. And also that an increase in stiffness equates to an increase in feel (discomfort).

I guess the intention of these STI parts is to *somehow* increase rigidity to a certain degree which may not be as large as we imagine - while minimizing the added discomfort that may come with it; ultimately not to be the one-all super stiffness upgrade.

The grimspeed one by virtue of being solid can add say +5 points of rigidty, but also -3 points of comfort. Netting out a net benefit of 2 points.

Perhaps what the STI is doing is adding +3 points of rigidity, but 0 points in impact to comfort, netting out a benefit of 3 points.

Thats how i arbitrarily see it )



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[JIM THEO]

...while the increase in rigidity makes the suspension to work better thus adding not removing comfort as all other solid bars!

[churchx]

Well, if "comfort" is less noise/vibrations, i guess some bracing (or tower bar as in this case) that reduces body flex will make car body to less absorb/dampen portion of those that goes to it, so probably "comfort" in such meaning might be reduced (and handling - enhanced, eg. car reacting sharper to driver inputs). Just that imho construction of modern cars from modern steel makes them much stronger against flex/twist vs easy to flex bodies of cars in past, so there is relatively little portion of vibrations/noise/car movements dampened/absorbed by car body itself, with by far biggest going through "classic route", tire sidewall flex, springs/shocks of coilovers, multiple rubber bushings/mounts and such.
That in turn imho makes impact both to good or worse, to handling and comfort/compliance from different bracing and tower bar of little extent, possibly - below "butt dyno" detection treshold. Though just as with less compliant bushings, just as with exhaust bolt-ons, i guess if it's not the only part/brace/alike installed but one of many one has installed, then much stronger towerbar, multiple braces in miscellaneous car body/suspension places, then there is greater chance for one to notice changes for both handling and NVH from cumulative change of all of them.
My subjective opinion is unless it's full track build to not bother with bracing/tower bars and alike, as their impact is of bad bang for buck, rather investing more in suspension bits, eg. quality coilovers fit for use, performance alignment and so on. For complete competitive sport build i'd think in addition to extra seam welding to make body stronger/more rigid, also rollcage may add some, and then, maybe stronger towerbar and misc. extra bracing too .. but not sure it's worth much to spend money for mostly DD car with rare trackdays for fun on bracing/tower bar. Lot of placebo feel & purchase affirmation bias might be needed to justify spending on them instead if on something else, with need for these being on level of .. eg. those TRD door stabilizers.

[JIM THEO]

Let's say you are right, why STI put those braces bushings etc over the standard model if there is no need for them as this frame is rigid enough?
I mean we all know that tS HAS handling differences, some due to better Sachs suspension and some due to bracing/bushing we talk about!

[nikitopo]

For those who don't know much about the STI tower bar, please check the test results between the flexible bar and a rigid tower bar. These are real data made on 60km/h and with a robot arm for precise steering:

https://www.sti.jp/en/parts/feature/...etowerbar.html

[churchx]

JIM THEO: why STI puts those braces etc? Well, there also can be reason why TRD sells fuel cap with TRD logo. - Because people buy it
But to summarize my previous post much shorter - imho they do work, but in my eyes not enough for their cost, better spent elsewhere with better returns.
BTW, "tS handling differences .. Sachs suspension" - i did mention coilovers as something i'd prefer to spend extra money on? - imho better shocks will give much more impact on handling (AND comfort) then tower brace.

nikitopo: many marketing words and nice graph that tells that yes, impact can be measured/graphed. But how it will tell if it can be actually subjectively felt in blind test by average driver? I can turn steering wheel extra 2-5 degrees to compensate, but not actually notice it when driving. Just as with eg. brakes master cylinder brace or braided lines. Yes, when hard braking there will be less flex .. but there are people that wouldn't feel that they pressed brake pedal slightly more to get same braking without those, they just adjust their driving inputs.
That mentioned TRD door stabilizer - it works. There were some pics/charts in product description of it. But for it's price - would you buy it?

[JIM THEO]

Originally Posted by churchx

JIM THEO: why STI puts those braces etc? Well, there also can be reason why TRD sells fuel cap with TRD logo. - Because people buy it
But to summarize my previous post much shorter - imho they do work, but in my eyes not enough for their cost, better spent elsewhere with better returns.
BTW, "tS handling differences .. Sachs suspension" - i did mention coilovers as something i'd prefer to spend extra money on? - imho better shocks will give much more impact on handling (AND comfort) then tower brace.

While I agree with you their value for money is quite low it's completely different thing when something is fitted by the factory on a special edition model, which means R&D and that it works in combination with the rest modifications, and when something sells as aftermarket part say TRD fuel cap and is mainly marketing.

In my case the "perfect" Ohlins coilovers didn't work on the roads I drive (due to shortened suspension travel) - no track use - while the tS setup works perfect in most of the situations so far!

[wparsons]

Originally Posted by norcalpb

Yes a horizontal bar will do its best to prevent vertical flex, but if it does it transfers all that shock to the other side of the car. Have a passenger in the car and a vertical bar will make nvh even worse but you are keeping the chassis in line which makes the suspension work better.

I have the controversial opinion that too much chassis stiffness can add discomfort even though it is letting the suspension geometry work in the most ideal conditions. I consider the V bars as part of the frame because I’d never run an 86 without them, so having slack in the chassis can add comfort.

If you look at how forces are applied from a bump or cornering forces they both exert force in the same direction as each other through the upper strut mount. It's not like a bump is changing suspension geometry compared to cornering loads.


A horizontal bar really only prevents the tops of the towers from flexing towards or away from each other, nothing to stop the shock tower from moving vertically.

[86MLR]

I've found Macpherson struts by design benifit a strut brace / bar during hard cornering.

Opinions may vary