School me on Strut Braces. Hard cornering or hard parking?

Discussion is what it says on the tin. Looking for objective data (better lap times, less measured flex when jacked, etc) where possible. Every dork with a 50 dollar ebay threaded rod swears they feel a huge difference, but I am skeptical of more weight helping.

Secondary points of contention:

1. Effect on McStrut vs SLA suspension. I understand the forces and perhaps effects are higher on mcstrut cars, as most have factory braces. Are oldschool civic and miata guys wasting time and weight?

2. Solid vs Adjustable. Some swear only steel, 2 bar will do anything, but i suspect they all do noting except in compression/expansion. Is there a reason to avoid the cheap adj ones?

3. 2 point vs Multipoint. There are some claims on either side. Most say 3 point bars help make the whole car solid. But lately I see more claiming that it throws off the natural flex of firewall vs fender, especially with the offset triangulation point, often on the brake booster. Ill also mention here there are also b and c-pillar bars. Usually attaching at seatbelt or hatch strut locations, some which triangulate to the shock towers.

4. Price vs Performance. Even if it does *something*, is the $50-500 better spent toward better shocks/rubber? Better off just waiting until I get to cage territory and just weld the supports? 

Any and all opinions welcome. I do not really have a strong opinion yet, and figured you guys would have some insight.

Depends on how strong the car is.

Most chumpcars don't have them.  I assume there are better bang for buck options for using the points.

I have a 2nd gen rx7.  Mac strut.  We don't run one.  We have in the past.  Adding caster was a WAY bigger improvement in feel and laptime.  Not apples to apples  but for.similar investment, it makes sense.

IIRC we had a big discussion about this just recently.

Ah - check this out.

https://grassrootsmotorsports.com/forum/grm/hinged-vs-solid-strut-brace/137159/page1/

Keith, without reading that entire thread, what's your opinion on if they are worth it?

Depends on the car and how well it's implemented and what you're using it for. Autocrossers seem to benefit more from weight savings than chassis rigidity, but I run one on my street car and my track car.

How well it's implemented is a big one. Put hinges in it and you've basically just installed a good place to put your hands when you're leaning over the engine.

Simple strut braces are not configured to resist chassis deflections from a strut suspension. Forces on the chassis are mainly vertical and a horizontal bar does nothing to resolve them. 

The "hinged" one I put on my 924 made a noticeable difference, I could disconnect one side and watch it move laterally as I jacked the car up.

The factory added gussets between the strut tower/inner fender and the frame rails on later versions of the 924/944 chassis, so obviously there is an issue and the factory race cars installed a bar between the strut towers and some tied it back into the firewall.

So while mine is not ideal, it can work better than nothing.  There are plenty of variables involved though and certainly for most casual enthusiasts it likely wouldn't make a noticeable difference, especially if it wasn't a solid bar.

ChasH said:

Simple strut braces are not configured to resist chassis deflections from a strut suspension. Forces on the chassis are mainly vertical and a horizontal bar does nothing to resolve them. 

 

I believe we had this discussion in the earlier thread.

It will all depend on the specific chassis as to if it is worthwhile or not.  The further the strut towers are from the firewall the more important they will be.

Modern cars where the strut towers are defined in part by the firewall and in some cases are incorporated into the rain tray/HVAC cowl, worthless.  Old stuff where the nose is four feet long and the towers are an acre away from the firewall, like the 240Z, worthwhile.

To play devils advocate to your view keith, I hypothesize that the bending moment, and twisting moment, are not resisted much even by a solid bar. The mechanical leverage, being enough to literally twist the chassis, is also enough to twist any bar of strut bar size. Add to that the small cross-section of the strut hat to bar interface attaching it, and the hinge seems moot. The only moment it can resist in a way the chassis can't, is the range in distance between strut towers.

Just something to consider. Clearly, each additional bit of stiffness helps, as is the reason we are adding a bar in the first place. So it might be worth it as long as you are spending the money. I just bring it up as most aftermarket are hinged for ease of manufacture and range of fitment. Many cars have no other option without fabbing a custom one. The best design, seems to be a cup surrounding the strut tower that can transfer vertical as well as horizontal load, but such designs seem rare in the aftermarket. Another consideration is mounting, seems like 3 bolts, in shear, is a suboptimal way to join the towers mechanically.

And to be clear, this is an in general query, not only to challenge oriented cars, which I suspect will do it with cage to a large extent. I was mainly curious of anyone has ever done any testing. 

 In the case of autox, I wonder if the chassis flex isn't a positive in some cars. I have seen an old cars handling 'ruined' by stiffinening the chassis, but it seems very platform and setup dependent.

And upon reading the linked thread, all the issued I brought up seem to be there. 

My synopsis of other thread: Most agree they do something. Most seem to feel solid is better, with some articulate dissidents.

Dissenting view is basically my devils advocate stance, that the vertical motion or twisting (paralellograming etc.) Is poorly resisted even my a solid bar due to shape and location. Keith counters it is an inherent limitation but still measurably (how much?) Beneficial.

My parsing so far:

1. Seems to help stability as much as grip. Higher speed users seem to like them more, lower speed users find them less valuable, but still like them.

2. Not a magic bullet. Many forces are at play and only some of the less important ones are strongly affected, but many secondary elements and driving feel, seem to improve. Hinging seems to possibly remove some additional benefits.

3. Popular band-aid when you ripped other chassis supports out. Most likely worth it in this case.

4. Great for resting yourself above a hot engine with. Everyone agrees here. Might be enough of a selling point for me honestly.

Did I miss anything? Thanks for chiming in. I have had them on some cars, and not others. It seems to be mostly feel to me. I noticed no difference between a solid and hinged, on crappy tires, but difference between hinged and none. I just wanted to calibrate the butt dyno with data. I will jack up a few different cars, and measure between towers and report back with some data, however limited to keep the discussion moving. It seems like there is a lot left on the table with most designs.

Depends on the car, as noted. On the rally car we have the rear strut towers linked to the cage and with a cross-brace. Front is a rigid (non-hinged) bolt-on brace. On a rally car anything that can be done to strengthen the suspension towers is a good thing. 

I have strut bars on my WRX as well (09). They were Christmas presents from my wife, but I can't say that they make much or any difference in handling or response.

Lower tie bars (linking the control arm mounts and chassis) seem to have a much larger effect, in my experience.

Nugi said:

To play devils advocate to your view keith, I hypothesize that the bending moment, and twisting moment, are not resisted much even by a solid bar. The mechanical leverage, being enough to literally twist the chassis, is also enough to twist any bar of strut bar size. Add to that the small cross-section of the strut hat to bar interface attaching it, and the hinge seems moot. The only moment it can resist in a way the chassis can't, is the range in distance between strut towers.

You're closing the box. The hinges won't make a difference in heave, as you see this mostly as a change in distance between the towers as you noted. You'll get this same behavior when you put a car on the lift - a bar set to the right distance between the towers when the car's on the ground will no longer fit when you get those wheels off the ground. This is why you want your crossbar to be as straight as possible, as it's mostly seeing compression when the suspension sees load.

However, when you're cornering you have different vertical loads on each shock top so you have more of a twist in the box. That's where you want to have your joints both minimized and solid. Sure, there are loads big enough to twist the chassis, but you want to improve as much as you can and that means putting material where it counts.

Mazda offered a hinged bar in 1999-00 on the Miata, and moved to a solid one with a nice connection between the towers and the bar in 2001 when they did a serious study of chassis stiffness.

Keith Tanner said:

ChasH said:

Simple strut braces are not configured to resist chassis deflections from a strut suspension. Forces on the chassis are mainly vertical and a horizontal bar does nothing to resolve them. 

 

I believe we had this discussion in the earlier thread.

Yes,the song is the same and so are the facts.

I don't sell tower brace bars, so I have no reason to be other than truthful.

Depends on the car i think. For example, Honda decided to add a strut brace to the 6th gen Si versus the normal Civic. I'd doubt the engineers at Honda would add one if it didnt help in the Civic. 

Having done FEA analysis on a formula SAE car, it doesn't take a large bar to have a large effect on the rigidity of a chassis. It just takes the right placement. 

In reply to Keith Tanner :

Both Porsche and BMW used jointed bars on their strut equipped race cars.

Mazda switched to a solid connection because it was cheaper- neither one did anything worth the weight.

Yeah, the fact that many cars come with them from the factory tells me that they do something, simply because every piece on a production car has to have justifiable value.

Sometimes the hard part is knowing what the part is meant to do.

I will say they are probably most  useful on strut cars where the position of top of the strut affects alignment (any car that can have camber plates). If you think about a car from the front during cornering, having the two strut tops stay static compared to the chassis is optimal in terms of having the rest of the suspension do what you designed it to. But if it can't stay static, then it would absolutely be beneficial to keep the tops simply equidistant from each other, so that at least your camber stays predictable from one wheel relative to the other. Tying the strut tops to the firewall helps keep the caster predictable.

My guess is the most important thing a strut bar does is resists the tension force created when the outside wheel in a corner pushes the bottom of the strut in and the top out. The strut bar allows the inside wheel strut top (that wheel is not forcing on its strut quite as much) to help resist the rolling of the outside tire to worse camber angles. I'd further guess that the biggest improvement from a strut bar comes on cars with poor camber curves, low static camber alignments, and not much castor. It's biggest benefit being just keeping the dang outside front tire from folding all the way over.

FWIW on my Yaris I have a "hinged" Tanabe bar on it.  Normally I would be a solid guy.  But with the rain tray right there and its kinda goofy I figured what the hell.

Well my dash used to do odd things during bumps and it stopped.  Did I "feel" any difference in the car?  Not particulary, however with the strut towers pretty much in the firewall I didnt expect much to gain anyways.

On my Tercel I made a SOLID steel square tube bar that also ties in the firewall.  The steering feel and inputs where alarmingly improved.  I can care less if its 1 minute slower.  The feel is damn good.  I suspect if I ran a soft suspension the difference would be not as much

ChasH said:

Keith Tanner said:

ChasH said:

Simple strut braces are not configured to resist chassis deflections from a strut suspension. Forces on the chassis are mainly vertical and a horizontal bar does nothing to resolve them. 

 

I believe we had this discussion in the earlier thread.

Yes,the song is the same and so are the facts.

I don't sell tower brace bars, so I have no reason to be other than truthful.

We can disagree and I'm happy to discuss technical reasoning, but if you're going to call my integrity into question we are done.

Perhaps I sell brace bars because they work, consider that. Enjoy the rest of the conversation, folks.

Robbie said:

Yeah, the fact that many cars come with them from the factory tells me that they do something, simply because every piece on a production car has to have justifiable value.

Sometimes the hard part is knowing what the part is meant to do.

You need to be careful with that sort of generalization -- sometimes the useful thing that they do is make the car look racier and sell more copies.  That's the case for most of the wings/spoilers that showed up on cars in the 90s. :)

Years ago on my FC RX-7, the windshield would make a kind of creaky-crunchy sound if I took a highway off ramp at significant speed.  I installed a beefy triangulated strut bar and the sound went away.  I could feel a difference as well.

Here's the Camaro chief engineer's take on the need for strut tower bars on the 6th gen car:  http://www.camaro6.com/forums/showthread.php?t=517935

codrus said:

Robbie said:

Yeah, the fact that many cars come with them from the factory tells me that they do something, simply because every piece on a production car has to have justifiable value.

Sometimes the hard part is knowing what the part is meant to do.

 

You need to be careful with that sort of generalization -- sometimes the useful thing that they do is make the car look racier and sell more copies.  That's the case for most of the wings/spoilers that showed up on cars in the 90s. :)

 

That was exactly what I was getting at

I once saw a video on the last-gen Viper and the people at SRT had numbers on how much chassis stiffness was improved by the massive X-shaped front upper strut brace...can't remember how much, but it was a large difference.

I have one on my E61 simply because it was cheap ($140-ish shipped from Malaysia) and it's the cleanest thing in the engine bay.

And as Keith noted earlier, it sure is nice just having something to lean on/put your hand on when you lean over in the engine bay.

Ultra Racing also makes 2pt and 4pt lower strut braces which can make an even bigger difference in chassis stiffness...just keep your ground clearance in mind if you get a 4pt (ask me how I know).

I had a 1980 Porsche 911SC that I autocrossed and used on track days. I put a strut tower brace on it but didn't notice a significant difference in handling, but then I cross braced the strut brace and it made a world of difference and even made the car squeak and creak less when driving around town. Attached is a picture of what I mean.