Chassis Stiffening importance...?

[shogun32]

Considering the engine bay is essentially an open square from plan view

aside from a space constraint, I'm surprised there isn't a brace over and under the radiator. Or does the crash bar do enough to tie the legs together? Or for the purpose of crumple zone we NEED the legs to be weak?

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[TeeLew]

aside from a space constraint, I'm surprised there isn't a brace over and under the radiator. Or does the crash bar do enough to tie the legs together? Or for the purpose of crumple zone we NEED the legs to be weak?

It's hard to know, but I'd guess it's a crash thing. Usually were interested in the area from the furthest forward suspension point to the furthest aft, but sometimes you can help between the points by stiffening outside of them. This might be one of those cases.

 

[KellTrac]

then Steeda and BMR are in big trouble.

Not at all. "Feeling" is what sells. That's why horsepower is the largest segment. People want the feel.

Truth is, street and occasional track/autoX/hpde cars dont need much of anything other than a good set of wheels and tires and a good driver. In some cases....'placebo effect' mods actually make a car handle worse. Example, a stock S550 Mustang with "upgraded" springs and anti sway bars. M6G will say the car handles better! When reality is, it feels better but actually handles worse.

It's similar to.......all the posts you'll see where people actually claim bracing eliminates their tramlining........ Thats extremely entertaining.

 

[kz]

@BMR Tech, @SteedaTech

Care to weigh in on what our expert here is saying? You guys are just selling snakeoil right? You don't employ engineers, or race test any products? Nothing you sell has been vetted extensively on and off the track. You don't stand behind everything you sell, and use them yourselves. You just slap together some cheap parts and then sell them to unsuspecting M6G members as a placebo. The people need to know the truth

I'm pretty sure Kelltrac used to have pretty direct relationship with one of the vendors you called out. And he's absolutely right - instead of upgrading tires and dampers, people go for springs (that look !) and then say "it handles like a gokart now !", but fancy wheel and put Nitto tires on them or replace bars because that's easy and they feel like they've modded the car.

 

[KellTrac]

Bring them in here. I'm just some normal dude who makes zero dollars 'selling' people said products. If you read my comment carefully it is 100% accurate. Nothing wrong with what I said. I'm fine with people having opinions. I'm all about helping - if people want to fall for marketing hype that's fine with me.

Im on my 5th S550 Mustang. My current one, the very first modification I did was BMR handling springs with some supporting GT350 items.

But. I also put some better wheels and tires on. ;)

 

[Norm Peterson]

Nah man, he made an asinine comment, then doubled down on it. This thread is about chassis/frame stiffening, which does have benefits. It's more than just about "feel". Wheel-hop is a real thing. Locking down the rear does help with that.

Locking the rear down to help a rear wheel problem is one thing. But wheel hop is not going to be affected by bracing a single vertical-transverse plane at the other end of the chassis.

Add-on stiffening has only local effects.

The front bracing I installed is present on the performance pack cars. I've "tested" it myself on some sharp turns in Nassau County. The speeds I'm able to hit before the tires start losing grip went up.

You're trying to find more there than there can possibly be. Unless you really can feel the difference that a tenth of a degree or so difference in outside front tire camber might make (it's not going to be very much at all).

That's because the front end of the car isn't as static system. In motion there IS flex. That flex translates to loss of grip up front.

Here's the problem. Yes, in theory that would be correct, but it doesn't stop there. Now you have to throw some numbers at the problem and then determine whether they amount to something significant or not.

Advertising copy only gives you the theory part, and leaves the potential customer to let his imagination run away with him about how much improvement might be there. In nearly all cases, imagination leads to exaggerated expectations. Advertising counts on this, even if the advertisers do understand the engineering (numbers) side of it.


Norm

 

[Jaymar]

@BMR Tech, @SteedaTech

Care to weigh in on what our expert here is saying? You guys are just selling snakeoil right? You don't employ engineers, or race test any products? Nothing you sell has been vetted extensively on and off the track. You don't stand behind everything you sell, and use them yourselves. You just slap together some cheap parts and then sell them to unsuspecting M6G members as a placebo. The people need to know the truth

Your mileage may vary with their products as no blanket statement can cover them all. The strut tower brace is included by Ford on the GTPP so somebody saw some gain high enough to justify the expense of the part in production. However, at least one of the big two you mentioned makes a "chassis brace" for GTs that bolts where my factory intercooler mounts. I'm pretty sure the intercooler isn't a structural member on my car so what possible advantage could bolting a bar there on a GT have?

 

[Grintch]

there's also the extra load and stress on one part can and often will translate into more stress and load down the line. some of you want to say how its a waste and zero gains and i'm very savvy on cost / gains and handling characteristics, my initial curiosity was on the load transference to other components resulting in excessive wear or extra load it wasn't intended for leading to problems, like the strut tower keeping the engine bay supported. The ride is already compromised with the GT350R suspension under it, lol.

I think i'll work on getting the strut brace and maybe rear IRS stiffeners and see where that puts me. but when I'm mid turn and hit a small bump and can hear the wind noise increase through the door from the bump, that's not placebo, that's chassis flex and it wasn't there prior to the suspension work. I'm also starting to notice a few other little creaks here and there.

I drive my car quite hard, I race off road desert and am not a weekend warrior looking to take out a honda. i drive how i drive and it's pretty hard with a stiff suspension on an otherwise stock chassis EB car. I can't imagine a little stiffening would hurt.

You didn't ask if it would hurt. You asked if it was important. I can't think of a single documented build in the last 10 years where a modern street car added extra bracing and it made the car significantly faster. Bushings maybe a little, but not chassis braces. Doesn't make the car go faster = not important in my book. Or at least not a priority. Not worthless, but the value depends a lot on your usage.

But it seems like you have made your decision, so have fun.

 

[KellTrac]

GT350...placebo Mustang

You are not very good at this stuff. Guess 'what else' a GT350 has, that I already stated was the best improvement on these cars and that I had done alongside my suspension mods? YEP - wheels and tires! So no, it's not a placebo Mustang.

 

[spaz mk will]

Thanks for the discussion, this is fun. I think this is a good reminder that two things can be true at the same time depending on how you measure it.

Objectively, the improvements from bracing may be significant or negligible depending on where they are located, the chassis in question, and your criteria for what qualifies as a worthy improvement vs cost/weight. Manufactures use it for a reason, though sometimes it could just be marketing, who can say.

Subjectively, if bracing at best makes a car more predictable, that can improve driver confidence (and thus speed) since it becomes easier to drive with consistency. Seems like a good thing if you value that.

That’s my takeaway from my very modest experience driving this car and trying to understand how it behaved after some bracing was added. For regular DD it isn’t needed at all, but you feel it in some instances. The reduction in cowl creak from the K braces for example is a noticeable benefit not directly tied to the assumed goals of the component. Am I really getting some great benefit from the weight and cost of these parts? It’s probably negligible until I’m a much better driver. My subjective experience is that rear bracing made the rear more predictable which is a plus as I learn. Overall I’m happy with my choices even if that’s just me justifying it to myself

That said. I agree wheels/tires should be the number one mod for handling improvements and offer the most upside for the cost. Dampers are often overlooked and they should not be, these cars are under damped in my opinion.

And while it’s kinda entertaining, I’m not here to beat the dead horse of marketing and consumerism. It’s obvious that plenty of us are convinced and oversold by advertising all the time. I’m as guilty as any other mustang owner for lusting after mods and spending on things with a low or 0 return. But it’s a hobby and makes me happy (and not broke) so it is what it is.

I do have a question for those who are more knowledgeable about suspension and mechanical engineering - I only took the general courses for all disciplines. Does bracing, such as IRS lockout let’s say, help the rest of the suspension “do its job” since you are (ideally) removing another source of movement/articulation from the system? I would think that having the suspension fighting both the wheels and the subframe movement would be worse than only needing to control the wheel, if you follow my question.

 

[jwt]

I am 99.99999% confident that the biggest improvement I can make to my car is between the steering wheel and the seat.

Driver training, lose weight, fitness etc etc.

That said when you do feel the car behave badly in a predictable and repeatable manner I have no issue making modifications and testing if the behavior is better or worse, while completely accepting this is a subjective and personal opinion.

And if it inspires confidence in the car I didn't have before and causes me to drive the car harder and better fantastic.

 

[Norm Peterson]

Your mileage may vary with their products as no blanket statement can cover them all. The strut tower brace is included by Ford on the GTPP so somebody saw some gain high enough to justify the expense of the part in production.

Gains don't have to be measured performance gains. Gains can be made in the areas of driver comfort and driver composure.

From post #29,

The engineering advantages aren't limited to performance driving; you need to look at what else they do. I'm going to refer you back to that Olds/Buick here, as GM wouldn't have included an STB for hard-driving performance reasons in those cars. Added for a more refined, upscale ride, sure.

You might not want to hear what I've heard - directly - from a real automotive suspension engineer concerning some other chassis/suspension component.


Norm

 

[Norm Peterson]

I've played around with this type of stuff a bit over the years. I agree with your pencil/paper analysis. I think it's correct, at least directionally, for the static case.

I did have to make a couple of assumptions . . . such as 10,000 lbs/in chassis-side stiffness against suspension link/strut forces. I'm sure they aren't 1000 lb/in or 100,000 lb/in, but I'm not worried about being off by a factor of 2 or even 3 as long as the estimated displacements are consistent with what panel gaps would allow.

Where I think most people will actually feel it is dynamically. If we consider a 3-point brace, then we're stiffening both the 'folding' mode of the front subframe about a longitudinal and vertical axis as well as the beaming mode of the entire car. Considering the engine bay is essentially an open square from plan view, I see this as an important area to stiffen. If you're loaded heavily into a corner and a series of bumps is able to excite one of these modes, it's not going to feel good. If we can stiffen things up, then hopefully, its resonant will be above the range where road inputs can 'ring the bell.' *If* we're able to eliminate this type of thing, whether or not you go faster, the car will feel better.

Yes. If you were really chasing chassis stiffness in the more overall sense, you'd probably want to do a 4-point brace, tying at least each strut tower to the base of the A-pillar on the opposite side of the car.

Something like this, except back to the firewall.

To touch on the subject of stiffening small sections of the chassis, I think that's to be expected. If we were to measure how the torsional stiffness changes along the longitudinal axis of the car, I bet we'd find the unibody is probably fairly stiff and a couple areas, such as the front subframe, which have a lot of deflection relative to the whole. I've found that the more consistent the torsional stiffness of the chassis is from end to end, the better it generally feels to the driver.

Yup. If you've got a torsionally soft region along the chassis it's kind of like having a stiffish hinge there. Driven hard it won't feel very good, and the chassis won't be as tunable with spring and bar stiffnesses either. Of course at somewhat more than 15,000 ft*lbs/°, there can't be any regions anywhere along the chassis that are torsionally soft enough to benefit very much structurally/mechanically from additional stiffening.

Bushings for subframe or cradle attachments, sure. Though I suspect that the stiffness of even the OE bushings against suspension loads applied to them would be on the order of several thousand lb/in.


Norm

 

[TeeLew]

Whatever assumptions you made, they seemed appropriate. The exercise wasn't for perfection, but just to get a feel for the magnitude of the numbers involved.

I think an 'X' brace would be the best, but I don't know if there's anything of substance to mount the front legs.

There's definitely a point of diminishing returns concerning chassis stiffness, but I have yet to hear a bad comment from a driver after increasing it. I do know of at least one situation where reducing chassis stiffness was used as a tuning tool, but that was a very specific situation and I think there were better ways to address the problem.

 

[shogun32]

You might not want to hear what I've heard - directly - from a real automotive suspension engineer concerning some other chassis/suspension component.

don't be shy, this isn't a vendor thread.

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