Stb
10-01-2010, 06:36 AM
#21
In a car with MacPherson strut suspension, the shock/damper is a stressed suspension member. This means load paths through the strut towers, which could warrant reinforcement. If you have double A-arms, the forces are not transmitted through the shock towers in the same manner.
FWIW...I installed both a 3 point STB, as well as 3 point SFCs in my car. I daily drive the car, so if there was any immediate difference, I didn't notice it. However, a friend of mine rode in the car before these modifications, then again, a couple of weeks later. He said he felt a difference...
10-01-2010, 08:45 AM
#22
What about the BMR guy who said that they measured flex between the shock towers while doing R&D on 4th gen susp? He said that there was .25 inch (!) flex under load with aftermarket springs and even more with higher race type springs. He reported this during a recent (within 6 months, I think) STB thread. Nobody agreed with him nor queeried his findings at that time. And yes, the usual gurus were in that thread as well.
10-01-2010, 12:01 PM
#23
You mean this video maybe? It was in that STB thread a while ago, and it measured deflection in a Camaro. This video was responded to, and this is basically why that has nothing to do with a 4th gen:
This is a 5th gen Camaro, and it uses a MacPherson strut which focuses all the load on the top of the tower (or near there). The 4th gen fbody uses a double A arm/spindle type setup, and most of the load of the suspensions is transferred through the lower A-arm into the K-member, NOT the top of the shock tower. This is one of the reasons that some cars like STB's, and some cars dont need them at all.
Also, I might add, I question the validity of videos like that. Without actually measuring strain in the STB, just seeing a video of an end bounce around doesn't tell me that the car is actually flexing. Try putting a STB into your car, and only bolting down one side. Now, give your STB a slight slap on the other side of the car....I bet you it moves! What do you think happens when you're driving down the road, hitting bumps, etc.? That's one of the things that happens when you have a piece of tubular steel about 3 ft long bolted down in 2 places (even 4 in the video).
Most of the forces go through the lower A arm.
This is a 5th gen Camaro, and it uses a MacPherson strut which focuses all the load on the top of the tower (or near there). The 4th gen fbody uses a double A arm/spindle type setup, and most of the load of the suspensions is transferred through the lower A-arm into the K-member, NOT the top of the shock tower. This is one of the reasons that some cars like STB's, and some cars dont need them at all.
Also, I might add, I question the validity of videos like that. Without actually measuring strain in the STB, just seeing a video of an end bounce around doesn't tell me that the car is actually flexing. Try putting a STB into your car, and only bolting down one side. Now, give your STB a slight slap on the other side of the car....I bet you it moves! What do you think happens when you're driving down the road, hitting bumps, etc.? That's one of the things that happens when you have a piece of tubular steel about 3 ft long bolted down in 2 places (even 4 in the video).
True, but in a unit body car like a 4th gen F-Bod, the a-arms are bolted to the shock towers via the tops of the shock/spring assembly, very similarily to a true MacPherson strut. Therefore, the cornerong loads ARE fed into the subframe.
FWIW...I installed both a 3 point STB, as well as 3 point SFCs in my car. I daily drive the car, so if there was any immediate difference, I didn't notice it. However, a friend of mine rode in the car before these modifications, then again, a couple of weeks later. He said he felt a difference...
FWIW...I installed both a 3 point STB, as well as 3 point SFCs in my car. I daily drive the car, so if there was any immediate difference, I didn't notice it. However, a friend of mine rode in the car before these modifications, then again, a couple of weeks later. He said he felt a difference...
10-01-2010, 12:11 PM
#24
^^^^ Nope - never seen that vid before! If there had been a vid (with debate) I wouldn't have posted what I did, lol! The BMR guy was talking 4th gen, (yes, not a macpherson set up) and had real big numbers for flex posted -not 2mm or so. Im not sold either way, but was curious as to whether anyone other than this guy measured the strut tower deflection?
10-01-2010, 12:26 PM
#25
Over the years this has definitely become a somewhat controversial mod. 12 years ago when we originally developed the strut tower brace for the 4th gen we measured almost 1/4" of strut tower movement on our test car equipped with higher rate springs and soft compound tires. If I remember correctly we were seeing over 1/8" movement even on the car in stock form when driven aggressively. If you are a drag racer, don't worry about it but if you like to push the car in the corners, it's probably the best $65 you'll spend....
10-01-2010, 12:28 PM
#26
I should add, I'm a member of the FSAE team here at UW. I should talk to one of the more senior members next week and ask if it would be possible to set something up to measure the deflection between the towers, and even from front subframe to rear. Might be a fun side project as most of our time is spent on design now instead of actual fun stuff 
Anyone interested in getting some numbers?
Anyone interested in getting some numbers?
10-01-2010, 12:30 PM
#27
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True, but in a unit body car like a 4th gen F-Bod, the a-arms are bolted to the shock towers via the tops of the shock/spring assembly, very similarily to a true MacPherson strut. Therefore, the cornerong loads ARE fed into the subframe.
FWIW...I installed both a 3 point STB, as well as 3 point SFCs in my car. I daily drive the car, so if there was any immediate difference, I didn't notice it. However, a friend of mine rode in the car before these modifications, then again, a couple of weeks later. He said he felt a difference...
FWIW...I installed both a 3 point STB, as well as 3 point SFCs in my car. I daily drive the car, so if there was any immediate difference, I didn't notice it. However, a friend of mine rode in the car before these modifications, then again, a couple of weeks later. He said he felt a difference...
All it takes for an aftermarket item to exist, is demand. In fact, the aftermarket has even come out with products, with no demand, and created demand with hype.
Even the OEMs equip their cars with items or specs, where the deciding factor could only have been marketing, and appealing to people's "common sense" understanding of what a sports car needs to perform.
I'm not claiming that I have done a before and after on a 4 post shaker, to actually have the data, but I am going to do some things to increase the torsional rigidity of my FD RX-7 (LSx swap), also with double A-arms all around; the first things I am doing are stitch welding the unibody, and "foaming" the unibody equivalent of the "frame rails". Torsional rigidity is very important to me, and you won't find an aftermarket strut bar on my car (there is one in the rear stock. I don't have the front stock STB, and they don't fit with an LSx. If I did have the stock front STB, and it did fit, I would probably just use it anyway.)
I
Last edited by JBarron; 10-01-2010 at 12:38 PM.
10-01-2010, 12:38 PM
#28
^^^^ Nope - never seen that vid before! If there had been a vid (with debate) I wouldn't have posted what I did, lol! The BMR guy was talking 4th gen, (yes, not a macpherson set up) and had real big numbers for flex posted -not 2mm or so. Im not sold either way, but was curious as to whether anyone other than this guy measured the strut tower deflection?
Cars are going to flex some when you drive them hard, whether it's at the drag strip or on a road course. Too many people are getting caught up in this, "I gotta stop ALL chassis flex!" idea when it's impossible, and impractical were it even achievable.
10-01-2010, 12:45 PM
#29
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Well, there is no such thing as a car being too rigid. It's just a trade-off between rigidity and weight.
I have to think it's possible that, even if the major load paths don't go through the shock towers, that at some point, with enough mechanical grip, the forces going through the other load paths become so great, that they get transferred through the whole car.
I have to think it's possible that, even if the major load paths don't go through the shock towers, that at some point, with enough mechanical grip, the forces going through the other load paths become so great, that they get transferred through the whole car.
10-01-2010, 12:49 PM
#30
Well, there is no such thing as a car being too rigid. It's just a trade-off between rigidity and weight.
I have to think it's possible that, even if the major load paths don't go through the shock towers, that at some point, with enough mechanical grip, the forces going through the other load paths become so great, that they get transferred through the whole car.
I have to think it's possible that, even if the major load paths don't go through the shock towers, that at some point, with enough mechanical grip, the forces going through the other load paths become so great, that they get transferred through the whole car.
10-01-2010, 12:56 PM
#31
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More rigidity = stiffer/harsher ride (body flex absorbs some road feedback). Suspension can soak up a lot, but it still has modes, just like everything else subjected to vibration, and it still transfers some road feedback into the mounting points. People already bitch about poly bushings being too "nasty" for the street - put them in a tube-chassis car with rod-end suspension and they'd cry for a week.
Any structure has a natural harmonic frequency at which it resonates. The more rigid it is, the higher this frequency. If I didn't know otherwise, intuitively, I would say the same thing as what you did. It is very counter-intuitive, until you do a little research; at which point it does become intuitive (your intuition is informed by your knowledge and experience, you know?).
10-01-2010, 01:29 PM
#32
The more rigid the unibody, the higher the frequency of the impact must be, to upset the structure. This means that ride quality will undeniably improve. Which means you can use a stiffer suspension, and have the same or better ride quality. It is best to let the suspension do it's job. A more rigid car will also have more consistent handling. This means that you will drive the car faster around a road course, among other things, because you will be more confident that the car will always act the same through a corner. It will also become easier to tune the car's handling though roll-rate tuning.
Any structure has a natural harmonic frequency at which it resonates. The more rigid it is, the higher this frequency. If I didn't know otherwise, intuitively, I would say the same thing as what you did. It is very counter-intuitive, until you do a little research; at which point it does become intuitive (your intuition is informed by your knowledge and experience, you know?).
Any structure has a natural harmonic frequency at which it resonates. The more rigid it is, the higher this frequency. If I didn't know otherwise, intuitively, I would say the same thing as what you did. It is very counter-intuitive, until you do a little research; at which point it does become intuitive (your intuition is informed by your knowledge and experience, you know?).
A more rigid frame will transmit more NVH not absorbed by the suspension (and in this context, we're not talking a town-car cruiser suspension; we're talking stiffer rates, higher-durometer bushings or rod ends, etc, meaning we can count on even less NVH dampening from the suspension on a performance car). Yes, it will also make handling better and more consistent, but you also have to keep in mind the fact that most people aren't going to auto-cross or road race, ever, and balance diminishing-returns modifications and NVH increase over the benefits seen in a daily driver.
While I'm sure most people would enjoy having a vehicle that handles as precisely as an F1 car, I doubt they'd be too happy with the comfort trade-off required.
Just to clarify, I'm not debating that a more rigid frame would in any way detract from the overall handling characteristics of a vehicle, it's simply my opinion that some chassis flex is permissible in non-race oriented vehicles, to maintain a broadly-appealing comfort level while driving, assuming a realistic expectation of what the majority of OEM-supplied suspension parts will achieve on the road during their lifetime.
10-02-2010, 06:49 AM
#33
I'm sure that the horizontal (side loading) forces do indeed go through the lower a-arm. However, the top of the coil/shock/ upper a-arm has to be located by something, it can't stand out in mid air. That "something" is the upper portion of the shock tower, which restrains the up and down motion of the spring/a-arm. The STB ties both shock/a-arms to each other, to resist this up and down loading.
10-02-2010, 01:32 PM
#34
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Harmonics is also directly related to total weight and density; rigidity isn't the only factor. Part of my job is vibration testing for endurance and prototyping; we see a lot of weird **** on the vib table, and not everything reacts the way you expect it to.
A more rigid frame will transmit more NVH not absorbed by the suspension (and in this context, we're not talking a town-car cruiser suspension; we're talking stiffer rates, higher-durometer bushings or rod ends, etc, meaning we can count on even less NVH dampening from the suspension on a performance car). Yes, it will also make handling better and more consistent, but you also have to keep in mind the fact that most people aren't going to auto-cross or road race, ever, and balance diminishing-returns modifications and NVH increase over the benefits seen in a daily driver.
While I'm sure most people would enjoy having a vehicle that handles as precisely as an F1 car, I doubt they'd be too happy with the comfort trade-off required.
Just to clarify, I'm not debating that a more rigid frame would in any way detract from the overall handling characteristics of a vehicle, it's simply my opinion that some chassis flex is permissible in non-race oriented vehicles, to maintain a broadly-appealing comfort level while driving, assuming a realistic expectation of what the majority of OEM-supplied suspension parts will achieve on the road during their lifetime.
A more rigid frame will transmit more NVH not absorbed by the suspension (and in this context, we're not talking a town-car cruiser suspension; we're talking stiffer rates, higher-durometer bushings or rod ends, etc, meaning we can count on even less NVH dampening from the suspension on a performance car). Yes, it will also make handling better and more consistent, but you also have to keep in mind the fact that most people aren't going to auto-cross or road race, ever, and balance diminishing-returns modifications and NVH increase over the benefits seen in a daily driver.
While I'm sure most people would enjoy having a vehicle that handles as precisely as an F1 car, I doubt they'd be too happy with the comfort trade-off required.
Just to clarify, I'm not debating that a more rigid frame would in any way detract from the overall handling characteristics of a vehicle, it's simply my opinion that some chassis flex is permissible in non-race oriented vehicles, to maintain a broadly-appealing comfort level while driving, assuming a realistic expectation of what the majority of OEM-supplied suspension parts will achieve on the road during their lifetime.
Again, I'd be very interested to hear about some of the idiosyncrasies you've encountered, or anything like that, that you found interesting.