Chassis Stiffening, Suspension Ideas, Handling Improvements

[onlytrueromeo]

I've decided I'm going to buy another MX3 when the time is right. My car has bad karma w/ it's many problems, and I want to start fresh and do things right w/ a clean title car.

One of the things that is most important to me is increased chassis strength, so I can improve the ride quality and performance.


Here are some of the ideas:

1) Frame rail braces/butterfly brace. This would be custom made, similar to the FM brace. It is PROVEN to work. This will also make the frame rails a viable jacking point.

2) Re-weld all unibody pieces on inside of the car. Race cars are built this way, and from what I've read it works. This should help stop some flex, and improve crash safety.

3) Foam frame rail and body filling. This has been sparking my interest lately. 8 to 16lb/cubic foot foam in the frame rails will reduce flex and increase strength. Filling the A/B Pillars and body "crumple zones" will also increase stiffness and provide excellent sound deadening. I would not want to reduce crash safety, so I will have to further research filling these areas.

4) Strut tower bars. I have them front and back, and love them. Some people say they don't make a difference. Here is an article these people should read! http://www.engin.brown.edu/courses/en17 ... roject.htm" onclick="window.open(this.href);return false;

5) Subframe braces / reinforced suspension member arms. I know Charlie (wytbishop) was talking about tying the lateral links together to improve the handling/strength but I would rather keep them separate. Since I just bought new poly bushings, and I would not want to custom make full suspension members, I am wondering if the existing members can be "improved" by welding braces onto them. I don't know how much the members flex, how much reinforcing them would stop flex, and what the benefits would be.

Any other ideas? I don't like the idea of a full cage, it takes up too much space. I might consider a partial cage for the rear.

[wytbishop]

I think a lot about this topic as well.

I think the thing that you'll find is that for the most part any change you make to the chassis and suspension will either improve handling or reduce ride quality or both. My feeling, just from the few things I've done, is that it's very difficult to improve handling without reducing comfort. Comfort and handling are sort of mutually exclusive. Anything that makes the car sharper will also tend to make it harsher. Lots of things can be done to make the car sharper. It's just a question of how much harshness you're willing to put up with.

As to your points I will offer my opinion.

I see no problem with bracing the frame. Frame braces are available for lots of cars and I doubt you could make the car dangerous by doing that.

Welding the seams would do little I think. The car has to flex a little. It wants to and ultimately you can't stop it from happening. I think many of the seams would wind up cracking anyway.

Filling non-crumple areas wouldn't bother me, but I would definitely not make the parts of the car designed to crumple in an accident any stiffer than they are. Because if they don't crumple in a crash, all that energy gets transferred to you...and you crumple.

Strut tower bars...I will read your article, but to me they are unproven and improvements would be nominal at best.

Control arms, front and rear, are an area of great interest for me. Installing the poly bushings has shown me that before I do anything I need to perform some tests. My car turns so hard and tight now it feels like the wheels are digging into the pavement and I think it's because the bushings have accentuated the 4WS effect. I don't necessarily think that this would be negated by linking the lateral links, but I know that I don't want to mess with it until I can do some testing. Flex in the members is not the issue at all. They are all 2 force members. At worst they might experience a slight amount of twisting by it would be very minimal. I have been visualizing a way to link the left and right sides of the rear suspension to better control the 4WS, but it's only in my head at this point.

I have also found that with the 70A bushings all around the car felt a little bit "oversteery", but I believe it was just a flaw in my initial installation. I'm running 80A all around right now and it's much tighter but the fact that I have dialed in the installation method has a significant affect on that fact. I'm going to go back to the 70A's now that I've perfected the installation and reassess them as soon as I have a chance. I also find the 80A's very harsh so I'm hoping the 70's will make me happier when they're properly installed.

[Ryan]

Part of the design process is thinking of ideas and playing with them before they get shot down, so:

What about swaybars... between FR/RR and FL/RL. We know the balance isn't 50/50, and even so, its intuitive that the front always compresses more than the rear. Sometimes even guys like CircleTrack report the rear inside tire sometimes LIFTS from the ground in a turn.

I can't imagine it would be too hard to do, either. Aside from finding a u shaped bar that length that won't flex torsionally.

[onlytrueromeo]

From the reading I've done, and what I know of physics, chassis stiffening alone will do nothing but IMPROVE ride quality AND handling. The energy transferred from the wheels goes into the suspension of the car, and then comes back out as rebound, or is absorbed by the dampers...at least that is what is supposed to happen. The problem is that the suspension is bolted to the frame/body, and that frame/body does not have an infinite strength so it yields. This means that instead of going into the suspension and absorbed or pushed back to the ground, it is being absorbed by the body and ultimately the person. "Rigid" body twists, you feel it.

With a more rigid body, less of the energy is transferred to the driver, and it is shown that a slightly softer suspension can be used to get the same results on the car.

There are compromises though. Chassis stiffening adds weight. Although it may not be a lot compared to a roll cage, it is still 100-150lbs for what I am talking about. The heavier the car, the more weight transfer that is going to take place and the tighter suspension components that are needed to compensate will reduce or negate the benefits of being able to go to a softer suspension. The weight added is all below the original CofG however, so it essentially lowers the CofG without affecting suspension geometry as lowering does.

I do not presume to know everything about this subject, I am simply stating what I have read, an informed conjecture if you will.

As far as crumple zones, yes that is my fear, that increasing body rigidity will increase energy transferred to me. I would not be using 8lb/cf foam above the frame rails of the car, but rather a 2lb/cf version in the A/B pillars since it can be injected rather than poured. While this may not increase the strength of them noticeably, these are areas we don't want to crumple and it also has the added benefit of sound deadening!

If I do not use some sort of foam in the body (ie when you remove the rear panels, there is all that empty space) then I will most certainly be filling those areas with sound deadening material. I will not use cellulose as SuperK did, but I got the idea from him. A fire retardant material that deadens sound and does not absorb water is what I am looking for. (Rockwool/mineral wool if I can find it, not popular in the US)


Ryan and anyone else: Sway bars link one side of the suspension to the other, effectively increasing the spring rate on whatever side is being compressed THE MOST, if the force on the suspension is equal on both sides, it does nothing.

Effectively, sway bars cause the car to LOSE traction/suspension movement on the side they are installed on for the benefit of reducing body roll.

Wait, LOSE traction? WTF are you talking about? In a front wheel drive car, you want the weight on the front wheels (duh) to get power to the ground. How do you reduce understeer? Increase the grip of the front end! Well, harder springs/struts work as does corner balancing, but harder springs means harsher ride, and potential for disaster on large bumps. (Amongst other things) Now you could decrease the size of the front sway bar, and in a perfect world you would just use tighter springs to compensate...but there is a reason sway bars (really anti-roll bars) are called what they are. Body roll has a very large affect on handling.

So now you go to increase the rear sway bar to reduce the traction on that side of the car so it feels more neutral. Most noticed on the limit like you mentioned the rear inside wheel lifting off the ground, rear sway bars change the weight distribution to be biased more towards the front. There are only 3 wheels on the ground so each of them is taking more weight, and the car is able to accelerate out of corners better with the tail end able to rotate around more freely. (no power on oversteer in fwd)

[onlytrueromeo]

This is a really good (not scientific) read and is basically a basis to what I want to accomplish here. I would eventually like to add calculated numbers to this thread. (obviously they won't be 100% accurate, but I'm hoping for somewhere in the ballpark of 10-15% error)

http://forums.nicoclub.com/zerothread?id=430701" onclick="window.open(this.href);return false;

[Inodoro Pereyra]

From the reading I've done, and what I know of physics, chassis stiffening alone will do nothing but IMPROVE ride quality AND handling. The energy transferred from the wheels goes into the suspension of the car, and then comes back out as rebound, or is absorbed by the dampers...at least that is what is supposed to happen. The problem is that the suspension is bolted to the frame/body, and that frame/body does not have an infinite strength so it yields. This means that instead of going into the suspension and absorbed or pushed back to the ground, it is being absorbed by the body and ultimately the person. "Rigid" body twists, you feel it.

With a more rigid body, less of the energy is transferred to the driver, and it is shown that a slightly softer suspension can be used to get the same results on the car.

Hmmm, no.
This sounds a lot like the "Achilles and the tortoise" paradox, in that your physics is sound, but you're forgetting one variable.

The energy transferred from the wheels is absorbed by the suspension only if the body is infinitely stiff, and INFINITELY HEAVY. Otherwise, the energy will be partially transferred to the body, and to the people in it.
So, being that the weight of the car is something you want to keep down, the less energy the chassis dissipates when it flexes, the more energy that will be transferred to the driver.
Stiffening up the chassis and/or the suspension will ALWAYS reduce ride comfort.

[Alexmdb]

This is a very interesting topic, anyone care to help me create an article about it on mechdb.com? There's so much to digest.

One thing I wanted to note though, you do not want full bead everywhere. If you look up unibody welding guides and etc online, you'll see that when it comes to welding a unibody you want to do short sections of bead all the way through, so it's about 50/50. Otherwise you will end up weakening the metal and it could crack around the full bead. Besides, if it's welded properly that 50% coverage will be strong enough.

I'm gonna get the article started, would be awesome if people could add on everything they find.

http://mechdb.com/index.php/Chassis_stiffening" onclick="window.open(this.href);return false;

Edit:
Damn, I just looked at that Nissan thread and it's pretty amazing. Some good reading!

And another thing, I still can't decide which one of you is right about ride quality. I kind of want to lean with what onlytrueromeo says, but Inodoro has a good point too.

[onlytrueromeo]

A good read for people wanting to learn some basics on suspension parts.

http://www.rqriley.com/suspensn.htm" onclick="window.open(this.href);return false;

[marcdh]

Out of interest, just how similar is our chassis to the 323 BG?
http://www.ultraracing.com.my/Catalog.a ... 0BG&page=1

[Ryan]

BG

Wheelbase
Hatchback: 2450 mm (96.5 in)
Sedan: 2500 mm (98.4 in)
Length
Hatchback: 4155 mm (163.6 in)
Sedan: 4356 mm (171.5 in)
Width
Sedan & 1993-94 Hatchback: 1675 mm (65.9 in)
1990-92 Hatchback: 1670 mm (65.7 in)
Height
1993-94 Hatchback: 1345 mm (53.0 in)
1993-94 Sedan: 1340 mm (52.8 in)
1990-92 Hatchback: 1380 mm (54.3 in)
1990-92 Sedan: 1375 mm (54.1 in)
AWD Sedan: 1385 mm (54.5 in)
Curb weight
1070 kg (2359 lb)


MX3

Wheelbase
2,455 mm (96.7 in)
Length
4,208 mm (165.7 in)
Width
1,695 mm (66.7 in)
Height
1996-98: 52.0 in (1321 mm)
1992-95 Base: 50.4 in (1280 mm)
1992-95 GS: 50.6 in (1285 mm)
Curb weight
RS: 1,095 kg (2,410 lb)
GS: 1,171 kg (2,580 lb)



Very similar.

[wytbishop]

the EC LCA's are longer than the BG ones. So the track is wider on the MX-3 than other variants. That 4 point frame brace might work depending on the connection points. I think the fender braces would work. Cool idea, not sure if it would really do anything.

[300zxrb26dett]

Hmmm, no.
This sounds a lot like the "Achilles and the tortoise" paradox, in that your physics is sound, but you're forgetting one variable.

The energy transferred from the wheels is absorbed by the suspension only if the body is infinitely stiff, and INFINITELY HEAVY. Otherwise, the energy will be partially transferred to the body, and to the people in it.
So, being that the weight of the car is something you want to keep down, the less energy the chassis dissipates when it flexes, the more energy that will be transferred to the driver.
Stiffening up the chassis and/or the suspension will ALWAYS reduce ride comfort.

Then why are the OE manufacturers constantly trying to increase chassis stiffness/rigidity?

Because it reduces NVH, allows them to run a little stiffer suspension to improve handling while keeping the harshness to acceptable levels.

You can find many articles/forum threads where people have used chassis foam to stiffen the chassis and achieved a better quieter ride from using it.
OE have also started to use the stuff more as well.

[Inodoro Pereyra]

Then why are the OE manufacturers constantly trying to increase chassis stiffness/rigidity?

Because it reduces NVH, allows them to run a little stiffer suspension to improve handling while keeping the harshness to acceptable levels.

You can find many articles/forum threads where people have used chassis foam to stiffen the chassis and achieved a better quieter ride from using it.
OE have also started to use the stuff more as well.

Ok.

First, answering with a question proves nothing. If you have any valid information to provide, do it. Otherwise, don't try to make a point by asking questions that neither one of us can answer.

Second, I don't know what NVH means, so I can't reply to something which meaning I don't understand.

Third, you can find many articles/forum threads saying you can power your car by peeing in the gas tank. That doesn't make it true.
I don't talk about chassis stiffening because I've read an article. I talk about it because I've stiffened and test driven several cars, from just a few chassis braces to welding the doors shut, and I know first hand what that does for ride comfort.

[300zxrb26dett]

I asked the question, because the statement your making regarding "stiffening the chassis always reduces ride comfort" really doesn't make sense when you see an article talking about a new car model that comes out and most of the time the OE made the chassis x% stiffer. It has been an observation I noticed from different reading.

The reason why I say this is because of the OE constantly trying to reduce NVH, which stands for Noise, Vibration and Harshness. Its a very common term and not something i made up.
Now if stiffening the chassis up has such a negative effect on ride comfort, then why are they doing it? is basically what I am getting at.

Your right I really cant answer that question for sure, but I took an educated guess at it. my apologies

Since this is not some college research paper, I dont have time to gather all materials and lay everything out for you professor, so why dont you go look and research yourself. There are plenty of resources out there on the subject. I would be days trying to find every little tidbit about it that i have come across.

Now since not everyone of us has the time or money to experiment with everything they read, the things I really dont have experience with, I do as much research as I can on the subject.

Now I will let you know how the chassis foaming works as soon as I get time to do it on my car. Considering the setup on my car, I will surely find out if the foam is worth all the hype.
And yes OEM's have started to use chassis foam, starting with luxury brands mostly, and the newest one I can think of off the top of my head, is a RX8----feel free to look that one up as well.

[onlytrueromeo]

With everything, there are pro's and cons...but I'm sorry, stiffening a chassis (car body/frame - NOT suspension) without adding weight has NO cons.

Inodoya, as per your weight comment which somehow I missed when you posted, nothing is designed with infinite weight. Suspension systems are designed for the given weight of the car, ride height, geometry and driving "style" that will be accompanied with a car. Sports cars have stiffer springs and dampers with usually less suspension travel than a luxury car, which is designed to absorb the bumps through its much longer spring/damper length.

Cars are not designed for torsional flex. This is just a side effect of cutting down weight and costs. Every bit that the car twists is less force being absorbed into the suspension, so the suspension is no longer working as it should. If the car had infinite weight, there would be no suspension. What you are referring to is fixed chassis placement, meaning the suspension moves while the chassis remains in the same place. In a perfect world this would be possible, but we know this is not the case. Many attempts have been made and come a lot farther than the conventional suspension, but once you deviate from straight line acceleration, things get more complicated.

Body roll loads suspension parts differently. As you increase lateral acceleration, you are increasing the weight transfer dramatically. To minimize this, stiffer springs are added, at the expense of ride comfort. But wait, if the car is not stiff enough, it will yield before the suspension does! This car flex has ALOT to do w/ NVH. Interior panels are attached to the body. When the body twists, the pieces grind against each other. Metal groans and creaks. The doors and hatch come out of alignment, and parts wear faster. Using foam filling adds a barrier between the road and driving, and acts as a sound barrier besides being a structural member.

I wish I had knowledge/experience and willpower/time to draw up some equations for you...but the answers are found plentiful in books and on the internet. Stiffer chassis = better. It allows a suspension to do more work, and have less unknowns in handling. It allows different springs to be used without wondering if the car will tear itself apart. It allows more bumps to be absorbed for a better ride.

If chassis systems were DESIGNED to flex, then they would flex much more than they do. A system that was designed to flex (separated passengers from suspension on a whole new level) might see significantly different results.