sway bars for the neon

[BMS]

we just bought front and rear Hotchkis sway bars for our racing neon srt-4, suspension and Mopar stage 3 are coming soon!!!

[Evo8kid]

are they the hollow ones?

[htheduck]

yes they are. not a bad choice btw.

[Wiisass]

Now you should get them tested before you put them on the car.

[S4toSTI]

Originally Posted by Wiisass

Now you should get them tested before you put them on the car.

Tested?

[TROLL]

yes, intersted in how these can be tested, and moving this to suspension forum since hopefully its about to get very educational...

[Wiisass]

To find out the true rate of the bar. Otherwise it's just another random piece of metal that you're bolting to the car in the hopes that it will do something good. But if you know what the bar is actually going to do, you can factor it in to the rest of the suspension design and come out with a much better set up car.

[S4toSTI]

HOw would whatever measurement you are doing affect how you would set up the rest of the suspension... and what are you weighting/measuring?

[Wiisass]

You are measuring the stiffness of the bar. A sway bar is simply a spring that acts only in roll ideally. It will act whenever one wheel travels more than the other. The idea is that you can run a softer main spring so that in ride the car will ride better and then when you are cornering the sway bar will add to the roll stiffness of the car. So without knowing the stiffness of the bar, it would be like not knowing the stiffness of the springs you are putting on the car and with a race car, you should know everything.

Here's something I wrote about sway bars on another forum:

Sway bars are an interesting thing. In one respect they help the handling of the car and in another they hinder the car's ability.

How they help. When you turn, the suspension moves the wheels in an arc. This is your camber curve. You want to have negative camber on the more heavily loaded wheel in order to produce the most possible lateral force. Depending on the tire, the amount of camber desired is different. Some tires love camber, so don't like it as much, but most tires will produce more lateral force with some negative camber versus zero or positive camber. This is due to construction and the way slip angles develop, but that's not something we're going to get into here.

Anyway, sway bars act on the unsprung mass of the car and tie it together with the chassis. So when you are cornering the body wants to roll due to acceleration but the sway bars are acting at this point and they're acting like another spring, which is all they really are. So this limits the amount the suspension will travel. So say you started off with -2 degrees of camber. And as you roll the suspension will gain camber relative to the car, but lose camber relative to the road. At least this is how it works with most suspensions. Stupid stuff like too low MacP cars will gain camber with jounce and make this effect even worse. So for the most part the wheels want to camber in a certain amount per travel but the angle the body is taking is usually more than the camber will be gaining, so you will essentially be losing camber relative to the road. If this goes too far when your car is at it's max roll angle, the camber will also be the closest to positive or you may even have positive camber. Sway bars just act as a stiffer spring in roll that will resist the movement of the body and stop the wheel from traveling as much, therefore allowing you to maintain more of the negative camber the tire wants.

The bad part of all of this is that the sway bar ties together the unsprung mass. On the outside wheel the springs are acting together which makes the spring rate much higher. But on the inside wheel the two springs are fighting. The spring is pushing the tire down while the sway bar is trying to pull the tire up. This will lower the max amount of lateral force that the car is able to provide. Two evenly loaded tires will produce more grip than one fully loaded tire.

So now you should see why sway bars can be good and why they can be bad. So now you have to find a balance between the two. For a softer sprung car that is only on the street, you can get away with a bigger sway bar. But for a real track car, I think that most of the bars on the market are too stiff. I think a softer bar paired with stiffer springs and good dampers is the best setup for a car that is meant to handle at the limit.

The thing with most bars, even with spring rates in the 400-500lb/in range (or 7-9kg/mm for everyone that doesn't realize that kg/mm isn't a real way to rate springs), is that the sway bars will be adding sometimes more than 50% of the roll rate. I don't think this is a good way to do. Ideally, I like to use sway bars to adjust the total lateral load transfer distribution of the car rather than to add to a large percentage of the roll rate of the car. This is the way it should be done for a real race car.

These percentages and numbers are coming from physical testing that I actually did. So there is no speculation there. Everything was measured and analyzed, so I'm not pulling numbers out of my ass to make a point. I wish the numbers were a little different and then I wouldn't have to figure out a better way to do a sway bar so it's not screwing up the handling of the car more than it's helping.

That's why adjustable bars are nice. Depsite being too stiff for the way I would setup a car, you can adjust the front to rear balance of the lateral load transfer. This is a way of defining which end of the car will slip first. So you can add understeer or oversteer through the bars. But this can be done with much softer bars than everyone is running, but most people think the bigger the bar the better.

That's it for now, I probably missed something, if I did, just ask.

Tim

So what you need to measure is the rate of the bar, how much the bar move relative to how much the wheel moves, the rate of the springs, how much the springs move relative to the wheel and then a lot of weights and the center of gravity and some other things like track, wheelbase, etc. This will give you a very good idea of the total lateral load transfer distribution of the car. So you can estimate whether the car will understeer or oversteer at the limit. All these measurements will also help when you are dialing in your dampers. But to set a car up right, you need to make sure the spring balance is correct before you start messing with the dampers. Some people do this by runninng the car without dampers or with the dampers empty or you could just do steady state testing like on a skidpad to make sure your springs are correct.

As far as what you are measuring just in regards to the sway bar. Since it is just a torsional spring, you need to measure the amount of deflection for a given moment. You want a number with the units of ft-lb/deg or some equivalent (in-lb/deg, N-m/rad, etc). So you would restrain the bar at it's mounting points and then apply a load where the endlink would bolt to. This will create a moment around the axis of rotation of the bar. It would be equal to whatever load is applied multiplied by the moment arm length. The moment arm length is the distance from the endlink mounting point to the axis of the bar. And you would need to fix the other side of the bar so it does not move and then measure the deflection of the side that the load is applied to. This will give you the physical stiffness of the bar. It is best to do this for a range of loads to you can see if the bar is going to have a linear rate or a progressive or digressive rate. Once that true stiffness of the bar is known. Then you can use the geometry measurements off of the car and the other variables that i mentioned earlier and get a good idea of how the car will handle.

Alright, I think that's about it for now, I was all over the place a little, but I missed something just let me know and I'll clarify.

Tim

[TTsupra911]

It's not like the Hotchkis Bar is some random Ebay piece of ****. The Hotchkis Sway bars for the SRT-4 are the best on the market for the car. I have never heard one negative comment on these bars.


ohh by the wya I am jeolous, but I will be bying a set in a few weeks.

[Wiisass]

Yeah, but you still don't know the rate. You missed the point of everything I typed. The car these are going on is supposed to be a full race car, so if you really want to be able to dial in the suspension and take a lot of the guessing out, the rate of the bar should be known.

I never made a negative comment about the bars. And what's that mean that they're the best on the market. That's like saying that a certain spring is the best on the market or a turbo, it should all be based on its function and desired performance. So by saying these are the best and comparing them to ebay bars just means that they are less likely of fatiguing and breaking it doesn't say anything about their contribution to the roll rate of the car.

[Big_John]

Originally Posted by Wiisass

To find out the true rate of the bar. Otherwise it's just another random piece of metal that you're bolting to the car in the hopes that it will do something good. But if you know what the bar is actually going to do, you can factor it in to the rest of the suspension design and come out with a much better set up car.

Interesting test setup.

Have you been able to duplicate the manufacturer's "advertised" roll rates? Any significant difference between bars of the same manufacturer due to manufacturing tolerances noted?

I'm curious about your "soft bar, stiff spring" statement. That differs from all the old school suspension theory of "soft springs, stiff bar". I'm no suspension expert by any stretch of the imagination, so I may not be fully understanding this. Can you elaborate?

[Wiisass]

I haven't been able to really find manufacturer data on any of the bars that I've tested. Some will say stuff like xx% stiffer than stock, but it seems like it's somewhat general and just based on the difference in OD rather than the actual difference in the stiffness of the bar. I haven't had the opportunity to test several different bars from the same manufacturer, so I can't say anything for different manufacturer quality control or tolerances.

The soft bar, stiff spring idea is more for a race car. Carroll Smith talks about this a little in some of his books. I don't like the sway bars to contribute more than the necessary amount to the roll rate. This amount is different depending on the setups and cars and tracks they will be raced on. But this is mainly because a sway bar will decrease the total amount of lateral force available due to the inherent increase in lateral load transfer. Ideally, I would like the sway bars to be adjustable to be able to adjust the total lateral load transfer distribution something like +-5-10% of ideal. This will give a good range of adjustment to balance the oversteer/understeer behavior of the car. So the softest bar that will accomplish this would be ideal for a track car. Of course this is assuming a decent track surface and that the springs required to get the control don't have any negative effects.

The balance between springs and bars and the amount of both needed are compromises based on a lot of things. And even for the same car, things can change on different tracks. There are several things to look at, which I won't get into here, but it's probably a lot more than most people think.

As far as the old school soft spring, stiff bar idea. People tend to have different theories on this. And depending on the application sometimes this is ideal. For a street car, softer springs and a stiffer bar can be a good setup. A street car won't get pushed to the same limits as a track car so the decrease in lateral force capacity from the larger bar won't matter as much as if it were a track car. Also on rougher surfaces softer springs may be necessary to maintain traction and the larger bar would then be needed to control the body in roll. You also have to consider suspension geometry into all of this. An indepent suspension will have a lower roll center than a solid axle, so the springs needed for both to have the same roll gain would be less on the solid axle car.

Like I said before there is a lot that goes into this. If you would like me to go more into it in a general sense, I can do that later, but this should be enough for now.

[htheduck]

wissass, thanks for the writeup. it's been ages since my mechanical engineering classes....lol

anyways, how is the device measuring the moment of the load vs. the mounting points...and what is the load: fluid poured into the jug?

and can you remind me why hollow is (more?) torsional strength than solid....thx.

[Wiisass]

measuring the moment of the load vs. the mounting points

What do you mean? I used a digital level to measure the change in angle of the moment arm. I also used on on the other side so I could cancel out any deflection of the jig. The load was water in the jug. The load ranged from 10lbs to 50lbs. This obviously wasn't the ideal way to test this, but it worked out pretty well and the results were repeatable so I was happy with how it turned out.

[htheduck]

Originally Posted by Wiisass

What do you mean? I used a digital level to measure the change in angle of the moment arm. I also used on on the other side so I could cancel out any deflection of the jig. The load was water in the jug. The load ranged from 10lbs to 50lbs. This obviously wasn't the ideal way to test this, but it worked out pretty well and the results were repeatable so I was happy with how it turned out.

digital level, copy that.
i couldn't determine what it was in the pic.

[Wiisass]

It's something like that. I have 2 of them and they're both different models. but they're awesome, I use them all the time.

[BMS]

To find the different rates and strengths is you could either call Hotchkis or it will say it in the paper pamphlet that comes with it. we will test it on the track!! More accurate results

[htheduck]

Originally Posted by BMS

To find the different rates and strengths is you could either call Hotchkis or it will say it in the paper pamphlet that comes with it. we will test it on the track!! More accurate results

seat of the pants tuning...i love it; good stuff.

[Wiisass]

Originally Posted by BMS

To find the different rates and strengths is you could either call Hotchkis or it will say it in the paper pamphlet that comes with it. we will test it on the track!! More accurate results

I think you missed my point entirely. Everything I said to do would save you time at the track. People just don't realize how important suspension is. Saying test it at the track is like installing the bigger turbo, injectors, etc and saying you'll tune it at the track.