F body sway bar or not

[BJM]

Okay, I did my springs and bushings last winter. I bought the big 36 mm F body bar but did not put it on yet. My car does not over steer at all and slightly understeers. Putting the big front bar on would make it handle worse.

Unless someone put on really stiff rear springs in their car I don't see how the huge front bar could be used.

Who has the 36 mm bar on their car and what do you have for springs front and rear. I have the 5660 (640 lb/in) fronts and matching variable rates in the back peaking at 160 lb/in. I would like to hear what other people's experience is.

I know the stiff front bar would feel cool up until it starts sliding but my car would perform worse I am sure.

 

[UNGN]

The big bar is hollow, so it may not increase understeer much more than the stock bar.

If you want your car to understeer less, do you have an ATR or equivalent rear bar? That will do it.

 

[Racer X]

If you want to reduce understeer get stronger front springs and a bigger REAR bar. A bigger front bar will increase understeer.

Hope that helps.

 

[BJM]

The F body big bar is about 65% stiffer than the stock GN one.

Stiffer front springs make understeer worse, its all in the proportions you choose. I stiffened front and rear springs equally and my understeer remained unchanged as you would expect. I am thinking of softening the fronts somewhat to make use of the big front bar.

I want to know who has used a F body bar without understeering. I bet no one has, that they like the tight and level response but that they wind up with understeer.

 

[Racer X]

Stiffer front springs make understeer worse

You need stiffer fronts than stock. I use 700# on the fronts and the understeer is there, but no where near where it used to be...according to the pyrometer.

Another thing here about understeer, if you are still using the 15" tires up front your car will still have some push to it. Your car will pogo around the corners from sidewall flex. If you want to do extreme cornering get some 16's or 17's so that you will have a good consistant feel to the car.

its all in the proportions you choose

Exactly! Just like the engine recipes we all use, there are suspension recipes as well.

 

[Two Lane]

Hollow F-Body Front Swaybars

Are all of the aftermarket bars hollow like the GM?

How much weight savings from factory unit?

TIA--------------------------

 

[BJM]

I did switch to 16" GNX rims with Michelin Pilots which are really stiff.

RACER X aren't you the guy advocating soft soft springs and stiff roll bars? I'm probably mistaken. Do you use your pyrometer to compare front to rear temps or across-the-tire gradients of temperature.

Let's hear recipes. I wish to have a soft ride only a little stiffer than stock. My 5660's are 50% stiffer which is a little too much, and they are too tall. I am going to drop down to 5658's in front.

I want flat cornering and would like to be able to use the F-body front bar. I will have to find a matching rear bar though.

 

[BJM]

I hear people saying the hollow bar is about 10 pound lighter. Its pretty light in my hands.

 

[Racer X]

Originally posted by BJM
I did switch to 16" GNX rims with Michelin Pilots which are really stiff.

Pilots are a great tire. Lotsa grip!

RACER X aren't you the guy advocating soft soft springs and stiff roll bars? I'm probably mistaken. Do you use your pyrometer to compare front to rear temps or across-the-tire gradients of temperature.

Nope Stiffer springs and the right sway bars. I use the Pyrometer for both to tune the chassis. I take three temps per tire. Outside, middle, and inside of each tire. I check for a comparision between all four tires to see if the car is pushing or if it's loose. I then compare the three temps relative to each tire(and this is more important on the Fronts for our cars) to check for proper camber settings. I am looking for no more than 20 degrees difference in the temps.

Let's hear recipes. I wish to have a soft ride only a little stiffer than stock. My 5660's are 50% stiffer which is a little too much, and they are too tall. I am going to drop down to 5658's in front.

I want flat cornering and would like to be able to use the F-body front bar. I will have to find a matching rear bar though.

Here is my set up One thing though, it shows that I am using an 1-3/8" front sway bar...I am now using the stock 1-1/4".

 

[UNGN]

If you don't like understeer, I repeat: ATR or Herb Adams rear bar. I don't think there's a front swaybar on the planet can make a car understeer with one of those out back. My big block 2+2 has an extra 200+ lbs over the front end and it will spin on a dime if I drive stupid. Eibach springs, stock 32mm front bar, -.5 degrees of camber, 255/50's all the way around, herb adams rear bar. I just have to think it around corners. I can even steer it with my right foot if I just wasn't going so darn fast and the road wasn't so unpredictable.

 

[MAP]

Greetings BJM,

I've never tried, nor even seen, the 36mm hollow F-body bar. But here's a way to take a crack at calculating its effect. First, determine if the bar is formed from constant wall-thickness tubing. If it is, as is probably the case, then estimate the bar's centerline running length from end to end, and then weigh the bar. The bar's volume is: pi*[phi(out)^2 - phi(in^2)]*L, where pi is 3.1416, phi(out) is the bar's outer diameter, phi(in) is the bar's inner diameter, and L is the centerline length of the bar. The weight of the bar is equal to the bar's volume times its mass density. Use 7.8g/cc for steel, and make the appropriate conversion to the units you like.

Note that if you weigh the bar, and have all of the parameters above except the bar's inner diameter, then you can re-arrange algebraically to solve for phi(in). Once you've got this, then you can compute the bar's relative torsional stiffness as: phi(out)^4 minus phi(in)^4. To compare to a solid bar, simply take phi(out)^4. The ratio of the two will allow you to make a fairly good judgment of relative stiffness to a solid bar you already know, or can get an opinion about. HTH!

Best,
MAP

 

[BJM]

MAP

Thanks, but I already know how stiff it is. Since the two bars are nearly identical shape wise I simply compared relative moments of inertia (MOI). I get about 65% stiffer for the F-Body bar.

What I really need to do is compared the cars roll stiffness in ft.lb/radian Front and back and factor is the front and rear mass to see if I can predict over or understeer.

 

[b4black]

Since you have it, put it on, see how it feels. Don't like it, take it off. It's just a sway bar, not a new set of heads.

Theory tells you what should be, experimentation tells you what is.


I like my F-body bar BTW.

 

[UNGN]

Originally posted by BJM
MAP

Thanks, but I already know how stiff it is. Since the two bars are nearly identical shape wise I simply compared relative moments of inertia (MOI). I get about 65% stiffer for the F-Body bar.

Moment of intertia...Try again. That doesn't have anything to do with the stiffness.

 

[Racer X]

Originally posted by UNGN
If you don't like understeer, I repeat: ATR or Herb Adams rear bar.....

Where did you get your Herb Adams bar? I thought he quit making them long ago. I would love to get me hands on one

An aside, are you going to Silverstate this year UNGN?

 

[BJM]

MOI has everything to do with stiffness! Area Moment of Inertia that is. You might quibble with my calling the torsional constant a MOI value.

Anyway Assuming a 10 mm wall thickness we get the following comparison:

(36^4-10^4)/32^4=1.59

 

[UNGN]

Sorry to get all math teacher on you, but...

Originally posted by MAP
Greetings BJM,

The bar's volume is: pi*[phi(out)^2 - phi(in^2)]*L, where pi is 3.1416, phi(out) is the bar's outer diameter, phi(in) is the bar's inner diameter, and L is the centerline length of the bar. The weight of the bar is equal to the bar's volume times its mass density. Use 7.8g/cc for steel, and make the appropriate conversion to the units you like.

I think you missed a number . Its pi*R^2 and not pi*phi^2. You have to divide by 4 to get the proper area.

Originally posted by BJM


Anyway Assuming a 10 mm wall thickness we get the following comparison:

(36^4-10^4)/32^4=1.59

If you assume a 10mm wall shouldn't the 10 in your equation be a 16?

It doesn't matter anyway because assuming a 10mm wall is a bad assumption. Using the difference in total weights 23 lbs vs. 13 lbs, I roughly calculated that the hollow core of the 36 mm bar would be at least 26 mm, giving a 5 mm wall thickness.

This gives about a 15% difference between the two, which makes a lot more sense than 65%.

Originally posted by Racer X


Where did you get your Herb Adams bar? I thought he quit making them long ago. I would love to get me hands on one

An aside, are you going to Silverstate this year UNGN?

I bought from Summit back when they were still available (3 years ago). It's even more brutal than the ATR bar. I really like it.

Our next Open Road race will be Big Bend in the spring. I would love to go to Speed weeks at Silver State but too many schedule conflicts. Maybe next year

 

[BJM]

UNGN

You were right about the wall thickness. My formula was right, the values were wrong. However I re-solved using the 23 and 13 pound values and I get a bar length of 1.66 m which seems too long so I will have to go and weigh the bar I have off the car, the 36 mm one.

Also the 10. mm wall is correct where I was looking in the drain holes on the ends. Obviously it can't be that thick throughout.

Has anyone weighed the stock bar? a 32 mm bar 1.66 m long seems off. I will measure the large bar for length as well.

If it does turn out to be only slightly stiffer, then why bother?

 

[MAP]

Greetings UNGN, BJM

UNGN> Thanks! Much appreciated. You're quite right, pi*r^2 it is, so one would take my first expression, and divide by four, as you wrote. That's what I get for writing so quickly at something like 1AM after a very long day!

About understeer/oversteer - there's much more to this than simply front/rear roll stiffnesses, and front/rear weight distributions. The conventional wisdom is that tire slip angles increase on the end with higher roll stiffness, due to greater "weight transfer" on that axle relative to the other in a turn, but changes in tire contact patch as a function of body roll and camber change, can offset this in a traction-limiting condition to a great extent.

Moral of the story: increasing roll stiffness at the front, relative to the rear, won't necessarily make the car understeer more; in fact, it may understeer far less: this is especially true on the G-bodies with their poor camber-gain characteristics at front.

Best,
MAP

 

[tcgn]

What year F bodies has the 36mm Hollow sway bar`s if I were to call a Junk Yard and ask for the front sway bar?Thanks
Thomas