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The effective spring rate (stiffness), of a fixed swaybar is proportional to the bar diameter raised to the 4th power. If all other variables remain the same (bar length, arm length, material selection, etc., a 10% increase in diameter results in a 46% increase in stiffness.

Sway bar Conversion Chart

135314
 

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Discussion Starter #23 (Edited)
Im not going to have a hollow sway welded. The diameter is not the only consideration. Settings if adjustable matter.
The material matters. How the bar is made also matters. Already bought a rear Hotchkis.
 

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Shoot hotchkis an email, they replaced my cracked rear sway bar at no charge. Perhaps they will refund you back on the purchase you just made.
It's worth a shot, however if you didn't catch his previous post, he said it's been like 15 years that it was on his car, and then there's this that I found:

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Im not going to have a hollow sway welded. The diameter is not the only consideration. Settings if adjustable matter.
The material matters. How the bar is made also matters. Already bought a rear Hotchkis.
Why do you have a problem welding tube? It would be more of a problem welding a solid bar.
 

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The effective spring rate (stiffness), of a fixed swaybar is proportional to the bar diameter raised to the 4th power. If all other variables remain the same (bar length, arm length, material selection, etc., a 10% increase in diameter results in a 46% increase in stiffness.

Sway bar Conversion Chart

View attachment 135314
How did you get the diameter raised to the fourth power, isn't it the radius to the third power?
I could be wrong too, as its been a while since I did it manually.
 

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A handful of reasons that dont matter cause I got another bar.
No worries, the reason I asked is I make most of my own sway bars. The rear one is proving a challenge due to the sharp 90 degree bend with larger diameter tube after the chassis mount.
 

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Gosurfun,
Information was obtained from;
Automotive Suspension and Steering Systems by Birch.
It's got an equation for the strength of a stabilizer bar:
R = 5e6 x D^4 / (0.4244 x A^2 x L + 0.2264 B^3)
where: (english units feet? inches?)
R = Torsion rate of bar
D = Bar diameter
A = Effective length of lever arm
L = Length of bar
B = Length of lever arm
Rear Wheel Drive (RWD) Cars:
A stiffer front sway bar on a rear wheel drive car will reduce oversteer. Typically, a rear wheel drive car will handle better with a front sway bar that is stiffer than the OEM piece. Some rear wheel drive cars, however, also understeer. If your vehicle understeers, front or rear wheel drive, a stiffer rear sway bar will make the car handle more neutrally.
What Affects the rate Of Sway Bars;
  • The length of the portion of the bar that will twist affects its rate. The longer this portion is, the softer the rate.
  • The outer diameter of the bar affects its rate. The larger, the stiffer it will be.
  • Hollow bars are less stiff than solid bars, so the wall thickness affects the rate. Since the elasticity of a sway bar is a result of cross sectional area, the overall diameter doesn't matter so much. For the most part, solid tube sway bars are stiffer than "larger" sway bars made of hollow tube. This is because the hollow metal tubing actually has less cross sectional area and therefore has less resistance to bending moments. May be some variables that may make a hollow bar stiffer than solid bar.
  • The arm length affects the rate, the longer the arm, the softer the bar rate.
  • The arm material can affect the rate. If the arm bends under load, the rate will be softer.
  • The hardness of the steel used for the bar affects the rate. There is a modulus of elasticity for each type of steel that relates to the mixture of metals and the hardening process used in the manufacturing of the steel. 4130 chromoly steel and 4340 nickel-chromium-molybdenum alloy steel (very high Tensile Strength), are common materials. This is the part we cannot know because it is almost never published.
135426

135427

Adjustable sway bar settings - Innermost hole is Full Stiff, Outermost hole is Full Soft.
 

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Gosurfun,
Information was obtained from;
Automotive Suspension and Steering Systems by Birch.
It's got an equation for the strength of a stabilizer bar:
R = 5e6 x D^4 / (0.4244 x A^2 x L + 0.2264 B^3)
where: (english units feet? inches?)
R = Torsion rate of bar
D = Bar diameter
A = Effective length of lever arm
L = Length of bar
B = Length of lever arm
Rear Wheel Drive (RWD) Cars:
A stiffer front sway bar on a rear wheel drive car will reduce oversteer. Typically, a rear wheel drive car will handle better with a front sway bar that is stiffer than the OEM piece. Some rear wheel drive cars, however, also understeer. If your vehicle understeers, front or rear wheel drive, a stiffer rear sway bar will make the car handle more neutrally.
What Affects the rate Of Sway Bars;
  • The length of the portion of the bar that will twist affects its rate. The longer this portion is, the softer the rate.
  • The outer diameter of the bar affects its rate. The larger, the stiffer it will be.
  • Hollow bars are less stiff than solid bars, so the wall thickness affects the rate. Since the elasticity of a sway bar is a result of cross sectional area, the overall diameter doesn't matter so much. For the most part, solid tube sway bars are stiffer than "larger" sway bars made of hollow tube. This is because the hollow metal tubing actually has less cross sectional area and therefore has less resistance to bending moments. May be some variables that may make a hollow bar stiffer than solid bar.
  • The arm length affects the rate, the longer the arm, the softer the bar rate.
  • The arm material can affect the rate. If the arm bends under load, the rate will be softer.
  • The hardness of the steel used for the bar affects the rate. There is a modulus of elasticity for each type of steel that relates to the mixture of metals and the hardening process used in the manufacturing of the steel. 4130 chromoly steel and 4340 nickel-chromium-molybdenum alloy steel (very high Tensile Strength), are common materials. This is the part we cannot know because it is almost never published.
View attachment 135426
View attachment 135427
Adjustable sway bar settings - Innermost hole is Full Stiff, Outermost hole is Full Soft.
Thanks for that appreciate it, one fault in there, hollow tubes do not have to be much larger in diameter than a solid bar to be more resistant to bending or torsion ("I" value is what matters). The best example of this is the tailshaft, light thin tube, large diameter, not much cross sectional area, light weight and takes large torque loads. A solid shaft has no strength in the middle 3/4 or more of the material, as the outside layer has to fail before it takes the load. If the outside layer has failed, the middle will fail as soon as the same load begins to be applied. The I value is normally in the steel manufacturers data spec sheets. I've forgotten the formula for tube, but for square and rectangular hollow sections the formula is proportional to the h^3 (height) from the centroid. For hollow sections the "I" value of the hollow part is subtracted from the "I" of a same sized solid section. It does not take much of an increase in the h when it is cubed to be greater than a bit smaller sized cross section.
 

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Gosurfun,
Information was obtained from;
Automotive Suspension and Steering Systems by Birch.
It's got an equation for the strength of a stabilizer bar:
R = 5e6 x D^4 / (0.4244 x A^2 x L + 0.2264 B^3)
where: (english units feet? inches?)
R = Torsion rate of bar
D = Bar diameter
A = Effective length of lever arm
L = Length of bar
B = Length of lever arm
Rear Wheel Drive (RWD) Cars:
A stiffer front sway bar on a rear wheel drive car will reduce oversteer. Typically, a rear wheel drive car will handle better with a front sway bar that is stiffer than the OEM piece. Some rear wheel drive cars, however, also understeer. If your vehicle understeers, front or rear wheel drive, a stiffer rear sway bar will make the car handle more neutrally.
What Affects the rate Of Sway Bars;
  • The length of the portion of the bar that will twist affects its rate. The longer this portion is, the softer the rate.
  • The outer diameter of the bar affects its rate. The larger, the stiffer it will be.
  • Hollow bars are less stiff than solid bars, so the wall thickness affects the rate. Since the elasticity of a sway bar is a result of cross sectional area, the overall diameter doesn't matter so much. For the most part, solid tube sway bars are stiffer than "larger" sway bars made of hollow tube. This is because the hollow metal tubing actually has less cross sectional area and therefore has less resistance to bending moments. May be some variables that may make a hollow bar stiffer than solid bar.
  • The arm length affects the rate, the longer the arm, the softer the bar rate.
  • The arm material can affect the rate. If the arm bends under load, the rate will be softer.
  • The hardness of the steel used for the bar affects the rate. There is a modulus of elasticity for each type of steel that relates to the mixture of metals and the hardening process used in the manufacturing of the steel. 4130 chromoly steel and 4340 nickel-chromium-molybdenum alloy steel (very high Tensile Strength), are common materials. This is the part we cannot know because it is almost never published.
View attachment 135426
View attachment 135427
Adjustable sway bar settings - Innermost hole is Full Stiff, Outermost hole is Full Soft.
I had a better look at the formula and have a few problems with it. There does not seem to be an allowance for the type of material used, or hollow and solid bars, there is no Pie value in there either. Trying to work out anything to do with tubes or solid shaft without using Pie (22/7) would be very difficult if not impossible. The centre section of the bar between the chassis mounts is subject to torque (twisting) and the parts outside of the chassis mounts are subject to bending (flex in the lever arm and the lever arm length applying the torque should be considered separately) and I don't know where or what they have derived this formula from. There is no separation of the lengths into the individual components. I figured out why the D value is to the fourth power, its due to using it for the area, so D cubed, is multiplied by another D to make D^(4) which might mean they are only considering solid bars. What is the "e" value?
Its no use to me, as I sometimes user small diameter tube or part of a stock sway bar (usually solid bar) for the lever arms.
 
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