Will a thicker rear sway bar make the back less tipsy and bouncy over bumps?
09-02-2010, 07:04 AM
#21
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You are incorrect. There is always some preload. Put two passengers in the rear seat... The Jeep settles on its suspension and the bar is loaded on both sides. Weight transfer when driving will load the bar. Virtually any motion will load the bar. Albeit, only very slightly. However, variations in ride height will occur and that will load the bar.
Technically, a sway bar provides no force, it provides resistance, which is returned as a force on rebound. It twists and stores energy, and then releases that energy with some small loss. Increased roll stiffness means reduced body roll relative to the axle. That we can agree on. Excessive roll resistance can lead to lifting a wheel under hard cornering. That's why you lose flex. Large diameter sway bars will limit wheel travel and tend to unload the inside wheel while cornering.
Going to a larger rear bar can have unwanted side effects. Typically, if the bar is bigger than needed to control body roll, you can induce oversteer. That's due to unloading the inside wheel too much. For the average driver, oversteer is like the plague; you don't want it.
2. I am not a race expert but when I was a kid racing my MGB (please keep your laughter to a minimum. I didn't even have a license) we stiffened the front and rear to reduce understeer and induce predictable oversteer. My method consisted of going to the junkyard with a measuring tape and finding the correct length bar that looked to be "fatter" (an engineering term) than the one I had. Oversteer is bad, but much better than the alternative.
In a race car, with extreme spring rates and damn little suspension travel, you tune the total spring rate by adjusting the sway bars. If you've watched racing on television, you may have heard a driver or announcer talk about adjusting handling. The driver does that by adjusting the sway bar. Early adjusting methods were as simple as repositioning the links to increase or decrease stiffness for a given deflection while actually racing. Therefore, you can change from understeer to oversteer and back again. In the case of the Jeep, you can reduce understeer (that's "tight" for you NASCAR guys) with a bigger rear bar. Go too big, and you will have oversteer (loose). The trick is knowing what is too thick. That falls under the control of the Engineer who designs the bar. It should be designed not only to reduce body roll (which is not the real issue. The real issue is what happens when the body stops rolling and sets), it needs to be tailored to decrease understeer without being so stiff as to unload the inside tire. I'll assume the sway bar in question is well designed. Just keep in mind that no mechanical change exists in a vacuum.
I mentioned body roll. Why is body roll bad? Inertia. Typically, when driven close to the limit of a tire's adhesion, body roll can induce bad behavior. Again, it's not the body motion, it's what happens a second later. Let's say the tires are at 95% of their lateral adhesion. Commonly, the tires reach their limit before body motion stops. When the body motion ceases, that sudden transfer of inertia goes directly into the tires. Very quickly, you exceed the mechanical adhesion limit of the tires, and (if you are lucky) you spin the vehicle or understeer off of the road. Thus, vehicles with lots of body roll can't be driven to the tire's limits without great risk of adventure. Decrease body roll and you can drive closer to the tire's limits. That however, isn't what hellhound13 is worried about. I think he finds the "tippsy" body roll to be very uncomfortable.
I mentioned body roll. Why is body roll bad? Inertia. Typically, when driven close to the limit of a tire's adhesion, body roll can induce bad behavior. Again, it's not the body motion, it's what happens a second later. Let's say the tires are at 95% of their lateral adhesion. Commonly, the tires reach their limit before body motion stops. When the body motion ceases, that sudden transfer of inertia goes directly into the tires. Very quickly, you exceed the mechanical adhesion limit of the tires, and (if you are lucky) you spin the vehicle or understeer off of the road. Thus, vehicles with lots of body roll can't be driven to the tire's limits without great risk of adventure. Decrease body roll and you can drive closer to the tire's limits. That however, isn't what hellhound13 is worried about. I think he finds the "tippsy" body roll to be very uncomfortable.
“stable” as defined by The Mechanical Engineering Reference Guide is “Lacking wobblyness, tippyness, and/or loosy-goosyness”. I meant cornering would feel more car like, less boat like.
To the point... Sway bars are absolutely part of the total spring rate. Relative to vehicles with comparatively low spring rates and lots of suspension travel, the resulting increase in rate due to minor deflections is small. Nonetheless, it is there. Will the driver notice? That depends on whether the deflection is limited to one side and how great the deflection is.
Feel free to argue that sway bars do not increase total spring rate. You'll still be incorrect, but you may avoid the headache.
Feel free to argue that sway bars do not increase total spring rate. You'll still be incorrect, but you may avoid the headache.
“I DO know that the spring rate is not affected by the sway bar when going straight down the road. When hitting RR crossing type bumps, speed bumps, or dips in the road you would not notice the difference in a 60mm bar or none at all. When hitting a pot hole the difference you notice would be negligible.”
09-02-2010, 07:36 AM
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09-02-2010, 04:53 PM
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Oh I love this kind of banter - in the end it will (hopefully) result in data the OP can use to draw a conclusion. Personally I can genuinely appreciate 'seat of the pants' experience and know it counts, big time. That said, the geek in me really enjoys reading every word of the 'engineering side' of the story.
I think one of the great accomplishments of a forum such as this is bringing people with a common interest, but from vastly different walks of life together - allowing a collaboration that otherwise would never happen.
Now...let's all go get a beer and play nice (actually I'm going to grab a scotch)
Oh...and clearly mkjeep has added the most valuable information to this post...a picture is worth a thousand words - and those were all good words.
I think one of the great accomplishments of a forum such as this is bringing people with a common interest, but from vastly different walks of life together - allowing a collaboration that otherwise would never happen.
Now...let's all go get a beer and play nice (actually I'm going to grab a scotch)
Oh...and clearly mkjeep has added the most valuable information to this post...a picture is worth a thousand words - and those were all good words.
Last edited by svalvasori; 09-02-2010 at 04:55 PM.
09-02-2010, 06:39 PM
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Happy times...
Of course I'd have to chill it to 32.6 degrees and serve it in a Dewar flask on a pneumatically adjusted hydraulically leveled serving table for it to be suitable
Just kidding Widewing
09-03-2010, 01:15 PM
#25
JK Freak
I'm just enjoying the discussion, no animosity here. If Widewing were here I'd buy him a beer and we could BS all night.
Of course I'd have to chill it to 32.6 degrees and serve it in a Dewar flask on a pneumatically adjusted hydraulically leveled serving table for it to be suitable
Just kidding Widewing
Of course I'd have to chill it to 32.6 degrees and serve it in a Dewar flask on a pneumatically adjusted hydraulically leveled serving table for it to be suitable
Just kidding Widewing
I work in a high tech aerospace environment... I have to write reports and communicate in technical terms. It's a now habit..
09-04-2010, 06:37 AM
#26
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Hell yeah, I'd share a beer, hell, more like a couple of pitchers. It's all in friendship. As to being an ass, my wife could provide you with references to that fact..
I work in a high tech aerospace environment... I have to write reports and communicate in technical terms. It's a now habit..
I work in a high tech aerospace environment... I have to write reports and communicate in technical terms. It's a now habit..
09-04-2010, 08:01 AM
#28
JK Freak
I understand.... Lots to consider.
Let me boil it down to a few things to consider. I urge you to discuss this with the manufacturer's rep before buying.
Increasing the diameter of the rear sway bar will reduce body roll. However, the bar in question appears to be designed for JKs with a minimum of a 3" lift and larger tires. Thus, it may be too thick for your stock suspension. So, you should talk with a tech rep at Full Traction, or ask the sales person to do it for you.
Why is this important? On the street, a sway bar that's too thick can increase roll stiffness too much. The risk is that when cornering briskly on a road, the rear inside wheel will unload (tries to lift off of the road). This causes a loss of traction at the rear and the Jeep may oversteer. It will get more pronounced if you back off the throttle when you feel it beginning to break loose (weight transfer to the front). I don't know if the ESP algorithm can compensate for that as it might be outside of what the software was written to handle. So, it's something to consider. That's why you should chat with Full Traction about installing it on your stock suspension JK.
There's a upside. This sway bar has three link locating positions that allow you tune the stiffness of the sway bar. I would suggest hooking it up at the softest position and adjust from there to suit what you prefer.
Let me boil it down to a few things to consider. I urge you to discuss this with the manufacturer's rep before buying.
Increasing the diameter of the rear sway bar will reduce body roll. However, the bar in question appears to be designed for JKs with a minimum of a 3" lift and larger tires. Thus, it may be too thick for your stock suspension. So, you should talk with a tech rep at Full Traction, or ask the sales person to do it for you.
Why is this important? On the street, a sway bar that's too thick can increase roll stiffness too much. The risk is that when cornering briskly on a road, the rear inside wheel will unload (tries to lift off of the road). This causes a loss of traction at the rear and the Jeep may oversteer. It will get more pronounced if you back off the throttle when you feel it beginning to break loose (weight transfer to the front). I don't know if the ESP algorithm can compensate for that as it might be outside of what the software was written to handle. So, it's something to consider. That's why you should chat with Full Traction about installing it on your stock suspension JK.
There's a upside. This sway bar has three link locating positions that allow you tune the stiffness of the sway bar. I would suggest hooking it up at the softest position and adjust from there to suit what you prefer.
09-04-2010, 09:38 AM
#29
JK Jedi
Thread Starter
I understand.... Lots to consider.
Let me boil it down to a few things to consider. I urge you to discuss this with the manufacturer's rep before buying.
Increasing the diameter of the rear sway bar will reduce body roll. However, the bar in question appears to be designed for JKs with a minimum of a 3" lift and larger tires. Thus, it may be too thick for your stock suspension. So, you should talk with a tech rep at Full Traction, or ask the sales person to do it for you.
Why is this important? On the street, a sway bar that's too thick can increase roll stiffness too much. The risk is that when cornering briskly on a road, the rear inside wheel will unload (tries to lift off of the road). This causes a loss of traction at the rear and the Jeep may oversteer. It will get more pronounced if you back off the throttle when you feel it beginning to break loose (weight transfer to the front). I don't know if the ESP algorithm can compensate for that as it might be outside of what the software was written to handle. So, it's something to consider. That's why you should chat with Full Traction about installing it on your stock suspension JK.
There's a upside. This sway bar has three link locating positions that allow you tune the stiffness of the sway bar. I would suggest hooking it up at the softest position and adjust from there to suit what you prefer.
Let me boil it down to a few things to consider. I urge you to discuss this with the manufacturer's rep before buying.
Increasing the diameter of the rear sway bar will reduce body roll. However, the bar in question appears to be designed for JKs with a minimum of a 3" lift and larger tires. Thus, it may be too thick for your stock suspension. So, you should talk with a tech rep at Full Traction, or ask the sales person to do it for you.
Why is this important? On the street, a sway bar that's too thick can increase roll stiffness too much. The risk is that when cornering briskly on a road, the rear inside wheel will unload (tries to lift off of the road). This causes a loss of traction at the rear and the Jeep may oversteer. It will get more pronounced if you back off the throttle when you feel it beginning to break loose (weight transfer to the front). I don't know if the ESP algorithm can compensate for that as it might be outside of what the software was written to handle. So, it's something to consider. That's why you should chat with Full Traction about installing it on your stock suspension JK.
There's a upside. This sway bar has three link locating positions that allow you tune the stiffness of the sway bar. I would suggest hooking it up at the softest position and adjust from there to suit what you prefer.
09-04-2010, 01:33 PM
#30
JK Freak
What you can do now that has no bad consequences is invest in better shocks to eliminate the bounciness. Improved compression and rebound damping can go a long way to making the JK feel far more secure, both on and off road. How many miles are on your OME shocks?