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Suspension 101

Old 07-02-2018, 06:52 AM
  #1081  
Sunset350ZR
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Is there any performance advantage to changing from bucket?
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Old 07-02-2018, 02:55 PM
  #1082  
guitman32
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Originally Posted by Sunset350ZR View Post
Is there any performance advantage to changing from bucket?
https://my350z.com/forum/brakes-and-...er-or-not.html

Originally Posted by r34 racer View Post
I've always been a lurker, but this thread made me come out of hiding.



The term kinematics is mostly used to refer to the effects of moving a suspension through the arc of its travel on alignment settings such as camber, caster, toe, etc. Moving the spring onto the damper at the upright does not change any of these settings.

If you’re referring to changes in wheel rate caused by moving the spring, then again, your assumption has errors. While moving the spring to the upright does increase the wheel rate, moving the spring to the upright does not create an additional moment that does not exist if the spring is mounted on the mid-link as stock. Moving the spring’s mount point on the unsprung mass farther outboard (to the upright, in this case) simply causes the moment on the suspension generated by a set spring force to be greater than if the spring was mounted farther inboard (on the midlink, as is stock). Remember your fundamental moment equations? Moment = Force * distance from pivot point. Increasing the distance increases the moment for a set force. That is the effect that increases the wheel rate when the spring is moved to the upright, not creation of an additional moment.

Increasing the wheel rate is not uncorrectable. You can compensate by running a softer spring.



I hate to break it to you, but the stock setup is progressive as well. The stock setup is rising-rate progressive until the point where the spring is perpendicular to the mid-link, at which point the suspension becomes falling-rate progressive with additional bump travel. There is no avoiding this progressiveness short of moving to an inboard spring/damper setup with a pushrod or pullrod configuration, or an outboard spring & damper with a nik-link configuration.



I don’t know what you’re talking about – if I remember correctly, the damper shaft rides in a spherical bearing mounted in the rear upper mount. This makes the rear damper a two-force member, meaning that it physically cannot transfer bending moments to the chassis at the rear upper mount.

The upper mount bolts are not particularly load bearing. They are only there as positioning studs, and to keep the damper from falling out of the rear shock tower if the suspension goes to full droop. The load is actually supported by the plate of the rear upper mount itself, as it loads the shock tower in compression in reaction to wheel loads. An overloaded rear damper would not break the bolts, but would rather tear the sheet metal unibody at the shock tower.



A wheel rate is a wheel rate is a wheel rate, and does not depend if the wheel is being loaded by longitudinal acceleration or lateral acceleration. I will agree that there is a good deal of anti-squat on a 350z, but changing the spring location will not change anti-squat effects short of the way you load bushings when the wheel is in ride. A spring & damper mounted on the rear upright will increase the load on that rubber bushing, causing increased bushing deflection, at worst reducing bushing life, and at worse possibly leading to a decrease in the spring & damper’s ability to control wheel travel.

As far as the “static moment” you talk about, the mounting of the spring on the mid-link (behind the upright) also creates the same moment, in a GREATER quantity, as the horizontal distance between the rear hub axis and the mid-link mount on the upright is greater than the horizontal distance between the rear hub axis and the damper mount on the upright.




The 350z does not have a macphereson strut setup – the shocks are never loaded in bending and are two-force members short of bearing drag in the upper and lower mounts. I’d be willing to be the bending loads in the dampers are negligible compared to axial loading.



Changing the spring location DOES NOT CHANGE ANTI- GEOMETRY! Anti dive and anti squat are determined by the declination of the lower and upper a-arms towards the vehicle center of mass. Changing the spring packaging has nothing to do with this! Also, what friction are you talking about specificially?

Spring rates don’t “match” wheel rates. Spring rates DETERMINE wheel rates. Wheel rate = spring rate * (installation ratio)^2. You don’t match your spring rate to your wheel rate, your spring rate DETERMINES your wheel rate!




Mounting the spring on the damper does not reduce unsprung mass except for the fact that you can run a smaller diameter spring with a lower spring rate (thinner spring coils) which, all else equal, probably weighs less.

Moving the spring to the damper does not mean there is no motion ratio between the suspension and the spring. There is still a motion ratio which changes based on the instantaneous inclination of the suspension. Unless you are referring to no motion ratio between the spring and damper, in which case you are correct.



Number 1 is wrong. Moving the spring farther outboard to the upright means you can run a softer spring and have the same ride and roll rates as a stiffer spring mounted inboard on the mid-link.

Spring rate does not mean anything – wheel rate does. You can run the same wheel rate regardless of spring packaging and have more or less the same characteristics under longitudinal acceleration.

I agree with the bushing comment, as well as your postulation that the chassis must be reinforced at the upper mount, either by adding metal thickness or tying the upper mount into a substantial roll cage (not the cusco ******** everyone runs on this site).



Hahah, this seriously made me LOL…you ran sheet metal unibody analysis on COSMOS? REALLY? I can’t imagine Cosmos would give you any meaningful results considering the complex geometry of the unibody. You realize that auto manufacturers spend millions developing proprietary chassis FEA models and solvers, right?

There is no moment on the upper mounts! Both ends are supported in such a manner that there is no bending load on the damper! The lower mount pivots on a bolt, and the upper mount rides in a captured spherical bearing.

Fatigue is an issue, I agree – the shock tower on the chassis must be reinforced. I disagree with the need for a third bolt, but agree with the necessity of chassis bracing in the area of the rear upper mount.
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Old 07-06-2018, 12:44 PM
  #1083  
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Hi,thank you for the in depth write up

I got my car corner weighted today along with a Alinement, the car is just used on track, they have changed a lot of the settings compared to the last company that did the alinement, I was hoping for some thoughts on my settings, the left document is the old settings the right are the new settings
Thanks Al
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Old 07-07-2018, 11:38 AM
  #1084  
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Originally Posted by Alistair White View Post
Hi,thank you for the in depth write up

I got my car corner weighted today along with a Alinement, the car is just used on track, they have changed a lot of the settings compared to the last company that did the alinement, I was hoping for some thoughts on my settings, the left document is the old settings the right are the new settings
Thanks Al
Add extra front camber.

Do you have adjustable rear arms ? I have a feeling you don’t.
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Old 07-09-2018, 08:17 AM
  #1085  
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Yes it has adjustable rear camber arms
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Old 07-15-2018, 10:07 AM
  #1086  
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Originally Posted by Alistair White View Post
Yes it has adjustable rear camber arms
Aftermarket toe bolts ?
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