General Suspension Questions

Norm Peterson

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Bullshit. Honestly, this is exactly what I'm talking about. Some don't realize the stuff which is readily visible from trackside even exists, but we're concerned with the finer points of ride frequency ratios? C'mon, folks, let's take a step back from _RCVD_ and maybe pick up an old, dog-eared copy of _Tune to Win_.
Ride frequencies taken individually can give a clue as to how good the ride quality of a dual-purpose car is likely to be. In combination - getting into flat ride stuff - is mainly a ride quality matter and doesn't matter as much on the strictly performance side (which should be including sufficient damping to minimize at least pitch oscillations).

Point being that it's not necessary for everybody to be able to run the math involved, but it is useful to understand as general concepts. Like, for instance, a ride frequency of 0.9 Hz would be considered 'soft' by most. Much over 1.5 Hz is getting toward the upper end of where lowering springs pitched as "handling springs" end up - definitely firm but still daily drivable if you're OK with firm-riding cars.

I have 'Tune to Win', and IIRC it's strictly limited to racing suspension design with no consideration given to the street aspects of suspension design. IOW, it's aimed a bit higher up the performance driving pyramid than dual-purpose street/occasional track day driving.


Norm

 

Shadow277

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Those motions are still there alright. Just not to the same horribly visible extents that they used to be until you're hustling the car a bit too hard for the existing spring, sta-bar, and damping rates. Chances are, you'd first notice pitch under extreme braking and possibly during a hard-ish launch on good pavement.


Norm
We got'em boys.

/s means sarcasm.
 

Shadow277

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Bullshit. Honestly, this is exactly what I'm talking about. Some don't realize the stuff which is readily visible from trackside even exists, but we're concerned with the finer points of ride frequency ratios? C'mon, folks, let's take a step back from _RCVD_ and maybe pick up an old, dog-eared copy of _Tune to Win_.
/s means sarcasm.
 

TeeLew

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Good for you. Now stop licking the windows.
 

Norm Peterson

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We got'em boys.

/s means sarcasm.
I'm afraid that's not part of my vocabulary. Never mind that HTML uses '/s' for closing out a "strike-through".

{s}XXXXX{/s} goes to XXXXX when the braces are swapped out for proper brackets.


Norm
 

Hanavarian

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Frankly on the street tires are everything Pirelli P7 AS+ are nothing short of transformative for street comfort while retaining performance with very gentle breakaway.
 

Järn

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I see a lot of people concerned about ride frequencies. I'm curious, how *exactly* are you using that number constructively (Not picking on you jarn, this is an open question)? What does it tell you that saying, "I've got a 300 #/in spring on the front of the car." Does not?

I'm all for people understanding their car and overall vehicle dynamics. To do that, start with understanding the statics of the system before diving into the dynamic aspects. Learn about ride, roll & pitch gradients. Understand different suspension layouts and what their geometry and designs imply. Learn about tires and the effects of alignment. Learn about damping curves and how they tend to affect the car. Learn how aero influences even mostly non-aero cars.

In my mind, there are 10,000 things to understand prior to any concern about ride frequencies.
Hi Tim,

My purpose in learning about ride frequency (I put the formula in Excel) and briefly explain it to others (with a chart), is to simply learn what is different about the various Mustang trim levels.
Once people learn this then they can then make an informed decision about what springs to use the get the basic ride characteristics of a target vehicle.
For example, a person with the Base Mustang wants to have their car handle like a GT350, or a PP2. What springs are necessary to accomplish this upgrade. (Yes there is a lot more than just springs and dampers...)

I see so many people in this forum asking the same question "What are the best springs to get for my Mustang?" and they are only concerned with the drop distance and how the car will look.

ModelNotesFront Spring lbs/inchRear Spring lbs/inchAverage Ride Frequency
GT non-PPOEM
160​
668​
1.36​
GT PP1OEM
165​
728​
1.40​
GT PP2OEM
198​
822​
1.51​
GT Mach1Standard
194​
657​
1.42​
GT Mach1With Handling Package
211​
742​
1.50​
GT350(2016-18)
194​
914​
1.53​
GT350(2019+)
211​
857​
1.53​
GT350R
240​
914​
1.62​
GT500
251​
885​
1.52​
GT500CFTP
268​
942​
1.58​
Popular Linear Springs
GTSteeda Minimum Drop & Ultralite Linear
200​
800​
1.50​
GTJ&M Products Minimum Drop Sport
210​
815​
1.53​
GTSwift Spec R #4X914R (5/14 Kg/mm)
281​
784​
1.63​
GTBMR Performance (SP763/SP080)
170​
740​
1.42​
GTBMR Handling (SP083)
250​
980​
1.67​
 
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Norm Peterson

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In my mind, there are 10,000 things to understand prior to any concern about ride frequencies.
And probably a few more than that before considering the effects of shock damping - I'm talking about %critical damping here - which can and does affect ride frequency (as %critical damping goes up, ride frequency goes down).


Norm
 

Hanavarian

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Ok
Hi Tim,

My purpose in learning about ride frequency (I put the formula in Excel) and briefly explain it to others (with a chart), is to simply learn what is different about the various Mustang trim levels.
Once people learn this then they can then make an informed decision about what springs to use the get the basic ride characteristics of a target vehicle.
For example, a person with the Base Mustang wants to have their car handle like a GT350, or a PP2. What springs are necessary to accomplish this upgrade. (Yes there is a lot more than just springs and dampers...)

I see so many people in this forum asking the same question "What are the best springs to get for my Mustang?" and they are only concerned with the drop distance and how the car will look.

ModelNotesFront Spring lbs/inchRear Spring lbs/inchAverage Ride Frequency
GT non-PPOEM
160​
668​
1.36​
GT PP1OEM
165​
728​
1.40​
GT PP2OEM
198​
822​
1.51​
GT Mach1Standard
194​
657​
1.42​
GT Mach1With Handling Package
211​
742​
1.50​
GT350(2016-18)
194​
914​
1.53​
GT350(2019+)
211​
857​
1.53​
GT350R
240​
914​
1.62​
GT500
251​
885​
1.52​
GT500CFTP
268​
942​
1.58​
Popular Linear Springs
GTSteeda Minimum Drop & Ultralite Linear
200​
800​
1.50​
GTJ&M Products Minimum Drop Sport
210​
815​
1.53​
GTSwift Spec R #4X914R (5/14 Kg/mm)
281​
784​
1.63​
GTBMR Performance (SP763/SP080)
170​
740​
1.42​
GTBMR Handling (SP083)
250​
980​
1.67​
Great chart!! Really puts things into perspective!
 

TeeLew

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Ride frequencies taken individually can give a clue as to how good the ride quality of a dual-purpose car is likely to be. In combination - getting into flat ride stuff - is mainly a ride quality matter and doesn't matter as much on the strictly performance side (which should be including sufficient damping to minimize at least pitch oscillations).
......
Norm
I agree with what you've written, but I see talking about the rates in terms of ride frequency unnecessarily complex. Human minds don't spend much time thinking in a frequency domain, so I just don't think it's a unit of measure which is helpful to many.

Generally, if you're comparing primary ride resonants, then you're doing it for significantly different cars. Let's say, a Mustang & a Miata. You can't compare spring rates, because a 200 #/in spring (whether that be at the spring or at the wheel) will act completely different based on which car it's used because of the difference in mass of the two. In this scenario, we can compare the two in an apples to apples way by looking at the ride resonants.

But that's not what we're doing. We've all got the same basic car that weighs about the same and has the same motion ratios (except for rear coil-over). We can just say 300 #/in or 1000#/in our whatever and it describes what we're talking about in a more readily comprehendible way.

I know 'flat ride' is a thing. It was a Maurice Olley (legendary GM suspension engineer) concept used to improve the ride quality of their cars in the 50's and 60's. I guess it did, but it did so before there was anything resembling a decent damper invented. The idea of running the rear stiffer than the front has fatal flaws on a couple fronts in my opinion. Here aremy thoughts after a few iterations.

In my mind, there's one thing that defines how far you are on the spectrum of road-to-track, and that's the front spring. The stiffer it is (up to maybe 750 #/in, beyond is unnecessary) the more performance oriented we are making the car. If we're concerned about flat ride, then choosing a front spring automatically defines the rear. We set the rate at ~10% higher (stiffer) rear primary ride resonant. The problem with this is the rear is significantly too stiff for anything else. On the ride side if the coin, the rear suspension lacks the compliance to absorb normal bumps and pavement changes. On the track side of the coin, the rear is too stiff to put power down on corner exit. The only advantage of using flat ride as the determining factor on rear spring is so the car moves a little more pogo and a little less teeter-totter when at some nominal cruise speed (eg. 70 mph). While this choice does indeed do what it is supposed to do, the compromises we're making with respect to street and track use means this is a strange variable to choose to optimize.

This is my approach:
1. Choose the stiffest front spring I think I can live with on the street because it rides rough (or softrst for the track because it allows too much pitch on the brakes).

2. Evaluate with stock rear spring rate. Next, increase rear spring rate by 250 #/in increments until the stopwatch says you've slowed or the ride starts to suck.

3. My guess is that we will add much less rear spring rate(in proportion) than front.

Since we have been speaking in terms of ride frequencies, I've consistently found having the rear about 10-20% LOWER than the front to be a guideline which gives a good 'first-cut' when choosing springs. I have no calculations from which to devine this number, it's just been something I've observed.

Those Phoenix guys showed what they were doing in Indy. They're moderately stiff on the front and chewing gum soft on the rear. The Ecoboost car was a little stiffer on the rear, but it didn't put the power down as well, either, which would be consistent logically. Both produced Runoffs championships so that choice was probably well justified. Whoever is screwing those things together must not be a complete jackwagon. They hauled ass all weekend and collected hardware at the end of it.
 

shogun32

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1. Choose the stiffest front spring I think I can live with on the street because it rides rough (or softrst for the track because it allows too much pitch on the brakes).
define "too much pitch"?

To me you want as much pitch as you can get but just short of dragging parts and also before taking so much weight away from the rear that it wants to come around. In bikes we *routinely* have the rear up in the air with a handy tendency to dance left/right as it pivots on the frame.

The same on a car would likely be disastrous - spin city
Even though the more weight on the front the more mechanical traction as you force that rubber into the surface. Well, till you exceed that limit too.

The Steeda DR are +2% front to back. I have 980 and 900 springs and that would put me at -7%. Hmmm
 
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Norm Peterson

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I agree with what you've written, but I see talking about the rates in terms of ride frequency unnecessarily complex. Human minds don't spend much time thinking in a frequency domain, so I just don't think it's a unit of measure which is helpful to many.
The short story here is that when you've been paid to do dynamic analysis of structures, thinking in either the time domain or the frequency domain and about the effects of damping actually comes in preference to considering only the spring part of a spring-mass-damper system. By doing so, there might be some insights you can't pick up on from comparing only spring rates . . . or even any of the simplistic guidelines like making the rear ride frequency 10% higher than the front ride frequency and calling it good.

More later.


Norm
 
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TeeLew

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define "too much pitch"?
It will be driver dependent, but it is either the driver feels there is excessive chassis motion to manage or the response of car is too slow to allow appropriately fast inputs.

We're dealing with a MacPherson strut front end. That means we've got very little camber compensation in roll, so we're forced to carry quite a bit of negative camber statically compared to a double wishbone car. If we allow excess front brake dive (pitch) then our camber will increase to some extent. The combination of the static + dynamic camber can make for some pretty leaned over tires. So we might have to reduce/limit the brake dive which, in turn, can hurt overall braking performance because of the excess negative camber.

On any sort of GT car, you have to somewhat ramp your pressure into the brake pedal. On an Indycar or something of that nature which is very stiff and reacts to every thought, much less input, one can just stomp on the brake pedal with as much aggression as you please. It will only stop faster. GT cars will never react that fast, but one can improve the response time of the car, and so the speed at which you can apply brake pressure, by increasing front spring rate. As a driver, you feel it gives you something pushing back into your foot. Excessively soft front springs lack the response characteristics to give the necessary feedback to the driver.

Last, a stiffer front end means you've reduced the vertical window (both up and down) that the car suspension will travel as it negotiates a corner. It will dive less on brakes and rise less on throttle application. This will often allow you to lower the front of the car (dragging bits is usually the limiting factor). Keeping that vertical window as narrow as you can will reduce the balance shift as the car travels through the corner. That alone is often a big gain. If you only have to deal with a single problem, as opposed to several balance shifts as the car travels through different phases of the corner, you're always better off. So, with a stiffer front end, you might have to deal with understeer, but you'll *only* have to deal with understeer. It won't see-saw back and forth with first this end sliding and then that one. It's much easier to only have to deal with 1 imbalance than it is trying to cope with several.

How's that for a long-winded answer to a relatively simple question?
 
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