SPRING RATES & DROPS: ALL IN ONE THREAD!!

Discussion in 'Suspension, Brakes & Chassis' started by Gibbo205, Feb 17, 2016.

  1. dsp4848

    dsp4848 Well-Known Member

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    Yeah, I agree with you that those are the advertised spring rates, but those would be for progressive spring rates. A linear spring rate should be a single number, not a range.
     
  2. K-Roll302

    K-Roll302 Well-Known Member

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    #142 K-Roll302, Nov 11, 2016
    Last edited: Nov 11, 2016
    So I'm given to understand that the Ecoboost PP springs are linear, so there shouldn't be much of a noticeable difference in ride quality if I go with linear lowering springs then? Compared to if I were to go with progressive springs? I want the a spring that does better than the EBPP spring in performance but doesn't compromise too much on comfort.
     
  3. prem

    prem Well-Known Member

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    Had the steeda progressive springs yesterday and very happy with the drop and stance of the car. I didn't see much difference in ride quality over my stock pp springs. I thought it was about as stiff as the stock ones or may be tad bit little less stiff.. Handling defintely improved
     
  4. Niz55

    Niz55 Well-Known Member

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    Change out the bmr handling to 1.6 -1.7 drop on the front. 1.2 is not accurate at all.
     
  5. BmacIL

    BmacIL Enginerd

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    #145 BmacIL, Dec 15, 2016
    Last edited: Jan 30, 2018
    Ride Frequency Sheet

    Updated 1/29/18

    I've compiled a list of all the linear spring options and combinations that I could see being used together (based on if they're sold in pairs or not) and uploaded it to google. Please put this one on the first page [MENTION=13598]Gibbo205[/MENTION]!

    Wheel Rate:
    Wheel rate is the effective spring rate the tire sees, based on the spring and the suspension's motion ratio. The motion ratio is the ratio of spring travel to wheel travel. On the Mustang, the front is ~1 because it's a strut, and the rear is 0.492, meaning for every 1" the tire moves up/down, the spring is compressed/released by approximately 0.5".

    Wheel Rate = Spring Rate * (MR)^2

    Ride Frequency:
    The ride frequency is the natural frequency of the body, with no damping considered. Higher = Stiffer.
    Empirically tested values by application are as follows:

    RF = 1/(2*pi) * sqrt(K/Msprung)

    0.5 - 1.2 Hz - Street-only/Passenger Cars
    1.2 - 1.5 Hz - Sporty Cars, Lower end of track-focused street cars
    1.5 - 2.0 Hz - Track-focused street cars to Low-downforce racecars
    2.0+ Hz - Racecars, HPDE/Auto-X-only street cars

    There's no cutoff of where you should be, but for the enthusiast who daily drives and occasionally tracks, 1.4-1.6 Hz is a good ballpark.

    One important aspect about ride frequency is the relative frequencies between the front and the rear. General rule of thumb is to achieve the best ride response, you want your rear ride frequency to be ~10% higher than your front. This is dependent on weight distribution, of course, and the more front-heavy, the closer to 1:1 you want. A 50/50 car would want 10% for optimum results. For our cars anywhere from 1-10% will achieve good ride response characteristics. The way to think of it is this: when you hit a bump, the body of the car hasn't settled fully before the rear hits it, so you need an appropriately high rate to manage that well.

    Ride is far from the only concern, so you may give up some of the ideal response characteristics for improved response/handling. See GT350R, for example.

    The reason I put all this up is that in going about deciding on spring selection, there are a few important variables to consider: Rates relative to chosen dampers, ride height drop front and rear, and relative rates if choosing something other than a set of 4 springs.

    Assumptions:
    Mass of car: 3736 lb (from what things weigh thread)
    Sprung mass: 3188 lb (from what things weigh thread)
    Weight Dist. 53% F/47% R

    https://docs.google.com/spreadsheets/d/1qExrjc7BqL7y8j1XQGotlHd9L3hT41aTpKySDTfhvCE/edit?usp=sharing Mustang_RF.JPG
     
  6. DivineStrike

    DivineStrike Doomsday

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    Does ride frequency change in relation to damper setting as well?
     
  7. Rebellion

    Rebellion Well-Known Member

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    From the little I know of...no, at least not at this level of analysis. This analysis relates to the first order oscillations, dampers related to the second order.

    On a first order, I'm not really clear on the implications of the actual ratio of front/rear frequencies, just don't let it be exactly equal or 1/1 (which is pretty much impossible in real life).

    On a second order, as ride frequencies increase, it becomes less important to be super precise on the dampening being critical. Of course, you'll want it to be as close to critical as possible, but the reaction times are so short that, let's say, an 10% difference in dampening on a high ride frequency will be much less noticeable that at a low ride frequency.
     
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  8. BmacIL

    BmacIL Enginerd

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    No, it is completely independent. Damper settings need to be matched to ride frequency, though.
     
  9. Bahndvr

    Bahndvr Roushcharged

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    I didn't see it, does anyone know the spring rates(progressive or linear) of the Ford 2015-2017 Mustang Track Handling Pack?
     
  10. Niz55

    Niz55 Well-Known Member

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    looks like progressive to me. But FRPP will not release the info on the rate.
     
  11. wildcatgoal

    wildcatgoal @sirboom_photography

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    Can add Steeda Dual Rate comp springs...

    Rates at curb:
    Front 350lbs
    Rear 1200lbs

    Lowers ride height .75 at all four corners
     
  12. wildcatgoal

    wildcatgoal @sirboom_photography

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    [MENTION=7748]tj@steeda[/MENTION] [MENTION=25806]SteedaTech[/MENTION]
     
  13. BmacIL

    BmacIL Enginerd

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    I will add to the ride frequency chart.
     
  14. dsp4848

    dsp4848 Well-Known Member

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    Added to spring spreadsheet!
     
  15. Bobsp12

    Bobsp12 Super Moderator
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    Does anybody know the stock total suspension travel distance for the front and rear of a GTPP?
    Our legal requirement for lowered cars is to retain two thirds of original travel and to have 100mm clearance to the ground from any part of the car.
     
  16. THE_AHJ

    THE_AHJ AuthorityHvngJurisdiction

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    Peeps, there were a couple of users mentioning that Eibach Pro-Kit is Linear and the spreadsheet shows them as Progressive, but I just got off the phone with Eibach and part# 35145.140, which is their Pro-Kit is indeed Linear and not Progressive. The info on the site is incorrect, he mentioned they went back to Linear so I'm assuming they might have been Progressive before :shrug: . The rates are correct as shown on the spreadsheet though :thumbsup:
     
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  17. wildcatgoal

    wildcatgoal @sirboom_photography

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    I just installed a set of the Eibach Pro-Kits for a forum member last weekend and they looked linear to me.
     
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  18. dsp4848

    dsp4848 Well-Known Member

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    Yeah you're the second person I can recall that called Eibach and had them say that the Pro's were linear - even though just about everything else says they're progressive. That's really odd.

    They definitely do look linear - nothing like a progressive spring (think Sportlines). I noticed this when I installed mine last year, but just took everyone's (including Eibach) word for it that they were progressive. Oh well, they're good springs and aren't coming out of my car.
     
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  19. Teezlr

    Teezlr Well-Known Member

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    So whats the most minimal drop with the best ride quality?
     
  20. BmacIL

    BmacIL Enginerd

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    BMR SP089 & SP082. 7/8" front and 1/2" rear drop. The GT350 (non R) springs drop 3/8" all around but are firmer than stock by quite a bit.
     
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