suspension setup advice? handles great but rear end is a brick

Discussion in 'Corner Carver Racing Tech Discussion' started by tabstang, Nov 25, 2020.

  1. tabstang

    tabstang Junior Member

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    Can my 07 GT be made to handle with comfort in my 95% street, 5% auto-cross driving? I thought I had what it takes:
    - Tokico single adjustable dampers
    - Ground Control adjustable springs ("coilover" setup, Eibach "street sport" stiffness, sold by Ground Control, not sure of actual spring rate), lowered about 1-3/4"
    - Ground Control adjustable strut mounts
    - Roush Stage 3 (I think) full metal heim joint rear suspension; UCA, LCAs, panhard
    - lowered LCA mounts
    - Steeda rear anti-sway bar
    This setup puts the power (482 rwhp from a tuned down Whipple 2.3l SC) to the ground for sure, and handles on rails, but look out for those speed bumps - ouch!
    I've played with damper rates, definitely makes a difference, but even at the softest setting the rear end is too stiff.
    So where should I start? I suspect it's spring rate or maybe sway bar (I've read most aftermarket sway bars are way to beefy) - but I don't want to go spending a bunch of $ unnecessarily.
    BTW you might wonder why I have so many different brands of suspension parts on this car - it's the 4th S197 I've owned, and many of these parts were from cars I formerly owned, and were on them prior to my ownership.
    Thanks for sharing your knowledge and experience!
     
    HRLNKN likes this.
  2. Norm Peterson

    Norm Peterson corner barstool sitter

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    Harshness over bumps is usually either a damper issue or a matter of hitting the bump stops.

    Springs much less so, and sta-bars not at all if you're hitting the bumps straight-on (both rear tires hitting them at the same time).


    Norm
     
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  3. HRLNKN

    HRLNKN Junior Member

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    Assuming that you're not riding on your bump stops, what wheel & tire combo are you running?
     
  4. Sky Render

    Sky Render Stig's Retarded Cousin S197 Team Member

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    You have all heim joints in the rear. WTF did you expect? Of course it's going to ride like a damn brick.

    I ran a similar setup for about 2 years before it annoyed me so much I switched to mostly poly.

    Your setup is way too hardcore for something primarily used on the street.
     
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  5. HRLNKN

    HRLNKN Junior Member

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    I was thinking something like that, but if he's had this setup on his previous Mustangs he probably was expecting a stiffer ride (maybe not). As a rule, I won't go bigger than 18's on a daily driver specifically because of rim damage from potholes & the hard ride. Also helps when looking for some good take-off tires. I've found that 18's are kinda the sweet spot
     
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  6. tabstang

    tabstang Junior Member

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    Thanks for all your input!
    I'm riding on 20's, Firestone Indy 500 305-35s rear, 275-40's front (great tires IMO). I like the look, and I've never had an issue with rim damage. When I got this car it was on 18's with stock suspension and it felt to me like it was on a trampoline. I kinda like the "race car" sound of the heims, and this thing feels great hooking up. I don't see why they would make "big" bumps worse. I can see why rubber or poly would be better on small stuff but that's not the problem. I'll check bump stop clearance 1st - easy fix. I'll ask the guys at Ground Control about spring rate, anything I learn I'll post back here on.
     
  7. PonyBoy

    PonyBoy Member

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    Check out Kenny Brown Performance. Contact them. Ask fir a 15 minute consultation with Kenny. You won’t regret it.
     
  8. Pentalab

    Pentalab forum member

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    So your rears are 28.4" diameter. I'm using a mpss in a 305-35-19. (27.4" diameter). We both have 106.75mm sidewalls = 4.2"
     
  9. Norm Peterson

    Norm Peterson corner barstool sitter

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    Most likely a case of the shocks/struts being long past their "best used by" date.


    Any compliance - "give" in more common usage - is better than none in street driving. What does tend to happen with rod ends is that they gradually pound extra clearance into themselves, which at least makes them get noisy before it makes any difference in handling that you can feel.


    Norm
     
  10. Pentalab

    Pentalab forum member

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    On full soft, your compression is still too stiff. I doubt the rear sway bar would even enter into the equation.
     
  11. Sky Render

    Sky Render Stig's Retarded Cousin S197 Team Member

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    That's what I was thinking. Blown dampers.
     
  12. tabstang

    tabstang Junior Member

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    The dampers only have a few k miles on them. I had dampers were the issue but I've had 3 sets on it with same results. Haven't had time to get under it since the post to check bump stops etc. Hopefully tomorrow.
     
  13. DieHarder

    DieHarder Member

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    I've had 3 different suspension setups on my car. Best combination I've found to date are Roush springs (https://www.americanmuscle.com/roush-lowering-springs-0514-gt-v6.html) paired with Bilstein B6 dampers and GT 500 strut mounts. Understand lowering concerns but from my experience I've never run across any issues. I did have to cut down the rear bump stops by 3/4" but other than that the setup has been great. I also run a 245/45/19 square setup. The Roush springs are thinner/more compliant (compared to the FRPP - P springs I used to run) and overall more comfortable for the street and have been a good handling combination IMHO. Of course the rest of the suspension components are urethane vice heim joints so I'm sure that makes a difference.
     
  14. stevbd

    stevbd forum member

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    OP it would help if you could say a little more what you mean by "like a brick".

    If you are talking about when you go slowly over a large speed bump, straight on, the rear has no absorption, that is mostly spring rate imo. But because of the inboard spring location, in order to get the roll stiffness you want for the car to "handle on rails," you sort of have to live with this increased ride stiffness. If it feels super stiff when you go at an angle across that speed bump, it could also be the larger ARB adding to the problem.

    If you are talking about slamming when you hit larger, sharper bumps at speed, like a bridge expansion joint, that likely is you hitting the bump stops. Which almost certainly is happening if you have lowered it almost 2 inches without modifying the oem stops. You really need to get more rear suspension travel and proper bump stops are a cheap and easy way to improve this.

    If you are talking about general skittishness around bumpy corners, that likely is poor damping combined with excess unsprung weight, plus again perhaps hitting the bump stops. It's always going to be challenge controlling the massive unsprung weight of a SRA. Get the best dampers you can. Depending on the make of your 20" wheels, they may be quite heavy and making this problem worse.

    Getting a true rear coilover and a smaller ARB (or removing it entirely) substantially improves several of these issues but the good options are limited and a little more money.

    Good luck!
     
  15. Pentalab

    Pentalab forum member

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    Is he talking about the steeda anti roll bar, used by hard core drag racers ? BMR also make their version of an anti roll bar. And neither of them look like a typ rear sway bar.... more like a girder on steroids. 1.75" rear drop is a bunch. Mine is 1.25"..with the Roush kit, and came with new, shorter bump stops. With a 1.75" rear drop, he won't have a lot of spring or damper travel. IMO, it's been lowered way too much, esp with 305-35-20 rear tires. (28.4" diam rears).
     
  16. tabstang

    tabstang Junior Member

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    OK I finally got under the car, looks like 331psi/in front, 200 psi/in rear springs (Eibach numbers 200.64.58 front, 1000.230.200 rear). That looks a bit high according to the list linked below but not out of the range. I have about 3" of travel B4 the bump stops (which seems OK to me but - ?). I'm emailing back & forth with Ground Control, there may be an issue with my installation. So more to come as I learn. Thanks for y'all's input.
    https://trackmustangsonline.com/thr...Eibach sportline 4.12535 (1.6"/,103-217 lb/in.
    Of most interest to me are the low rates on the Boss 302 ... 148F/186R lbs/in,
    Boss 302 Laguna Seca 137F/191R lbs/in. These seem REALLY low for a performance oriented car - and higher in rear than front - ???. Am I missing something here? I'm just a weekend garage hack trying to learn how to optimize this car for excellent performance while maintaining drive-ability. (That's why I got the adjustable dampers, looking for daily (relative) comfort with weekend track-ability.) I'm amazed at how much variability exists around the question of spring rates.
     
  17. stevbd

    stevbd forum member

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    [QUOTE="I have about 3" of travel B4 the bump stops.[/QUOTE]

    That's with the car lifted. On the road with a nearly 2" drop you are almost certainly riding on your bump stops.
     
  18. Norm Peterson

    Norm Peterson corner barstool sitter

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    There's a difference between a "performance oriented" car that's primarily a street driven car and a race car that may or may not ever be driven on the street. Ford builds the former kind of car, and keep in mind that they do sell a pretty good number of these cars to people who buy them for the name or the image or what it looks like rather than for the performance itself.

    I have a feeling that when it comes to modifying in general, it's easy to fall prey to the "if some's good, more's better, and too much is just enough" line of thinking, and that if it's OE or has numbers comparable to OE it can't be very good.

    With good shocks & struts, and reasonable roll stiffness, you don't need all that much spring stiffness to end up with a good-handling street driver.

    It turns out that you don't need to go with crazy stiffnesses in a mildly-developed dual-purpose car, either. Somewhere in the 220 - 250 lb/in range of wheel rate (think BMR's GT500 handling springs here) puts you in a place comparable to the S550 GT350R. And that much wheel rate doesn't ride all that bad, even with more sta-bar stiffness than OE as well.


    Just because, here's a lap or two at speed in my '08, still on the OE springs (only something like 130 lb/in). I was running a little more bar than OE (Strano's 35/22), Koni yellows, and a lot more wheel and tire than OE GT. The tires were into their 8th track day and weren't quite as grippy as they once had been.




    Norm
     
    Last edited: Dec 4, 2020
  19. tabstang

    tabstang Junior Member

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    stevebd, I had the car up on wheel cribs, so it was at "standard" ride height. I had already cut the bump stops off (about 1") but flat, whereas I now see that Ground Control recommends cutting them at an angle, leaving what appears like an upside-down tent. I tried to insert a graphic but could only get this link in here:

    https://drive.google.com/file/d/1fcYrXlp9o28IPIVaujkQYanYBMtCmo6N/view?usp=sharing

    Norm, I hear you loud and clear, I do believe I've crossed that line beyond streetable mods, to a track-car orientation, the springs are too heavy. I like the adjustability of the Ground Control setup, but now I gotta figure out what springs to buy. For instance, do I need to replace all 4, even though the front of the car rides OK (although stiffer than stock), and keeping in mind I added about 110 lb with the whipple & intercooler.
     
  20. Norm Peterson

    Norm Peterson corner barstool sitter

    Age:
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    There's a rather clunky work-around involving PrintScreen, cropping, and saving as a .jpg, as GC doesn't provide the picture as an image directly. Incidentally, there's no reason you'd have to precisely match their cutting, so I'd start by cutting smaller slices off. There's other tricks as well.

    GC bump stop mod.jpg



    If I was shopping for OE-style "big springs" for a GT with forced induction, I'd be looking at GT500 kits. But for sure I'd be looking for a lot less drop than 1.5" (let alone 1.75" or more).

    My own experience with Tokico shocks and struts is that their damping tends to be rather harsh. That's based on their 'Illumina' line, but I suspect that the same general philosophy on damping goes into their other products.

    Individuals differ on what they consider acceptable vs unacceptably stiff, so there's some risk in trying to make specific rate suggestions. What I can tell you is that over roads that aren't too badly broken up (and with the shocks & struts dialed down toward full soft) my wife wasn't unwilling to ride in my car even with the 260f/220r BMR springing. Just so you know, we've both been retired a few years.


    Norm
     
    Bullitt2954 likes this.
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