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    Results 1 to 9 of 9
    1. #1
      Join Date
      Feb 2007
      Location
      Tinley Park, IL
      Posts
      1,163
      Country Flag: United States

      Softer Coil Spring Rates

      My current combo is a bit on the stiff side, years ago when building this car my vision was cruiser during the week and casual autocross on the weekends. Well the reality is I use this car as a spirited cruiser and in 5 years have only auto-crossed once on a Hot Rod Power Tour stop.

      I'm thinking of softening the suspension a little bit, currently it rides nice on smooth roads (of course) but it struggles to absorb impact from any type of quick/harsh bump on the road. Even at low speeds (driveway curbs for example) the car feels too stiff like it rocks over the curb, instead of the suspension absorbing it.

      Front:
      SPC upper and lower control arms w/tall upper and lower ball joints
      UMI 4050F 530 lb rate springs
      Spacers in driver LCA only to fix the lean
      ridetech HQ single adjustable Fox shocks
      Hellwig sway bar with poly end links
      255/40/18

      Rear:
      UMI lower trailing arm, poly bushing on frame side & rod end on axle
      UMI upper trailing arm, rod end on frame & rubber bushing in axle housing
      Hypercoil 11" 175 lb rate springs
      ridetech HQ single adjustable Fox shocks
      Hellwig sway bar
      285/40/18

      The chart shows what UMI suggests when using coil-overs up front. Assuming this is also accurate for non coil-overs, then the 530 lb springs I have now are way too stiff for my small block Olds with alum heads & intake, lightweight battery and no heat or AC.


      Name:  UMI coil over rates.jpg
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      Also, UMI 2" drop rear springs are 135 lbs rate, again suggesting my current 175 lbs rear springs are too stiff.

      I'm thinking of changing to 11" 150 lbs rear coils, will lower it a touch more and also ride a little softer. Then up front move to a 400 or 450 lb spring. I'm not opposed to switching to coil overs up front, but would rather not do coil overs in the rear since I just finished my exhaust and I really don't want to risk having to move it.

      Thank you for any suggestions and comments.
      Last edited by Mr Nick; 05-24-2020 at 05:02 AM. Reason: Change from SC&C to SPC

      Nick ~
      1969 Cutlass

    2. #2
      Join Date
      Feb 2007
      Location
      Tinley Park, IL
      Posts
      1,163
      Country Flag: United States
      SC&C site shows rates for SPC springs, which also suggests my current springs are too stiff for my vehicle and usage.

      Name:  SPC spring rates.jpg
Views: 563
Size:  14.0 KB

      Nick ~
      1969 Cutlass

    3. #3
      Join Date
      Nov 2006
      Location
      Mountain Springs, Texas
      Posts
      4,488
      Country Flag: United States
      ridetech streetgrip progressive rate front springs might be worth consideration.
      1969 Camaro - LSA 6L90E AME sub/IRS
      1957 Buick Estate Wagon
      1959 El Camino - Ironworks frame
      1956 Cameo - full C5 suspension/drivetrain
      1959 Apache Fleetside

    4. #4
      Join Date
      Feb 2007
      Location
      Tinley Park, IL
      Posts
      1,163
      Country Flag: United States
      Thanks, I did look into those a bit since they are designed for comfort and performance. However, I'm starting to convince myself that if I take the time to replace the front springs I'll probably just do coil-overs so I can nail the ride height.

      Nick ~
      1969 Cutlass

    5. #5
      Join Date
      Apr 2008
      Location
      Virginia Beach VA
      Posts
      381
      Hi Nick,

      Here's what I'm running and the car ride is really nice - no different then stock on the harshness side of things with incredible handling:

      Suspension: Front – SPC front coil springs 1.2" drop 14 1/8 inch 550 rated
      - Helwig sway bar
      - AFX spindles = 1” drop
      - SC&C adjustable tubular upper arms -aggressive street set up
      - SPC lower control arms with progressive rate jounce bumpers and a 1" drop
      - note: total down = 1.2” (springs) + 1” arms + 1” spindles = 3.2”
      total up = Mark’s .5” alum spring seat-top(#1106) , Frank made 1.7” thick
      alum spacer in place of 4 ½” shims – saved 3 lbs on each side
      - net front ride height overall = about a 1” drop w/about 26.5” tall tires
      - SC&C Chassis Brace
      - Varishock dbl adj fronts

      Rear - SPC rear coil springs 1” drop 14 ¼ inch 135 rated
      - Air bags for pre-load launch and/or rear seat passengers or heavy cargo in the trunk
      - Hotchkis adj uppers – both exact same length with pinion angle @ -3*
      - Jegs adj lowers
      - UMI relocation brackets #4012
      Top hole street & autocross– rear bars parallel to ground
      - UMI 1” chassis mount adjustable rear sway bar # 4047-xxx
      1st hole (longest sway bar = least amount of “lever force”) = street (soft)
      2nd hole (middle length = avg amount of “lever force”) = Auto X (medium) – note if rear breaks loose too much during autox change to 1st hole for “softer” setting
      3rd hole (shortest sway bar = max amount of “lever force”) = Drag Race (hard)
      - Varishock dbl adj rears

      I had QA1 coil overs and when I went back to springs the the ride was SOOOOO much better. The problem that most don't realize is with coil overs even though you can adjust the ride height if you go too far up or down outside the suggested "range" you compress or extend both the spring and/or the shock and they don't function properly and the ride is lousy. If you go back to old school springs and and run high end dbl adjustable shocks you don't have to worry about any of that. Also the rear of our 68-72 GM A-bodies should NOT be lowered more than 1" if you're running the stock frame. If you do the already ridiculously high roll center goes even higher and the car handles worse. I was told all this by Mark Savitske at SC&C and thought there was no way all this could be right. I drove my car with 2" drop springs in the rear and then swapped back to 1" and it's night and day better handling. So....even though most won't tell you this if you go back to old school with "softer" springs, high end adjustable shocks, and lower it 2" front and only 1" rear - you will be blown away with how much better it handles. Also the AFX spindles were by far the best upgrade I ever did for fixing the geometry issues but I know they are really expensive. Last is a good dialed in quick ratio steering box.

      This set up is nice on the street, autox, and drag racing with just a few adjustments (shocks, sway bars, maybe tires)

      -Joe

      Joe Lincoln
      Lime Green 71 Olds 442 Convertible

      Upgrades thread: https://www.pro-touring.com/showthre...ible&highlight=


    6. #6
      Join Date
      Apr 2008
      Location
      Virginia Beach VA
      Posts
      381
      Here's the way my car was for a few years. Loved how it looked with 550 QA1s front and 2" 175 drop springs rear:



      The car was NOT fun to drive. Had the bottom out feeling and stiff spring ride and honestly did not corner very well. The only reason I know that is the difference on how it drives now with the non-coil over springs and high end shocks and raising the rear back up. I'll be honest I love the old slammed look it used to have but in the driver's seat the difference is night and day.
      Joe Lincoln
      Lime Green 71 Olds 442 Convertible

      Upgrades thread: https://www.pro-touring.com/showthre...ible&highlight=

    7. #7
      Join Date
      Feb 2007
      Location
      Tinley Park, IL
      Posts
      1,163
      Country Flag: United States
      That's a lot to think about Joe, thanks for sharing your experience. The rear of my car is lowered about 2.5" now, I recently had a set of 2" drop coils in the back and really didn't like how it looked. I took them out and put the 2.5" drop springs back in.

      The roll center stuff is a bit over my head, I should get Mark's book so I can become better educated. I'm wondering if having my car lowered more than 1" in the back would really have a noticeable affect on ride quality and daily spirited driving and not just aggressive handling.

      Nick ~
      1969 Cutlass

    8. #8
      Join Date
      Apr 2008
      Location
      Virginia Beach VA
      Posts
      381
      Nick - I was in the same position as you a while back. If you're going for looks only then slam it how you want. If you want better cornering/handling and you're going to run a stock frame and a standard rear suspension, you shouldn't go lower then 1" in the rear. There are other alternatives but those are upgrading to a new high end frame ($15k ish) or you can do some changes to the rear suspension that are over my head (Watts link I believe it's called?). To be honest I think most guys with our cars (68-72 GM A bodies) either don't know or don't give a F because it just looks so much better slammed down and intuitively you expect it to handle better. That's just not the case. You should call Mark to have him explain. I don't explain it very well but can confirm it was 100% true for my 442. The difference is dramatic.

      There are more issues with lowering too much in the rear for our cars besides roll center. There's just not enough room to do that. The springs have to be really stiff and as Mark explained to me there's not enough room for the springs and shocks to have full extension/travel. You will experience "bottoming out" and a terrible ride in the rear. You may also have the rear upper control arms make contact with the body. Ever notice when you fill the tank with gas that the rear drops 1/2" to even 1" - that makes the situation worse and forget about rear seat passengers. One thing that can help with that is the old school air bags in the springs to fill up for long cruises if you have rear seat passengers. Anyway could go on for a while on all this stuff. To say it's been a learning experience for me would be an understatement.

      -Joe
      Joe Lincoln
      Lime Green 71 Olds 442 Convertible

      Upgrades thread: https://www.pro-touring.com/showthre...ible&highlight=

    9. #9
      Join Date
      Oct 2004
      Location
      IL/TN
      Posts
      909
      Country Flag: United States
      It MUST be understood that rate it load over distance, if you change the load or the distance you MUST change the rate accordingly.
      First advise I can give you is to not even look at those chart recommendations they are utterly useless because they do not take into account YOUR car, there are many variables between suspension systems wheel rate ratio is a big one.
      Secondly when I see recommendations of stock rates for lowered cars it makes me cringe, remember load over distance, if the car is lowered the DISTANCE changed in turn you MUST go up in spring rate you you will bottom out hit bump stops, etc.
      3rd lowering a car requires stiffer shorter springs AND shocks to reduce suspension travel, unfortunately this limits the range of motion to convert shock energy into motion energy to ultimately dissipates it as heat.
      4th you need a more linear shock valving, adjustable shocks does not mean you can adjust it to where it needs to be, the valving rage has to be correct and the softer you go on the spring the higher the shock velocity when you hit a bump creating more resistance from the shock (look at a shock dyno graph velocity vs resistance)
      https://www.protouringf-body.com "doing what they say can't be done"





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