Suspension Brakes 1st Gen Coilover Spring Rates

Discussion in 'Tuning and Performance' started by quikmni, Sep 23, 2015.

  1. quikmni

    quikmni Moderator

    Jun 6, 2009
    775
    173
    43
    Aerospace Engineer
    Orcutt, CA
    Ratings:
    +173 / 0 / -0
    I have been looking at coilovers for my 2006 MCS GP and I have a general question about spring rates. Many coilover setups have a higher spring rate in the rear than front, such as 7 kG (392 lb) in the front and 8 Kg (448 lb) in the rear, which seems backwards to me because the front has 60% of the vehicle weight. If I use some of the spring rate calculator programs I come up with something more like 7 Kg (392 lb) in the front but something more like 4.5 Kg (252 lb) for the rear for my Mini Cooper.

    Why do most coilover setups have such a high rear spring rate 450# verse the expected lower 250# when using 400# in the front?

    I have a couple theories but could be all wrong so I would like your inputs:
    1. Just trying to stiffen the rear end to reduce understeer and assuming a stock size rear sway bar and no front camber plates.
    2. If the car has a large adj rear bar, such as 22mm solid, and front camber plates (-2 deg or more) the rear spring rate could be closer to the 250# range.
     
  2. cct1

    cct1 Well-Known Member
    Lifetime Supporter

    May 5, 2009
    3,378
    3,368
    113
    Ratings:
    +3,369 / 0 / -0
    The answer is number 1, but usually with a stiffer rear sway bar and camber plates. My spring rates are 400 on all corners (or will be I should say); but most are running 400 up front 450 rear to get to a slight oversteer for the track. I'd rather be closer to neutral, but it's really a personal preference thing, if you like sliding the rear out, then go with the higher spring rates on the back. If you're more point and shoot, go a little lower on the rear.

    Thing is, the rear end is very easy to catch on a MINI, so you can get away with a little oversteer.

    It all works together though--front and rear camber and toe, sway bar, tires, coilovers and springs, it all depends on your setup.
     
  3. quikmni

    quikmni Moderator

    Jun 6, 2009
    775
    173
    43
    Aerospace Engineer
    Orcutt, CA
    Ratings:
    +173 / 0 / -0
    Thanks for the input. That makes sense.
    My car is a daily driver that I Auto-X but I want to lean to the softer side for street driving and compromise the Auto-X handling. I plan large bar and camber plates. Sounds like the 400#/400# range or even 350#/350# would make sense for me depending on coilovers.
     
  4. M^Cubed

    M^Cubed Member

    May 24, 2009
    315
    12
    18
    Ratings:
    +12 / 0 / -0
    The motion ratio is different in the front and rear.
     
  5. M^Cubed

    M^Cubed Member

    May 24, 2009
    315
    12
    18
    Ratings:
    +12 / 0 / -0
    Careful running too low of a spring rate. With a coilover you are reducing the amount of suspension travel you have available. Running too soft of spring will lead to bottoming out the damper.
     
  6. quikmni

    quikmni Moderator

    Jun 6, 2009
    775
    173
    43
    Aerospace Engineer
    Orcutt, CA
    Ratings:
    +173 / 0 / -0
    I agree the MR is different front to rear. I believe the MR is about 0.99 (1) for the front and about 0.875 in the rear. I used those numbers in the spring rate calculators.
    I do not think I would go below 350 in the front, and I will only be dropping about 5/8-3/4". Do you think 350# is too soft?
     
  7. cct1

    cct1 Well-Known Member
    Lifetime Supporter

    May 5, 2009
    3,378
    3,368
    113
    Ratings:
    +3,369 / 0 / -0
    350 still should be ok--it is for the KW V2's for example--but you always have make sure the spring rates are compatible with whatever coilover you choose.
     

Share This Page