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Spring rates?

Discussion in 'S30 (240Z,260Z,280Z) Suspension,Brakes and Steerin' started by johnymd, Aug 29, 2017.

  1. johnymd

    johnymd
    Z Club Member

    I have experimented with coilover spring rates on a couple of zeds and these are my findings so far.

    On the blue car with GAZ suspension I originally went for 350lb fronts and 300lb rears. People told me the rear felt a bit soft on the track so I changed the rear to match the fronts at 350lb. This made a noticeable difference and the car felt very neutral in its handling. It should be noted that the car weight is 602kg front and back with 30lt of fuel.

    On the red 260z I had Fourways sectioned struts and the car sat too low at the back and felt soft. I increased the rear spring rate to 250lb, same as front, and raised the rear ride height. This also improved the feel and general ride quality. In my opinion this is the perfect road setup for the heavier 260z.

    On the silver car I have just swapped out the standard suspension for BC racing coilovers with 4kg(224lb) front and 5kg(280kg) rears. This is the BC recommended springs for a road/track car. The car feels a bit bumpy on the back and I don't think there is sufficient weight in the rear of the car for this weight of spring. I'm considering going down to a 4.5kg(252lb) spring.


    I'm looking for advice on this as I'm no expert but do have some experience as above. Why do they recommend a stiffer rear spring on a car that weighs less at the rear? What am I missing?
     
  2. Rob Gaskin

    Rob Gaskin Treasurer in training Staff Member Committee Member

    John, I only ever had a max of 250 on my old car and it was fine.

    The front and rear rates are probably that to cater for the weight of you and a passenger and tank of fuel and a bit of luggage. You sit quite far back in a Z of course.
     
  3. racer

    racer
    Z Club Member

    Your set up felt quite nice to me the other day John.

    I wouldn't make any final decision yet until you finalize your wheel and tyre set up, and of course what motor/power you end up with.

    The car could feel very different once the changes are made and you may be glad of the stiffer rear? Only testing will tell though.
     
  4. johnymd

    johnymd
    Z Club Member

    Rob - that's why I'm thinking of lowering the rear spring rate.

    It did feel better with the extra weight of Matt in the car but I wont be carrying that extra 100kg around all the time. It's very rare that the car will be loaded up and I would probably not be using the cars performance then.

    Do you know what spring rates are on your blue car Rob?
     
  5. SKiddell

    SKiddell Having a bad day

    Changing the corner weighting of the car....which car have a dramatic effect.
     
  6. franky

    franky
    Z Club Member

    swap the springs around? they do seem very heavy though.
     
  7. Albrecht

    Albrecht Well-Known Forum User

    With respect, talking about spring rates is academic without taking damper (both bump and rebound) rates into account.

    The two are inextricably linked. You can have a spring rate of 100lbs that feels like riding on the bump stops, and a spring rate of 300lbs that feels like riding on a feather bed. Key point is choosing spring rates that are within the working range of the dampers, and vice-versa.

    I've asked before what bump and rebound rates BC quote for the dampers they offer for the S30-series Z conversion, and I never got a straight answer. Perhaps they are not really sure?
     
  8. rich

    rich New Forum User

    I ended up buying the bc coilovers so will be watching how you get on with them but from my experience with coilovers it's a case of playing with the set up untill you find what works.
     
  9. racer

    racer
    Z Club Member

     
  10. johnymd

    johnymd
    Z Club Member

    Why are the spring rates different front to back?

    I see that most kit are supplied with harder rear springs than the front's. Could someone explain why this is? If you put a zed on the scales you will see that the front is a bit heavier than the back so I would assume from this that the front needs stiffer springs. On my blue car the weight distribution is pretty much spot on 50:50 with 642kg on each axle. This is with half a tank of fuel and me in the car. The silver car runs 50lb stiffer springs on the back to the front and the back "feels" too hard.

    I'm obviously missing something as you would think the kit suppliers would know best compromise of rates.
     
  11. SKiddell

    SKiddell Having a bad day

    Spring rates front back depend on many factors least of all is the need to promote/demote understeer/oversteer
     

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