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Thread: What suspension rates for Coil Overs on a JZA80 or just general suspension advice

  1. #1
    Junior Member Automotive Encyclopaedia Alchemist's Avatar
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    Default What suspension rates for Coil Overs on a JZA80 or just general suspension advice

    Hi Guys,

    I have a cheap(ish) set of JZA80 HKS Hipermax Drag coilovers I have my eye on at the moment. Now as far as I can tell from the HKS website the

    HKS Hipermax Drag coilovers have

    9Kg/f/mm Front & 5 Kg/f/mm Back

    and the HKS Hipermax RS(track) are

    10Kg/f/mm Front & 7 Kg/f/mm Back.

    Now I don't know an awful lot about suspension, but the setup I am looking for is something that will help keep the car more level and stable on bends, whilst still absorbing some shock, and not launching me airborne or destroying the bump stops if I hit a pothole or rise in the road. The ride is great at the moment, but it is a little boaty at times...I have a feeling the RS may be more suited to normal road use, but this guy only has the drag coilovers....

    Does anybody know what the standard rates for springs are for the Bilstein suspension on the JZA80? Would a change to this suspension possibly be worse than the standard Bilstein setup?

    Also, would the difference between the Drag & the RS be all that noticeable? I'm assuming that the greater the Kb/f/mm, the stiffer the suspension, the better the handling but the rougher the ride? I'm doing my own research at the moment, but any advice would be appreciated

    Also fitment of these, would anything else need to be purchased, or is mostly swap in swap out case...
    Last edited by Alchemist; 07-09-2006 at 11:37 PM.

  2. #2
    Junior Member Backyard Mechanic jonra23's Avatar
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    Default Re: What suspension rates for Coil Overs on a JZA80 or just general suspension advice

    Quote Originally Posted by Alchemist
    the setup I am looking for is something that will help keep the car more level and stable on bends, whilst still absorbing some shock, and not launching me airborne or destroying the bump stops if I hit a pothole or rise in the road. The ride is great at the moment, but it is a little boaty at times...
    From your description you are not after a higher spring rate.

    Springs are for holding the car up and providing travel, not for stopping body roll or damping oscilation.

    To decrease body roll increase front sway bar diameter and add a rear sway bar if not fitted.

    To dampen oscilations go for a bit better quality shock.

    Coilovers are not a magic wand, just a way of packaging an adjustable height spring platform with a sometimes adjustable shock.

    regards
    jon

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    Junior Member Automotive Encyclopaedia Alchemist's Avatar
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    Default Re: What suspension rates for Coil Overs on a JZA80 or just general suspension advice

    Hi Jon,

    Thanks for that. I have a strut brace on the way, and uprated front & rear sway bars were also on the cars, looking at the Whiteline ones at the moment.

    The Supra has a front & rear sway bar, but going around corners quickly you can really feel the body roll, I'd like to try to minimise that if possible.

    I guess I have been treating coilovers as a silver bullet in a way

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    Junior Member Backyard Mechanic jonra23's Avatar
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    Default Re: What suspension rates for Coil Overs on a JZA80 or just general suspension advice

    What diameter sway bars do you have front and rear?

    Do you you have aftermarket bushes on sway bar mounts and links?

    How are your shocks?

    regards
    jon

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    Toymods Pimp Chief Engine Builder Norbie's Avatar
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    Default Re: What suspension rates for Coil Overs on a JZA80 or just general suspension advice

    One thing to note when choosing spring rates, your car has wishbone suspension which means the wheel rate will be lower than the spring rate by a constant factor. You will need to find out (a) what that factor is and (b) whether the rate advertised on your coilovers is the wheel rate or spring rate.

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    Not your average Grease Monkey nb86's Avatar
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    Default Re: What suspension rates for Coil Overs on a JZA80 or just general suspension advice

    the hks drag spring rates and valve codes are designed for rearward weight shift on a dragstrip, not what you want on the street. they are still very stiff though. the 10/7kg/mm combo is quite stiff for street use, would be awesome for track days but pretty harsh day to day. swaybars are a good solution for the street. they decrease roll while still allowing a plush ride. they do hamper independant wheel travel though, especially with larger diameters. this can make the car swoopy on undulating road surfaces and bounce over potholed roads etc.
    jonra23 is on the ball here. spring rates are a major consideration in terms of body roll though. often swaybars have to ve adjusted/removed with uprated springs. some production race cars run sans swaybars as the spring rates are so high that swaybars become redundant.
    also, i think that most of the jap suspension companies, and euro ones for that matter, advertise spring rates, not wheel rates. wheel rates can be a grey area when alignment products and different wheel offset etc. come into play.
    This is a really far out, witty and clever signature.

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    Founding ****** Automotive Encyclopaedia Mos's Avatar
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    Default Re: What suspension rates for Coil Overs on a JZA80 or just general suspension advice

    Another example of different people doing things differently

    Personally I choose springs rates with roll control in mind, so they end up stiffer than someone who focusses on sway bars for roll control. On the sprinter I left the factory sway bars alone yet the springs provided brilliant roll control, without (IMO) being too uncomfortable, however some disagree on the comfort level. Billzilla was running stiffer springs with no front sway bar on his sprinter and his roll control was better than mine.

    My personal view on shocks is that they should be set up to properly control the spring - ie shock too soft and car will bounce, shock too hard and the spring will not be able to push past the shock, so car might skip over bumps. I guess I'm not convinced of adjusting shocks to get a harder or softer ride.

    In general larger swaybars will decrease grip on that axle - IE fitting a larger front swaybar will increase understeer, so people favour increasing the rear swaybar, or increasing the rear swaybar more than the front (looking at most performance part sites the rear swaybars generally increase the stiffness more than the corresponding front swaybar, because the factory front swaybar tends to be stiffer than the rear, proportionally speaking).

    I think the best way to work out what you should get, is to go for a ride in cars that have various setups that you're considering. For the IS, I chose 12kg/mm front and 10kg/mm rears (options as low as 8/6 are available), because I went for a spin in one with those rates and to me it wasn't anywhere near uncomfortable and provided good roll control.

    A brief look at greenline suggests 10kg/mm for the front is the "soft" option for a JZA80

    Someone who raced a clubman (a lot; successfully) once told me his idea of setting up a race car is to pick springs for roll control, set up the shocks to properly control the springs, and use swaybars to tune the car to suit a particular racetrack.

    Thoughts?

    Mos.
    Last edited by Mos; 09-09-2006 at 02:27 AM.
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    Junior Member Automotive Encyclopaedia Alchemist's Avatar
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    Default Re: What suspension rates for Coil Overs on a JZA80 or just general suspension advice

    Thanks guys, lots of great info there. I would give you all rep, but I've given too much out lately! It won't let me

    Jon, my shocks are OK, not great though, the fronts are starting to feel a little spongy, that's why I thought getting a set of the HKS Drag Coilovers in pretty good nick could be a good solution for $800.

    I'm not looking for a ride that doesn't let you feel any bumps, I've just been driving lately around some corners and you get to a point where you can feel the stock suspension "let go" to a degree and you start feeling the weight shifting...well thats what I think.

    Seems like a combination of sway bars and coil overs would yeild a good mix for the street.

    Bushes are still stock. That's something I should also look at changing..

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    Junior Member Automotive Encyclopaedia Alchemist's Avatar
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    Default Re: What suspension rates for Coil Overs on a JZA80 or just general suspension advice

    Curses someone beat me to them, should have really snapped them up for that price.

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