Spring rate for tarmac rally?

[klint]

Just wondering what spring rate do MX5 NA use for tarmac rally e.g targa tasmania.

[greenMachine]

Spring rates work with shock absorber rates - no good just picking the 'best' of one, they need to be matched to each other and the car.

See also the discussion of bushes, which also have a major bearing on the handling of the car.

[klint]

would 6kg/mm front and 4kg/mm rear be ok?
damper can be revalved to suit spring rate

[greenMachine]

I run PSS9s in my NB, which have identical spring rates front and rear, not sure what rates but they are on the stiff side I believe. Others swear by heavier fronts than rears. All I will say is I have no intention of fiddling - Mr Bilstein got this one right enough for me

I suggest you drive a selection of cars to better understand the tradeoffs of different setups, at least search for past threads on the subject. You could also talk to the engineers at a good suspension shop - one that does serious race cars as well as road cars. Be prepared to buy a package of springs/shocks/bushes. Not necessarily all at once, but know what springs go with what shock absorbers with what bushes. Also, if you are pulling springs/shocks out, how many times do you want to do it (or what is the least number of times you can afford to do it)?

By the way, what use will the car have - fast road, road/track, track only? If its a road car, especially a daily driver, think carefully before going stiff. A test drive won't give you much idea of how you will feel about that setup in six months.

Good luck, its a complex subject, with as many views as there are posters on this board

[Ted]

I ran 250F/200R in my car (1990 NA) in Targa Tas 2000 on Koni yellow bodies revalved. Pretty ordinary setup really. I know that Murray had a square setup (300) in the factory cars (NB), but running good short stroke shocks. You can get away with heavy springs if you have a good chassis and excellent shocks to control the body.

[klint]

PSS9 is 335f/335r which is 6kg/mm.
i think track setup will definitely be too stiff for road. I think tarmac rally like targa tassie setup will be the the stiffest i'll go, after all targa tassie raod are pretty rough.
I found some tarmac rally wrx runing 279f/224r ,5f/4r or 224f/168r,4f/3r

My NA is for track/road, so maybe tarmac rally spec would be good

[Ted]

Its not so much the spring rate that was tricky, more amount of clearance, wheel travel and shock degradation. Some of the front running cars will see upwards of 600lb springs, but have the shocks to control it. Good fast bump and rebound as opposed to slow bump. Another problem was simply the shocks getting too hot, 30-50km stages will do that to you.

I have seen track MX5s running anywhere from 350 to 650lb fronts. I like 350-375 fronts.

[greenMachine]

Klint, I haven't looked at what other cars use, but fwiw I suspect that might be worse than useless, it could lead you in the wrong direction.

Things like weight, and weight distribution, suspension travel and geometry of suspension and shock absorber will be quite different on a WRX (as a frinstance) compared to a MX. Put another way, compare apples with apples.

As I said, this is a complex subject if you plan to master it yourself.

[4sfed5]

dont the TEIN coilovers come with 6kg/4kg springs from the factory??????????

[klint]

350-375 front is almost 6kg, so i must be on the right track.

tein flex is 7kg/6kg
tein mono flex 6kg/5kg
tein allowed +-2kg/mm special order.
I have been wondering what kind of race spring thay use for their coilover,
60mmID or 2.5in ID.

I am thinking of getting PSS9 or Tein monoflex but with 6kg/4kg or 5kg/3kg. Arosgosta use 5kg/4kg

[CT]

Doesn't matter which spring they come with - you can get springs made to suit. Kings have made springs for me to suit the Flex. I have also found that NB cars take more rear spring than NA cars - most likely due to increased chassis rigidity. For anything but a racetrack smooth surface, you want to make sure you have very good suspension travel and compliant spring and damping rates.