Suspension researchings on NA FRC; '91 for the Slug

[slug_dub]

Since before I even owned the Slug I've been reading up on suspension for the NA's. Its ongoing and never ends... some post on m.net likened it to a rabbit hole, and they aren't wrong!

There's always more questions to have answered, but as I am gradually approaching a plan, I'm consolidating some things here, hopefully some I can be corrected on my understanding, or maybe it will help others a bit...

To the status of the Slug...
It rides on some shocks and red lowering springs I can't rightly identify, both of an unknown age.

That's the only sticker still present... look familiar to anyone?

I measured the ride height and its low... Front 305mm, rear 310mm. Well clear of the 100mm ground clearance so I wonder if this height is likely ever to be a problem (hasn't so far!). The dead remains of OEM dustboot/bumpstops are present.

When sitting on the ground, the lower control arms are pretty horizontal with the ground, which I think is about right, however the springs are very compressed and it appears that the rings towards the top all rest on each other (bound?).

My preference is to drive twisties and backroads and the like, and I do desire handling over ride but only up to a practical point. I have no need to specify for the track, when (and if! ) I get to the track it'll be hella fun whether I go as the car is right now, or have changed anything... the car isn't going to be the limiting factor.

After much practice to understand FCM's calculator I have been playing about with what I can do to hit ~60% FRC.
I have Whiteline 24mm front and 16mm adjustable sways in addition to the stock sways to play with.

I've tried various combinations of the sways I have and multiple spring brands to see how the FRC looks. Flyin Miata springs 318 front/233 rear push the FRC way up and would appear to work with the 24mm front bar and no rear bar, but the bounce frequency is too high for my liking. Springs with this high a rate and indeed coilover kinds of rates (450 front/350 rear region) seem to make for quite high bounce frequencies and FRC only seems to come back to ~60% using fat front sways and no rear sway, I'm curious is that always the way with coilovers?

I called King Springs and was able to get info on the spring rates for their current MX5 90-05 springs: 165-215 front/105-160 rear. Not too dissimilar to what was quoted in an older thread here relating to the older style Kings.

I'm not sure what out of the range stated makes for the most accurate entry in the FCM calculator for modelling purposes... if I use the minimum values it doesn't look real good on the FRC, but using the max values 215 front/160 rear, it looks to be 59.2 FRC with Kings, 24mm sway front, stock 12mm sway rear, and 1.44 front and 1.57 rear bounce frequency, which seems pretty close to what I'm after.

I'm guessing that the current springs being so tightly packed could be just the age or crappiness of those springs, so if I was to change to King springs, I'm presuming (hoping) that they would be less bound, and the height would come up that little bit more?
Also might relieve the shock with some more travel room.
FCM bumpstops (36mm/46mm) are a definite, though the FCM site seems to differentiate between shock brands, which makes me worry that I should be particular about which ones I get... identifying the shocks would be of some benefit here. Unless I can get away with using any of them.

When it comes to the shock, I'm happy to replace that a bit later if the bumpstops and springs will sort some handling and the ride height is raised a bit. My preference is for Bilsteins although HD's seem not to be appropriate without high spring rates. I guess I may to then need FCM mounts as well to maintain ride height, I like a lowered look but don't desire any more low than I've got

I know I'm one of the worlds great ramblers, so thanks if you read this far... hows my reasoning?

[tbro]

Hey Randyroo!!

Ok, first things first, go and weight the car with approx 1/2 tank of fuel and get it split front and rear.

Then measure your after market sway bars for length overall and arm length and bolt spacings, and weigh your wheels and tyres.

Now you can start to play with the FCM chart.

Those who know me well know how I set Scooter up to be easy to race and use on the road, being an old cripple and with no power steering the car needed to be easy to steer but also also very easy on brakes.

I spent many hours working out what I was going to do and then threw the whole lot to a bunch of fabricators/engineers who worked for a mate of ours at Britec. Hard suspension is not fast and no-one has yet found the perfect way to sort out suspension setting Yaw/pitch etc at a level that most people can afford. I wouldn't pay someone $2000 to give me a bunch of figures and hope it works perfectly. I'll PM the setting for Scooter and hope fully that might give you some start.

I can't fathom why people who will never race their cars will out lay $3000 to put in shock kits in a $5000 motor car. Start with some second hand dry Bilsteins add some springs with what ever rate you come up with, add FMC bump stops and if you want to lower it some more use the NB top plates with FMC fitting kits. Get Gary at Fulcrum to do an alignment to the same specs as the clubman was and you'll end up with a comfy ride that handles the track and roads with aplomb. If you decide to go with after market bars come and see me and I sort out the bits you'll need to do it properly and so the bars WILL work the way their supposed to.

Terry

[slug_dub]

Hi Terry,

I've had some other data like the wheel/tyre weight and my weight in the calculator but I didn't have the car weight yet. I just looked up how to do that and will give it a go.

I remember how you had set up Scooter, and from previous conversations we've had about it and have been keeping that in mind in working out what to do.

Thanks for the input mate