Setting up Suspension

[Johno]

I know this has been covered numerous times on loads of forums but what and how is the best way to setup the car.
The reason I ask is my suspension is different to the book. My front top wishbones are adjustable with inboard rose joints for caster and the threaded adjuster is slightly further back than book spec also.
The front lower wishbones are also modified to clear the steering rack extension for the Mx5 version with the outer pickup point lower on the bottom ball joint bracket.
I've read that you have your lower wishbones level as a reference point for setting up but on mine they will need to be angled down slightly, is this correct.

I guess what I'm really looking for is advice on the following questions for an Mx5 based Haynes.

1, Ride height front and rear.
2, Camber front and rear.
3, Caster front.
4, Toe in/out front and rear.
5, How to eliminate bump steer.
6, Where and what order to start first.

I know it probably seems lazy on my part but as there are more Mx5 builders joining the forum I thought this would be useful for a lot of new members also.

[jason 82]

Hi Johno, try Rich at Great British Sportscars, he is really helpful, and he will give you the dimensions of the mx5 gbs zero. That should give you a really good basis to start with, then just fine tune to suit. That's what I am doing, because the mx5 roadster build spec is so vague, I don't think that anybody has even gone into this.

[alga]

From what I've read here, spud69 designed the SSC MX-5 suspension with the aim of having the geometry, roll centres, etc. as close as possible to the Sierra-based roadster. So I would think the initial set-up should be almost the same.

Front: 5.5° caster, -2° camber, ~1° toe in. 110-120 cm ride height.
Rear: 0 caster, -0.5° camber, 0 toe, 120-130 mm ride.

[Enoch]

Like Albert says except that you may need to go with a bit of toe out to get it to self centre enough for IVA.
It's a matter of trying it out really, with the sort of accuracy the average home builder can get it's always going to vary slightly from build to build so be prepared to take your time and adjust it until it feels right, or rather until it gives you the feel that you want. Your driving style and personal preferences will have as much influence as the design itself.

[vmax1974]

Front and rear toe can be got pretty dam close by making yourself a string computer

Get 2 lengths of wood the width of an inch or 2 wider than the car clamp them together and drill a hole in either end then take 2 equal lengths of string about 6 inch longer than the car and feed them into the holes and tie

Now using tone stands the same hight as the wheel centres to support the wood so the string is either side of the car measure from the string to the wheel centre making sure its square on all corners (this may take a while) then you can set the toe by measureing the front of each wheel

Its a bit long winded but its basically what they do in garages only the do it with lasers these days

[alga]

I measured rear toe by clamping a spirit level to the spindle and measuring distance from the chassis.

Front toe is also pretty easy to measure with a long straight edge touching the front of the wheels and a set square, or by clamping two pieces of suqare section tube to the front wheels.

I tried the string method too, but found it more difficult.

[skov]

Nobody knows what the best settings are for the Saturn build yet, even less so for your build as it's that little bit different again

I'd agree with Alga that using the Sierra settings is probably a good a starting place as any though (it's more or less what I did).
Once it's on the road you can worry about fine tuning it.

One thing you didn't mention was spring rates.
My car seems very sensitive to these, and it had some horrible handling traits with the spring rates recommended by NTS...

[jason 82]

Have you bought your new 300lb front springs yet ?

[Talonmotorsport]

When AndyH from SSC built his car he told every body that he used 300lbs front and 250lbs rear and said that the car felt more planted, how ever these spring rates are sodding hard for road use. In the 90's Westfield used to use 175lbs front and 150lbs rear for their road cars and the ride was supple and compliant on rough roads and roll was controlled by winding the dampers up. A race spec locost which is lighter than a Roadster 560kg ish runs 400lbs springs on the front and they run on ice rink flat tarmac.

[Johno]

Thanks guys for all your advice.
I guess starting with the Sierra based settings is the way to go for a start.
Hoping to get the car on the floor soon so I can see what I've got.
Forgot all about spring rates John.
I got the same springs as you from SSC but IIRC you changed the rates?
I haven't got a clue where to start to sort the correct settings for these but the guys on Locost forum keep going on about Procomp to set up your car properly, but that costs around £250 I think and based in Birmingham.
I'm guessing the MX5 version should have different springs to the Sierra because of the weight issue but where do you start?

Jason82 do you know what GBS fit to there cars for the MX5?

If we can sort out this between us it would be a big help to new MX5 builders for the future as the Sierra is becoming endangered donor

Hi Phil, you added your post while I was typing..LOL. Where do you think we should be looking regarding spring rates. Now you are a convert to the Dark Side your input would be most grateful.
Lets see what we can come up with and pin it to the MX5 dedicated page.
Thanks again guys.