Measurements or design for front wishbones

[Aussie_Haynes_MX5]

Hi all, i am from Australia and am currently working on getting the plans laid out for my build.

The chassis will be a standard book build, with extra triangular bracing to help with the torsion and twist testing that i will be required to do over here to get it passed for rego. (The Australian version of your SVA) And it's a bugger of a thing to go through

I will be using NC Mazda MX-5 uprights. Wheels i will be using will be 15x7 4x100/4x114.3 15 Offset and will have a 205/50 R15 tyre. The rear track will be made using a Toyota Hilux differential, and will be 1350mm (axle flange to axle flange).

So far i've found out that i should have 5 degree castor, and the king pin inclination from a standard NC MX-5 is 11 degrees.

So, what i need to find out is
- What height does the roll center need to be
- what should the front track be given the rear will be at least 1350mm
- is the KPI of 11 degrees workable, if not what is a better option
- any other things i need to find out to start the drawing and claculations for setting out where i need to mount the front arms.

Reason for mixing and matching the MX 5 bits and the hilux bits is that getting an independant rear end over here is pretty expensive. This will be my first car, and with some experimenting and experience, i should be able to make the IRS work. I was thinking of using a Subaru rear diff assembly as they are more common over there than a Sierra, which are as rare as rocking horse poo.

Thanks in advance

Ben Sherlock

[alga]

Why don't you use the rear axle from the MX-5? Also, people say that Landrover Freelander diff is quite good.

[Aussie_Haynes_MX5]

Originally Posted by alga

Why don't you use the rear axle from the MX-5? Also, people say that Landrover Freelander diff is quite good.

Finding an MX5 diff at a reasonable price is the hard bit. I was lucky and got the front hubs for $100 for the two (about 35 pounds).They are also pretty hard to find at a reasonable price.

[ozzy1]

I dont know about NSW but in WA the engine has to be '99 or newer.Maybe worth checking.I agree with you on the mx5 prices being ridiculous here,maybe pick up a crashed one from an auction?
A few guys at the car club i go to have used to suburu diff with good results.
In regard to front arms etc it maybe worth waiting until saturn have finished their work on the demo car and then getting the drawings etc from them.

[spud69]

Welcome to the forum Ben,

There are a few Aussie and New Zealand builders we have supplied to and they have had all the parts shipped in one go on a pallet, keeps the costs down a bit but takes about 5 weeks to get to port then you need to arrange customs and pay tax on value. Any other parts you need to purchase could also be shipped together.

The Mx-5 front uprights we are working on next with plans / jigs available for them or fabricated bones to buy. Pics and plans will be available soon.

Maybe some of the other local builders could help with the build, if they have put the chassis design through the same test do you need to do the same for the same chassis? Also consider using 2mm wall thickness section as this will certainly help with the torsion and twist test you need to undergo.

All the Best.......Andrew