Mx-5 Donor - SSC

[spud69]

Originally Posted by TQ_uk

Just to clear things up a bit, this is all theoretical from my end as I don't have a chassis built as yet, just an MX5 front end (to look at wistfully )

I'm assuming from Andy's pics etc the MX5 rear end seems to be used un-narrowed and thus the rear and front track will be as per MX5.

So I'm then guessing the new front wishbones are longer than stock MX5, (ie the pivots
are closer together than the rusty bits in my garage) so making original rack
inappropriate?

I thought that maybe the reason for using the Escort rack came from the Haynes being an adaptation from the original Locost and its just sorta 'stuck'

What ball joints are you using Andy?

Sorry for so many questions; I'm just trying to understand the geometry changes and rationale behind using certain parts is all.

Cheers

Hi TQ,

I think as everyone realises suspension geometry is a bit of a minefield luckily , coincidence or not, the Mx5 geometry is very similar to the roadster the main work was to adapt wishbones to work with the mx5 uprights and the Haynes chassis keeping the wishbone brackets in the same place and the haynes chassis as close as possible to the original and adapt the wishbones to give the correct geometry. The safest option for me was to use the tried and tested geometry of the roadster as is. Rear geometry is quite straight forward and uses mx5 track width with adjustable lower wishbones to alter camber and toe in of rear wheels. The front was setup using the software below:

http://www.flickr.com/photos/saturns...7625932340212/

giving a SAL figure of 1134mm giving the following ride:

Hints: From the Competition Car Suspension book.

Short SAL (500 – 1000mm) gives very good roll centre location, keeps the outer wheel vertical in corners, but going badly to positive camber in droop and negative in bump (accelaration squat and braking).

Long SAL (1800 – 4500mm) provides lower roll centres but less control over their sideways movement, minimal scrub (track variation), poor outer wheel control going into positive camber, but only small camber change in bump/droop.

Medium SAL (1000 – 1800mm) is the transition area between long and short with, as you might expect, a bit of this and a bit of that.

Ultra-long SAL (near parallel) provides excellent vertical control of very low roll centres but possible enormous sideways movement, wheel angles virtually unaltered in bump/droop but very poor control of wheels in roll, with near equivalency to body roll angle.

Also the front can be fully adjusted with twin adjusters on lower wishbones for camber, castor, track width.

Ball joint are standard Mx5 lower joints and transit drag links for top with upright reamed out slightly. With Sierra drag link ends. Escort rack used mainly to retain the Haynes chassis design as much as poss plus escorts racks are readily available new in different ratios.

I suppose the proof will be in the pudding, shouldn't be too long before we can give it a try it - cant wait......

Also starting to mold up a grp rear diffuser for the car this week, which will fit the standard Haynes to. Should be good.

Andrew