Suspension - the important ratios?

[TQ_uk]

Originally Posted by Airhead

That is a very good idea

http://www.roadrunnerracing.net/rr-g...d-gallery.html


Front shocks look like they're at quite a shallow angle

[Airhead]

Hi

Yep hoping to keep the track et all the same. From what I can find out on the internet the track width on a Sierra is 1450 front and 1470 rear which is narrower than the MX5 at 1490 and 1495 respectively - can't see it myself but there you go.

The Roadster is quite a lot shorter than the MX5 so if the track is narrower I can't see it adversely affecting the handling.

The steering rack is too long due to the reletively short front wishbones on the donor, the Escort rack is the right size and can be modified to work with the MX5 spindles.

I am in esscence doing what you suggested by keeping the dimensions from the donor apart from the longitudinal distance between the mounts.

I noticed that Talon Motorsport have claimed to have done some work with MX5 suspension; I'm just waiting for them to return my call...

Matt

[TQ_uk]

Sorry, think I've confused both of us with my previous post....

Am I right in:

a) you're keeping front & rear track as per MX5
b) the wishbone mounts on chassis will be book 'width' (or thereabouts), ie 670mm top, 494 lower, thus new wishbones will be need to be longer (than
standard MX5) to retain MX5 track, and as a consequence MX5 rack will be too wide

Think thats rephrased my previous post in a clearer fashion....

[TQ_uk]

Btw, info I've got re track is:

Sierra: F 1452mm/ R 1468
MX5: F 1405mm/R 1430

from http://www.carfolio.com

[Airhead]

a) Yes

b) Yes absolutely correct but the steering rack issue is relating to bump steer rather than fit. (the mazda front subframe is 727 and 654 respectively between mounts)

I have just got off the phone with Talon who already have prototype suspension mocked up, their setup uses a book build with regards to mounting points, his figures tie up with the ones you posted above so my build will have a fractionally narrower track - about 2" overall.

[3GE Components]

What does the MX5 upright measure in comparison to the Sierra upright? Unless they are exactly the same in dimension across the ball joints then the front geometry using "book" mounts probably won't work.

There's far more to suspension design than just making it fit the car. Apart from getting the camber & castor right there are a host of other factors in suspension design to consider, some of them quite critical. My advice would be to get yourself a good suspension book ( i can recomend a few) and read it thoroughly.

With Chris's new book he has spent a lot of time getting all these factors correct, so much so that we have had to make custom uprights for him to get exactly what he wants, as nothing was available off the shelf.

Kind regards

John

[Airhead]

Yep, I appreciate that there is a lot goes into it which is why I am asking here rather than botching it. I will post up the measurements for the front later

As far as the rear is concerned if I replicate the mazda layout on the vertical and widthways with variation only longitudinaly I shouldn't run into any problems should I?

Matt

[Big Vern]

As 3GE says,
There is a lot to getting the suspension geometry right and you'll need to draw it out on a suspension design program to understand exactly whats going on especially with regards to the geometry designed into the MX-5 uprights.
You won't be able to use wishbone lengths the same as the MX-5 ones as they're totally unsuitable for the Haynes roadster.
I would put the haynes design into a suspension design program to see how it works then replace the sierra upright with the mazda one to see how it changes Akkerman, TOOT, and caster. The steering rack will need mods to bring bump steer to an acceptable level. (some is desirable for stability under heavy braking).
Or you could cheat......Find a MX-5 based westfield and get your tape measure out!!!

BV.

[TQ_uk]

Originally Posted by 3GE Components

What does the MX5 upright measure in comparison to the Sierra upright? Unless they are exactly the same in dimension across the ball joints then the front geometry using "book" mounts probably won't work.

There's far more to suspension design than just making it fit the car. Apart from getting the camber & castor right there are a host of other factors in suspension design to consider, some of them quite critical. My advice would be to get yourself a good suspension book ( i can recomend a few) and read it thoroughly.

With Chris's new book he has spent a lot of time getting all these factors correct, so much so that we have had to make custom uprights for him to get exactly what he wants, as nothing was available off the shelf.

Kind regards

John

Hi John,

I'd be most interested in good suspension book recommendations as would like to know more about this area

Cheers

Tarquin

[TQ_uk]

Airhead - don't know if you've got/seen this, its a handy Excel file/program someone sent me this a while back that shows the effect of geometry changes. Worth getting your head around


EDIT - attachments not appeared (too big) PM me your email & I'll send it to you