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.

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

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

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.

Thanks for the input BV.

When you say that the MX5 wishbones aren't suitable are you talking front, rear or both? The only reason I ask is that the rear mounts arent a million miles off the book anyway and in order to retain the track (and the halfshaft lengths) the rear wishbones will end up a similar length to the book and Mazda have already done the maths with regards to their rear uprights. I appreciate that the weight is different tho'...

Hi John,

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

Cheers

Tarquin

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

Just my 2p worth, sound like HandyAndy now......;)

Why not ditch the Mx5 front uprights and buy a new set of sierra uprights from Rally Designs, about £95, and use the Haynes designed front suspension to run the car on. The suspension layout and geometry was meticulously designed, on Lotus own design software, to give an ideal ride between road and track use and is a major design in the Haynes to give it the excellent ride and handling that it has. Obviously would need discs, £18, and callipers, ???, to go with it but i believe this would be the best solution. We are just about to star putting a car together based on the Rx-8 and will be doing it this way.

All the Best....AndyH

Where's the fun in that?! ;)

Seriously though, I'm way off starting a build, and also following the Midlana project (which uses MX5/Miata uprights) so much of my quest is to collect knowledge & info before getting stuck in, ensuring I have a clear idea, so (hopefully) the project won't stall.

I don't want to make things (any) harder for myself than necessary, so in all likelihood will stick to book at the end of the day.

Just exploring my options :)

Appreciate all the feedback and expertise this forum provides from those who've been/seen/done!

Do you know what? I was thinking about just that this morning in the shower, the only issue would be the rear track but I could use spacers to compensate.