Downforce

[jules]

I've had worn shocks cause the symptom you are describing.

Jules

[CT]

The MX5 really only benefits from aero above 120-140 or there abouts (actually thats most cars). But, any front lip that extends the bumper towards the ground will reduce the air passing under the front which adds to a low pressure area which does two things. Firstly, it helps to draw air through the radiator and secondly the low pressure area can help to suck the car to the road. A splitter or undertray adds to the area of low pressure by increasing it's size etc etc. A rear lip or spoiler is mostly effective with a hardtop on as the flow of air across the car is kept attached to the car and the lip helps to keep the turbulence behind the car and not on it. With the top down and no hardtop, there is great turbulence in the cabin and the effect is very much negated. A big rear wing will generate downforce but it is also easy to stall the air and slow the car down if placed in the wrong position.

A rear diffuser such as those fitted to Ferrari's and Lotus's helps to draw the air out from under the vehicle hence making the lower pressure area under the car larger and stronger which further helps to keep the car planted to the road. There are some excellent books on vehicle aero which are certainly worth a read. Yes it works, but not a road speeds. Agreee with the others - sounds like a very poor alignment, ie too little castor or shagged shocks and dodgy bushes.

[CT]

-HP Books How to Make Your Car Handle has a good section on aero and other things handling
-Competition Car Composites and Competition Car Aerodynamics by McBeath are also good reading especially if you want to make and test your own stuff
- The bible is probably Miliken's Race Car Vehicle Dynamics which I have read bits of but it's mostly it's way above my mental capacity!! Check out Pitstop bookshop in WA as they have most of them.

[Mr_Q]

thats a little too far for me to drive for a book, seeing as i live in brisbane. will se if i can find them online or something.

http://www.pitstop.net.au/view/products/page/query/plu/5454/

Ouch on the price - maybe we need a club library.

[Alex]

i havent sat in any mx5 that feels 'planted' over 120(maybe the NC's may be different?)...

our cars DO have really bad aerodynamics with or without roof on unfortunately...but i guess that all goes out the window when u can see the stars when ur driving gotta love topless driving

mine feels alright on the straights with moderate turns up until about 150 as long at there isn't too many crosswinds

done on a private road ofc

[greenMachine]

From the big forum: http://forum.miata.net/vb/showthread.php?t=185026

It's a long read, but worth it.

[kitkat]

Thanks everyone for the feedback, muchly appreciated

Cheers, greenMachine ill make my way through that when i find a quite moment here at work

[The Pupat]

200kg heavier

I think you found the answer. It'll always it squirmy in the wet since you are running relatively big tyres on a light car so it's very easy to aquaplane.
just about no spoiler will do anything. Get a hardtop though should help aerodynamics with it on, windows up and AC on on the highway (since the gearbox makes the cabin rather hot AC is a must), mine doesn't have any problems with getting blown around...at least not compared to the pajero.