Are any of you guys cutting away behind the front wheel to allow better pressure release?
Im sure Ryan will comment(I can see he has done some work on his to help)
Relieving the pressure there isnt just about reducing lift, while thats one of the reasons its not the primary.
Wheels and tyres make really good vacuum cleaners, in which they suck all the air into the wheelarches, but then if it has nowhere easy to go, the pressure increases and creates lift, you can vent from the top of the arch and also the rear part of the arch.
One of the important things about venting arches is to keep the pressure as close to ambient as possible.
Your splitter works by forcing the air that travels underneath it to speed up and as such becomes a low pressure area.........now if you have low pressure heading straight into a high pressure area, thats exactly what it doesnt want to do.
Imagine opening a bottle of fizzy pop, the air always wants to go from high pressure to low pressure
The only way you can force it is with lots of velocity, but effectively its still like hitting a brick wall.
If you can reduce that wheelarch pressure you reduce the 'wall' and the splitter allows more air to pass out of it and hence works better.
This is also why I suggest front diffusers to allow that pressure gradient to be more gradual to reduce the 'wall' scenario.
So your now making more front downforce, you can then add more to the rear to balance the car for a net increase in overall downforce more than just a little reduction in lift in the wheel arch.
Its not as easy on a miata to remove as much as I have but it will be possible with some chopping and welding, a very good example of this would be Under Suzuki
This is what i did with my car, I know its not a miata, but one of the guys on here has said it would help if i joined in with my thoughts