Rubber boot mod (front tire air deflectors)
 

I have been making these deflector prototypes since 2008 and most of them do the job but does not look professional at least to my liking.

yesterday it clicked in my head and I think I found the solution at least for use who drive with narrow tires like I have 165/65R15 at the moment. I was just looking for rubber to buy for making these deflector but picture search kept showing me rubber boots :D.

Just buy some rubber boots that look like this:
https://scontent-dus1-1.xx.fbcdn.net...uw&oe=66DCB511

Those are not actual rubber they are some EVA-Material (Ethylen-Vinyl-Acetat). they seem to be little higher in which is better for aero than normal rubber boots. But the matt look is what I needed.

There with one pair of these in size 47 costs 18.85€. estimated impact to drag is 0,02 but when I try to make them also to rear and tweak also the wheel well front lip I would estimate and hope I can lower the drag even 0,03 to 0,04.
In my car that means at 100 km/h speed or 62 mph
Cd -0,02 = 0,16 l/100km=0,24€/100km savings or ~104km/h=100km/h consumption
Cd -0,03= 0,24l/100km=0,36€/100km savings or ~106km/h=100km/h consumption
Cd -0,04= 0,32l/100km=0,48€/100km savings or ~108 km/h=100km/h consumption

Even the lowest drag reduction of 0,02 gives payback estimate that its under 10000km so one oil change interval

Cannot wait to start cutting these when they arrive.

Most likely it's PVC instead of EVA. I often use boots like those when it's raining heavily.

Boots arrived and they are shape wise as good as I estimated. One problem migth be that the tip of the rubber boot migth be too stiff. It flexes but takes reasonable force to do that.
https://scontent-dus1-1.xx.fbcdn.net...rw&oe=66E08B4F

https://scontent-dus1-1.xx.fbcdn.net...SQ&oe=66E05891

https://scontent-dus1-1.xx.fbcdn.net...gw&oe=66E0621A

Conserning the positioning it still needs tweaking between the car and 3d model. I need to double verify the tire contact patch width and how apart the tires are actually from each other.

But overall it looks already very promising. Target is to direct air 10-20mm past the tires on both sides of the tire...

Height of the boot is 60mm which I think is pretty ideal at least for my low Audi A2. Height even increases 10mm when going towards the tire like it should. Still I will build extra 10mm lip at the end so total height will be around 80mm.

The smaller shoes are planned to be installed at rear but will see do I just use pieces from the bigger boots or what will be the best looking vs functioning solution.

Quite predictable regarding those safety boots, as they're meant to be used on construction sites and other dangerous jobsites.

That is a winter "hunting" boot.

No metal tip protector...

It had wool liner sock. It's about 8mm thick on the head/tip (reason why it's stiff) and even more on the bottom. Reason is insulation. First one is already cut to shape. Always make it first too big as it's easier to go smaller direction...

Summer versions are lacking the height, but then again other brands are 2 to 5 times more expensive.

Size is 47, but my 48 foot fits nicely without the inner wool sock.

https://scontent-fra3-1.xx.fbcdn.net...2g&oe=66E4A6F5

https://scontent-fra3-1.xx.fbcdn.net...Dw&oe=66E4B42B
First boot is in place. At the moment seems and feels that the 40mm high boot might be better option.
It was difficult to estimate that rear edge where it will land but 45mm ground clearance might be too much. It also direct the air too much down.
Also the front edge is still pretty stiff and sits at 80mm ground clearance. Height wise that would be ok, but being so stiff that the underside plastic panels flex before rubber need to think what to do with it.
Video on the matter: https://youtu.be/tQpKmE3fATc

The ones I buy don't have a metal tip either.