Tire Deflectors/Spats

[IRONICK]

Originally Posted by Vekke

In that picture (Audi A5) is a small deflector that no one has considered so far to mount. Is the one mounted on the central cross member.
On the Audi A6 there is another one mounted at the end of the central deflector.
Those deflectors also help evacuate hot air faster from the exhaust area.

[Autobahnschleicher]

Originally Posted by freebeard

I drew this for a truck owner, but the proportions could be adapted. The idea is two u-shapes, one strap metal and one conveyor belt material (which would be curved instead of flat). They would be fastened along the sides but not the end, so the belting can deform on impacts.

I'm curious what TÜV would say.

I think it would make more sense to direct the air sideways around the tire instead of mainly under it.
Basicly creating somewhat of a streamline fairing for the leading edge of the tire.

TÜV would ask for a Materialgutachten and Einzelabnahme or not norice if it looks OEM-enough.

[freebeard]

Post:10
Sorry, new users are not permitted to post links in their signatures.

Is that your signature verbatim, or is there a link in it? I thought five posts was enough.

A smaller, more upright (downright?) and curved unit would do so.

[Autobahnschleicher]

Originally Posted by freebeard

Is that your signature verbatim, or is there a link in it? I thought five posts was enough.

A smaller, more upright (downright?) and curved unit would do so.

That is not my signature, I just have my Spritmonitor link in there and as it seems I'm still too new.
Currently in place 1 out of 57 cars of the same model.

Anyway, I'd assume a downsloped fairing would be less than ideal as it creates a high pressure zone of stagnation in front of the tire.
If it was designed like the leading edge of an airfoil, you wold have far less stagnation in front of it and divert the airstream around the tire more efficiently.
Also:
Keep in mind the straight flaps from the factory usualy tend to have some angle to divert the airstream away from the tire.

[Vekke]

New mercedes EQS has quite big flaps I estimate 60mm in heigth in front covering the wheel width. Flaps will get smaller when you come towards the center of the car so they still cover the suspension arms nicely. Difficult to find good pictures but in this video they are most clearly visible that I have been able to find. Cd of EQS is 0,20.

In the rear is seems flaps size is about 30mm so much smaller there.
https://youtu.be/j-7yHruH0PM?t=28

https://media.daimler.com/marsMediaS...9NDA2MzA!&rs=9

[IRONICK]

Originally Posted by IRONICK

In that picture (Audi A5) is a small deflector that no one has considered so far to mount. Is the one mounted on the central cross member.
On the Audi A6 there is another one mounted at the end of the central deflector.
Those deflectors also help evacuate hot air faster from the exhaust area.

"Spolier Strip"

[Vekke]

Originally Posted by JulianEdgar

Yes even the first Honda Insight 20 years ago had shaped front tyre deflectors. Not to mention the Ford Probe IV concept car. My points are that (1) I have never seen any publication that suggests that flat plate deflectors are fitted because of potential kerb impact, and (2) I cannot see how such a tiny change will be measurable outside of a wind tunnel. I had hoped we’d gone beyond the ‘guess and rule of thumb’ approach to aero modification here.

https://publications.lib.chalmers.se...512/250512.pdf

Here is a cfd study on spats. lower is better for wheel drag but whole car drag starts to rise after 40mm flap heigth in this test. I measured roughly the ground clearance in that model is 150mm and tire width 210mm (205 or 215). They tested only flat spats. That 40mm flap leaves 110mm ground clearance and that 60mm flap leaves 90mm ground clearance.

Max savings in that cdf study just on front flaps was 5,5% on drag. I believe that is easily measurable on road.

If you are able to get those lower flaps working that lower wheel drag 18,8%, without increasing too much body drag more is possible than that 5,5%. And this was just for front spats. So different shapes and sizes will give different results.

[JulianEdgar]

Originally Posted by Vekke

https://publications.lib.chalmers.se...512/250512.pdf

Here is a cfd study on spats. lower is better for wheel drag but whole car drag starts to rise after 40mm flap heigth in this test. I measured roughly the ground clearance in that model is 150mm and tire width 210mm (205 or 215). They tested only flat spats. That 40mm flap leaves 110mm ground clearance and that 60mm flap leaves 90mm ground clearance.

Max savings in that cdf study just on front flaps was 5,5% on drag. I believe that is easily measurable on road.

If you are able to get those lower flaps working that lower wheel drag 18,8%, without increasing too much body drag more is possible than that 5,5%. And this was just for front spats. So different shapes and sizes will give different results.

You seemed to have moved the goal posts. My comment that measuring a drag change on the road would be difficult related to what you said you were going to do - use shaped deflectors instead of flat deflectors.

[Vekke]

5.5% Savings came already with straight flaps...

More flaps here https://www.wrcwings.tech/2018/09/19...-of-a-wrc-car/

[JulianEdgar]

Originally Posted by Vekke

More flaps here https://www.wrcwings.tech/2018/09/19...-of-a-wrc-car/

Interesting pics but the explanations are at the typically quite confused level of so many similar websites.

The amount of air flowing under the car is small, due to the presence of the front splitter in all cars, for what air flows faster there. By Bernoulli, this means lower pressure, and this is how downforce is generated, by the pressure difference with the high pressure above the car, caused by the considerable bigger amount of air which is forced to flow over the car (as we already saw in a previous post on Underbody aerodynamics).

At least two major mistakes... in just the second paragraph.