Tire Deflectors/Spats

[freebeard]

Once you're past the nits, waiting to be picked; it gets interesting.



www.wrcwings.tech/2018/09/19/wheels-impact-on-the-aerodynamics-of-a-wrc-car/

It would appear that spreading the interaction of the oncoming air up the face of the tire reduces the interaction, and substitutes for a spat.

It's interesting to see how WRC cars are dialed-back time attack designs. The wheel diffuser would be less vulnerable to debris. Anyone with an old pickup truck with running boards could take note.

[JulianEdgar]

Originally Posted by freebeard

Once you're past the nits, waiting to be picked; it gets interesting.

I just have this really weird idea that showing a complete misunderstanding of the subject might actually invalidate the writer's interpretations of the pictures.

The pictures themselves are interesting, as I said.

[freebeard]

I was just covering for the fact I could one find one complete misunderstanding.

And that could just be poor phrasing.

[JulianEdgar]

Originally Posted by freebeard

I was just covering for the fact I could one find one complete misunderstanding.

And that could just be poor phrasing.

Yes it could be poor phrasing, but only for one of the errors, not the other. Either way, it's misleading - as is so much about car aero that's around on the web. While not trying to labour the point, you'd think people here would think twice before linking to incorrect material (or at least flag the errors).

Anyway, together with another quote (a comment on my channel that YouTube stopped because it contained a swear word) I did a video on this today:

https://www.youtube.com/watch?v=qvbNuHB1qC4

[AeroMcAeroFace]

Considering the frontal area, the drag reduction is, on the scale of the car, very small. How much of the frontal area of a car is tyre? I cannot see comparisons of deflector shapes being able to be measured on the road, far too many variables.

you'd think people here would think twice before linking to incorrect material (or at least flag the errors).

Not just that, being clear with what is actually being quoted is important too, so people aren't misled.

[Vekke]

Originally Posted by AeroMcAeroFace

That is quite misleading, for those that haven't read the referenced document, the 5.5% comes from just the wheel and wheel arch drag. And not, as it would appear from Vekke's comment, the whole car.

Considering the frontal area, the drag reduction is, on the scale of the car, very small. How much of the frontal area of a car is tyre? I cannot see comparisons of deflector shapes being able to be measured on the road, far too many variables.



Not just that, being clear with what is actually being quoted is important too, so people aren't misled.

Did you read it and understood it?

Table 4,1 says it clearly (at least in my opinion):

Total Cd of the whole car 0,216 without any flaps. (body 0,159 + wheels 0,053 + flaps 0) Here is error in chart as the sum up is not same in all of the configurations!
With 40mm flaps Cd 0,204 of the whole car

To my eye it shows 5,55% reduction in whole car drag coefficient is that 5.55%. I put the decimals which are also at the dokument, those who like round ups you can round up to 5,6%->6% or 10% which ever makes you happy. That does not change the flaps in that test changed the whole cars drag coefficient 5,5% better. And again just with front flaps.

Those results mentioned in the test are propably not final and best as the study has been done to automotive manufacturer the best will be something that is not mentioned in the test. That goes to all studies you can find on the internet do they tell everything or do you have to adapt the results to your case or not. I really don`t believe that was the only with and position and width tested for that car as its so easy to test different versions and get better results.

If you take those 60mm flaps wheel drag drops that 18,8% part of the whole car, (0,043/0,053)-1 but the flaps incease drag 0,007 and body drag increases 0,017 giving the whole car drag coefficient 0,215. If and when you design flaps which are more aerodynamic than those vertical plates you can lower you whole car drag coefficient more than 10%. Again my estimation on the savings potential.

[alexshock]

Originally Posted by AeroMcAeroFace

Considering the frontal area, the drag reduction is, on the scale of the car, very small. How much of the frontal area of a car is tyre?

FYI, On my Auris, factory Cd are following depending on wheels only:
15: 0.25
16: 0.26
17: 0.28

There are no other aero mods or differences in these 3 trims.

[freebeard]

I put the decimals which are also at the dokument, those who like round ups you can round up to 5,6%->6% or 10% which ever makes you happy.

Just being granted a little slack makes me happy.

Active spats controllable from the driver's seat are probably within the home experimenter's purview, with choke cables or electric stepper motors.

[JulianEdgar]

Originally Posted by freebeard

Just being granted a little slack makes me happy.

Active spats controllable from the driver's seat are probably within the home experimenter's purview, with choke cables or electric stepper motors.

Yes, that's good idea and not that hard, technically. Easiest with solenoids - just two positions - up/down, based on speed.

[Vekke]

I am back in finland and the deflector testing has continued in my ID3.



This shape has worked best in the Id3. I have tried today. 2 versions of the flat plate, which I had previously, and no flaps at all. The straigth flap is still behind this curved flap. At the moment car is lowered 30mm by H&R springs. In front lowest point of that deflector is now in 80mm ground clearance. This hard 2mm abs is only for testing more flexible solution will be needed in the end.

Same/similar curved deflector at rear (can be seen at the pic) which was 20mm shorter did not work at the rear and the oem one worked better. Will test other version front and backif I will find ever better solution.