Tire Deflectors/Spats

[JulianEdgar]

Originally Posted by Vekke

Most oem cars big factor is can you drive the nose of the car on top of 100mm heigth curb without braking the flaps.That is reason most flaps are just straigth vertical.

That's interesting - I've not seen that in any textbook / tech paper on car aero. Do you have a reference for that? (Plus I have seen the same design used in front of the rear wheels.)

I will have new design coming for the ID3 flap testing.

How will you determine if it is better or worse than the standard one? The change (either) way is likely to be tiny.

[Vekke]

Not all obvious thing need to be read from articles. There are articles also in this matter posted in this forum that lower is better for the spats. If you look how people have to park cars inside cities the front of the car is totally on top of the curb. Almost half of parkings is done like that for example in dusseldorf where I currently live.

Cars which have some kind of bumb in front the flap usually have little higher ground clearance. The id3 has also bumb in oem bumber but ground clearance is close to 180mm to the bumb. Optimal shape in general is round like to front of the cars bumbers. The ID3 oem has round shape which is in the bumber.

All super slippery shell ecomorathon cars etc air is directed away from tires and little as possible tire is visible from front perspective.

If your flaps are longer and due to that closer to ground when you try to drive over the curbs they are broken instantly. Flap bends and is tear off by the curb and tire. If you dont drive in areas where you have to park close to curbs or drive over them again you can optimise the shape more to suit your driving situation. Thats is the situation in kitee Finland that almost never that curb parking is needed.

[AeroMcAeroFace]

I haven't heard of the kerb issue, however in the UK we have regulations for speed bumps that are a maximum of 100mm high. Some in certain areas are just 45 degree ramps up to a flattened plane and then a 45 degree ramp down. With suspension compression there isn't much space for contoured tyre spats that don't bend or conform or lift in some way.

Vekke, I don't think that is the case entirely, that the reason they are vertical is so you can drive up to a kerb. Because they could make them any shape as long as they don't extend below 100mm.

I think the reason is, given the restrictions of needing to drive up to a kerb, the flat plate gives the lowest total drag.

Using a flat plate creates downwards and sideways air movement, giving the effect of a larger deflector but at the expense of higher deflector drag compared to a sculpted contoured deflector.

[Vekke]

In eu mimimun ground clearance for vehicle is 80mm and you cannot build higher speed bumbs than that as all legal cars need to be able to go over. For curb heigths there migth be more sizes for curbs but most are around that 100mm. Usually stock car flaps have about 120-150mm clearance to ground on cars I have measured for the R&D process. What also matters is the distance to the wheel. When flap starts to bend 90 degrees will it touch the tire or not.

[Vekke]

If you want to have better aero the audi ultra models at least have these kind of flaps. Again the heigth is limited to my estimation by usability of the car to certain level. Air when hitting a vertical plate cannot decide itself which way the air should go. It will go to way which is easiest. Thats why bigger flat plates are not always better as you can find results and test to prove that claim.

If you drive the air pass the tire in controlled manner you will see better results. That is the purpose of that front facing rubber piece. It was about the same width as the tire. If you have more panels in your suspensions arm the other flap does not need to be so wide. Only to cover the tire surface area.

New range rover evoque has flaps that are just the size of the wheel. I would estimate they would come more towards outside if aestheticts would not ban that. On the inside they are exatly on the edge of the tire. That I got from online aerodynamic seminar of range rover development.

[Vekke]

Model 3 has shaped bumbs:

[Vekke]

On vw xl1 cd 0.189 the bumber is the flap and its pretty low. This car is not meant to be driven on curbs as its special purpose car.


On the underside there big boattails before and after tires:

[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.

[Autobahnschleicher]

I find the design of the XL-1 tire deflectors interesting.
It would be interresting to see if I could DIY something simmilar for the leading edge of my rear tires as well as a cover for the inside part.
Due to my cars super short overhangs I won't be able to do any trailing edge mods on the rear tires or much on the leading edge on the front.

Underbody aerodynamics seem to be underappreciated.

[freebeard]

Underbody aerodynamics seem to be underappreciated.

You got that right.



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.