Tire Deflectors/Spats
 

I went to a few dealerships and took pictures of the deflectors on different vehicles. Only one salesman was even remotely interested in what I was doing, the rest lost interest when they realized I wasn't buying. :) These are all on the front tires. No Prius or Insight was available.

I thought the Ford Focus was really interesting. Three deflectors that wrap around the tire!
http://ecomodder.com/forum/attachmen...9&d=1306402733
http://ecomodder.com/forum/attachmen...0&d=1306402733

Full width dam on the Ford Fiesta:
http://ecomodder.com/forum/attachmen...8&d=1306402733

Doubles on the Honda CRZ:
http://ecomodder.com/forum/attachmen...7&d=1306402733

I forget what cars these were, I think Toyotas and/or Subarus:
http://ecomodder.com/forum/attachmen...4&d=1306402733
http://ecomodder.com/forum/attachmen...5&d=1306402733
http://ecomodder.com/forum/attachmen...6&d=1306402733

the third to last one looks good, just big enough to cause a wave off to each side around the tire, just small enough that the air will minimally affect the apparent frontal area

Great post, Fumes, gives me food for thought.

It's interesting to note how small the OEM deflectors are compared to some of the DIY jobs on here (if you've acres of coroplast then you might as well use it), maybe the manufacturers are saving material/cost or maybe they don't want the aero parts to impact on the car's styling. I don't know, but I'm beginning to think that it's often the little things that can make a big difference to FE.

Wish i could post the ones we're fitted here at Bentley all of the continent series run deflectors and front and back belly pans (mainly to help top speed though ;) )

Smaller OEM ones might be more efficient, or they might just be more practical. Like the Fiesta's deflector - it is probably in three pieces so that people can hit curbs without damaging it, or so that snow doesn't collect in it, or something like that.

It is definitely encouraging to see that the mfgs go to the troule of putting even small flat ones on - tells me that even if you can't put a large, streamlined one on, whatever you put on will probably help.

Also notable to me on that Fiesta is the giant, smooth front undertray. Very nice.

i think it's fair to say all these dams where sized in the wind tunnel to be as eficient as possible without compromising minimal ground clearance and likely style too.

i read in an old autospeed article on these things that to large would once again cause drag, but that these dams also had an effect on front lift, so it's likely they're designed to strike a balance between these things.

to me it seems most are more aimed at keeping air away from the gap behind the wheel where the suspention is, rather than the tire itself

I can't help posting the FJ Cruiser! :eek:
http://ecomodder.com/forum/attachmen...1&d=1306427413

Good job, GF:thumbup:

So, are front spats useful if the car already has a full width airdam under the front bumper?

Thanks for these images. Nice little archive. It's really interesting how often the spats cover only the inside half of the tire. I take it the idea is to avoid lift and to avoid a blast of air shooting out the side of the car like a snowplow in a blizzard. I built mine of a modest size, in imitation of some testing done on a first gen prius that one of you all shared on this site. They're small, but they cover 2/3 of the tire and they block the inside bottom of the wheel well (as the modded Prius had).

i think they could be.. the 2011 opel astra has this combination, i can't find a drag figure for it so it may not be all that great, but considdering ground clearance and approach angles airdams can never go as low as you'd want them, but being closer to the tires wheel dams can.

http://i77.photobucket.com/albums/j5...6696050917.jpg

the combination i think is best and what a lot of low Cd cars run is a central undertray, lower side airdams in front of the wheels and suspention and small wheel dams as pitures

Oooo, that Opel also seems to have small spats in front of the rear tires.

Those look like they're made to deflect air so it doesn't hit the suspension components.

one thing i think to keep in mind when looking at these things is that the dams in themselves are very unaerodynamic shapes, so they will generate a rather wide "wake",

i suppose they don't need to be the full width of the tire to send the air cleanly around it
http://i77.photobucket.com/albums/j5...efficients.jpg

so when reverse engineering it's best not to assume "bigger is better"

That's part of what I did with my DIY spats too. I have been meaning to test them.

They are also looking at the simplest installation possible.

The larger flaps are also somewhat flexible; they will bend with airflow. I remember the early Ford Contours had flaps in front of the wheels. At the time I had no idea what they were there for.

In the week I spent driving a Fiesta, that air dam scraped on at least a dozen driveway/lot entrances. It's a little on the "too low" side.
http://ecomodder.com/forum/attachmen...8&d=1306402733

About half of the cars I looked at had rear tire spats as well. Pretty much all the same back there. Small, flat and straight. Here's the Honda CRZ rear spat:
http://ecomodder.com/forum/attachmen...1&d=1306522873

I have been doing testing on these flaps a lot lately and they do effect the consumption a lot.
https://www.youtube.com/watch?v=E_OsWefoYjU

https://www.youtube.com/watch?v=NNo0u1BrDxs

I took 10mm off from each flap after this video and consumption got back to 0,1liter higher to 5,5 liters.

Flap width is usually narrower than the tire. Do notice that inner side is wide because it also directs air away from the suspension lower a arms etc. just 10mm changes to shape and size can have measurable impacts.

Tip is that build adjustable flaps in heigth first and get the heigth best setup After that build flaps that you can adjust the width also.
Optimum heigth of the sparts are aroung 40-70mm. And width needs to be about 40mm.

Conserning the A arms the best heigth is around the lowest point af the nearest body structures behind the flaps. Usually lowest point of the body.

You have to be able to test these mods in calm conditions as wind do effect fuel consumption of the results close to 10% and easily 5%. So best is that you try to find level road for 3-5km and test the consumption to both directions. make fast changes and repeat the test. Try to keep measuring speed high so its easier to see the differences. I test usually at 100 km/h, but I will try the method I described and will test at 120 km/h to see better results. To get the smaller differences. I also keep records of the consumption at various points on my test route to see if the consumption changes earlier or later compared to previous setup. That is because in Finland near me is not perfecly level roads so there is up and downhills on the route.

I will also try to test to put angled flap when I have found the best setup if that brings even more gains.

I wonder if the angle has any influence?

Also if they produce some noise one could put a small sawtooth profile on the end.


http://www.windfarmbop.com/wp-conten...serrations.jpg

wide wake
 

From the upper image you could imagine the tire training within the wake of the spat and on others,that the flow might jump the void of the wheelhouse and then re-attach once beyond it.Goro Tamai did this at MIT for their solar race cars.:)

Most of the spats I see are on smaller passenger cars that are already fairly low to the ground. Vekke brings up a point about height of the spats making a difference. My question (being I know little about aero stuff) is this.....with shorter spats, is it that the spat covers less of the tire or that the spat is farther away from the ground that makes the difference.

The reason I ask is that I am trying some "reverse mud flaps" on my truck. They are definitely taller than anything I see on Festivas and Prii. But my truck also sits much taller than those. A shorter spat like those from a passenger car (at least in my mind) wouldn't work as well for my application. Or would they?

Is there an optimal "ground clearance" for spats and air dams and such? Or at least a general "rule of thumb"? I seem to remember JRMichler (at least I think it was him) that said he had the best results with an air dam that was 3" above the ground.

This triggered a thought, the designs we see from manufacturers may be as or more influenced by NVH, than by efficiency. I had thought that many designs seemed to be more about keeping air out of the wheel well than away from the tire. An oversized spat vs none at all could potentially create a similar amount of drag, however the vehicle with an oversized spat would likely have less noise coming from the wheel wells.

rule of thumb
 

With the variety of vehicle designs I believe that a rule of thumb is impossible.And you might be looking at $50,000 in wind tunnel time to optimize a design for any specific vehicle.

This is what I did to touareg. They use similars in big trucks and they work there in windtunnels. So it routes the air to the side of the tire. There are still smalle flaps in normal positions for the air that escapes behind that flap.
https://scontent-hel2-1.xx.fbcdn.net...ca&oe=5DF8BCA3

Looks very nice and OEM.

Vekke.......that's more what mine will look like. Just not near as polished and OEM looking as yours. Very nice work.

At least mine were cheap. $10 at the pick-n-pull for all 4. I can always get another set someday and cut them shorter and see if it makes much difference. For now I'm leaving them alone.

Too new here and cant post any photos yet, and sorry for the necroposting

yesterday I saw a bluemotion golf tdi upclose, rear spats seem to be a rather plain simple flat straight rectangle while the front are smaller than 1" dont cover the entire width of the tyre , curved, and seem to deflect the air away from the front suspension / front lower arms

so completely different design, I thought they could do more, especially in the back

just my 0.02

They could do more for drag, probably. But there might be a lot of optimization going on in those designs that take into account other priorities, especially brake cooling.

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

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.)

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

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.

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.

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.

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.
http://135jik1bbhst1159ri1ax2pj.wpen...dirty-side.jpg

Model 3 has shaped bumbs:
https://cdn.shopify.com/s/files/1/02...g?v=1538803508

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.
http://2.bp.blogspot.com/-X4K05k_bCK...oors-openf.jpg

On the underside there big boattails before and after tires:
http://i.auto-bild.de/ir_img/1/0/6/1...6fc7503c90.jpg

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.

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.

You got that right.

https://ecomodder.com/forum/member-f...42-mudflap.jpg

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.