Tire Deflectors/Spats

[aerohead]

Originally Posted by lunarhighway

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


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

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.

[hat_man]

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.

[2000mc]

Originally Posted by teoman

Also if they produce some noise...

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.

[aerohead]

Originally Posted by hat_man

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.

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.

[Vekke]

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.

[teoman]

Looks very nice and OEM.

[hat_man]

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.

[eagle]

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

[California98Civic]

Originally Posted by eagle

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.

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