Tire Wind Deflector Question

[alohaspirit]

I think figure A is better since it deflects air away
from your underbody but Id like to hear your reasoning

[MetroMPG]

The airflow near the front tires is rarely travelling straight towards them, so the design of successful tire deflectors may not be intuitive.

High pressure at the bumper may be forcing flow both down and outwards, which is one reason why OEM spats don't extend out to the edge of the tires (they'd be overkill if they did, pushing air further out than necessary).

Some OEM spats that are angled similar to your Figure B would be subject to perpendicular flow! (Of course, it depends on the vehicle.)

One Volvo study found that even very small changes in spat size / positioning can have a negative effect (increase drag). I'll see if I can dig it up...

This is a tough one to guess at!

[MetroMPG]

Here it is. No surprise that Julian covered it at Autospeed!

Modifying under-car air flow part 2

The table on that page shows how in the case of tire spats/dams it's not a simple matter of slapping something on.

[winkosmosis]

Why are some spats parallel to the front of the tire? Why not just let the air hit the tire? It's not like it's less aerodynamic than the spat.

[alohaspirit]

Originally Posted by MetroMPG

Here it is. No surprise that Julian covered it at Autospeed!

Modifying under-car air flow part 2

The table on that page shows how in the case of tire spats/dams it's not a simple matter of slapping something on.

Thanks. Thats a good link.

Almost all the defectors helped except for the biggest one.

Which basically means "Bigger doesnt equal Better"

*insert joke here*



sadly what came stock on that prius is what i was thinking about making

[doviatt]

Sounds like a good candidate for tuft testing. Though a difficult one to set up and observe. Tuft the raw car underneath front and note the flow directions then try with the spats placed according to preceding results.

[skyl4rk]

The ideal shape for tire covers is a symmetric NACA foil. The rear of the tire is more important than the front.

The design of a symmetrical foil has been worked out in detail for design of boat rudders. You can use some of their tools and theory to make your tire covers.

NACA 4 Digits Series

Foil FAQ

[alohaspirit]

something like this then?

[Otto]

Hucho has a nice picture showing smoke flow from the front as it hits the tire. Turns out, the smoke trail deflects ~60 degrees from centerline parallel, outward. This would be due to bow wave where it impinges on the pavement.

You need elliptical deflectors, canted inward (pigeon-toed), as seen in one of the Julian Edger photos. The tire also needs fairings behind the tires, to smooth the turbulent air there. Prius made a weak attempt at this with their back wheels.

[skyl4rk]

Behind the tire, make a long trailing edge that comes to a point. In front of the tire, either do nothing, or put a small rounded deflector that approximates the curve of a naca foil.

Between the front and rear tires, you can put in a catamaran which is a box between the wheels.