Air dams on 2014 Silverado
 

I'm thinking of making an air dam for my Canyon. The factory air dam is made of brittle plastic held together with Gorilla tape, and I like to think that I could make something that would work better than the factory air dam. So I started by looking at the air dam on a 2014 Chevrolet Silverado.

The center portion is 1 to 1.5 inches higher than the oil pan:
http://i1251.photobucket.com/albums/...psa412f817.jpg

The outer portions extend down about 1.5 inches below the center portion to about even with the bottom of the front suspension:
http://i1251.photobucket.com/albums/...ps43b59e0a.jpg

They also have little air dams in front of the rear wheels:
http://i1251.photobucket.com/albums/...ps0cfe7211.jpg

The tires on this truck are P265/65R18. Does anybody know if that's a base size, or an optional larger size? Both the front and rear tires extend about an inch beyond the front and rear air dams. If I build an air dam for my Canyon, should I make it like this Silverado air dam, or should I make it extend out even with the outer sides of the tires? Can I assume that the Silverado air dam is the best design for a pickup truck air dam, or should it really be an inch or so lower in the middle? I'll be using conveyor belting, so it's OK if it scrapes occasionally.

Ideas? Suggestions?

I think the air dam shape is a focus on keeping air out of the wheel wells. I think how far a front spoiler or tire spats come to the outer edge of the tire depends on the shape of the spoiler/spat. a flat square spat seems to be used far in from the edge, where a spoiler that follows the bottom of a rounded bumper of a sedan will be virtually as wide as the tires

Sounds right for the factory tire size. The factory is full of comprimise. I think the reason they raise the center is to maintain the center ground clearance. Straight across I think would be easier and more effective.As far as hot rod magizine says for air dams they also spent wind tunnel time testing go as low as you can without ripping it off the truck. The other school of thought is go as low as the lowest part of the suspension to lessen frontal area.

Conveyor belting is a good idea as stock airdams are notoriously flimsy, as are the clips that hold them. I damaged mine within the first month on a small snowbank then proceeded to hit it several more times while doing a little winter offroading. Frozen slush blocks off other vehicles also took their toll on it. Soon after it was taken off and put into the trash.

The stock tire size will vary quite a bit depending on trim level and cab size but that size is fairly common.