wheel dams started to appear on cars a couple of years back and now almost all cars seem to have them is some form.
they seem simple enough to retrofit, but theres little info available on how big they need to be...
i've been looking at a lot of examples on real cars as they pass me or sit in a parking lot, but afterwards it's difficulty to say how big they where. and since i don't think most people would like to find me on my knees with a tape measure stuck in their wheelwell, i took a different approach
what i did is did a google search for some cars which i remember to have these dams and which i believe all have pretty good Cd's...
i tried to find profile pictures of either the front or the side to avoid perspective distortion and than used the free inkscape vector drawing software to import the picture and use vertical lines to measure the distance of the center of the bub to the ground and measured the height of the bumper and the height of the dam from the center of the hub down.
this gave me some percentage relative to the radius of the wheel, and lo and behold, despite using different cars the figures seemed to be strangely consistent!!!
B gives the percentage of the tire radius the bumper projects below the tire axle
D gives the percentage of the tire radius the wheel dam projects below the tire axle
i did a quick and dirty measure on some pics so i don't know each model exactly... but the numbers speak for themselves
Code:
model B D
bmw1 30 55
Bmw 7 hidrogen 38 53
audi 42 58
opel insignia 42 57
mercedes 41.5 58
prius 37 57
average 38 56
the conclusion i draw is that roughly 56% of the tire surface below the axle should be covered with a dam. or, the distance between the bottom edge and the ground should be 44% of the tire radius.
because the different shapes the bumper height is more difficult to determine, i always used what seemed to be the lowest point, so at the front of the car some of these bumpers might be quite a a little higher. also this value was measured in front of the tires and not the middle which on a lot of cars is even higher
yet reasonable to assume sticking to these figures will give you something which could be fairly well dimensioned while not running the risk of the average curb or elevation doing any damage to it