Shapes of vehicle backsides: which is the best for drafting?

[FLAteam]

After driving on the highway about 90% of the time for the past 3 weeks, I've found that drafting works for me.

However, I've noticed drafting a normal semi doesn't do much for me (besides letting me p&g in peace). I've noticed the lower the vehicle is to the ground, the better draft I can get. However, I was wondering: How does the shape of the backside of the vehicle (sloping like a coupe, straight down like a truck/suv) affect drafting?

Basically, if you had to make a vehicle thats sole purpose is for someone to draft behind it, what would it look like? Any examples on the road currently?

[theholycow]

I'd guess these:

[FLAteam]

I usually love finding FedEx Ground trucks and semis:





I also like chartered buses:



Note that they're all vertical backsides...is that a good thing?

[Jay2TheRescue]

The more vertical the backend of the vehicle is (and square), the larger the air pocket is that's dragged behind the vehicle. If the rear of the vehicle slopes, then it will drag a smaller pocket behind it. For drafting purposes you want to be in as large of a pocket as possible. This means that under ideal situations you want to be behind a low riding semi truck. Moving companies use low riding trailers a lot.

This is my ideal vehicle to follow... Low riding semi with a low trailer...

[1cheap1]

Gas truck or liquid carrying type truck is the best, even had good results with cement trucks. I watch the debris that is kicked up by different type trucks and the tankers give a smooth draft and great for eoc in the draft. The semi seams to have to swirling columns on the left and right, i hang back a little farther with these types. The lower they are the better the draft applies to the semi as well. I don't have a scan gauge so i have to go with over all rpms and end results for that particular tank.