I'm going to build 2 wheels for a homemade light trailer using wheelchair hubs and 28 hole 20" rims. Not sure about the crossing, some trailers have 3x and some 0x (radial). I'd like to know the opinions of the expert wheelbuilders here.

Build them 2x or 3x with the spokes laced over/under at the cross.

Since they're essentially front wheels (no torque) tangent spoking doesn't confer a direct benefit, but it allows for the over/under lacing, which builds a bit of resiliency into the wheel.

I'll ditto FB- 2x would be my preference just to get a little more lateral strength. (Interlaced spokes share sideways load where radial tends to concentrate the load on fewer spokes.)

FWIW: what are you using for rims? I'm building front wheels for my recumbents, and I'm having a heck of a time finding decent 20", 28-hole rims (that aren't Sun CR-18).

Aeroheats are available in 28 hole. Sadly all Universal is stocking are 32s.

What are the hubs designed for?

An issue with radial laced wheels is whether or not the hubs have enough "meat" between the spoke holes and the edge of the hub flange to handle the load. Using a crossing pattern solves that problem because the spoke is pulling at an angle where there's more material between the spoke hole and the edge.

Another thing you might want to look at is the thickness of the hub flange. If it's a steel hub with relatively thin flanges it might be a good idea to use spoke washers to fill in the extra space at the elbows.

My Burly uses 2 cross 28 hole ( 3 would be like 4X on a 36 hole wheel)
there is a longer set of spokes on one side, of each wheel.

the wheels are asymmetrical, to make the wheel track wider , to increase stability..

Thanks all, 2x it is.

I had always thought the reason why Burly used offset/dished wheels was to increase the clearance between the tire and the trailer body. Cornering forces would work against the dish (spoke angle will have less bracing) that the wheels have and the slight increase of track width (maybe 1" over a 30" width) is an unlikely reason to go to the effort of dishing wheels.

What was ingenious with the Burley trailers was the offset hitch. So the right side wheel/frame was no further off center then the bike's handle bars or pedals. Andy.

+1, it would be easier to make a 1" longer axle/wider frame. Dishing also makes a weaker wheel.

Yeah, I wouldn't try to do 3 x on a 20" with 28 spokes. That would be a real wrestling match to get the spokes into place and too much angle out of the rim I'm sure. With a large hub flange, I even go 1x on 20" wheels, even with higher spoke counts.

2X

Also, if the hubs are sleeve type with journals - do not use bearing equipped end caps when truing and tensioning the wheels. You need to use a false sleeve with bearings to mount in truing stand when truing/tensioning.

If you try to use end caps alone like you might do with over sized hollow axle disc setups - you'll end up truing the hub - not the rim. One result will be extremely high tension on several spokes and the opposite on others as well.

=8-)