Question:
Why is it that spread axles are pratically the norm on flatbeds while not on dry vans and reefers as a whole?
Thanks

Answer:
While I dont know the complete answer part of it at least has to do with king pin and bridge laws and the length of the trailer. Many states do not allow 53 foot trailers to have the wheels (tandems) all the way to the rear.
Answer:
With a 10'1" spreed you are able to have 40,000# on the tandem. It makes it easy to axle out and never have to slide anything.
Answer:
*just a guess.
I would figure the box trls don't have it b/c the spread is difficult to turn and some of the loading docks in alley ways -> tight turning radius would make it very difficult to accomplish.
The only time I have ever pulled a spread was with a highboy loaded with 20 (15') evergreen trees. Went to pick the trees up on a tree farm, trl pulled nice round corners. However, driving through the powdery dirt roads loaded, leaving the place, I had made a sharp left turn and it was like I side swiped something, the drives started to buck as the front trl axle was carving in.
Answer:
A) I saw a flatbed the other day with three, not two, three spread axles on the trailer. Explain.
1) It had New Brunswick tags on it.

Answer:
They're sweet especially if you have dump value on the rear set of tandems. It makes the trailer react quicker and will take a turn tighter. I wouldnt want to pull any other kind of trailer. Many other drivers try to get in a tight spot and cant, with the dump value your able to get in there with out any problem. Its great technology!

Answer:
A Canadian triple
Lets see a Canadian triple is OK in Canada and has a wheel base of 140+" but a US double with a wheel base of 121" is not allowed into some provinces, Alberta and BC are the ones that came to mind first I think there is 1 or 2 others.
Their reasoning is that our spread axles 'ruin' the road, while theirs are OK.
What it really means is that Canada is using protectionism tactics to prevent some US trucks to go up there and deliver and pickup which is a direct violation of NAFTA.
I wish we had a government that did the same to 'some' Canadian trucks, and 'some' poorly maintained Mexican trucks (junkers).

Answer:
Spread axles have become common on flats because flats are most often loaded close to gross and many times loaded in areas with no access to scales.
With 40,000 being allowed on the spread, it is pretty hard to get one over axle. Have seen a few morons who managed it however.
They're not used much on vans, etc. for 2 reasons.
One being that vans seldom approach gross weight.
The other being the aforementioned tight places a van has to back into. Even with a dump valve, a spread does NOT take kindly to being backed around in a really tight area.

Answer:

This is known as a Tridem. The spread axle (10' 1" Tandem) is only good out east, from Onatrio to the Maritimes. The Tridem spacing is 10' to 12' out west, with BC allowing an 8' tridem axle spacing.
Answer:
With the Canadians that I see here, and many New England drivers that haul bulk and logs, it is not uncommon to see a tri-axle trailer.
On a daily basis I see one. It is hooked to a truck sitting in my yard.
I see Tri-axle spreads all the time. Once in a while I will see a quad axle (Canadian) spread. Very rarely I will even see a 5 or 6 axle trailer. These are almost always Canadian, and are being pulled by tri-axle tractors (2 drive axles with a pusher/lift axle and the steer axle up front.
In my opinion, a Canadian spread on the drive axles on the tractor is a very good idea and rides better than a close set of axles.

Answer:
A tridem is three fixed axles, and tri-axle is a tandem plus a lift axle. Here in ontario we have alot of 5 and 6 axle trailers, some even with 7.
Usually a tridem plus 2 or 3 lift axles. Also alot of super B trains with 5-7 axles on the trailers. Not many tractors with lift axles in southern ontario.

Answer:
Those spread axles will axle at 40K,mostly for hauling steel coils. If you go into Michigan the covered trailers up there might have 10 axles on 1 trailer.Michigan has a higher weight limit for intrastate hauling.I've also had to back a spread into a dock before and some of them have airbags on 1 axle that you can lift up off the ground just for that reason because if you don't it is very hard on the trailer and tires when turning really tight.

Answer:
Wuzzy/Charlie has it right. Spreads are used on Flats because of weight. You can haul more with less trouble. The same reason you'll see alot of Chicken trucks (reefers) using them. They can axle out alot closer to max with alot less trouble. It is hard to over gross the spreads. But not impossible.

Answer:
I just recently noticed a Reefer that had all the bases covered.
Two Single axles on Air Ride sliders.
Answer:
We can put 40 000 lbs on a normal tandem here in ontario. 12k on steer,40k on drives,40k on trailer. I drive a tandem straight truck, and it's legal for 52 000 lbs 12 on steer, 40 on drives.