I have been planning the purchase of goose neck, 8 or 10 ton GVW dual axle trailer. To haul a tractor and other related crap after my retirement. My truck was ordered with this in mind. With single rear tires I know my towing caps are slightly less than a dooly.
I was given some good advice a short while ago that has made me think. The pulling power of my truck is the same as a 3500 dooly. What I am now questioning is what this advise has laid in front of me. With extreme loads on the trailer and proper loads it places on the rear of my truck,,, the main difference between single and dual wheels is stopping power. This friend told me that he has had heavy loads push him thru several stoplights with rear wheels locked. He said the dual wheels have more rubber on the road and greatly increase your safe stopping qualities. I know there are other godlike quilities of a dooly and that is not in question.
Has anyone had these problems with single rear tire 2500/3500 trucks?

C.

As in all things, there are compromises, and give and takes. There are a few principles involved in increased braking.

First, roughly 80% of your braking is proportioned to the front axle, which is where weight will shift when you push the pedal. If you are at or near max Gross Axle Weight Rating (GAWR) on your rear axle, and the trailer is loaded 15%-20% of the weight on the Goose Neck (GN) while sitting still, the weight of the load will also shift forward when braking.

This can overload your truck's rear axle, counter the shifting of weight forward when braking, and you will "slip" past red lights on downhills whith the front wheels locked up (more than likely, you will find yourself tap-dancing on the pedal, with the ABS).

Then there is "unsprung weight". On the dually all these forces react differently than on a SRW truck under loads. This is the weight of the drivetrain (tires, wheels, axles, etc.) beyond the shock and spring mounts.

This weight tends to not want to leave the ground, and the heavier the better when braking (opposites is true when trying to get that Caddy ride, or when trying to break 10 sec. on the quarter mile).

The dually, has a greater GAWR than the SRW, as well as higher unsprung weights. When braking, the tongue weight of a GN/5th is less likely to "lift" the front axle (less lift, not no lift), while the unsprung dually wheels and axle provides better braking traction.

Additionally, the lower tire air pressures in the duallies allow more sidewall flex under heavy loads, softening the rides, but also providing a larger contact patch with the road. also improving braking.

When your talking an 8 or 10 ton (16,000-20,000 lbs.) rated flatbed or low-boy trailer, which can be used to haul varying weights from one load to another, you may not always be certain as to the tongue load being transfered to the rear axle. If this is too much you overload the rear axle. What's worse is when this is too light.

When accelerating, there is a tendency to "lift" weight off your rear axle, which you may not see as a problem untill you apply the brakes, and the rocking motion of the trailer tends to override your rear axle's traction with the road. Compound this condition with slippery road conditions, and it becomes very easy to end up jacknifed in a ditch somewhere.

If, for some reason(s), living with a dually truck is unacceptable, then rethink your choice of trailer, one that has a tongue load that is within the GAWR of your SRW truck loaded. Get your truck to the CAT Scales and find out what it weighs at each axle, then subtract the scale weight on your rear axle, subtract it from your GAWR of the rear axle, and this will tell you what the maximum tongue weight that your truck can handle.

For example:

Truck wt. = 6870 lbs.
F-Axle = 3880 lbs.
R-Axle = 2990 lbs.
R-GAWR = 6500 lbs.

R-GAWR - R-Axle wt. = 3510 lbs max tongue wt.

Tongue wt. can be calculated by scaling the trailer with the truck. For example:

Trailer Axle Wt. = 11,600 lbs.
Truck F-Axle Wt. = 3120
Truck R-Axle Wt. = 6370,

F-Axle Wt. Loaded (3120 - F-Axle Wt. Unloaded (2990) = 130 lbs.
R-Axle Wt. Loaded (6370) - R-Axle Wt. Unloaded (2990) = 3380 lbs.
Trailer Tongue Wt. (F-Axle Diff. 130lbs + R-Axle Diff. 3380) = 3510 lbs.

Trailer weight (Trailer Axle Wt. (11,600) + Tongue Wt. (3510) = 15,110 lbs.
Wt. Distribution on tongue (min. 15% - max. 25%) = approx. 23.5%

(A balanced and safe load).

The formulas in these examples are "rules of thumbs" that the industry uses for safe towing operation, including the vehicle manufacturers. The sole purpose of these are safety and durability. Working beyond the rated weights of your vehicles will reduce its service life, and may cause dangerous sittuations.

Hope this answers your question.