2/3rds of the way back from the ball.
A single axle utility trailer measures 12'x77" and a tandem axle utility trailer measures 16'x77". In the USA, a utility trailer can be no taller than 13 ft. 6 inches.
On a 5' X 8' Utility Trailer you would want a 60% / 40% axle weight distribution for optimum towing/tracking of trailer. A design of 96 total inches in length would produce a 54" length from the front of the trailer to axle center. Adding an additional 10 inches to the rear of the trailer would then produce a optimum 63" length from the front of the trailer. Extending this trailer by 10 inches would fall into a safe range as long as you take into consideration the weight distribution of the load.
What type of truck and trailer? For all I know, you could be talking about a Ford F650 and a single axle utility trailer. If you're referring to Class 8 vehicles, something like a single axle tractor towing a single axle trailer would be allowed an interstate GVW of 52,000 lbs.
12000 pounds
That depends on the axle configuration. If it a closed tandem typically 17,000. If it is a spread axle 20,000. If it is a single axle (Front of a Semi) typically 12,000. Those would be the "legal weights", but states allow different amounts of weights with a permit for over weight. That all depends on the state. Wisconsin will allow 23,000 per axle.
The definitive answer is...it depends. Very few trailers are made with axels of 2000lb (or less) capacity. Most are 2500 to 5000 llbs (per axle). So if you have a dual axle trailer with two 3500 lb axles you can haul 7000 lbs MINUS what the trailer weighs. I have a single axle 6X12 with a single 3500 lb axle. The trailer weighs approx 500 lbs, so I would feel relatively safe hauling a 3000 lb load.
A few trailer spindles bolted on to the axle but most spindles are welded to the axle.
In the UK, the maximum axle weight for a trailer axle on a 6 axle trailer is 8500 kg. In addition it must have road friendly suspension. With a 5 axle vehicle the maximum axle weight is 11.5 tonnes.
Front axle 12,000, Front tandem 34,000, Rear tandem 34,000 unless it is a spread axle trailer; then it is 40,000 for the two rear axles combined. Total weight not to exceed 80,000 lbs.
A ten foot spread axle trailer is allowed 20,000 lbs. per axle, for a total of 40,000 lbs.
This depends on the axle rating on the trailer...most likely a 5X8 has a light duty axle wich is less than 2000# but may be less doesnt matter what size trailer a load is on,but the legal height for any load on any vehicle is 13'6" however,common sense would tell you if a load is to high for safe towing
Five foot wide? A six foot six axle measured hub face to hub face is about right. BUT What you need are 4 foot 10 inch ish spring pads. I allways call my axle supplier and ask them what they can build me. A new axle for my 4 foot wide quad/Golf cart/toy trailer cost about $180. Standens axle Calagary Alberta big thumbs up!