Moving The 5th Wheel
 

I'm pulling a 48ft flatbed, trailer it's hitting headache rack when making turns or backing. If I move the 5th wheel back will that affect the weight on rear drives and if so how much.

yes....and it really depends but a unwritten rule of thumb is something like 300lbs per notch.

And it will only transfer weight from the steers to the drives. It won't affect the tandems.

More like 75lbs per notch. If you slide it back, it transfers the weight to the drives, forward moves it to the steers.

300lbs per notch is on a "standard" tandem trailer.

I thought 300lbs sounded good. I slide mine a lot and mine is 250lbs/notch.

My fuel tanks sit forward. With my co's maxed loads I can only run 1/2 fuel and put my 5th wheel ahead. When light, I can fill my tanks and have to put 5th wheel back again.

It depends on where your tanks are and what kind of notches you have. Not sure how to word this. Some fifth wheels have notching that is close together and the pins are relatively thin and others have the notching spread apart a little and the pins are relatively thick.

I run a KW T660 with aero sleeper and the tanks are 140 gals a piece. My tractor scales in at 21k with the a/c system in back and chains loaded behind it. I run the bulkhead of the trailer just behind the quarter flaps. 6 of the 7 loads I pulled this week were 41k to 44k and everytime I weighed no heavier than 12,200 on the steers and aprox 33,500 on the drives depending on where the shipper put the last 4 of 8 rolls onboard and whether I could move the tandems to lighten up the drives. Tomorrow's dog food load may be a different story, but I scale everything that is over 35k. I suggest you try to find a sweet spot for the fifth wheel where you don't have to move it very often and still have clearance for the bulkhead. You're going to have loads that run the heaviest and be set for them. The lighter loads might just run heavier on the tandems ocassionally, but that shouldn't be a problem.

Other contributing factors to your problem could be the placement of the "head-ache rack", and the wheel base of your tractor. Most "flatbedders" use tractors with a minimum of 245 inches for the wheel base. 270 + inches is the norm.

why is 270 the norm?

Hmmmmmm. I guess I consider that number the "norm" because of the numbers of flatbed and step-deck "Owner Operator" units I see every day that are far longer in tractor wheelbase than most other operations. They have that extra frame to allow over hang of product on their trailers, and prevent the situation the OP has asked about.

But....I could be wrong. I know that companies like Melton, Maverick and Wylie run 245 to 250 inch wheel base.