Wow, this is getting confusing! And I think someone may have used the word tandems when they meant DRIVES.
Moving your fifth wheel FORWARD is simlar to moving your tandems forward (but with a reverse affect. Consider, for a moment your drives and your tandems and the weight over them. If you slide your tandems forward MORE of your trailer is "hanging over" them adding weight to those axles.
If you slide your fifth wheel forward, you are moving your drives BACK, so MORE weight is now hanging over them, adding weight to them AND REDUCING the weight being shared by your steers. (they act like a "fulcrum.")
Sorry, Uturn. I think you are wrong on this one.
As someone said, adding MORE weight to your DRIVES, by sliding the 5th wheel FORWARD, will in most cases, tend to LIFT your steers off the ground, so to speak. They will get "loose."
Remember, sliding the 5th wheel forward does NOT move the weight BACK toward the tandems. It moves the weight FORWARD onto the drives. The drives do NOT move forward with the "wheel" and therefore the weight does NOT move Backward.
Now, SOME 5th wheels have slots of about 2 inches, (and ONE bar) and move approximately 500 lbs each slot (depending on how the trailer was loaded.) Others have a two pronged "fork" that fills two separate slots of about 1 inch each. If you move the "fork" so that you only move to the next slot, you have moved approximately 250 lbs. If you move the whole fork to TWO completely new holes, you have moved approx. 500 lbs (or the same as the single bar style.) Picture both prongs of the FORK as the same as the bar, and each slot as only HALF the fork (or half a bar.)
Dan: Your trainer's formula is absolutely correct, if a bit technical. I do it like this: If my TANDEMS are 1200 lbs overweight, I divide by 400 lbs, and move them BACK 3 holes. This will ADD approx 1200 lbs to my drives. Will that be legal? If yes, do it. If you can move another 400 lbs without making your drives over.... go 4 holes. (Remember the fulcrum? The more weight you can put on your drives, the less on your steers IN MOST CASES, and the more fuel you can carry.) Try to even them out for a good ride.
Here is what you said you did:
Quote:
Today my weights were steers, 11660; drives, 25420 and tandems, 19800. I thought I am good to go, and so I went down the road. Well the truck just felt "weird" so i stopped and moved the fifth wheel back 4 holes and it now feels normal again.
|
Although your steers were close to the max IN SOME STATES, your drives were much heavier than your tandems. Because of the fulcrum effect, your steers were "loose" in comparison, and your "tail" was light and bouncing.
By moving your 5th wheel BACK, you moved your drives FORWARD! This put more weight on your TANDEMS, LESS on your drives (the fulcrum) and a bit MORE on your steers .... JUST enough more to give you more steering traction, and took weight off your drives so you felt less in the cab with each bump.
There is a dynamic here that is hard to explain. Your steers and drives are on the same frame so they SOMEWHAT share the load on the front end of your trailer. But, if you overload the DRIVES, the fulcrum comes into play and lifts the steers off the ground (so to speak... like doing a "wheelie" or playing "tiddlywinks."
If you lighten the load on the drive axles, A LITTLE MORE of the weight from the front end of the trailer is then transitioned along the frame to the steer axle, but it is in proportion to the overall weight distribution so, since you moved MORE weight to the rear of the trailer (tandems,) you can actually have less weight on your steers.... and STILL have more "steering" traction because their weight is higher in proportion to that of the DRIVES!
Conversely, if you put a maximum load on your tandems, leaving your drives "light," you will RAISE the fulcrum point off the ground (so to speak,) and increase the weight on your steers, lose necessary traction on your drives, cause your bunk to bounce more easily with every bump, and due to the "lag" effect, cause your engine to work harder to pull a weight that is further away from the power source. You will also lose "braking efficiency" due to the lag time to get brake pressure to your tandems.
A good "rule of thumb" is to set your 5th wheel so that your drive mudshields (not flaps) are flush with the front of your trailer. Then, if your loads CONSISTENTLY make you heavy on your steers and you cannot put on fuel, move your 5th wheel FORWARD a slot or two to take weight off your steers. As long as your fairings aren't getting crushed, you can always move your tandems forward to take weight off your drives, and won't run afoul of California Bridge laws.
Remember, moving the 5th wheel forward, puts the front of the trailer closer to the cab, takes weight off your steers, and ADDS weight to your drives. You are essentially moving your drives BACK to accept more weight, and allowing you to move your tandems FORWARD to balance the weight, meet the bridge laws, and shorten your turning radius.
What YOU did was to move your drives FORWARD (in relation to the weight in your trailer) which shifted MORE weight to your tandems (and a slight bit more to your steers.) If possible, the easier answer would have been to move your tandems FORWARD to "accept" more of the weight from your drives, which would have given you more steerability.
Remember, 5th wheel BACK means drives
forward means weight BACK towards tandems. Same as moving your tandems BACK to move weight FORWARD. The idea is to get the weight evenly distributed between drives and tandems. But the tandems are easier to move!
MAN! I hope I got all that right! I know the theory is sound. But ONE typo could make a MESS of it all!
Hobo