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Thread: How many holes to slide the fifth wheel formula?

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    Danisawannabe is offline Rookie
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    Default How many holes to slide the fifth wheel formula?

    My trainer taught me a formula to slide the tandems that has worked every time so far.

    It goes like this
    (higher weight - lower weight = sum) /2) /350 = number of holes to move tandems.

    example: drives=34500 lbs tandems=29300 lbs
    34500-29300=5200
    5200/2=2600
    2600/350lbs=7.4
    move tandems 7 holes
    [if # to right of decimal is 6 or higher round up a hole, 7.6 will need to move 8 holes ]
    So far this has worked well for me.

    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.

    After all that my question is, is there a formula for sliding the fifth wheel? Or take an educated guess and go back for a reweigh.

    Thanks,
    Dan Isa Wannabe
    My Blog is at www.danisawannabe.com
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    Rockee is offline Member
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    I like your formula for the weight issue but since I am no good at math I would just do.....34,500 on the drives...move it three or four holes and call it good. I figure usually 300 per hole. I dont (especally since I'm unemployed right now) hardly ever slide my fifth wheel if I dont have to, I keep it centered between the two drive tires which has worked for me. Make sure when sliding it forward that you have enough clearance between your mudflap/frame and the landing gear as not all trailers are the same. I have heard people say about 250 lbs per hole on the fifth wheel

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    Fozzy is offline Senior Board Member
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    Quote Originally Posted by Rockee
    I like your formula for the weight issue but since I am no good at math I would just do.....34,500 on the drives...move it three or four holes and call it good. I figure usually 300 per hole. I dont (especally since I'm unemployed right now) hardly ever slide my fifth wheel if I dont have to, I keep it centered between the two drive tires which has worked for me. Make sure when sliding it forward that you have enough clearance between your mudflap/frame and the landing gear as not all trailers are the same. I have heard people say about 250 lbs per hole on the fifth wheel
    I'll have to dissagree on this one guys, Fifith wheels move between 5 hundred to 8 hundred per "hole" and it only mainly effect the steering axle weights the drive axles. By pushing weight on to the steer axles it "might" give you some room to add a little to the tandems, but when it gets that close to being overweight or over bridge, you probably will out of luck.

    So set the bridge, set the fifthwheel and if the load is too heavy, have them rework that by moving freight forward, or removing cases off of the load.

    did you check your axles weights AFTER you slid up to twelve hundred pounds off the steering axles to the drives, This is potentially fatal moving that much weight off of the steering axles. In my opinion,you should have done nothing to this as everything was legal and decently spread out.. if you HAD to do something, maybe slide the tandems up a little to take a small amount of weight from the drives.

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    I think almost every different driver will give a different answer on this....alot of it just plain flat out depends on how the truck is load....location of the weight in the trailer makes a big difference when sliding tandems and fifth wheels

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    Rockee is offline Member
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    I cant disagree with you Fozzy but now I can say "I have heard people say between 250 and 800 per hole on the fifth wheel". In my driving career its been almost a non issue with me so I just "set it and forget it"

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    Uturn2001 is offline Senior Board Member
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    Regardless of the 5th wheel or trailer tandems, how the weight of the load is distributed in the trailer will effect how much weight is moved per "hole".

    Also how the "holes" are spaced will greatly effect how much weight is moved per notch.

    Trailers with small holes spaced close together generally move between 200-300 pounds per space, and these seem to be the most common slide arrangement today.

    If you have a trailer with very large holes the you are gonna be moving 400-500 lbs per slot.

    Same goes on the 5th wheel. The slides with the notches will move less per unit than the ones with the bigger holes that have a "bar" in them to lock it down.

    When it comes to figuring weight I applied a "KISS" principle.

    Trailer with the small holes I used 250 lbs per hole. Took the axle weight minus 34,000 divided by 250.

    For the 5th wheel I used 500 lbs and the forumla of weight of overloaded axle (steer or drive) minus the legal weight divide by 500.

    Rarely did I ever have to do a second slide on either.

    In the rare event a second move after the re-weigh was called for then I would figure out exactly how much weight was moved per hole and figure out how much to slide.

    As far as the 5th wheel goes, if you keep it pretty well centered over the drives on most trucks it is rare for you ever need to adjust it. In 6-7 years I think I only had to move mine twice.
    Finding the right trucking company is like finding the right person to marry. I really comes down to finding one whose BS you can put up with and who can put up wih yours.

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    BigWheels is offline Senior Board Member
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    Fozzy & Uturn make some great points about moving the 5th wheel....

    1. Load the trailer as best as you can (shipper's help can either be brilliant or utterly stupid when it comes to this).
    2. Slide the tandems.
    3. Slide the 5th wheel (on rare occassions).
    Anything worth living for is worth dying for.
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    Danisawannabe is offline Rookie
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    First of all, thanks to all who replied Good info to keep in mind from all.

    Quote Originally Posted by Fozzy
    I'll have to dissagree on this one guys, Fifith wheels move between 5 hundred to 8 hundred per "hole" and it only mainly effect the steering axle weights the drive axles. By pushing weight on to the steer axles it "might" give you some room to add a little to the tandems, but when it gets that close to being overweight or over bridge, you probably will out of luck.

    So set the bridge, set the fifthwheel and if the load is too heavy, have them rework that by moving freight forward, or removing cases off of the load.

    did you check your axles weights AFTER you slid up to twelve hundred pounds off the steering axles to the drives, This is potentially fatal moving that much weight off of the steering axles. In my opinion,you should have done nothing to this as everything was legal and decently spread out.. if you HAD to do something, maybe slide the tandems up a little to take a small amount of weight from the drives.
    Hi Fozzy. About checking the weight after taking so much off the steers, help me understand what the issue may be. I was at 11660 on the steers, 25420 on the drives and 19800 on the tandems. The fifth wheel was all the way forward and I moved it back 4 holes. I hav'nt reweighed yet but maybe I will just to see what the effect was. My guesstimate for the current setup is about 10200 on the steers and 26500 on the drives. When I slid it to the front, it changed about 600lbs per hole, cargo weight was 44400lbs, this load it is 21012lbs.

    That word "fatal" has me concerned and I'd like to hear more about this. Oh Yea, I'd also like to live. BTW, after the move the "funny" feeling left the truck and I went through the scale house in AR, I40, MM280ish and got the green light to keep going.

    Uturn2001, thanks, I think you put the important points together in a nice list. When I get home I'll print it out and tape it to my clipboard for future reference.

    Again, thanks to everyone, all of you are a big help.

    Dan
    My Blog is at www.danisawannabe.com
    and it's rarely updated anymore.

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    BigWheels is offline Senior Board Member
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    Quote Originally Posted by Danisawannabe
    ...That word "fatal" has me concerned and I'd like to hear more about this....
    Not sure what "fatal" meant to Fozzy but here's my take....

    Ever experience the feeling of turning the steering wheel in a car while its snowing and the steering doesn't respond? In other words you turn the wheel but the vehicle continues to go straight?

    Something similar can happen when you combine more speed along with less weight on the steer tires (having the 5th wheel all the way forward towards the steering axle). Say you're rounding a gradual turn doing 65MPH and hit a major bump. The bump could cause you to careen towards the shoulder. You compensate the other way but the steering is loosey-goosey because you don't have enough weight on the front axle. In seconds you find yourself oversteering first one way and then the other to compensate for the lack of steering response....

    So...having the 5th wheel centered over the drive axles is a good way to go most of the time....
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    Danisawannabe is offline Rookie
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    Quote Originally Posted by BigWheels
    [snip]
    Something similar can happen when you combine more speed along with less weight on the steer tires (having the 5th wheel all the way forward towards the steering axle).
    [snip]
    I might not understand correctly, but doesn't "having the 5th wheel all the way forward towards the steering axle" put as much weight as possible on the steering axle?

    Dan
    My Blog is at www.danisawannabe.com
    and it's rarely updated anymore.

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    GMAN's Avatar
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    You move your tandems or 5th wheel toward the weight to shift it. For instance, if you are heavy on the drives, you move the trailer tandems forward or toward the tandems to shift weight from the drives to the trailer. If the trailer is heavy then you move the tandems back toward the back of the trailer. By moving the trailer tandems forward you will also take weight from the steers. I haven't moved my 5th wheel in years, but I don't recall ever moving 500-800 pounds by moving my 5th wheel. Of course, it depends on how your trailer is loaded as to how much weight is distributed or moved. If your 5th wheel is positioned properly, you should never need to move it. The way I have my 5th wheel set, I have NEVER been over on my steers.

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    Uturn2001 is offline Senior Board Member
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    I might not understand correctly, but doesn't "having the 5th wheel all the way forward towards the steering axle" put as much weight as possible on the steering axle?
    Yes.

    One thing to keep in mind though is that the farther forward you have your 5th wheel the less of a turn radius you will have before you start crunching things on your truck.

    IMHO if you ever need to slide the 5th wheel more than 2 or 3 spaces forward of center then it is time to head back to the shipper for a reload.
    Finding the right trucking company is like finding the right person to marry. I really comes down to finding one whose BS you can put up with and who can put up wih yours.

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    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:

    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
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    BigWheels is offline Senior Board Member
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    Quote Originally Posted by Danisawannabe
    Quote Originally Posted by BigWheels
    [snip]
    Something similar can happen when you combine more speed along with less weight on the steer tires (having the 5th wheel all the way forward towards the steering axle).
    [snip]
    I might not understand correctly, but doesn't "having the 5th wheel all the way forward towards the steering axle" put as much weight as possible on the steering axle?

    Dan
    Oops--my bad. ops: Had it wardsass-back (back-asswards). Sorry Dan!

    The snippet should have read:

    Something similar can happen when you combine more speed along with less weight on the steer tires (having the 5th wheel all the way back towards the driving axles).
    Anything worth living for is worth dying for.
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    Quote Originally Posted by BigWheels
    Quote Originally Posted by Danisawannabe
    Quote Originally Posted by BigWheels
    [snip]
    Something similar can happen when you combine more speed along with less weight on the steer tires (having the 5th wheel all the way forward towards the steering axle).
    [snip]
    I might not understand correctly, but doesn't "having the 5th wheel all the way forward towards the steering axle" put as much weight as possible on the steering axle?

    Dan
    Oops--my bad. ops: Had it wardsass-back (back-asswards). Sorry Dan!

    The snippet should have read:

    Something similar can happen when you combine more speed along with less weight on the steer tires (having the 5th wheel all the way back towards the driving axles).
    No, BigWheels! You had it right the FIRST time! I was not talking about YOU.

    Fact: Something similar can happen when you combine more speed along with less weight on the steer tires (having the 5th wheel all the way forward towards the steering axle).

    Having the 5th wheel all the way FORWARD, puts more weight on the drives and takes weight "proportionaly" away from the steers! Due to the "fulcrum."

    FACT: Moving the trailer weight forward does NOT necessarily add weight to the steers. They are not really "weight bearing."

    I guess I should have been more specific. I believe it was GMAN (heaven forbid) who used the wrong term.

    And, although I don't like to disagree with him, Uturn was incorrect I believe, when he said "yes."

    I might not understand correctly, but doesn't "having the 5th wheel all the way forward towards the steering axle" put as much weight as possible on the steering axle?
    The correct answer here is NO! The weight if forward, yes, but it is borne by the DRIVES! Because of the fulcrum effect, this causes a "wheelie" action, and the steers are now lighter, and LOOSE.

    I gotta go out and meet the public now. I'll be back later if anyone wants to disagree with my theory.

    He!!, the original poster has moved on by now, anyway!
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    Quote Originally Posted by roadhog
    SHUT UP ! ....just please shut up!

    Ha Ha! MAKE me!!! You overgrown "Tweetie Bird!" :lol: :lol: :lol:
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    Quote Originally Posted by GMAN
    You move your tandems or 5th wheel toward the weight to shift it. For instance, if you are heavy on the drives, you move the trailer tandems forward or toward the tandems to shift weight from the drives to the trailer. If the trailer is heavy then you move the tandems back toward the back of the trailer. By moving the trailer tandems forward you will also take weight from the steers. I haven't moved my 5th wheel in years, but I don't recall ever moving 500-800 pounds by moving my 5th wheel. Of course, it depends on how your trailer is loaded as to how much weight is distributed or moved. If your 5th wheel is positioned properly, you should never need to move it. The way I have my 5th wheel set, I have NEVER been over on my steers.
    Since I HAD the audacity to question the GMAN, I suppose I should clarify:

    You move your tandems or 5th wheel toward the weight to shift it.
    I believe you meant to say "drivers" instead of "5th wheel." Moving EITHER set of wheels TOWARD the heavier end of the trailer will "shift" or "accept" more weight and relieve the "other" set of axles. Also, the HIGHLIGHTED word should be DRIVERS, not tandems. Although, SOME oldtimers use the word "tandems" for "dual drives," it is NOT taught that way in the current CDL schools, and will confuse the newbies if used interchangeably.

    But, moving the 5th wheel toward the tandems, is actually moving the DRIVERS "away" from the tandems, thus shifting the weight OFF the Drivers and ONTO the trailer tandems.

    Another way of looking at it is this: Moving the 5th wheel in one direction, moves the drivers in the opposite direction. So, if you want to move your drivers BACK to accept more weight (like you would move your tandems FORWARD to accept more weight,) you must move your 5th wheel FORWARD.

    Or you can look at it this way.... if you move your tandems forward to accept more weight, then moving your 5th wheel forward will ALSO "accept" more weight.

    You are "coming at" the trailer weight from opposite ends. Moving the axles toward the center of gravity, adds weight to that axle. To move the drivers toward the center of the trailer, you must move the 5th wheel AWAY from it.

    YES.... this moves the front of the trailer closer to the steers, but since it is increasing the amount of weight "overhanging" the DRIVERS, it is increasing the weight on them, not the steers.

    At some point, the "dynamic" I mentioned earlier comes into play... but NOT in this "newbie" lesson.
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