Discussion:
Continuing Driver Education - kingpin/tandem distance
(too old to reply)
tscottme
2004-01-28 12:29:01 UTC
Permalink
At work this issue is getting under my skin, for the last 5 years, so I
thought I would make sure everyone here understands it. In several
states, maybe federally as well, there is a maximum distance from the
kingpin of the trailer to the trailer tandems. Sometimes drivers
mistakenly call this the "bridge law" or they correctly call it the
"kingpin law." The various states measure it in various ways and that
particular distance varies some. But for this example, let's use
Tennessee's rule. In TN when pulling a trailer longer than 48 feet,
that means this applies to 53 foot trailers, you are not allowed to set
the trailer tandems more than 41 feet from the trailer king pin. In TN
the measurement is taken from the kingpin to the middle of the trailer
tandems. Notice I didn't mention the weight of the truck/trailer
combination or the weight of any payload. This law applies even to
empty trailers. You are not allowed to pull a 53 foot trailer on any
public road with the trailer tandems slid behind the maximum, 41 feet in
this case. The last ticket I saw for a driver at my company was a $75
fine for pulling an empty trailer on the road with the tandems slid to
the rear of the trailer. By the way, that fine is payable by the
driver, not the trucking company.

The Rand-McNally atlas details what the kingpin/tandem distance is for
the various states, and how to measure it. It would be wise to either
check it for each state or to at least note which states have uncommon
length requirements. Which brings us to checking if you are in
compliance or not. Here's an easy way if you are checking for the 41
foot distance and the trailer is 102 inches wide, I believe this is the
most common 53 foot trailer on the road: when the trailer doors are
pinned in the open position, (folded against the sides of the trailer),
the edge of the trailer door that is now closest to the tractor, which
touches the other door when they are both closed is about 41 1/2 or so
feet behind the kingpin. So when you pick up a trailer if the rear
mudflap of the trailer tandem is somewhere in front of the open trailer
door, you are "good to go" with respect to this kingpin law.

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O O

Do not depend only on any "41 foot marks" that may be placed on the
side of the trailer. That mark may or may not be correctly located. My
company has a few thousand trailers, all with equal dimensions, that
have the "41 foot mark" correctly located and some not. Some of our
trailers use a similar mark to indicate tandem position for a particular
customer. Some of our trailer have no mark. There is also variation on
what part of the tandem should line up with any mark. Some of our
drivers think the front wheel or the rear wheel of the tandem should be
under the mark to be in compliance. There are a lot of drivers that
rely on rules of thumb about "put the tandem pin in the X hole." While
that may work if your company only buys one brand of trailer and that
trailer manufacturer makes every trailer exactly alike, you have no way
to double-check that advice. You also may not know if they count every
hole in the rail, or only count holes that the pins may reach. On many
of our trailers there are one or two hole in the front of the rail that
you could never put the tandem pins in since the rail has a stop placed
between those holes and the rest of the holes in the rail. The trailer
door/tandem mudflap method is easy to see and unless you use trailers
that are very much wider or more narrow (trailer doors are very
different dimensions) good enough.

When OTR, it's often easy to go for years and always adjust the tandems
ahead of legal limit, if only for weight distribution. It may be that
only if a customer lies about the weight of a load or loads it fully to
the rear of the trailer will this ever come up. Don't learn this lesson
on the side of the road or at a weigh station. I am shocked at the
number of OTR drivers that transfer in to my section of the company and
don't know this. I made this mistake when I started. Every time I
explain this to them they answer exactly the same: "but the trailer is
empty." Weight is irrelevant to this issue.

In TN, at least, there is no question that this applies to 53 foot
trailers and includes empty trailers. I can post the law from the
official TN code, I've done this already at work. What I've described
is the law in TN. The TN law simply phrases it in a confusing manner,
so I've not posted it.




--

Scott
--------
The French, God bless them, are finally joining the war against Islamic
extremism. Their targets, which will now confront the full force of
l'état, are schoolgirls who wear Muslim head scarves in French public
schools.
Wall Street Journal
tscottme
2004-01-28 12:39:37 UTC
Permalink
The diagram is off due to formatting. Let me know if someone needs me
to try again.

--

Scott
--------
Pat Durkin
2004-01-28 14:03:07 UTC
Permalink
"tscottme" <***@blah.net> wrote in message news:1tudnZCq9pyQNordRVn-***@comcast.com...

Very good point Scott and a valuable tip about how to visually line things
up with the trailer door.

In California the allowable distance is 40', and it is measured from the
kingpin to the center of the last axle. On a 53' trailer with a typical 36"
KP dimension, that means there will be 10 feet of trailer hanging aft of
trailer axle #2. I don't have any quick tip about how to measure that with
trailer doors but a practiced eye can tell at a glance of it is about 120".

This means that our law is more restrictive than many states, and if an OTR
unit arrives in California with a configuration that is legal in certain
other states they are in danger of a citation here.

The position of the last axle in a 5-axle combination is critical to bridge
formula calculations. In California the distance from axle #1 (steer axle)
to axle #5 must be the legal equivalent of 51' in order to legally gross
80,000#. California law recognizes 606" as being equivalent to 51' - in
other words they round up to the next highest foot.

The overall distance from the steer axle to axle #5 is determined by 5th
wheel position and is also affected by the relative position of the front
axle behind a tractor's front bumper. This "BFA" dimension varies with
different tractor designs.

The rationale used by states to determine the kingpin to last trailer axle
position has to do with a trailer's tendency to "off-track" in a turn, and
the effect this unavoidable off-tracking will have on tractor/trailer
maneuverability in heavy urban traffic.

Pat
tscottme
2004-01-28 15:04:25 UTC
Permalink
Post by Pat Durkin
Very good point Scott and a valuable tip about how to visually line things
up with the trailer door.
In California the allowable distance is 40', and it is measured from the
kingpin to the center of the last axle. On a 53' trailer with a typical 36"
KP dimension, that means there will be 10 feet of trailer hanging aft of
trailer axle #2. I don't have any quick tip about how to measure that with
trailer doors but a practiced eye can tell at a glance of it is about 120".
This means that our law is more restrictive than many states, and if an OTR
unit arrives in California with a configuration that is legal in certain
other states they are in danger of a citation here.
The position of the last axle in a 5-axle combination is critical to bridge
formula calculations. In California the distance from axle #1 (steer axle)
to axle #5 must be the legal equivalent of 51' in order to legally gross
80,000#. California law recognizes 606" as being equivalent to 51' - in
other words they round up to the next highest foot.
The overall distance from the steer axle to axle #5 is determined by 5th
wheel position and is also affected by the relative position of the front
axle behind a tractor's front bumper. This "BFA" dimension varies with
different tractor designs.
The rationale used by states to determine the kingpin to last trailer axle
position has to do with a trailer's tendency to "off-track" in a turn, and
the effect this unavoidable off-tracking will have on tractor/trailer
maneuverability in heavy urban traffic.
Pat
What's funny is that as TN words the law you can drive around with a 48
foot trailer's tandems farther set than you can have a 53 foot's
tandems. In TN you can slide 48 foot tandems to the rear of the
trailer, which is a few feet behind the 41 ft kingpin/tandem distance on
a 53.

Thanks for the "off track" explanation. The few times I forced myself
to think about the "bridge law" I had assumed it was for weight
distribution on bridge segments, but I couldn't figure out how. The
people in school and the one Dir of Safety at my first company whipped
out the mathematical formula and I started daydreaming about a nap. I
had though, heck if you could slide the tandems far enough on a mythical
trailer, your total weight wouldn't be on the bridge, ever, just half of
the total and then the other half. It seemed to me that if they should
worry about anything it should be short trailers.

Let this be a lesson kids, don't mix math and life without adult
supervision.


BTW, for drivers headed to CA or any other non-41 foot state, you can
use the open door, plus outstretched arms, think "standing Jesus". For
example, with your right finger tips touching the "forward edge" of the
open trailer door, notice where is the mudflap, rear axle, or mid-point
between axles. While that spot of the driver's choosing will vary form
driver to driver, if it varies from day to day on the same driver, he's
probably got bigger problems than a ticket. ;-)

--

Scott
--------
The French, God bless them, are finally joining the war against Islamic
extremism. Their targets, which will now confront the full force of
l'état, are schoolgirls who wear Muslim head scarves in French public
schools.
Wall Street Journal
realitytrucker
2004-01-30 07:20:53 UTC
Permalink
Post by Pat Durkin
Very good point Scott and a valuable tip about how to visually line things
up with the trailer door.
In California the allowable distance is 40', and it is measured from the
kingpin to the center of the last axle. On a 53' trailer with a typical 36"
KP dimension, that means there will be 10 feet of trailer hanging aft of
trailer axle #2. I don't have any quick tip about how to measure that with
trailer doors but a practiced eye can tell at a glance of it is about 120".
This means that our law is more restrictive than many states, and if an OTR
unit arrives in California with a configuration that is legal in certain
other states they are in danger of a citation here.
The position of the last axle in a 5-axle combination is critical to bridge
formula calculations. In California the distance from axle #1 (steer axle)
to axle #5 must be the legal equivalent of 51' in order to legally gross
80,000#. California law recognizes 606" as being equivalent to 51' - in
other words they round up to the next highest foot.
The overall distance from the steer axle to axle #5 is determined by 5th
wheel position and is also affected by the relative position of the front
axle behind a tractor's front bumper. This "BFA" dimension varies with
different tractor designs.
The rationale used by states to determine the kingpin to last trailer axle
position has to do with a trailer's tendency to "off-track" in a turn, and
the effect this unavoidable off-tracking will have on tractor/trailer
maneuverability in heavy urban traffic.
Pat
The only state I ever had trouble with the kingpin law WAS CA. I had
to slide the tandems back to make the trailer level with the loading
docks and forgot to slide back forward afterwards. Got ticketed at
the Gilroy scales. Never seemed to have any problems elsewhere. Are
there any other states that are as restrictive as CA?
John Morgan
2004-01-30 14:18:05 UTC
Permalink
"realitytrucker" <***@aol.com> wrote in message news:***@posting.google.com...
<snip>
Post by realitytrucker
The only state I ever had trouble with the kingpin law WAS CA. I had
to slide the tandems back to make the trailer level with the loading
docks and forgot to slide back forward afterwards. Got ticketed at
the Gilroy scales. Never seemed to have any problems elsewhere. Are
there any other states that are as restrictive as CA?
Our company made it a little easier to keep up with the tandem locations by
lettering the sides of all the trailers A, B, C, D at different positions
from the rear of the trailer. (Since they all ran 53 footers, and kept the
kingpin to rear of trailer measurement the same on their trucks it was
easily done.) We were given a list of states in our permit packet that
listed the position for the center of the rear axle. California was an "A",
as well as Louisiana. A was for furthest forward spot for our tandems. When
we picked up a load, we noted our route and destination, and set the tandems
for the most restrictive. Worked very well.

Stay safe,

John

Richard
2004-01-28 16:52:46 UTC
Permalink
Post by tscottme
At work this issue is getting under my skin, for the last 5 years, so I
thought I would make sure everyone here understands it. In several
states, maybe federally as well, there is a maximum distance from the
kingpin of the trailer to the trailer tandems. Sometimes drivers
mistakenly call this the "bridge law" or they correctly call it the
"kingpin law." The various states measure it in various ways and that
particular distance varies some. But for this example, let's use
Tennessee's rule. In TN when pulling a trailer longer than 48 feet,
that means this applies to 53 foot trailers, you are not allowed to set
the trailer tandems more than 41 feet from the trailer king pin. In TN
the measurement is taken from the kingpin to the middle of the trailer
tandems. Notice I didn't mention the weight of the truck/trailer
combination or the weight of any payload. This law applies even to
empty trailers. You are not allowed to pull a 53 foot trailer on any
public road with the trailer tandems slid behind the maximum, 41 feet in
this case. The last ticket I saw for a driver at my company was a $75
fine for pulling an empty trailer on the road with the tandems slid to
the rear of the trailer. By the way, that fine is payable by the
driver, not the trucking company.
"KPRA" is not the "bridge law".
I once asked an inspector if it mattered where the kingpin was and he said
no.
As most trailers use fixed kingpins, then you should measure from there to
the rear axle.
It matters not if a tractor is hooked.
There is a system available whereby the kingpin can be slid under the
trailer, not just the tractor.

It should also be noted that this rule applies only when off the federal
interstate network.
So if you have no intention of scenic driving off an interstate in that
state which has a KPRA rule, you can not be cited for it.
Although in california they will just to wirte more tickets.


Speaking of the bridge law, if you drive a standard 5 axle truck, and an
inspector gets out the tape measure and says you're over the limit, pull out
your trusty rand mcnally truckers guide and show him the bridge law formula.
Then point out the "Exception to the rule".
As long as there is 34 feet between axle 3 and and 4, you are legal.
Pat Durkin
2004-01-29 02:59:50 UTC
Permalink
Post by Richard
Speaking of the bridge law, if you drive a standard 5 axle truck, and an
inspector gets out the tape measure and says you're over the limit, pull out
your trusty rand mcnally truckers guide and show him the bridge law formula.
Then point out the "Exception to the rule".
As long as there is 34 feet between axle 3 and and 4, you are legal.
More bad advice from somebody who doesn't know what he's talking about.

The Bridge Formula relates to two principal dimensions with regard to a
5-axle tractor/trailer combination.

FIRST - the overall "L" Dimension (the distance from axle #1 to axle #5)
must be 51', or it must 'round up' to 51'.* A 50' "L" Dimension allows
79,000#. You can use a Keller chart for this or you can calculate it
yourself if you understand the math. Actually a 50' dimension = 79,250# but
they round it down to the next lowest thousand. 49' Equals 78,625# but it
gets rounded up to the next highest thousand. And a 48' measurement would
calculate to 78,000# exactly.

SECONDLY, all the above is null and void if the trailer length/KP
measurement/tandem axle placement will not allow at least the legal
equivalent of 34' between the extremes of any two 'groups' of axles**. This
is sometimes referred to as the Inner Bridge. A group can be a tandem or
three axles or even one axle - but the important thing to recognize is that
the idiot above was utterly in error when he said 34 feet between axles
number 3 and 4. The 'extremes' are considered to be the OUTER wheels - in
other words axles #3 and #5. Trust me - if you're pulling an old 40 footer
you'll never get enough distance between your forward drive axle and your
last trailer axle. In which case you will be limited to 32,000# on your
drivers and 32,000# on your trailer tandems...and this is true NO MATTER
WHAT your overall "L" Dimension is. It could be 55' and you'd still be
limited to only 76,000#.

Got it? Good.

Pat

*States have some leeway on whether or not to allow rounding up. California
allows it if a dimension is at the six inch mark. Some other states may say
it has to be 7" or more.

**Trying to get long enough for the Inner Bridge to equal 34' can be kind of
tricky with some of the older, shorter trailers. A 42-1/2 footer for
instance, might need the 5th wheel to be slid back almost to the centerline
of the dual drive axles in order for the Inner Bridge to be legal and allow
34,000# tandem loads. The problem is that in sliding back to the rear
center you have pulled 100% of your trailer and payload weight OFF of your
steer axle, which now might weigh only 9,750# instead of 12,000# --- and now
you'll find yourself OVER on your drive axles, which might be 36,250#
instead of 34,000#. Modern trailing equipment is longer and can usually be
balanced a little easier.
Pat Durkin
2004-01-29 04:22:11 UTC
Permalink
"Pat Durkin" <***@pacbell.net> wrote in message news:GG_Rb.17453$***@newssvr27.news.prodigy.com...

Yikes!

If I'm going to be critical I guess I ought to proofread my own text. The
sentence below...
Post by Pat Durkin
The 'extremes' are considered to be the OUTER wheels - in
other words axles #3 and #5.
Should in fact read "axles #2 and #5.

Sorry 'bout that.

The sense of the rest of it was correct.

Pat
Pat Durkin
2004-01-29 04:44:27 UTC
Permalink
Glad I spotted that before somebody else came back and said "Pat you dumbass
you're drinkin' your bath water".

If I'm so smart, how come I'm so stupid sometimes. Hmmm.

Pat
DGM
2004-01-29 02:28:03 UTC
Permalink
One other thing to consider, if you are driving interstate and you are
running close to max weight you could end up with overweight issues. For
example all the axles weights are fine in a state that allows 41' from the
kingpin to axle (you weighed out just to be sure) Then you cross the state
line and have to pull the axles forward, now you are overweight on the
trailer axles. And people wonder why I think it takes brains to be a GOOD
driver.

Rflagg
Post by tscottme
At work this issue is getting under my skin, for the last 5 years, so I
thought I would make sure everyone here understands it. In several
states, maybe federally as well, there is a maximum distance from the
kingpin of the trailer to the trailer tandems. Sometimes drivers
mistakenly call this the "bridge law" or they correctly call it the
"kingpin law." The various states measure it in various ways and that
particular distance varies some. But for this example, let's use
Tennessee's rule. In TN when pulling a trailer longer than 48 feet,
that means this applies to 53 foot trailers, you are not allowed to set
the trailer tandems more than 41 feet from the trailer king pin. In TN
the measurement is taken from the kingpin to the middle of the trailer
tandems. Notice I didn't mention the weight of the truck/trailer
combination or the weight of any payload. This law applies even to
empty trailers. You are not allowed to pull a 53 foot trailer on any
public road with the trailer tandems slid behind the maximum, 41 feet in
this case. The last ticket I saw for a driver at my company was a $75
fine for pulling an empty trailer on the road with the tandems slid to
the rear of the trailer. By the way, that fine is payable by the
driver, not the trucking company.
The Rand-McNally atlas details what the kingpin/tandem distance is for
the various states, and how to measure it. It would be wise to either
check it for each state or to at least note which states have uncommon
length requirements. Which brings us to checking if you are in
compliance or not. Here's an easy way if you are checking for the 41
foot distance and the trailer is 102 inches wide, I believe this is the
most common 53 foot trailer on the road: when the trailer doors are
pinned in the open position, (folded against the sides of the trailer),
the edge of the trailer door that is now closest to the tractor, which
touches the other door when they are both closed is about 41 1/2 or so
feet behind the kingpin. So when you pick up a trailer if the rear
mudflap of the trailer tandem is somewhere in front of the open trailer
door, you are "good to go" with respect to this kingpin law.
-------------------------------------------------
|
|
|
|
|
|
|
|
-------------------------------------------------
O O
Do not depend only on any "41 foot marks" that may be placed on the
side of the trailer. That mark may or may not be correctly located. My
company has a few thousand trailers, all with equal dimensions, that
have the "41 foot mark" correctly located and some not. Some of our
trailers use a similar mark to indicate tandem position for a particular
customer. Some of our trailer have no mark. There is also variation on
what part of the tandem should line up with any mark. Some of our
drivers think the front wheel or the rear wheel of the tandem should be
under the mark to be in compliance. There are a lot of drivers that
rely on rules of thumb about "put the tandem pin in the X hole." While
that may work if your company only buys one brand of trailer and that
trailer manufacturer makes every trailer exactly alike, you have no way
to double-check that advice. You also may not know if they count every
hole in the rail, or only count holes that the pins may reach. On many
of our trailers there are one or two hole in the front of the rail that
you could never put the tandem pins in since the rail has a stop placed
between those holes and the rest of the holes in the rail. The trailer
door/tandem mudflap method is easy to see and unless you use trailers
that are very much wider or more narrow (trailer doors are very
different dimensions) good enough.
When OTR, it's often easy to go for years and always adjust the tandems
ahead of legal limit, if only for weight distribution. It may be that
only if a customer lies about the weight of a load or loads it fully to
the rear of the trailer will this ever come up. Don't learn this lesson
on the side of the road or at a weigh station. I am shocked at the
number of OTR drivers that transfer in to my section of the company and
don't know this. I made this mistake when I started. Every time I
explain this to them they answer exactly the same: "but the trailer is
empty." Weight is irrelevant to this issue.
In TN, at least, there is no question that this applies to 53 foot
trailers and includes empty trailers. I can post the law from the
official TN code, I've done this already at work. What I've described
is the law in TN. The TN law simply phrases it in a confusing manner,
so I've not posted it.
--
Scott
--------
The French, God bless them, are finally joining the war against Islamic
extremism. Their targets, which will now confront the full force of
l'état, are schoolgirls who wear Muslim head scarves in French public
schools.
Wall Street Journal
Pat Durkin
2004-01-29 03:09:32 UTC
Permalink
Post by DGM
One other thing to consider, if you are driving interstate and you are
running close to max weight you could end up with overweight issues. For
example all the axles weights are fine in a state that allows 41' from the
kingpin to axle (you weighed out just to be sure) Then you cross the state
line and have to pull the axles forward, now you are overweight on the
trailer axles. And people wonder why I think it takes brains to be a GOOD
driver.
Rflagg
Absolutely correct. Sliding the trailer axles forward puts more unsupported
trailer length aft of the axles and has the effect of re-balancing the
tractor/trailer combination. The effect is that the trailer axles are now
supporting more weight, while the kingpin weight has been magically reduced.

Pretty basic stuff for experienced hands but sort of foggy for people just
starting out.

Pat
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