Author Topic: What's the difference between axle back and axle forward?  (Read 7001 times)

Offline Merkava_4

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What's the difference between axle back and axle forward?
« on: November 19, 2010, 01:14:33 PM »
At the Mack Pinnacle web page, they show two different trucks but they're both named Pinnacle. The one Pinnacle that looks a little more aerodynamic is "axle back," while the other Pinnacle that looks a little more conventional and squared off is "axle forward."  scratchhead

Click on "SLEEPER"
http://www.mackpinnacle.com/

Offline flashpuppy

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Re: What's the difference between axle back and axle forward?
« Reply #1 on: November 19, 2010, 01:21:40 PM »
I couldn't really see any difference.  Maybe wreckerologist will know...
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Offline skfarmer

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Re: What's the difference between axle back and axle forward?
« Reply #2 on: November 19, 2010, 01:33:43 PM »
the axle forward has the axle pushed closer to the front bumper, it gives a better ride and may allow more weight carrying cappacity but i doubt that is an issue with a sleeper. the axle back would allow for a more rounded aerodynamic front and fenders, shorter wheel base and tighter turning radious. i have even seen some that have the oil sump of the engine in front of the axle.
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Offline Uncle Buck

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Re: What's the difference between axle back and axle forward?
« Reply #3 on: November 19, 2010, 02:57:57 PM »
I believe the term axle forward or back would be in reference to the front axle's relationship to the engine. As SK noted this would impact some of the handling characteristics of the truck. Also as SK noted, the greater the distance between the axles the better the ride would be.
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Offline Fins/413

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Re: What's the difference between axle back and axle forward?
« Reply #4 on: November 19, 2010, 04:08:00 PM »
Boy I was looking at the interiors of the cabs and sleepers really plush.
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Offline Uncle Buck

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Re: What's the difference between axle back and axle forward?
« Reply #5 on: November 19, 2010, 04:16:28 PM »
I didn't like that web site. I thought it difficult to negotiate. I never did find the pics of the sleepers Fins spoke of!
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Offline wreckercologist

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Re: What's the difference between axle back and axle forward?
« Reply #6 on: November 19, 2010, 04:48:01 PM »
i have even seen some that have the oil sump of the engine in front of the axle.

I can tell you certain Freightliners w/ Detroit's are like that.....I'm sure there are others.  I can also tell you that those fiberglass/plastic oil pans don't bend worth a damn when someone picks up one with axle forks that are too short! th-spit  "better go get the oil dry"............and tell the boss he needs to order another oil pan."  :D
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Offline skfarmer

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Re: What's the difference between axle back and axle forward?
« Reply #7 on: November 19, 2010, 07:06:05 PM »
volvo's are also equipped with that setup. my cousin has a triaxle grain truck  with a front lift pusher axle. pos is worthless empty. all of the weight hangs in front of the steer axle and the front wheels are an anchor. can you say stuck? smackmyself
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Offline rvannatta

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Re: What's the difference between axle back and axle forward?
« Reply #8 on: November 19, 2010, 10:49:53 PM »
volvo's are also equipped with that setup. my cousin has a triaxle grain truck  with a front lift pusher axle. pos is worthless empty. all of the weight hangs in front of the steer axle and the front wheels are an anchor. can you say stuck? smackmyself


I'm not sure I completely agree but maybe its a play on Words.



I drive a log truck with what is known by International as a "set back' front axle.    The more common configuration
has the front axle  'set forward' ---- just about as far forward as you can and not have the tires hit the front bumper.
Indeed  quite a few truckers  'bob' off the ends of the front bumper so that if they hit a deer or something it won't bend the bumper back a couple of inches and stick it into the tire--- causing them to lose steering.

Ifyou take a look at my International, it is set back about 18 inches.     It's a configuration often used
where you want to get some extra weight on the front wheels.   IN specing out a truck there is always a conflict between
getting as much wheelbase as you can for the weight / bridge formula,--- and also being able to get the weight far enough forward.   This truck is made with a 14,000 lb front axle and I run 12 inch tires on the front.   I then put the booster axle
behind the drivers, instead of the more conventional position in front of the drivers.    This way the booster axle
transfers some weight to the front axle.   In Oregon this allows me to get the truck  GVW up to 54,000 lbs.

This is a fairly uncommon configuration but now doesn't make much difference here in Oregon.

Oregon allows double trailers, and in the 'rocky mountain doubles' configuration  I can GVW to 105,500 and the length
limit is 68 feet of  'hauling area'.   The length of cab/engine etc in front of the bed is unlilmited so this 18" more or less
stickingout in front of the front wheels changes nothing.

With a single trailer, my gross is generally limited by my wheelbase of the last 5 axles.   The problem with log hauling
is that you can't get the last 5 axles quite long enough because the logs are only 41 feet long.   You just need
a truck wheelbase that is 'long enough' and this one is.    I have axles enough for 88,000 lbs, but I"m usually stuck
at 86500 with a single trailer because of the last 5 axle group.



This is the 105,500 lb configuration which works I believe in Oregon, Washington, ID,  MT.  and I think WY. and CO.
but not in California.

Offline Mickey O

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Re: What's the difference between axle back and axle forward?
« Reply #9 on: November 20, 2010, 05:15:59 AM »
City truck, highway truck?
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Offline skfarmer

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Re: What's the difference between axle back and axle forward?
« Reply #10 on: November 20, 2010, 07:19:46 AM »
rvannatta, i think the word you missed in my quote is empty. the grainbox weighs very little on this truck. the  hood, radiator and most of the engine weight sit in front of the axle. the transmission, hoist, push axle, fuel tanks, battery boxes and of course cab sit in front of the tandem drivers.much of this weight is carried on the front 2 tires and very little on the drivers when it is empty. as the truck is filled it balances out giving the rear wheels weight and traction. i think this truck would be better suited with a rear lift tag so one could lift the axle and add weight to the drivers and seesaw some weight off of the front axle when it is empty.
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Offline rvannatta

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Re: What's the difference between axle back and axle forward?
« Reply #11 on: November 20, 2010, 08:58:30 AM »
rvannatta, i think the word you missed in my quote is empty. the grainbox weighs very little on this truck. the  hood, radiator and most of the engine weight sit in front of the axle. the transmission, hoist, push axle, fuel tanks, battery boxes and of course cab sit in front of the tandem drivers.much of this weight is carried on the front 2 tires and very little on the drivers when it is empty. as the truck is filled it balances out giving the rear wheels weight and traction. i think this truck would be better suited with a rear lift tag so one could lift the axle and add weight to the drivers and seesaw some weight off of the front axle when it is empty.

Agreed.    This is one of the benefits of the rear lift axle that you see on my log truck although there it shows when loaded.

Log trucks usually do preetty well empty because they haul their trailer which gives you enough but not too much weight
on the drivers.      Load the thing  to a typical 85,000     You shoot for a 53,0000 on the truck and 32,000 on the trailer. (with thet legal max of 42500 and 34k respectively---but wheel base delimited for the combined number.   We have 'on board scales' which are fairly accurate.

Off the highway you leave the lift axle up.    The truck front axle is around 12k or a little less and  the driving axles
at 41k or a little more.    You got your weight in a good configuration for off highway pulling.--- lots of weight on the driving wheels.

Get to the highway, drop the rear lift axle.   It will shove 2000k  or so up to the front axle----you can by adjusting the air pressure on the lift make it load the front axle to exactly what you want and it will do it consistently on every load.
That tranfers that weight out  of the 5 axle bridge that will ultimately restrict your gross,  and at the same time the lift axle
will reduce the weight on the driving axles to less than 34k  (the legal max for tandems). now providing you with a highway legal combination.


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Re: What's the difference between axle back and axle forward?
« Reply #11 on: November 20, 2010, 08:58:30 AM »