Axle question

Submitted: Wednesday, Jun 29, 2005 at 17:27
ThreadID: 24292 Views:1722 Replies:4 FollowUps:8
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Look under most small trucks and you will see that the front axle kindof dips in the middle. What I mean by this is that the centre of the wheel is higher than the centre of the axle. I don't know the correct engineering terms but I would call it off-centre.

My bus is the same.

I had the idea of fliping the axle over exactly 180 degrees and the "dip" would now be a "rise". Giving me an instant lift and much more ground clearance.

Everyone I have asked says it can't be done.

I believe them but I want to know why not in laymans terms.

I think all the angles for refitting all the bits and pieces would be the same as it is an exact 180 degree flip.

I have asked some very smart people on EO and in no way do I want to offend them by asking again. They all say it can't be done.

I just want to know why I cant do it in a way that either eliminates it from my mind alltogether or gets me of my ass to do it.
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Reply By: Nudenut - Wednesday, Jun 29, 2005 at 18:06

Wednesday, Jun 29, 2005 at 18:06
some thoughts on why not....
gear cogs designed to operate one way
as are any locking arrangements etc etc etc
AnswerID: 118088

Reply By: Lone Wolf - Wednesday, Jun 29, 2005 at 18:24

Wednesday, Jun 29, 2005 at 18:24
Think of it like this...

You are in your yard, pushing an empty wheelbarrow, just high enough so the 2 legs don't hit the ground. You come across a large bump, or garden edging you have to get over, no big deal.

Now, try holding the handles of your barrow really high, like at chest height, or higher, and try to do the same thing...

It's all a matter of where the axle is in relation to the intended travel, in engineering, it's called... moment.

I broke a swing arm on my Yamaha 250, because I landed after a weapon jump, and the bike was still to upright, the load just went through the whole arm.


AnswerID: 118092

Follow Up By: Member - Poppy (QLD) - Wednesday, Jun 29, 2005 at 20:58

Wednesday, Jun 29, 2005 at 20:58
Hey Wolfie
Sometimes I think my lot in life is to ask stupid questions, so here goes again.
What is a weapon jump?
Cheers Poppy
FollowupID: 373317

Follow Up By: Lone Wolf - Wednesday, Jun 29, 2005 at 21:09

Wednesday, Jun 29, 2005 at 21:09

Weapon, as in... really high, or... "Cool Dude!!", or... AWESOME!!

I have a 21 y/o & 19 y/o, and Tracy & I just have to be with it, or we are just so like....

The buggers do keep us young!


Hip Wolf
FollowupID: 373320

Follow Up By: Member - Poppy (QLD) - Wednesday, Jun 29, 2005 at 21:27

Wednesday, Jun 29, 2005 at 21:27
oohhhhhhhh, now I should have known
Onya Hip Wolf
FollowupID: 373324

Reply By: GaryInOz (Vic) - Wednesday, Jun 29, 2005 at 18:29

Wednesday, Jun 29, 2005 at 18:29
In laymans terms....

Your bus has its springs connected to the dip in the axle. The weight of the bus keeps the axle in a "u" shape and stable.

If you invert the u to an n with the wheels lower than the weight on the axle, the axle will try to invert itself to its more stable "u" form with any minor forward/backward motion of the axle. The leaf springs will end up looking like a lying-down s shape.

To give an example, get a piece of wire (old coathanger), cut a piece and shape it into a similar shape to youraxle (a Greek Omega shape). Now place the two straight bits (representing the wheel hubs) on two books with a gap between them and you will see the u fall through the middle and hang there. Now place your fingers on the bottom of the "u", apply direct pressure downwards and try to get it to swing (the harder you push the more stable it is, obviously don't push so hard as to bend the wire).

Next, lift the "u" to form an "n" and gently hold it there by the "axle" (bit on the books). Now apply the same sort of pressure that you did previously. You will see that it does not take much to get it to invert to its "u" shape again, and that you could not stop it by the axle. This represents the twisting load that would be applied to your springs turning them into the aforementioned "s" shape, and explains why without anything being added to your suspension the system would not work. The initial fwd/bkwd movement of the axle to get it to go off center could easily be applied by bumps in the road, braking, etc.

In short the system is unstable...heed the advice of those that you have spoken to.
AnswerID: 118094

Follow Up By: Member - Blue (VIC) - Wednesday, Jun 29, 2005 at 19:03

Wednesday, Jun 29, 2005 at 19:03
Master of the "lay" speak... very good example there Gary. I was racking my brain trying to find a good analogy, all I did was confuse myself... Of course that doesn't take much ;-p

OT, how goes the KIA?
FollowupID: 373301

Follow Up By: Member - iMusty (VIC) - Wednesday, Jun 29, 2005 at 19:13

Wednesday, Jun 29, 2005 at 19:13
Thanks Gary.

Im a bit like Blue. All I was doing was going around in circles trying to reason it to myself ... as I said pretty smart cookies said it can't be done but WHY NOT was all I kept coming up with.

Now I see why not. Thanks.

I think it's a case of back to the drawing board for me...

FollowupID: 373304

Follow Up By: Member - Poppy (QLD) - Wednesday, Jun 29, 2005 at 20:55

Wednesday, Jun 29, 2005 at 20:55
Hi GaryInOz
Just sitting here wondering what made you ever try the coathanger/books thing?.. LOL
FollowupID: 373316

Follow Up By: GaryInOz (Vic) - Wednesday, Jun 29, 2005 at 23:07

Wednesday, Jun 29, 2005 at 23:07
Glad to see it made sense to someone other than me. LOL


Kia is still going but minus 4WD due to another fried front diff :-/. Getting lockers and lower diff ratio into modified rear LSD hat installed in the front, which should sort out the strength/traction issues. Bit busy with a career change to do much ATM.


There probably would not be a good reason why you could not go with a dead straight underslung axle (sping under axle), or possible get real radical and search for a 4WD front axle (DYNA 4x4 running gear???) and put a transfer case behind your gearbox..... way cool


I knew what i wanted to explain, but it took a few mins to work out how. Coathanger and books came to me in a flash of ?????? (not brilliance that's for sure...probably madness)
FollowupID: 373335

Follow Up By: GaryInOz (Vic) - Wednesday, Jun 29, 2005 at 23:10

Wednesday, Jun 29, 2005 at 23:10

looking at your signature line, my grandfather probably had a line you could relate to as well

"Don't grow old, there's no future in it"
FollowupID: 373337

Reply By: desert - Thursday, Jun 30, 2005 at 13:45

Thursday, Jun 30, 2005 at 13:45
Well, it's got nothing to do with the "U" section swinging to the lowest point. Why then to M.A.N trucks use a straight axle beam? The reason you cannot invert the axle is because of a suspension geometry setting called "King Pin Inclination", where the centre line of the king Pins is canted over, not verticle. So, obviously if you reverse the axle you reverse the angle of the King Pin and you would not be able to hold the thing on the road. Full stop!
AnswerID: 118248

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