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Old 7th June 2006, 14:17   #1
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Default Crabbing

What do you call that problem? The busses moving at an angle to the road like crabs! I have seen many busses like that, and have travelled in a few.

Today, I saw an indica xeta, New black, with an L sticker on the rear window, moving in airport road like that. For the first time I saw a car in this state. Quite funny and the crab(My term) angle was noticable. Sorry cpould not take any pics. Imagine if the twist is noticable on a small car the angle should be quite something.

I thought, the problem was due to mis-aligned rear rigid axel with the c-frame ladder chassis. But Indica is a monocoque with independent wheels suspension. So I wonder how is this possible?

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Last edited by tsk1979 : 14th June 2006 at 03:07.
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Old 14th June 2006, 02:39   #2
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Hey DRC,
I've seen loads of of padmini taxi's and some old mahindra jeeps with the same problem. It's always intrigued me too...
Hope someone can throw some light on this.
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Old 14th June 2006, 10:16   #3
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this happens a lot in the state transport buses and some trucks. the main reason is accidental chasis. sometimes the chasis bends at an angle when involved in an accident. for larger vehicels its very very hard to repair so when they run these u can see the crab in them.

there are only a handful of vehicles that can actually crab. it will require all the vehicles 2 b turned in one direction.
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Old 14th June 2006, 11:12   #4
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Most of the cars today use monocoque bodies, meaning there is no separate "chassis" and "body". Everything is a single entity, which makes them light yet strong and rigid.

I think "crabing" can happen due to suspension problems also... one side getting more compressed than the other or uneven loading (?) Many times trucks are heavily loaded raising their CG to a very high position, so much so that they lean towards one side. Worser, they can topple before skidding in case of fast sharp turns or accidents!

DRC, which angle are you talking about? Is it the angle w.r.t. road as seen in front or back side view (leaning to the left or right) or is it the angle between the direction of the actual movement to the length of the vehicle as could be seen in the top view? The later case has to be due to mis-alighnment between front and rear wheels.

Last edited by aah78 : 14th June 2006 at 22:00.
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Old 14th June 2006, 11:28   #5
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Quote:
Originally Posted by santosh.s
DRC, which angle are you talking about? Is it the angle w.r.t. road as seen in front or back side view (leaning to the left or right) or is it the angle between the direction of the actual movement to the length of the vehicle as could be seen in the top view? The later case has to be due to mis-alighnment between front and rear wheels.
I think he's talking about the angle between the direction of the vehicles motion and the vehicle itself, atleast thats what i got.
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Old 14th June 2006, 12:00   #6
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crabbing in heavy vehicles is generally due to accidental chassis..
In case of indica it might be due to a bad allignment.
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Old 14th June 2006, 12:16   #7
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Yeah, angle wrt direction of movement.

I dont know how difficult to fix in heavy vehicles?
Once, I travelled in a bus from Somwarpet to Mysore which had this defect, then, next day the same bus was plying on the same route corrected!
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Old 14th June 2006, 12:31   #8
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Yep u c it in bycycles to cars and buses...
in bikes its usually the chassis and the swingarm and when u c the bike head on the rear tyre is not in line with the front....I noticed this in my frnds m-800....indeed it was a chassis problem....
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Old 14th June 2006, 12:39   #9
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\drc what u seen is front wheels not moving inline with rear wheels.

These are mostly accident vehicles where chassis is bent. its quite common to see this in bikes which have had a couple of nasty falls.

"chassis bends are very costly to repair and this CANNOT be done in our country"
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Old 14th June 2006, 12:51   #10
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Well to clarify...

The Indica I saw was a brand new one, not a spec of accident signs, no dents, decoloration, anything (well I could see only for a few minutes driving behind it). It can't be accident.

Alignment ? may be, but off the alignment by so much ?
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Old 14th June 2006, 12:59   #11
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Crabing in heavy vehicles is caused when the leaf springs breaks. Or when the bolt holding the leafs breaks (usually the center bolt). Not very hard to repair.
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Old 14th June 2006, 14:23   #12
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Quote:
Originally Posted by DRC
Well to clarify...

The Indica I saw was a brand new one, not a spec of accident signs, no dents, decoloration, anything (well I could see only for a few minutes driving behind it). It can't be accident.

Alignment ? may be, but off the alignment by so much ?
can be out of factory with bad alignment. Most cars on the road have improper wheel alignment and owners dont even know about it. Its quite simple for a person with an "eye" to see improper wheel alignments. A weekly brief inspection is sufficient Learnt this when i got my car passing (annual registration) first time.

Last edited by 2fast4u : 14th June 2006 at 14:27.
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Old 14th June 2006, 14:45   #13
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Yes, some heavy vehicles do seem as if one side (left or right) is moving ahead of the other. In cars its the alignment mostly.

Wonder if anyone has noticed some doggies running in similar fashion and yes, so as the crab.


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