Bus whose body is diagonally oriented when going straight ?!

last SG · 2008-01-01T21:40:43+00:00

Looking only from that rear photo, i'll say it could be front tyre puncture & / or right side suspension air imbalance i.e. either of both cases certainl...

hseochin SG

Saw that last night around 7:30 PM along Selegie Road !
Was walking opposite to the direction of the coming bus (Alexander double-deck body on either Leyland or Volvo Olympian 3-axle chassis on SBS route) when i sensed something not right as it was coming ~ 50 km/h & i could see the tyres of the front & mid axles judding out as if it was turning left BUT in actuality it was going straight, meaning the bus body was 'slanted' instead of being parallel to the direction of travel as is normally expected from any vehicle !

The danger i can imagine of that is the driver may over-estimate the clearance between his vehicle & anything to the left of it, since from his view @ the front it seems to have plenty of space on the left side BUT by the time the back-side portion of his bus catches up with any slower moving object on it's left (say another vehicle or worse a cyclist or pedestrian) then the left side clearance of the bus becomes lesser by say 15 CM which may result in hitting anything slower than it on the left of the road !

I understand in this type of city-bus 3-axle chassis, the mid-axle is also a steering-axle (in addition to the front axle) but with angle of rotation confined to 10 to 20 degrees & supposed to be operational below 20 km/h while @ higher road speeds the mid-axle wheels are 'locked' in position laterally to be in-line with the rear driven axle ?

So it appears on that bus the locking mechanism failed resulting in the bus being able to go much higher than 20 km/h with such undesirable 4-wheel steering effects ?!?

Wonder if that's the 1st such incident or any known cases elsewhere & any accidents as such ? Whatever the case, high time they sent it for maintenance service !

ZYX2005 SG

hmm i've seen this before

but my case is cause by the slope of he road. it cused the bus to slant to one side.

nevertheless, the bus engineers when building the bus will have account for a tilt of the bus. they set the maximum tilt of the bus body. if the case the bus has electronic suspension tilter and the thing erm spoil...

the bus wun topple over over biang gantry

in the bus industry such things are decided by the bus tilt test conducted at many bus producing plants around the world. or even some bus depots worldwide.

therefore no fear of them crashing into 4.5m gantry or fall over.

ZYX

The_Bus_Guide SG

I have seen one before and its a MB O405. I was sitting at the front row on the upper saloon of a DD whch was following behind. I noticed that the O405 had its front slightly to the right while travelling straight. Is this problem due the steering or wheel alignment?

ZYX2005 SG

my thinking is the poor bus air suspension has an eror such that one sides' fluid continuously leak and cannot charge up causing the poor bus to shift to one side.

haha

ZYX

Transtar Solitarie SG

Maybe one of the bus air-balloon has just pop up,thats why the bus slanted to the left or right.If the bus uses a spring type,it can’t happened.Eventhough one of the spring-iron bar break,it can’t slanted to the left or right.

sinicker SG

seen it on an SBST WA-bodied MB0405. did ask around in this forum and carbikebus said it’s a characteristic of buses/coaches…

SBS9818A SG

it is not about the suspension AT ALL! hseochin is talking about the alignment of the bus. the bus is facing towards the right when it is actually going straight!

Scania N113CRB luver SG

Wah . Drifting arh? Laughing

But it kinda seems like wheel alignment problem . Hmm . Confused

brotherchen1982 SG

Drivers of many heavy vehicles with rear view blocked often drive their vehicle a bit slanted towards the right while going straight.

More obvious when U are inside the vehicle... Cool

Mainly due to to the way the driver adjustment of the rear mirror so they can see the vehicle's rear view unlike cars which the driver can see the rear view easily... Sad

SBS7484P SG

this i never seen b4.. but bus skid i got see. Laughing hougang int there, lots of vo3x will skid on rainy day.. just vo3x's..

caleb_chiang SG

seen that before too... maybe due to the road? Rolling Eyes

XiaoTaro SG

is this caused by the differential unit of the real axle? some sbst o405s have this problem too... just go jln toa payoh's bridge and stare at the o405s driving slant... Confused

carbikebus SG

SBST Bridgestone are really slippery during rainy days.Tyres use 2x before throw.(Rethread)

Scania SG

I think its that the body isn't fixed onto the chassis properly, hence, when going straight, bus seems to be turning.

hseochin SG

Up to the time of your post, seems you're the only person who precisely get my point.

I don't think all the others before you really understood my observations despite that i went into quite some background details.

I wish to add that the road was normally dry, the bus didn't seem to be skidding (i.e. no screaming sounds from the tyres & no skid marks) & it was even trying to accelerate to maintain speed as it went pass me.

The funny thing is that i was looking @ a near VERTICAL standing double-decker BUT whose bodywork is slanted diagonally (from the point of view looking @ the front of the vehicle) in the LATERAL plane & the whole thing was moving forwards in a STRAIGHT path with the front & middle tyres judding out as if it was going to turn left but it just went straight on !

Perhaps by now the picture becomes clearer ??

My own analysis of this observation would be that as the bus seem fully packed with people (sitting + standing) the bulk of the vehicle's weight was transferred to mainly the front & middle axles & the bus-chassis may not then be as 'straight' as it should be if the weight distribution was more even.
Therefore in this situation the chassis may have sagged down between the front & mid axles thereby causing the 3rd (driven) axle wheels to become less in contact with the road i.e. less driving traction than normal which may explain why the driver was trying to accelerate just to maintain speed on that flat road. ADDED to this situation any possible FAILURE of the mid-axle lateral wheel lock which enabled the 4-wheel steering to be ON even when the road speed was higher than 20 km/h collectively resulted in the bus moving straight in the direction guided by the parallel aligned wheels in the front & mid axles while momentarilly 'ignoring' the direction of the wheels in the 3rd driven axle since those have less weight acting on them to 'grip' the road then ?!

The fact that Selegie Road is straight before a SLIGHT BEND towards the LEFT after the traffic junction with Middle Road may explain why the steered wheels were oriented towards the left (instead of right) when i saw the bus coming straight on the later straight stretch of Selegie Road, where i made my observations while walking along that road.

Hopefully by now the picture is even clearer. But you have to read carefully in order to understand..

hseochin SG

No reason to associate with differential unit.

O 405, having only 2 axles, therefore cannot have such problems since only the front axle is steerable.

Even O 405 G, having 3 axles, not possible to behave like that as only front axle is steerable.

The 'slant' you observed more due to suspension maintenence due on the air-bellows as the vehicle can tilt to the left, right, front or rear because of uneven / in-sufficient air distribution among the air-bellows.

hseochin SG

As O 405 has only 1 steered axle such situation cannot happen, unless it's a skid.

The front tilted towards right most certainly due to uneven / insufficient air distribution among the air-bellows i.e. maintenence due on suspension.

I've seen an old MAN (on SJE) where the front was raised so high that the passengers boarded via the rear doors because even the the 1st step height @ front entrance was too high to climb !

Of course there's also that Scania L94 with the rocking-boat sensation where the entire body constantly tilts left to right & back whenever the bus is stationary. Somehow cannot control itself ?!?

But my starting post has nothing related to suspension.
I know the causes lie elsewhere.

alleggerita SG

I took before one CAC B10M Mk2 which was about to leave the interchange, it went over a hump and stopped at a traffic light..after the rear axle went over the hump, the rear axle just won't stop bouncing! It kept going up and down for as long as the traffic light stayed red..making me so dizzy..It was at least 10 to 20 seconds before the rear axle stopped moving.. Laughing

Too much air in the air bellows?

The_Bus_Guide SG

Thank you, but actually I understood what you meant. Sorry if my description wasn't clear. The O405 wasn't lopsided as would happen due to faulty suspension. From my point of view, on the DD and looking down at the O405, it actually looked as if it was going to turn right as it travelled straight.

XiaoTaro SG

I understand what u meant, but i believe the threadstarter is talking about the alignment of the bus while driving straight (correct me if i am wrong)

Heres a illustration of what i have interpreted:
[Bird's eye view]

Threadstarter, pls correct me if this is not what u mean...