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Old 17th February 2009, 17:35   #61
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Dear all - to take this extremely healthy discussion further, it all depends on how you set up a suspension system, what are your slip angles, what are the cornering forces that your end users will be comfortable with, what is your tyre delivering in terms of performance characteristics etc. Essentially, what is the vehicle behaviour that the end user is looking for. IFS v/s leaf spring on these properties.

I am very happy to see very good detailed knowledge amongst our forum members.

Digressing a little:


Have you driven the latest Scorpios? Please do let me know. If not, please drive and let me know. You will be surprised.

Best regards,

Behram Dhabhar

Last edited by DHABHAR.BEHRAM : 17th February 2009 at 17:39. Reason: add info
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Old 17th February 2009, 17:41   #62
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Originally Posted by DHABHAR.BEHRAM View Post
Essentially, what is the vehicle behaviour that the end user is looking for.
We are demanding folks looking for a vehicle with a suspension that can take us offroad - leaf springs, solid axle type and then comfortably take us home too with good comfort and handling - coils, IFS type.

i.e. Best of both worlds.

Possible?

Last edited by Spitfire : 17th February 2009 at 17:44.
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Old 17th February 2009, 19:02   #63
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Originally Posted by DHABHAR.BEHRAM View Post
[b]
Have you driven the latest Scorpios? Please do let me know. If not, please drive and let me know. You will be surprised.
How latest? You mean the mHawk?
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Old 17th February 2009, 22:05   #64
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Originally Posted by ex670c View Post
1) ...What other type of steering can you put. (M&M used a crossover linkage PS on the Bolero with the BA10s that is 8 Ball Joints and vague, Tata did that with the SUMO & Estate)

4) Its not about after market parts, the catch is in assembly and dis-assembly as the front differential is bolted to the chassis.

I sincerely hope its as easy as adjusting the pre-load on the torsion bar.

Larger Tyres will affect the Turning Radius and more weight on the upper and lower arms.

Pinzgauer VS Suburban

Regards,

Arka
Hi,

Check the steering on a Safari. It is power assisted recirculating ball with 4 ball joints. R&P steering also has four ball joints, but is unsuitable for non-compititive off-road driving as the steering ratio is too high.

Torsion bar preload can be adjusted on Tata vehicles near the anchor point on the chassis.

Large tyres affect turning radius on all types of suspensions. Heavier tyres will have the same effect on IS/rigid axle.

The diff has to be removed from the chassis because of poor access. This is a problem on tightly packaged modern rigid axle vehicles too. Fortunately jeeps being so old in design dont have too many accesibily problems. But it is difficult to work on the dana 44 if it is mounted on the vehicle (compared to a workbench).
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Old 18th February 2009, 10:48   #65
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Originally Posted by DKG View Post
As we all know the solid axle assembly is much heavier compared to the unsprung components of an IFS system.....

But in cars with a solid axle when one wheel hits a bump and moves up, due to the rigid connection, the other moves up too. On a slope if that happens not only does the wheel hitting a bump lose traction but it causes the other to bump up too weakening traction
The difference in unsprung weight between IFS and solid axle does favor IFS but not by what I would call a huge dgree. Please keep in mind you still have axle shafts, differential, control arms, torsion bars.

DKG, Arka is correct. On a bump on one front wheel the other front wheel moves down not up. Or, if no movement is possible, more weight from the bump side will transfer to the non-bump side. Any picture of a ramp test will bear this out. A ramp is just a bump taken at slow speed. Higher speed does not change the physics.

Let us suppose that some manufacturer was thing of switching to IFS.
I am not so sure I want to shell out 7 or 10 lakhs for the honor of being a test bed for some manufacturer's attempt to widen the niche of their vehicle by making it more comfortable. I will reserve judgment until I see the actual execution of the concept, the quality of the components and the difficulty of maintenance.
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Old 18th February 2009, 11:53   #66
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First of all I am not a technical person so you'd have to excuse me if I get a few issues wrong.

Its been ages since I studied force vectors to figure out the behaviour of wheels on a solid axle. Possibly Arka is right about the pivotal action of the beam. We are however losing the forest for the trees.

Let me explain what I understand of suspensions

A suspension primarily is meant to track road surfaces efficiently retaining traction at all times and dampen oscillations that get set forth in its components during action.

Lets go with the fact that in a solid axle setup the behaviour of one wheel affects the other wheel across the axle (whether directly or inversely is not the issue). Hope we are all in agreement on that.

Extrapolate this fact onto onroad behaviour. Lets say you are driving a car with a solid axle and one tyre hits a bump. Lets for discussion sake go along with Arka's statement that the other wheel moves down as the wheel which hits the bump moves up.

Now the wheel that moves down does not need to move down !!! That is the height of inefficiency in any system design, when components do stuff they are not supposed to do. Besides the wheel moving down when it needn't is unnessarily increasing traction when it doesn't need it (increased drag and tyre wear). Waste of power here !

Next visualise what happens when one wheel goes into a ditch. By Arka's logic the other wheel should move up ! Right ? Notice what happens. The other wheel running on flat surface ends up moving up when it really shouldn't. You lose traction on that wheel.

In summary the solid axle has a brain of its own and keeps reacting in a manner which is not called for leading to an over all compromise of traction. Wheels should react to road conditions and not on account of the behaviour of other suspension components.

In summary solid axles are inefficient when it comes to traction in a moving vehicle as the rigid connection interferes in the behaviour of wheels which in any case have no reason to react.

Any designer will confirm that a solid axle offers poor traction in a moving vehicle.

Which is why IFS is inherently superior to solid axles both offroad and onroad when it comes to traction.

That said solid axles are still used extensively as they are cheaper to manufacture and the load bearing quality of the axle is unrivalled as the shaft does only what it is supposed to do, turn and not bear other forces out. In a rock crawling situation the stressing of the drive shaft is immense and hence solid axles rule. You'd need a very high quality, expensive to mfg IFS to bear the forces of a rock crawl exercise. But should a mfg desire to they can build an IFS that can handle any rock. Solid axles also have the benefit of a fixed GC but this can be addressed in IFS systems too allowing for ample GC in most situations.

In IFS the shaft often is an integral link of the suspension setup and often gets loaded with forces other than what it is meant to handle namely the driveline force, which may stress the driveshaft more than a solid axle would. The implications of this additional stressing of the IFS driveshafts at best would be limited to material fatigue and failure. But it does not affect traction as negatively as the solid axle's behaviour does.

Over all offroaders are not only used for rock crawling where the solid axle will have an edge. For most applications IFS with its superior traction ability rules in my humble opinion.

To not come across as someone biased against solid axles I'd like to state that if a mfg wants to deliver a VFM offroader built to a cost target solid axles are the best option provided the offroader has limited application ie only for rock crawling. Bring in the wide gamut of surfaces an offroader handles an IFS still is the best option, albeit a costly one.

I will once again reiterate that I am not a technical person and am open to corrections if someone can explain my getting suspension fundamentals wrong.

Last edited by DKG : 18th February 2009 at 12:07.
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Old 18th February 2009, 12:31   #67
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Arka, you may be a knucle walking simian throw back but I am beginning to understand your point about the tie rods. Sprung or unsprung you still have weight to deal with. So how about bigger nastier tie rods?
What else can you do to make an IFS bullet proof?

Last edited by DirtyDan : 18th February 2009 at 12:35.
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Old 19th February 2009, 12:58   #68
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Default Sas !!!!

Quote:
Originally Posted by DirtyDan View Post
What else can you do to make an IFS bullet proof?
SAS - Solid Axle Swap, how better to make it bullet proof than scrap it and hope they become bullets.

Regards,

Arka

PS - I'm still stuck on Leaf-Springs let me progress to Solid Axle Coil Springs, by then maybe I will learn a few tricks about the IFS/IRS.
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Old 19th February 2009, 15:28   #69
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Default No IFS, No Buts Only JUTTS!!!!

Quote:
Originally Posted by DKG View Post
Let me explain what I understand of suspensions

A suspension primarily is meant to track road surfaces efficiently retaining traction at all times and dampen oscillations that get set forth in its components during action.

Lets go with the fact that in a solid axle setup the behaviour of one wheel affects the other wheel across the axle (whether directly or inversely is not the issue). Hope we are all in agreement on that.

Extrapolate this fact onto onroad behaviour. Lets say you are driving a car with a solid axle and one tyre hits a bump. Lets for discussion sake go along with Arka's statement that the other wheel moves down as the wheel which hits the bump moves up.

Now the wheel that moves down does not need to move down !!! That is the height of inefficiency in any system design, when components do stuff they are not supposed to do. Besides the wheel moving down when it needn't is unnessarily increasing traction when it doesn't need it (increased drag and tyre wear). Waste of power here !

Next visualise what happens when one wheel goes into a ditch. By Arka's logic the other wheel should move up ! Right ? Notice what happens. The other wheel running on flat surface ends up moving up when it really shouldn't. You lose traction on that wheel.

In summary the solid axle has a brain of its own and keeps reacting in a manner which is not called for leading to an over all compromise of traction. Wheels should react to road conditions and not on account of the behaviour of other suspension components.

In summary solid axles are inefficient when it comes to traction in a moving vehicle as the rigid connection interferes in the behaviour of wheels which in any case have no reason to react.
Hi DKG,

You explained the behaviour of Solid Axle and IFS very well but however you have missed out the role played by the Suspension in a SASetup.

1) When one wheel goes up the other comes down, if that wheel is in a ditch with no traction or completely in the air, the weight will be on the wheel which is up (for ideal plane) however if the plane is off camber the weight will shift to the wheel which is in the ditch.

The similar exercise on a ramp -- Ramp travel index - Wikipedia, the free encyclopedia

2) In a IFS vehicle When one wheel goes up the other remain independent, if that wheel is in a ditch with no traction or completely in the air, the weight will be on the differential As it it attached to the Chassis(for ideal plane) however if the plane is off camber the weight will still remain on the differential, to a to a higher degree, before shifting to the wheel which is in the ditch.

3) In the above case due to suspension pre-load and the weight bias on either sides of the suspension, the vehicle will bottom out.

To sum up, IFS relies largely on maintaining a contact patch for traction where as the SAS relies on vehicle weight for traction.

IFS will work better on washboard/corrugated road where axle/cross axle articulation is not the criteria.

The same applies on inclines (comparative statement)
1) The IFS compresses to conform to the slope, but is not able to maintain GC and under acceleration dives more.

On Down Slopes
1) The IFS Dives lifting off the rear

A Few IFS 4x4 in Action
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Old 19th February 2009, 17:20   #70
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Arka the benefits of solid axles even on account of traction due to weight apply primarily in very slow rock crawling or ditch offroading. I did mention the solid axle rules in such an environment.

Its when a faster pace is called for offroad that the solid axle loses out to IFS on the traction front. I'm sure you'll agree on this.

BTW did you ever feel your offroad ability was compromised owing to the IFS setup of a vehicle you drove?
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Old 19th February 2009, 17:48   #71
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Originally Posted by DKG View Post
Arka the benefits of solid axles even on account of traction due to weight apply primarily in very slow rock crawling or ditch offroading. I did mention the solid axle rules in such an environment.

Its when a faster pace is called for offroad that the solid axle loses out to IFS on the traction front. I'm sure you'll agree on this.

BTW did you ever feel your offroad ability was compromised owing to the IFS setup of a vehicle you drove?
I agree a faster paced OTR situation will be the Dakar or Baja 1000. IFS/IRS would be the order, however I present the...
Bowler Wildcat - WildcatDakar

I feel the modern Off-Roaders demand more driver input, rather being easy it gets more complicated.

OTR my worry with IFS is Suspension Dive & GC.

Regards,

Arka
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Old 20th February 2009, 16:32   #72
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LOL, I think you are a hermit in the Himalayas!
I need a good 4x4 to carry food and ammunition up to my cave.

Quote:
Originally Posted by DHABHAR.BEHRAM View Post
I for one feel that the one thing that will see a vehicle through a tight situation is sheer grunt / power and torque and also a beneficial power to weight ratio. A balanced driveline ratio will help. Please let me have your thoughts in this regard.
Mid chassis mounted engine with horizontally opposed cylinders for low profile and balanced weight over all four wheels. This has low center of gravity as well. Put somebody on it, 'ay BD?
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Old 20th February 2009, 17:30   #73
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Mid chassis mounted engine with horizontally opposed cylinders for low profile and balanced weight over all four wheels. This has low center of gravity as well. Put somebody on it, 'ay BD?
Dan the Porsche 959 is your vehicle . It had AWD and did well at the Paris Dakar rally way back.
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Old 31st March 2009, 11:44   #74
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Portal axles are another wrinkle in suspension design. Sir Alec and learned friend Brutus noted in a 4x4 tractor thread that some vehicles use both portal axles and alternate modes of transmitting drive to wheels. Here is a picture of a portal axle....with luck the blasted Team-bhp logo will not be branded into it making it unreadable....anyway, in such an application the axle does not bisect the wheel center lines. Instead the axle rides above the center line of the wheels and gives more ground clearance. This technique could be used in both IFS and solid axle design, I suppose. The concept is used by Unimog among others.
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Old 31st March 2009, 12:51   #75
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Here is a more radical portal axle concept. Note the ground clearance.

It also has hydraulic drive. Fluid is pumped by the motor to the wheels under high pressure. There are no shafts at all.

The diesel locomotive concept of using a diesel motor to generate electricity and then mounting electric motors on the wheels was tried by Mahindra 6 years ago on a test bed MM550. But, the electric motors kept fouling in wet off road conditions. During one such test in the rain a village woman and her cow allegedly received severe shocks standing near the jeep. In the litigation that followed the cow won and the woman's case is still pending.
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