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Old 17th February 2009, 10:53   #46
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Dear Arka - reply is as follows - NEF is NEF (SZ2600 block) and mHAWK is mHAWK (mHAWK block). Period. These are the best diesels that you can buy today for the class of vehicles they power. They are new engines. There is no commonality with XDP4.90/XD3P.

Times have changed, it's time to move on.

Best regards,

Behram Dhabhar
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Old 17th February 2009, 11:04   #47
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Originally Posted by DHABHAR.BEHRAM View Post
Dear Arka - reply is as follows - NEF is NEF (SZ2600 block) and mHAWK is mHAWK (mHAWK block). Period. These are the best diesels that you can buy today for the class of vehicles they power. They are new engines. There is no commonality with XDP4.90/XD3P.

Times have changed, it's time to move on.

Best regards,

Behram Dhabhar
the NEF249 send to South Africa which had turbo & Head troubles was a 2498cc block.

Its reassuring to know M&M can kit bash a engine and develop light-weight blocks, however the displacement and dry weight of the block tell me something more about the Genealogy of the Engine.

Regards,

Arka

Last edited by ex670c : 17th February 2009 at 11:05. Reason: typo
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Old 17th February 2009, 11:11   #48
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Originally Posted by ex670c View Post
Traction = Weight (of vehicle) X Contact Patch (of Tyre) X Co-efficient of Friction(Tyre & Surface)
Arka the traction of a vehicle improves with reduction in unsprung weight. I don't know if you are saying the same thing. Essentially the unsprung weight of solid axles is more than that of an IFS setup. Therefore IFS offers superior traction.

Perhaps you missed noting I was referring to a vehicle tackling an incline sideways (at times you need to do that). Here the weight does not shift back but you want each front wheel to independently track the surface.

On solid axles the behaviour of both wheels are dependent on each other. For traction that is detrimental.

The only benefit I see solid axles having is their inherent ability to handle greater loads and a constant in ground clearance. That said its an archaic setup and apart from monkeying around on rocks it has little value offroad especially if you intend travelling offroad at higher speeds or tackle trails where traction is paramount.

Last edited by DKG : 17th February 2009 at 11:17.
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Old 17th February 2009, 11:43   #49
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Default Traction and Weight

If you see the above equation

Traction = Weight X Contact Patch X Co-Efficient of Friction

Reduce any element and you reduce traction.

Un-sprung weight improves traction but affect handling, turning and cornering and ride quality.

on a side-slope/off-camber slope again the Solid Axle will provide better traction because

1) The entire vehicle weight (Sprung & un-sprung) are on each wheel.
2) In a Solid Axle the wheel which goes up, pushes the other wheel down
3) GC will be constant.
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Old 17th February 2009, 12:05   #50
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Since I regularly travel same stretch of bad roads in both solid axle & IFS 4WD vehicles, I can probably contribute my 2 cents.

Since most of these are familiar stretch of bad roads (there is no other kind around here), I do make full use of these high GC vehicles and drive fast. In certain rough stretches, the Jeep literally floats above the roads without any trace of traction. I simply have no control over the vehicle at this point. The same stretch on GV, at even higher speed the vehicle remains glued to the road and I don't lose traction. If such stretch occurs in a curve, I really slow down in the Jeep, but can easily turn in the GV without slowing down.

In my experience GV being a IFS 4WD is a much better trail or bad road vehicle, way superior to solid axle CJ340. But when it comes to rock crawling and offroad hill climbs, the roles reverse completely. On bad roads CJ340 can follow the GV, albeit much slowly. But when it comes to rock crawling, slush or hill climbing, CJ340 leads and GV can't even follow.
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Old 17th February 2009, 12:08   #51
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Quote:
Originally Posted by ex670c View Post
Traction = Weight X Contact Patch X Co-Efficient of Friction

Reduce any element and you reduce traction.

Un-sprung weight improves traction but affect handling, turning and cornering and ride quality.
Arka perhaps its the semantics that is confusing me but your asserting that unsprung weight improves traction seems contrary to what is widely considered as the bane of traction. Why else do we switch to lighter alloys? Its to reduce unsprung weight. Traction improves when the unsprung weight reduces. A lighter material used in any of the suspension parts reduces the mass that has to move up and down tracking undulating surfaces. When the mass is higher then it becomes increasingly difficult for a wheel to track the surface. Lighter radial tyres have an edge on nylons for this reason. As we all know the solid axle assembly is much heavier compared to the unsprung components of an IFS system

I seriously doubt that equation will hold true in conditions where a vehicle is moving. Perhaps for a stationary object your equation may apply. But in movement as the wheel tracks undulating surface you obviously want a lighter setup (laws of inertia, resistance to change direction, lighter the better).


Quote:
2) In a Solid Axle the wheel which goes up, pushes the other wheel down
I should think only if it is pivoted in the centre. 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
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Old 17th February 2009, 12:16   #52
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In certain rough stretches, the Jeep literally floats above the roads without any trace of traction. I simply have no control over the vehicle at this point. The same stretch on GV, at even higher speed the vehicle remains glued to the road and I don't lose traction. If such stretch occurs in a curve, I really slow down in the Jeep, but can easily turn in the GV without slowing down.
Very true. What is happening is the wheels on the Jeep are bouncing off the surface and losing traction. Much of this is on account of solid axle (heavy weight)

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In my experience GV being a IFS 4WD is a much better trail or bad road vehicle, way superior to solid axle CJ340. But when it comes to rock crawling and offroad hill climbs, the roles reverse completely
Spot on. There is no contest for the solid axle in extreme terrain offroading, ie rock crawling etc at slow speeds. This setup is far too robust and can take a lot of hammering.

As you rightly say its on the score of traction that solid axles lose out, which is critical at higher speed trail blazing or for that matter bad roads being handled at higher speeds. Basically any terrain where traction is paramount IFS rules. Any terrain where a fixed GC is important and robustness of mechanicals required then solid axles rule. So it depends on the use offroad
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Old 17th February 2009, 12:19   #53
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Dear all - there are benefits and shortcomings of both systems (leaf v/s IFS) and we can all go back and forth till the cows come home. The best thing to do is put a vehicle through its paces. 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.

Best regards,

Behram Dhabhar
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Old 17th February 2009, 12:40   #54
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Quote:
Originally Posted by DHABHAR.BEHRAM View Post
Dear all - there are benefits and shortcomings of both systems (leaf v/s IFS) and we can all go back and forth till the cows come home. The best thing to do is put a vehicle through its paces. 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.

Best regards,

Behram Dhabhar
I was actually enjoying reading the PROs & CONs. Are you biased, Mr.Dhabar ?

With my limited off-road experience, I feel with the right suspension, articulation etc etc, we will not get into that tight situation where grunt/power only has to see us through.
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Old 17th February 2009, 12:42   #55
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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.
So to overcome the limitations of either of the above suspension systems a good engine and driveline is essential?

But havent we a lot of times seen a better engineered vehicle with much lesser power bettering a far more powerful system?

The Gurkha thread comes to mind where there was talk about a 70 odd bhp powered Gurkha running rings around bigger machinery.

Can we have an optimised solution? Or is it asking for too much?

No argument on power to weight ratio front.
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Old 17th February 2009, 12:54   #56
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Originally Posted by ex670c View Post
Let me list out the disadvantages, we can then discuss each point to death.

1) Complex Construction
2) Variable Ground Clearance - Each wheel moves independently and pivot on a CV/Universal Joint.
3) Steering - Rack & Pinion - Weakest Link and wider tyres will rub on the chassis at lock-to-lock turns
4) Upgrades/Modifications - Because of the complex IFS we cannot Upgrade to Taller Tyres, Differential Ratios/LSD/Lockers, Winches.
1) A coil sprung rigid axle is usually more complex to engineer and manufacture compared to IS. There are far more joints and compromises have to be made with wheel geometry.

2) True, but it can be engineered such that lowest GC is still better than a rigid axle. This is the case on many off-road vehicles today.

3) R&P steering has nothing to do with IFS. Mahindra uses it because it is cheap and easy tp package. And R&P steering need not be weaker than any other type od steering.

4) Partially true for India as few aftermarket bits are available.
But changing the diff ratio/LSD etc has nothing to do with IFS.

If the IFS empoys torsion bars, then it will be relatively easy to acomodate winches and other heavy stuff to a degree by changing the preload on the springs. Torsion bars can be adjusted with a couple of spanners and a jack. On the other hand, it is very difficult to fine tune leaf springs. They always have to be removed and recambered/ springs added etc.

As far as bigger tyres are concerened, it has nothing to do with IFS again. It is a matter of tyre clearance (which happens to be very tight on modern vehicles either for packaging reasons or because dimwit stylists think tight wheelarches look good) and axle ratios.
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Old 17th February 2009, 12:57   #57
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Dear all - this is a great discussion. Thanks to all. Little light nimble vehicles even with less power use the advantage of FLOTATION to run rings around heavier machinery. That's how I drove 27 M&M GEs. Not every GE is a walk in the park, one was deadly, there were 30 vehicles stuck in 400 meters which we pulled out with one CJ340 and one Commander HT 4WD with winch. However, the need for sheer grunt just cannot be undermined.

I FEEL THAT IT IS A BALANCE OF BOTH WHICH WILL DELIVER RESULTS.

I have absolutely no bias of one over the other. The best thing to do would be to put the vehicle through its paces.

Best regards,

Behram Dhabhar

Last edited by DHABHAR.BEHRAM : 17th February 2009 at 12:59. Reason: add info
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Old 17th February 2009, 13:28   #58
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Default Traction

what is TRACTION ? and why do we need traction?

Light Weight Alloys Wheel Disc improve the unsprung mass considerably and a more suited to vehicles driving at higher speeds where handling and cornering also come into play.

In an IFS setup on corrugated or wash board, the Independent Arm move up and down (compression & rebound) independent of the vehicles weight (not fully independent this is the suspension preload), this allow the wheel to contact the road surface (contact patch) thereby increasing suspension.

Regards,

Arka
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Old 17th February 2009, 13:50   #59
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Quote:
Originally Posted by Alfa_Kilo View Post
1) A coil sprung rigid axle is usually more complex to engineer and manufacture compared to IS. There are far more joints and compromises have to be made with wheel geometry.

2) True, but it can be engineered such that lowest GC is still better than a rigid axle. This is the case on many off-road vehicles today.

3) R&P steering has nothing to do with IFS. Mahindra uses it because it is cheap and easy tp package. And R&P steering need not be weaker than any other type od steering.

4) Partially true for India as few aftermarket bits are available.
But changing the diff ratio/LSD etc has nothing to do with IFS.

If the IFS empoys torsion bars, then it will be relatively easy to acomodate winches and other heavy stuff to a degree by changing the preload on the springs. Torsion bars can be adjusted with a couple of spanners and a jack. On the other hand, it is very difficult to fine tune leaf springs. They always have to be removed and recambered/ springs added etc.

As far as bigger tyres are concerened, it has nothing to do with IFS again. It is a matter of tyre clearance (which happens to be very tight on modern vehicles either for packaging reasons or because dimwit stylists think tight wheelarches look good) and axle ratios.

1) Partially True (MB, JEEP, Toyota, Nissan & Land Rover) have managed to give Solid Axle Coil Spring before introducing IFS, never on their premier Off-Road models though.

2) There are 3 example, Tatras 81X series , Styer Pinzgauer and Toyota Mega Cruiser & Hummer. That is with Portal Axle/Reduction Hubs. The manufacturing cost goes up.

3) 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

Last edited by ex670c : 17th February 2009 at 13:52. Reason: addl. info
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Old 17th February 2009, 15:41   #60
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Hi,
I feel the way a vehicle is engineered for a particular use is what matters.we have seen the rally raid vehicles , almost all have independent suspensions.They go over rocks climb dunes,cross rivers , etc. all at very high speeds.even the M&M axe is with independent suspension.Of as pointed before the solid axle is cheaper and easier to repair.
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