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View Poll Results: Diff locks or Articulation, what do you choose?
Diff locks - I think they are more important than articulation 21 61.76%
Articulation - With excellent articulation, diff locks are not really needed 13 38.24%
Voters: 34. You may not vote on this poll

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Old 23rd March 2010, 14:50   #31
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Originally Posted by ex670c View Post
Even the Gearbox and Divorced T-Case (where applicable) flexes, so do the cross-members.
Arka, T-Case i agree, due to the nature of its geometry it is bound to flex, but Transmissions AFAIK need to be restrained as far as possible, see the new generation trannys, they are supposed to flex only to the limit the resilient mounts allows, it needs to be mentioned that transmission members are castings and not forgings, hope this clarifies.

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Originally Posted by tsk1979 View Post
Well if the tires are grippy, then there is no case of losing traction.
No my friend,if you have the grippiest of tires and still if your tractive effort exceeds the road load forces (aerodynamic, rolling resistance, gradient loads), you are bound to loose traction, this is called as "Traction Limited Acceleration".

Spike
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Old 23rd March 2010, 14:54   #32
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Originally Posted by adc View Post
But if it is a more or less straight line in ice or mud with width available, with front locked there would be more traction A front locker with rear LSD is a good start - before one gets funds for getting the rear locked?
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Originally Posted by Jaggu View Post
So if i have a choice of having these 2 options in any of the vehicle, which will i pick up?! and hence the reply.
@ADC
If you have to add a Traction Aiding Device (LSD/Locker/MLD/Diff-Locks)

Add it to the Rear Axle First, then Front Axle.

If the you have to one LSD and one (Locker/MLD/Diff-Lock) then

LSD - Front Axle
Locker/MLD/Diff-Lock - Rear Axle

The Rear Axle does most of the work on Road and Off-Road.

Between an LSD & Locker, LSD Front & Locker Rear.
This is because the LSD fades with regular use, and since it does not lock up its better on the Front Axle, relieves the steering during OTRs. On Road The Front LSD can be negated with FWHubs.

Between Locker and Diff-Lock (Selectable ARB/OX/ECTED)
Locker Front and Diff-Lock Rear.
Since most of our driving is still on the road (95%) it is better to run an open diff. The Front Locker can be negated with FWHubs.

RedMM340, 4x4Addict and Shahnawaz Khan can give their personal preferences and suggestion and elaborate on this issue.

My Preference is LSD Front (with FWHubs) and Locker Rear.

Regards,

Arka

Quote:
Originally Posted by SPIKE ARRESTOR View Post
Arka, T-Case i agree, due to the nature of its geometry it is bound to flex, but Transmissions AFAIK need to be restrained as far as possible, see the new generation trannys, they are supposed to flex only to the limit the resilient mounts allows, it needs to be mentioned that transmission members are castings and not forgings, hope this clarifies.

No my friend,if you have the grippiest of tires and still if your tractive effort exceeds the road load forces (aerodynamic, rolling resistance, gradient loads), you are bound to loose traction, this is called as "Traction Limited Acceleration".
Hi Spike,

Thank for the info on Transmission members (Casting vs Forging)

Traction Limited Acceleration Please explain with charts/figures/diagrams
Please explain Gradeability and if possible the Figures for the M&M 4WD vehicles CJ340, MM540, Bolero et al.

Regards,

Arka

Last edited by Jaggu : 23rd March 2010 at 21:19. Reason: Back to back posts, use Multi Quote (Quote +) instead. Thanks
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Old 23rd March 2010, 17:40   #33
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Quote:
Originally Posted by ex670c View Post
Thank for the info on Transmission members (Casting vs Forging)

Traction Limited Acceleration Please explain with charts/figures/diagrams
Please explain Gradeability and if possible the Figures for the M&M 4WD vehicles CJ340, MM540, Bolero et al.
Arka, i will explain traction limited acceleration tonight (need to compose pics and write down some information), also i will tell you how to calculate gradeability for vehicles with equations. I will leave it to you for further interpolation of this data, please give me some time.

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Old 23rd March 2010, 19:29   #34
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Post Traction limited acceleration & Road Loads due to Gradients

Dear Arka,

As you know, the basic funda for torque calculations is Tractive force F= (torque available at wheels T / rolling radius of the Tyre r), hence if you measure the torque coming to wheels (chassis dynamo-meter, this give the torque/power at the wheels after all the power train and drive line losses), you can easily make out the tractive force available at the wheels. Now, there are basically 4 kinds of road loads that an automobile encounters 1. Aerodynamic loads 2. Load due to rolling resistance 3. Load due to gradients 4. Drawbar loads or loads due to hitching. If the sum of 1,2,3,4 is lesser than the Tractive force your tires will slip no matter how grippier (tread pattern, material composition) they may be, this is called as Traction limited acceleration. This means if you put a 600 BHP engine in a SUV it need not accelerate, it may skid/slide depending on the reactive forces available to its wheels. As long as the traction available from the ground is more than the tractive force wheels will not slip. I am attaching 2 pics for clarification on gradient loads and drawbar forces. Usually roads have gradients ranging from 1 to 12% occasionally they may reach very high values. Vehicles as a thumb rule are usually designed for 70% gradients which means (tan@=0.7 -> 35 degrees). Hope this clarifies.

Spike

P.S.-There is one more thing called as Power limited acceleration, the acceleration here depends on the maximum power that can be extracted from the power-train, this means minimizing power train losses.


Mods i don't know if this is the right thread to post this info, please move it to the appropriate section if deemed necessary.
Attached Thumbnails
Do Diff locks compensate for lack of articulation?-1.jpg  

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Last edited by SPIKE ARRESTOR : 23rd March 2010 at 19:32.
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Old 24th March 2010, 11:04   #35
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Originally Posted by SPIKE ARRESTOR View Post
Dear Arka,

As you know, the basic funda for torque calculations is Tractive force F= (torque available at wheels T / rolling radius of the Tyre r), hence if you measure the torque coming to wheels (chassis dynamo-meter, this give the torque/power at the wheels after all the power train and drive line losses), you can easily make out the tractive force available at the wheels. Now, there are basically 4 kinds of road loads that an automobile encounters 1. Aerodynamic loads 2. Load due to rolling resistance 3. Load due to gradients 4. Drawbar loads or loads due to hitching. If the sum of 1,2,3,4 is lesser than the Tractive force your tires will slip no matter how grippier (tread pattern, material composition) they may be, this is called as Traction limited acceleration. This means if you put a 600 BHP engine in a SUV it need not accelerate, it may skid/slide depending on the reactive forces available to its wheels. As long as the traction available from the ground is more than the tractive force wheels will not slip. I am attaching 2 pics for clarification on gradient loads and drawbar forces. Usually roads have gradients ranging from 1 to 12% occasionally they may reach very high values. Vehicles as a thumb rule are usually designed for 70% gradients which means (tan@=0.7 -> 35 degrees). Hope this clarifies.

Spike

P.S.-There is one more thing called as Power limited acceleration, the acceleration here depends on the maximum power that can be extracted from the power-train, this means minimizing power train losses.


Mods i don't know if this is the right thread to post this info, please move it to the appropriate section if deemed necessary.
Hi Spike,

Thanks for taking time and making such elaborate replies.

Waiting for the post on Power Limited Acceleration.

Regards,

Arka

PS - Mods, we should start a "Thus Spoke, Spike" thread for all our JEEP & Tech queries
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Old 24th March 2010, 11:52   #36
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Quote:
Originally Posted by SPIKE ARRESTOR View Post
Dear Arka,

As you know, the basic funda for torque calculations is Tractive force F= (torque available at wheels T / rolling radius of the Tyre r), hence if you measure the torque coming to wheels (chassis dynamo-meter, this give the torque/power at the wheels after all the power train and drive line losses), you can easily make out the tractive force available at the wheels. Now, there are basically 4 kinds of road loads that an automobile encounters 1. Aerodynamic loads 2. Load due to rolling resistance 3. Load due to gradients 4. Drawbar loads or loads due to hitching. If the sum of 1,2,3,4 is lesser than the Tractive force your tires will slip no matter how grippier (tread pattern, material composition) they may be, this is called as Traction limited acceleration. This means if you put a 600 BHP engine in a SUV it need not accelerate, it may skid/slide depending on the reactive forces available to its wheels. As long as the traction available from the ground is more than the tractive force wheels will not slip. I am attaching 2 pics for clarification on gradient loads and drawbar forces. Usually roads have gradients ranging from 1 to 12% occasionally they may reach very high values. Vehicles as a thumb rule are usually designed for 70% gradients which means (tan@=0.7 -> 35 degrees). Hope this clarifies.

Spike
Spike, wonderful info and explanation.

You have given us the formula, though we dont have dynometer here but at our own level we can calculate tractive force while tyre upgrades by suitable alterations to the axle ratios so that real performance does not suffer!

p.s Arka- Time for calculations your own style with different set of common tyre sizes and engines and torque figures. would be interesting!

Or can we start another thread " Calculate tractive force of your 4x4?"

Last edited by vinod_nookala : 24th March 2010 at 11:55.
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Old 24th March 2010, 17:18   #37
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Quote:
Originally Posted by ex670c View Post
@ADC
If you have to add a Traction Aiding Device (LSD/Locker/MLD/Diff-Locks)

Add it to the Rear Axle First, then Front Axle.
Yes, good input. locked rear diff will cover ~70% of your needs.

Quote:
If the you have to one LSD and one (Locker/MLD/Diff-Lock) then

LSD - Front Axle
Locker/MLD/Diff-Lock - Rear Axle
Again, a very good input and the way to go.

Last edited by khan_sultan : 24th March 2010 at 17:19.
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Old 24th March 2010, 19:04   #38
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Originally Posted by ex670c View Post
Thanks for taking time and making such elaborate replies.

Waiting for the post on Power Limited Acceleration.

PS - Mods, we should start a "Thus Spoke, Spike" thread for all our JEEP & Tech queries
Arka, Thanks, will post on "Power Limited Acceleration" soon, but where?
Quote:
Originally Posted by vinod_nookala View Post
Spike, wonderful info and explanation.

p.s Arka- Time for calculations your own style with different set of common tyre sizes and engines and torque figures. would be interesting!
Vinod, you are right that would be really interesting. I am attaching one more pic to make that calculations more simpler (this can be used as a thumb rule)
Attached Thumbnails
Do Diff locks compensate for lack of articulation?-1.jpg  


Last edited by SPIKE ARRESTOR : 24th March 2010 at 19:09.
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Old 24th March 2010, 19:59   #39
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Originally Posted by SPIKE ARRESTOR View Post
As you know, the basic funda for torque calculations is Tractive force F= (torque available at wheels T / rolling radius of the Tyre r), hence if you measure the torque coming to wheels (chassis dynamo-meter, this give the torque/power at the wheels after all the power train and drive line losses), you can easily make out the tractive force available at the wheels.
Spike, few months back I was trying to explain why it becomes difficult to climb a steep hill despite having a grippy tyre. I was writing by gut feel rather than any engineering know how. Can you comment on this.

Quote:
Originally Posted by Samurai View Post
If I understand the theory correctly, this is how it goes. Torque is nothing but the minimum force required to turn the wheels. When you slowly raise the throttle, if the wheels have traction, the wheel will start turning when enough torque is transmitted, and the vehicle starts moving. However, if you floor the pedal, lot more torque is sent to the wheels. This force may not be enough to suddenly move the vehicle faster up the incline, but certainly enough to overcome the traction between the tyre and terrain. It always takes the easier path.

If the hill gets steeper as you climb, you can raise the throttle slowly to match the increased need for torque, but soon you will overcome the traction of the tyres. Between the increasing difficult of lifting the vehicle up the incline and overcoming the traction of tyres, the latter become easier. Therefore, if you donít raise the throttle enough, you will stall the engine. If you raise the throttle enough, you will lose the traction and spin the wheels. This is when you need to switch tactics and use momentum. Experts feel free to jump in and correct me if I am wrong.
Link: http://www.team-bhp.com/forum/4x4-ex...ml#post1479755 (Monsoon Offroading/Trail-driving in Sakleshpur and Bisle Ghat)
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Old 24th March 2010, 21:03   #40
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Post Traction

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Spike, few months back I was trying to explain why it becomes difficult to climb a steep hill despite having a grippy tyre. I was writing by gut feel rather than any engineering know how. Can you comment on this.
Q1."Torque is nothing but the minimum force required to turn the wheels." However, if you floor the pedal, lot more torque is sent to the wheels." Ans-What you say till here is spot on, correct.
Q2."This force may not be enough to suddenly move the vehicle faster up the incline, but certainly enough to overcome the traction between the Tyre and terrain. It always takes the easier path."
Ans- Correct again, it needs to be mentioned here why you should raise the throttle for more torque? This is simply because your "Road Load due to Gradient" has increased (for more info please refer my earlier posts on road loads). So, in order to overcome that resistance, engine needs to develop more torque/power. Sharath your understanding is correct (i agree with the guy who complimented you for explaining things in such simple manner), I hope the funda is clear now.

In a nutshell what happens to the vehicle is determined by the resultant of the forces acting on the wheels. I will explain this theory with pics in much more detail tomorrow.

Spike

P.S. I will go through your write up also, i love reading them.

Last edited by SPIKE ARRESTOR : 24th March 2010 at 21:04.
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Old 24th March 2010, 21:38   #41
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Thank you very much Spike ji (rhymes with Spike Lee) for confirming my gut feel science. Looks like some of the engineering principles I learnt in college in the 80s somehow has remained in my sub-conscious mind.
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Old 24th March 2010, 23:34   #42
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[quote=Samurai;1801279]Spike, few months back I was trying to explain why it becomes difficult to climb a steep hill despite having a grippy tyre. I was writing by gut feel rather than any engineering know how. Can you comment on this.

It is a common-sense/gut feeling thing, but can also be derived mathematically.

Irrespective of the vehicle/tyres/torque at wheel etc.

Your traction depends on the weight of the vehicle (dunno what you call it, wheel-down force?).

While on the flats, the weight of your vehicle will be acting perpendicular to the surface. This is the case in which you will have max. Traction.

On a gradient (assume 45 deg. being taken head-on) the weight of the vehicle will be acting at 45 deg. (with respect to long. axis of vehicle). So for all practical purposes, only half the wheel down force will acting in the proper direction (i.e. towards the earth's core) <the other half will be merrily trying to drag your vehicle backwards>.

On a gradient, the wheel down force will be Tan A X Tmax and in this case, Tan 45 is 1/2. (I seem to forgetting alot of my basic triginometry, so am not 100% sure, Spike pls. help).

In any case, this is why momentum is required for long and steep inclines. Besides this, individual vehicle parameters definitely play a role, Gurus please enlighten us.

A question I wanted to ask is what role does diff-locking and articulation have in the above scenario? IMO Diff-locks will ensure that the torque and speed of each wheel is the same, ensuring maximum traction. What about articulation? Does the flexibility of the suspension mysteriously aid traction while on a gradient?

Am sorry I could not aid my statement with a nice Diagram, am really bad at drawing programs. Can someone please help? Also if someone can come up with drawings for the diff-lock/articulation effect it would really be super.

Thanks and best regards.
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Old 25th March 2010, 00:07   #43
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Originally Posted by '72 Bullet View Post
A question I wanted to ask is what role does diff-locking and articulation have in the above scenario? IMO Diff-locks will ensure that the torque and speed of each wheel is the same, ensuring maximum traction. What about articulation? Does the flexibility of the suspension mysteriously aid traction while on a gradient?
If it is an uniform plain surfaced steep hill offering same amount of traction to all tyres? Articulation and diff locks will have no effect.

And that was proved in the hill I am talking about. A SPOAed Gypsy with insane articulation, rear diff locks and mud tyres, could not overcome that hill using traction alone. It had to climb using momentum.
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Old 25th March 2010, 00:20   #44
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If it is an uniform plain surfaced steep hill offering same amount of traction to all tyres? Articulation and diff locks will have no effect.

And that was proved in the hill I am talking about. A SPOAed Gypsy with insane articulation, rear diff locks and mud tyres, could not overcome that hill using traction alone. It had to climb using momentum.

Interesting.. Was thinking that articulation may help the vehicle squat (or weight transfer in another way) and somehow help it.

Coming to the gut feeling topic, I think SPOA(or very high COG) is not really the way to go.

One reasoning is that as the gravitational (wheel down) force is going to work on the COG, the higher up it is, the more of it is going to be diverted into pulling you backwards. Does that sound right or is it just me? A diagram of course would help here. But it's just the gut-feeling that would make me prefer a vehicle with a lower stance on a steep climb.

We lean forward when we walk uphill, this helps us optimise traction as by changing our angle, we counter the force pulling us backwards.
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Old 25th March 2010, 04:10   #45
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Originally Posted by Samurai View Post
Spike, few months back I was trying to explain why it becomes difficult to climb a steep hill despite having a grippy tyre. I was writing by gut feel rather than any engineering know how. Can you comment on this.
This is why 'pump the throttle' technology was invented


@ Arka, Why LSD in the front when you can have the locker? Its only going to be called in when it is needed anyway (I'm not talking air lockers here, im referring to free wheeling hubs). I'm saying we as well as might go all out.

@ 72 bullet, Good articulation becomes a necessity if the uphill track is very uneven. A good example is the track that vinod put pictures of. Right?

Last edited by fiery enzyme : 25th March 2010 at 04:11.
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