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Old 1st October 2013, 13:23   #76
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Default Re: Low-Ratio

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Originally Posted by ex670c View Post
The Crawl Ratio of the Fortuner would be
4.313 X 2.566 X 3.965= 43.88:1

multiply it with the Torque in Kgm = 43.88 X 34.3 = 1505.12Kgm (Geared Torque)

Divide the vehicle weight by the Geared Torque = 1955kg/1505kgm= or 1.29:1 is the weight (Kerb) to geared torque ratio.

Please calculate this without low ratio. = 379kgm (Geared)

1955kg/379kgm = 5.1:1 Weight (Kerb) to Torque Ratio (geared)
Shucks ! I should have listened to Dad and taken Maths seriously in school.

Thank you for the explanation Arka - would deduce as mentioned before, on the 4X4 excursion thread, that LL in Fortuner everytime you truly go off road - and play around with the gears for suitable speed. And for slippery tarmac/hard surface due to water/rain/ice/sand etc - HL.
Will try that out for sure next time around...
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Old 1st October 2013, 14:42   #77
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Default Re: Low-Ratio

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Originally Posted by ex670c View Post
The Crawl Ratio of the Fortuner would be
4.313 X 2.566 X 3.965= 43.88:1
Thanks for the explanation Arka

Btw, I had made a mistake, the differential ratio should be 3.583 as per what I have found on the net (such info is not easily available). Which gives a crawl ratio of 39.65:1

If so, then geared torque should be 39.65*34.3 = 1360 kg.m

Then if I divide by low ratio of 2.566, then I get normal geared torque to be ~ 530 kg.m

Now (from just a theoretical point of view) if we could get ballpark figures of increased resistance (coefficient of friction) from different type of surfaces and the extra force required for inclined planes (different grades of slopes), then we could have a very approximate ready reckoner (a totally academic exercise) for force needed to get the vehicle moving in various scenarios e.g. at certain grades, surfaces, combinations etc.

Yes, I can see why 4H might not be sufficient in many cases.

Anyway, need to brush up on my Physics after years. Thanks for the maths logic behind qualitative statements.

Last edited by nilanjanray : 1st October 2013 at 15:07.
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Old 1st October 2013, 16:33   #78
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Default Surface Resistance

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Originally Posted by nilanjanray View Post
Now (from just a theoretical point of view) if we could get ballpark figures of increased resistance (coefficient of friction) from different type of surfaces and the extra force required for inclined planes (different grades of slopes), then we could have a very approximate ready reckoner (a totally academic exercise) for force needed to get the vehicle moving in various scenarios e.g. at certain grades, surfaces, combinations etc.
Hi Nilanjan,

Some information from winching force calculations.

These give an idea of surface and slope resistance.

http://www.benzworld.org/forums/unim...ks-guys-2.html

http://www.pangaea-expeditions.com/r...eet/index.html


Approximate Resistance Values
It is important to remember that these values are "approximate".
Surface Resistance
The exact makeup of mud, type of sand etc all affect the actual resistance. When calculating out resistance values, its always better to err on the side of caution.
Surface Type Resistance
Hard Surface 4% of vehicle weight
Grass 15% of vehicle weight
Gravel 20% of vehicle weight
Dry Sand 25% of vehicle weight
Clay Mud 50% of vehicle weight

Grade (slope) resistance:
Up-Slope (vehicle has to be recovered up a slope or grade)
15 degrees - add 25% of Vehicle Weight
30 degrees - add 50% of Vehicle Weight
45 degrees - add 75% of Vehicle Weight

Down-Slope
15 degrees - subtract 25% of Vehicle Weight
30 degrees - subtract 50% of Vehicle Weight
45 degrees - subtract 75% of Vehicle Weight


Regards,

Arka
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Old 1st October 2013, 17:22   #79
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Default Re: Using 4L for all offroading needs... good or bad?

The answer is simple. Low range is there for you to use. Use it freely and actually take advantage in off road situations.

If low 4 is engaged, the gear ratio becomes 2.46 : 1 it is good for climbs on snow, mud and sand, on a shorter steep climb maybe Low 3.

Low 4 is always more powerful than high 2nd in most vehicles.

It should never be done on hard surfaces but no matter if your vehicle is A?T or M/T judicius use of low range is always good.
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Old 2nd October 2013, 11:46   #80
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Post Re: Using 4L for all offroading needs... good or bad?

Dear Tejas, Samurai & Arka,

Thanks for the heads up on the use of LL gears during offroad sessions.

This has cleared quite a few doubts and misconceptions regarding the specific usage of HL & LL gear. I had my assumptions and theories based on the 1 day Toyota Fortuner Boot Camp.

Further on what Arka mentoned:
Quote:
The reason is once you engage 4H, you might as well engage 4L and work the Main Gear Box.
One quick question: Does HL slot in a secondary gearbox, whereas LL uses the Main Gear Box?
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Old 2nd October 2013, 12:41   #81
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Default Re: Using 4L for all offroading needs... good or bad?

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Originally Posted by Monaro CV8 View Post
Dear Tejas, Samurai & Arka,

Thanks for the heads up on the use of LL gears during offroad sessions.

This has cleared quite a few doubts and misconceptions regarding the specific usage of HL & LL gear. I had my assumptions and theories based on the 1 day Toyota Fortuner Boot Camp.

Further on what Arka mentoned:


One quick question: Does HL slot in a secondary gearbox, whereas LL uses the Main Gear Box?
They taught you to use High ratio in the Bootcamp? That was wrong. In the two that we did, our team never advocated that!

Coming to your query.

There are two basic things in your vehicle. One is the gear box (GB) and the other is the transfer case (TC).

The GB transfers the engine power to the prop shaft through a series of gears (as you call the main gear box).

What is does the TC do?

It does two main things:

- Transfer case locks the front and rear propeller shafts together.
- Transfer case provides for low range

When in high, it just locks the prop shafts together without providing the reduction gear range necessary to increase the torque.

In low range, the shafts are locked together and the torque is magnified.

In HL (High ratio with center dif locked) or LL (Low ratio, locked) it is great for straight ahead traction but can be disadvantageous in corners – propeller shaft bind up exerts load on drive train which is called the drive train windup.

Driving around in circles with a Part time 4WD transfer case engaged (HL or LL) on a traction perfect surface can cause severe driveline damage.
Symptoms include difficulty disengaging the 4WD transfer case.

Hope it helps.

Last edited by Tejas@perioimpl : 2nd October 2013 at 12:43.
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Old 2nd October 2013, 14:21   #82
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Default Re: Using 4L for all offroading needs... good or bad?

One issue that I face pretty often on inclined rocky trails (say in a Nilgiri estate) - shifting to 4L makes for relaxed climbing or going down. But usually the trails are curvy, and sometimes have good traction when the weather is dry. I am usually in two minds whether to risk drivetrain windup by using 4L or make the going up or coming down more difficult in normal 4H mode. I end up using 4L anyways, but this nagging worry about windup always remains.

Even when we see photos or videos of vehicles doing steep climbs on good traction rocky surfaces - where it is obvious that 4L has to be used - I wonder 'what about windup?'

Any thoughts on this?
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Old 2nd October 2013, 14:32   #83
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Default Re: Using 4L for all offroading needs... good or bad?

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Originally Posted by nilanjanray View Post
One issue that I face pretty often on inclined rocky trails (say in a Nilgiri estate) - shifting to 4L makes for relaxed climbing or going down. But usually the trails are curvy, and sometimes have good traction when the weather is dry. I am usually in two minds whether to risk drivetrain windup by using 4L or make the going up or coming down more difficult in normal 4H mode. I end up using 4L anyways, but this nagging worry about windup always remains.

Even when we see photos or videos of vehicles doing steep climbs on good traction rocky surfaces - where it is obvious that 4L has to be used - I wonder 'what about windup?'

Any thoughts on this?
Hi Nilanjan,

After using the vehicle in 4WD, its is advisable to drive the vehicle back and forth in a straight line, to unwind the Drive line Wind up, and then shift to 2WD (4H for AWD/full-time 4WD)

Regards,

Arka
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Old 2nd October 2013, 14:49   #84
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Default Re: Using 4L for all offroading needs... good or bad?

In case of center LSD equipped vehicles like Fortuner, just unlocking the LSD and driving should relieve the windup. Or just one wheel slipping or going up in air too would do the trick.

Last edited by Samurai : 2nd October 2013 at 14:51.
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Old 3rd October 2013, 11:44   #85
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Default Re: Using 4L for all offroading needs... good or bad?

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Originally Posted by Monaro CV8 View Post
One quick question: Does HL slot in a secondary gearbox, whereas LL uses the Main Gear Box?
Hi Monaro,

The sequence of drive/power is

Engine to Gear Box(via clutch)
to T-Case(via Hub Gear or Prop-Shaft)
to Differential (Via Prop-Shaft or Torque Tube)

The Transfer Case diverts the Drive to the Rear Axle, and Front Axle can be engaged on Demand = Part Time 4WD

The Transfer Case diverts the Drive to the Front AND Rear Axle, and the CENTER Differential Can be locked on demand to make is 4x4(HL/HLc) = Full-Time 4WD or AWD.

The Center Differential Lock, High and Low Ratios are engaged in the T-Case.

Ford 250 E128 T-Case Animation



Regards,

Arka
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Old 3rd October 2013, 17:06   #86
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Default Re: Using 4L for all offroading needs... good or bad?

One should also understand the relationship between torque and traction. Often people who drive CRDe vehicles think superior torque will help them in slush. It is not that simple.

This might provide some understanding: http://www.team-bhp.com/forum/4x4-te...ml#post3224688 (XD3P or MDI Motor for Mahindra CL / CJ340)
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Old 3rd October 2013, 17:47   #87
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Default Re: Using 4L for all offroading needs... good or bad?

I am no 4x4 person, but as per the mechanics here is what I understand:

- The acceleration (linear or angular) is directly proportional to force/torque times Mass/Moment of Inertia (or I as its called).
- If one presses the accelerator the engine revs faster. As per the speed Vs torque characteristic of the motor, it would deliver a rated torque to the wheels which should result in acceleration.

- Now how to get a higher acceleration ? Depending on speed (rpm)-torque of the motor one needs to get to that particular rpm (by flooring the pedal) of the motor which may result in higher torque (if the motor is rated accordingly) and hence a higher accelaration.

- Now the question is: Does that torque actually result in the required acceleration of the vehicle?
- That will also depend on the traction/friction of the surface. If the reaction of the surface (rolling friction) is not enough, power would lost.

I hope I remembered my physics correctly! Do correct me if I am wrong.
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