[Samurai]

Originally Posted by nishkamm

One query though. Does the latest Thar (post Aug 2015) not have an automatically locking differential in the rear. How does it fare compared to the Trailhawk's mechanism of applying the brakes automatically and releasing them when required?

Ah, you are right. Since all my Thar experience is with pre-MLD models, it completely slipped my mind. My Bad!

Yes, the MLD will make a huge difference for Thar. When the difference between wheel speed exceed 100rpm or 1.6rps, the rear differential sends all the torque to the wheel with traction. Unlike Trailhawk it doesn't waste 1/2 the torque for braking. That's a major point for Thar over Trailhawk.

PS: I put a footnote in that post, reflecting the above info. Thanks a lot for pointing it out.

[Jaggu]

Originally Posted by psispace

Although a Thar would be fun to go off road with, the family wouldn't find it any fun. The only other similarly capable vehicles I can think of are the Force Gurkha and maybe to some extent the Duster AWD (properly modded). The former even has front and rear differential locks ! Though these cost only half as much as the Compass, they won't offer the same level of sophistication and comfort.

A friend has a duster 4x4 and we have taken it for pretty good offroading stuff, I would say it could do almost 60-70% of what my GV could do, so I would rate it close to Compass territory in Offroad performance.

[nishkamm]

Originally Posted by Samurai

Ah, you are right. Since all my Thar experience is with pre-MLD models, it completely slipped my mind. My Bad!

Yes, the MLD will make a huge difference for Thar with MLD. When the difference between wheel speed exceed 100rpm or 1.6rps, the rear differential sends all the torque to the wheel with traction. Unlike Trailhawk it doesn't waste 1/2 the torque for braking. That's a major point for Thar over Trailhawk.

I better correct the report. Thanks a lot for pointing it out.

Thank you Samurai. I drive a 2000 MM 550 Ex- Army. It does have a LSD in the rear and it keeps me out of most of the tricky situations .

[cool_dube]

Originally Posted by psispace

For those who haven't seen it, heres' an interesting comparison with the upcoming Renegade (in Trailhawk guise). Although its' two years old, its' still relevant.

Thanks for sharing this video. Quite interesting - when the Compass tried to get over the last obstacle (around 11:50 min into the video) and got stalled, both of the front wheels just lost power - neither of them was rotating at all!!! Why would that happen? Shouldn't at least one wheel spin? Or is it because of the electronic sensors : one of the front wheels loses traction, auto-braking kicks in slowing it down, power transmits to the other wheel which also might not have traction and as a result, is auto-braked as well, by the sensors. This leads to a cascading effect (sensors going into an infinite loop?!) wherein eventually both wheels are practically down to zero-power.

Looks like it was a similar situation for the rear wheels as well.

Edit: I am assuming here that since the Compass was in "4WD Lock", torque transfer to the front axle was happening all the time. So where was all this torque going, if the wheels are not spinning? Frying up the brakes, I guess

Experts - please comment!

[headers]

Nice information about the crawl. Sad to note that driver skill is being replaced by electronics, wheel sensors and computer algorithms!! :(

But this is exactly how I felt when our group did a offroad program for Mercedes a while ago!

The vehicle would do everything and the driver just had to turn the steering to point the wheels where one wanted the vehicle to go.

And of course, select the right mode!!

[Samurai]

Originally Posted by cool_dube

Thanks for sharing this video. Quite interesting - when the Compass tried to get over the last obstacle (around 11:50 min into the video) and got stalled, both of the front wheels just lost power - neither of them was rotating at all!!! Why would that happen? Shouldn't at least one wheel spin? Or is it because of the electronic sensors : one of the front wheels loses traction, auto-braking kicks in slowing it down, power transmits to the other wheel which also might not have traction and as a result, is auto-braked as well, by the sensors. This leads to a cascading effect (sensors going into an infinite loop?!) wherein eventually both wheels are practically down to zero-power.

Any intelligent system would try to preserve the drive-train. As the expert in the video said, it shut off power to all wheels. I think the ECU is smart enough to figure if the torque is not enough to overcome the obstacle.

If only one wheel had traction, only 1/4 torque is going to it. If that is not enough, the car won't move. The ECU can detect that car is not moving. In that case, I think ECU will shutdown power to all wheels instead of frying the brakes in other 3 wheels. Smart thing to do.

[cool_dube]

Originally Posted by Samurai

If only one wheel had traction, only 1/4 torque is going to it. If that is not enough, the car won't move. The ECU can detect that car is not moving. In that case, I think ECU will shutdown power to all wheels instead of frying the brakes in other 3 wheels. Smart thing to do.

So essentially this means that the clutch disengages automatically, even if the driver is flooring the throttle! If so, I'm afraid the system is too smart for my comfort What if it malfunctions one fine day and misinterprets the situation, leading to loss of power to all wheels even if the situation does not warrant it?

[Fortunerider]

Fantastic write up Samurai. Technical explanation was so simple and understandable.

[nishkamm]

Originally Posted by nishkamm

Thank you Samurai. I drive a 2000 MM 550 Ex- Army. It does have a LSD in the rear and it keeps me out of most of the tricky situations .

Hello Samurai, one question on the MLD.
Does it work even in 2wd mode in a Thar as it is in the rear differential?

[Samurai]

Originally Posted by nishkamm

Does it work even in 2wd mode in a Thar as it is in the rear?

Yeah, it will. I don't think it can be turned off.

[cool_dube]

Originally Posted by headers

Sad to note that driver skill is being replaced by electronics, wheel sensors and computer algorithms!! :(

Could not agree more but like it or not, that's where the world is headed, what with self-driving cars et al. I for one, like to be in control of what I am driving - heck, I have not been able to get myself to switch to an auto-transmission yet - and therefore, it will be some time before I relent to the changing times.

[Samba]

Excellent review Samurai. Rated 5*.
Was waiting for this review for a long time. Its 100% worth the wait.

Many offroaders might say, that the added electronic aids killed the fun. The car itself do whats required. So there is nothing left for the driver to show his/her driving skills.

I will say these cars are not fun for hard core OTR's but for touring, i will prefer these cars. The added electronics make the drive headache free. For example while driving on sand or slush, one might get stuck with an old school off-road vehicle if the driver is on a wrong gear or by giving wrong accelerator input.
Whereas these modern vehicles auto-correct the drivers mistake.

To learn off-roading, an individual must learn on an old school vehicle.

This review has drawn an excellent comparison with the Thar.

As i own a Duster AWD, it was fun, drawing a comparison between the Duster AWD and the Compass Trailhawk in terms of off-road capability. Sharing the data-

Duster AWD

The 1st gear ratio of the Duster AWD is 21.63.

Peak torque- 245 Nm @ 1750 RPM.

1.5L engine churning out 109 Bhp at 4,000 Rpm

6 speed MT

Ground clearance- 210 mm

Approach Angle - 30 Degree

Departure angle - 34 Degree

Brake traction control - Activates when ESP is switched off.

Hill descent control - Absent

Hill hold assist - Present

Modes- 2wd, Auto, 4wd Lock

BTC getting activated in Bhpian Papabravo's Duster AWD-

https://www.youtube.com/watch?v=M-7SvqMJFdU

Jeep Compass Trailhawk

The 1st Gear Ratio of the Compass TrailHawk is 20.35

Peak torque - 350Nm @1750-2500 Rpm.

2.0L engine churning out 170 Bhp at 3,750 Rpm

9 speed AT

Ground clearance- 205 mm

Approach Angle - 26.5 degree

Departure Angle- 31.6 Degree

Brake traction control - Present

Hill descent control - Present

Hill hold assist - Present

Modes- Auto, snow, sand, mud , rock (More specifically given for different driving conditions).

BTC getting activated in Compass Trailhawk-

https://www.youtube.com/watch?v=CkVy-iG1IgM

My hunch is, both the cars will fare pretty similar to each other in terms of off road ability.

[Sutripta]

My thoughts on the much talked about low range, or lack of it :-

As I think I've mentioned a couple of times before, if a crawler first has to substitute for a low range, one should also have a crawler reverse.
To me the main purpose of a low range is not to send humungous tree stump pulling torque to the wheels, but to send sufficient torque to the wheels to get vehicle moving at very low speeds in difficult conditions. Lets say the vehicular equivalent of inching. This is most often needed in rock crawling. Where you need the ultra low speed under power to control the vehicle and not damage it. And you need the torque for one or two wheels to climb up a boulder. Much like climbing a staircase. Essentially the engine is at idling, or fast idle (the manual fast idle control really shows its mettle here.) At these speeds the engine develops very little torque. More so if it is a turbo, as this is below where the turbo cuts in.

The other reason to have a traditional low range is that it means it has a XFer box. Which can easily accommodate a PTO. But I agree, these vehicles are not meant to work on a farm.

I am all for driver aids, as long as one has some control over these. Say driver aids by Android, not Apple.

Regards
Sutripta

[Guna]

Great report!

Originally Posted by Samurai

Traction happens to be the most important aspect of offroad driving. That is the sole reason why offroad vehicles have 4-wheel drive instead of 2-wheel drive. In a two-wheel drive vehicle with an open differential, if one tyre loses traction, that tyre starts spinning and the other tyre will stop turning. This is because an open differential sends the same amount of torque to both wheels. The tyre without traction demands just enough torque to spin the wheel, and that is the amount of torque sent to both the drive axles. That amount is not enough to move the tyre with traction, so it just stops. This puts very little load on the engine, which generates just enough torque to spin the tractionless wheel, and nothing more. To put this in numbers: let’s say 10 Nm of torque is required to overcome the traction of one of the tyres, then the engine will generate 20 Nm of torque, and the differential will send 10 Nm to each drive axle. It doesn’t matter if the engine is capable of generating 100 Nm or 200 Nm or 400 Nm of torque. The torque generated is entirely dependent on the load, which in turn, depends on the traction. The maximum torque generated is also limited by the engine capacity, that goes without saying.

Another way to explain the behavior of an open differential:
Power coming from the engine is split and sent to both left and right wheels through the differential(typically 50:50). But by design (it is actually a flawed design), the differential has the tendency to send more power to the wheel having least resistance. If the left wheel is on a tarmac and the right one on a loose soil, split may be come (left:right=20:80) and the right wheel starts to spin a little. If the right wheel is on slippery slush the split becomes 0:100 and the wheel is happily spinning without moving the vehicle.
Differentials are present to provide slightly different speeds the left and right wheels need to be doing while taking a turn. But it is amazing that often the same differential puts us in to trouble. How difficult will it be to come up with a differential design which allows only partial spinning (like in LSD)?

[1100D]

Originally Posted by Sutripta

if a crawler first has to substitute for a low range, one should also have a crawler reverse.

While I agree to everything you have written. Just a little note, that in case of the Trailhawk, the higher crawl ratio over the "Limited 4x4" is achieved through a higher axle ratio:-

Originally Posted by Samurai

Torque: The Trailhawk's axle ratio is 4.33, while it is 3.73 for the Limited 4x4. The first gear ratio is 4.7 for both 4x4 variants. .

So the crawl ratio difference holds in reverse too (but only by the percentage difference of the axle ratio's of the two variants - a meagre 16%)