Go Back   Team-BHP > Buckle Up > 4x4 & Off-Roading > 4x4 Technical


Reply
 
Thread Tools Search this Thread
Old 28th September 2010, 12:04   #136
Senior - BHPian
 
suman's Avatar
 
Join Date: Sep 2005
Location: Gurgaon
Posts: 4,589
Thanked: 256 Times
Default

Quote:
Originally Posted by tsk1979 View Post
How will 4H mode help in steep tarmac?
That's a strange question - more traction than 2wd mode that's all (even if the gearing is the same). That's the way I look at it.

And if I can see that it's a short stretch, it saves me the hassle of stopping & changing to 4L
suman is offline   Reply With Quote
Old 28th September 2010, 12:06   #137
BHPian
 
Join Date: Jul 2010
Location: New Delhi
Posts: 298
Thanked: 835 Times
Default

Quote:
Originally Posted by tsk1979 View Post
How will 4H mode help in steep tarmac?
4L will help on steep tarmac as you will not need to half clutch as on some stretches, esp when reversing, in normal drive there is not enough torque.
in 4H, there is no change of gearing rations
1st gear in 4H is as tall as 1st gear on 2H.
So if you are on tarmac, you would need to use 4 wheel drive only if its rained etc., and you are getting wheel spin.
If the tarmac is so steep that the vehicle is tending to stall, and you need to half clutch, then you can use 4L which effectively gives you lower gearing.
Hey Tanveer,

What you said does make sense technically. However the 4H does help sometimes, at the least that's what i feel. A particular example, which i can think of recently, is the climb to Hadimba temple in Manali. There are two hairpins on the climb (near Hotel Broadway Inn) which are quite steep. I've tried doing it in 2H however, i frequently stall if going at a lower speed. But in 4H i manage them quite easily. Maybe it's the increase in traction? Dunno.

Quote:
Originally Posted by tsk1979 View Post
Referring to question of harsh
1. 4H on dusty roads is fine, just do not cross 60kmph
Thanks, Never done that.
2. Even in 2H mode do not cross 60 if you have not reversed the vehicle after disengaging 4WD, as the hubs are still engaged, and at speed there is chance of damage
Always do that, @ reversing the vehicle to disengaged the hub locks
3. For very steep slopes(tarmac) if 1st gear does not provide enough pull, use 4L for a very short distance(for example hairpins). After that try to maintain speed so that you never fall below 1500rpm in first gear
Somehow i am still not convinced, 4H mode has helped me practically, or maybe it's just in my head
4. On Rohtang like climbs, the tarmac is severly broken. 4L can be used there as such terrain gives ample opportunity for slip. It will save your clutch as 8kmph on 1st gear 1000rpm may be too fast as you follow a slow moving truck. So instead of half clutching to proceed at lower spee, its always better to use 4L for a short distance, or if the grade is not steep and tarmac is good, fall back 4-5 car lengths.
Makes sense, however i use 4L only for VERY tricky situations, otherwise for Rohtang generally 4H suffices. Though this time 4L was engaged for the slush fest of a Rohtang
Replies in between marked in bold.
vardhan.harsh is offline   Reply With Quote
Old 30th September 2010, 16:15   #138
Senior - BHPian
 
ex670c's Avatar
 
Join Date: Nov 2004
Location: Chennai
Posts: 2,454
Thanked: 1,789 Times
Default Sotf

Quote:
Originally Posted by tsk1979 View Post
How will 4H mode help in steep tarmac?
Hi Tanveer,

4H will definitely help by providing traction, through the Live Front Axle, instead of 2 Wheels, 4 Wheels will carry the weight of the vehicle.

This is precisely one of the reasons the 4H in most vehicles is SOTF.

The Front Axle will Pull the weight, and the Rear Axle will Push the Weight.

Low Ratio will increase the Torque and Slow the Vehicle Down, as can be used in situation described by you.

Regards,

Arka
ex670c is offline   Reply With Quote
Old 1st October 2010, 09:58   #139
Team-BHP Support
 
tsk1979's Avatar
 
Join Date: Feb 2005
Location: New Delhi
Posts: 22,852
Thanked: 15,406 Times
Default

So lets say incline is so steep that I have to half clutch or the vehicle will stall, I can engage 4H and I will not need to half clutch.
The vehicle will not stall, I can slowly release clutch and drive normally?
tsk1979 is offline   Reply With Quote
Old 1st October 2010, 10:20   #140
Senior - BHPian
 
ex670c's Avatar
 
Join Date: Nov 2004
Location: Chennai
Posts: 2,454
Thanked: 1,789 Times
Default Half-Clutch

Quote:
Originally Posted by tsk1979 View Post
So lets say incline is so steep that I have to half clutch or the vehicle will stall, I can engage 4H and I will not need to half clutch.
The vehicle will not stall, I can slowly release clutch and drive normally?
Hi Tanveer,

Using Half-Clutch is bad technique in any situation. By Pressing the clutch you are trying to slow down the vehicle and at the same time accelerating to get to the Peak torque RPM.

It is better to use a Lower Gear (2nd-1st, 3rd to 1st or Hi-Ratio to Low-Ratio).

Most vehicles can handle most of the Slopes on the road in 1st Gear, if it cannot then, its advisable to shift into 4H or Low-Ratio(If Available).

Do you think a Truck Driver, driving up to Leh, would even consider using Half-Clutch technique, I have seen most drivers shift to the lower/lowest gear to make a steep climbs in the mountains.

Regards,

Arka
ex670c is offline   Reply With Quote
Old 1st October 2010, 10:45   #141
Team-BHP Support
 
Samurai's Avatar
 
Join Date: Jan 2005
Location: B'lore-Manipal
Posts: 22,042
Thanked: 13,490 Times
Default

Quote:
Originally Posted by tsk1979 View Post
So lets say incline is so steep that I have to half clutch or the vehicle will stall, I can engage 4H and I will not need to half clutch.
The vehicle will not stall, I can slowly release clutch and drive normally?
Tanveer, one of the things I learned via offroading is that you never have to half-clutch. If you stall in an incline, which happens a lot in offroading, how is half-clutch going to help you? If you can't climb in 1st gear, you won't make it in half-clutch either, that gives you even less torque. You just have to retry with better momentum.

When I stall, I simply slip out of gear and stay on brakes.

Even in traffic, if the traffic speed is slower than 1st gear idle speed, I come back to neutral and coast than use half-clutch.
Samurai is offline   Reply With Quote
Old 1st October 2010, 15:04   #142
Team-BHP Support
 
Jaggu's Avatar
 
Join Date: May 2004
Location: Bangalore
Posts: 17,491
Thanked: 6,768 Times
Default

Yes you don't get the torque, instead you waste your clutch and try to look for higher rpm's by half clutching. Instead move to a lower gear/ratio.

Swift D is a classic case, sometimes one gets stuck in inclines where even 1st or Reverse might not help. I prefer to move back and give it a try with higher momentum compared to half clutch, thanks to super sensitive clutch. So idea is ensure you attack the incline keeping the engine in the boil, turbo spool rpm.
Jaggu is offline   Reply With Quote
Old 1st October 2010, 15:20   #143
Senior - BHPian
 
Blue Thunder's Avatar
 
Join Date: Jul 2007
Location: Right here .
Posts: 1,630
Thanked: 328 Times
Arrow no transmission windup

Quote:
Originally Posted by tsk1979 View Post
...
2. Even in 2H mode do not cross 60 if you have not reversed the vehicle after disengaging 4WD, as the hubs are still engaged, and at speed there is chance of damage...
This will not cause damage, as it is in 2WD; the FWH not being disengaged means slightly additional load on the engine/steering, BUT no transmission wind-up.

Quote:
Originally Posted by vardhan.harsh View Post
... 2. Is it ok to use 4H mode for short very steep stretch (100m - 200m) or so...
4H for short steep stretches of straight road is fine; hairpin bends will cause undue stress in 4H/4L.


Quote:
Originally Posted by tsk1979 View Post
... if 1st gear does not provide enough pull, use 4L for a very short distance(for example hairpins)....
I would never try that in my vehicle...in a hairpin bend, in 4L , the stresses on the driveline will be enormous.

The effect of the driveline stresses may not show immediately.

Last edited by Blue Thunder : 1st October 2010 at 15:29.
Blue Thunder is offline   Reply With Quote
Old 1st October 2010, 15:54   #144
BHPian
 
Join Date: Jul 2010
Location: New Delhi
Posts: 298
Thanked: 835 Times
Default

Quote:
Originally Posted by Blue Thunder View Post
4H for short steep stretches of straight road is fine; hairpin bends will cause undue stress in 4H/4L.

I would never try that in my vehicle...in a hairpin bend, in 4L , the stresses on the driveline will be enormous.

The effect of the driveline stresses may not show immediately.
So is the crux never to use 4H/4L on hairpins? What does on do on very steep roads which have hairpin ?

The only solution that comes to my head is that to split the hairpin in straight edges, do each edge in either 4H or 4L and the shift to 2H to do the U-turn. That would be super-cumbersome :(.

Although i have noticed some "discomfort" to the vehicle while does U-turns in 4H mode. Somehow the turning radius increases marginally. Why does that happen ?
vardhan.harsh is offline   Reply With Quote
Old 1st October 2010, 16:12   #145
Team-BHP Support
 
tsk1979's Avatar
 
Join Date: Feb 2005
Location: New Delhi
Posts: 22,852
Thanked: 15,406 Times
Default

Quote:
Originally Posted by Samurai View Post
Tanveer, one of the things I learned via offroading is that you never have to half-clutch. If you stall in an incline, which happens a lot in offroading, how is half-clutch going to help you? If you can't climb in 1st gear, you won't make it in half-clutch either, that gives you even less torque. You just have to retry with better momentum.

When I stall, I simply slip out of gear and stay on brakes.

Even in traffic, if the traffic speed is slower than 1st gear idle speed, I come back to neutral and coast than use half-clutch.
Actually, I engage 4Low, so do not have to abuse clutch. 2WD vehicles have no option.
They depress clutch a bit, start revving to torque area(2200rpm), and then start releasing clutch.
Another scenario is a flyover traffic jam where traffic is so slow that you will stall.

But since it is an offroading thread, lets stick to vehicles with 4WD.
So if the stretch is too steep, and there is not enough space to build momentum, and you have adequate traction, shift to 1st gear in low ratio, and gently start climbing up, right?
4WD high will help you in climbing inclines if your wheels start spinning(low traction surface).
If its tarmac(proper road), and rear wheels are not slipping at all, will engaging 4WD high help in any way?
tsk1979 is offline   Reply With Quote
Old 1st October 2010, 16:22   #146
Distinguished - BHPian
 
SS-Traveller's Avatar
 
Join Date: Jan 2009
Location: New Delhi
Posts: 6,564
Thanked: 10,477 Times
Default

Quote:
Originally Posted by Jaggu View Post
...you waste your clutch and try to look for higher rpm's by half clutching.
Right! A howling engine with the clutch half-pressed is not going to make the car climb any better. In case one is really unable to take a car up a steep slope decorated with a sharp hairpin, the simple solution is to offload a couple of people; ask them to walk up the slope!

Taking an M-800 (carb model) to Gangotri and Badrinath, we'd faced this sort of challenge repeatedly.
Quote:
Originally Posted by vardhan.harsh View Post
So is the crux never to use 4H/4L on hairpins? What does on do on very steep roads which have hairpin ?
Quote:
Originally Posted by tsk1979 View Post
Actually, I engage 4Low, so do not have to abuse clutch. 2WD vehicles have no option.
If its tarmac(proper road), and rear wheels are not slipping at all, will engaging 4WD high help in any way?
Till today, at least in the Garhwal-Kumaon region, I've not yet come across a hard-tarmac steep-slope sharp-hairpin situation in real life requiring 4L engagement, which would leave me worrying about transmission windup if climbing up on 4L.

Plus, with a steep slope and weight transfer to the rear, the front wheels would find it easier to spin free and release windup.
SS-Traveller is offline   Reply With Quote
Old 1st October 2010, 16:27   #147
Team-BHP Support
 
tsk1979's Avatar
 
Join Date: Feb 2005
Location: New Delhi
Posts: 22,852
Thanked: 15,406 Times
Default

SS, I suggest you attempt rohtang pass, and get caught behind a slow moving truck etc., you will find rpms dropping to 1200(as the truck lumbers on at 10kmph), and then vehicle tending to stall.

At high altitudes(5200m+) also I have found that the engine loses quite a bit of power, and inclines which were doable become undoable, and hence the need for a lower ratio gear.
tsk1979 is offline   Reply With Quote
Old 1st October 2010, 16:28   #148
Senior - BHPian
 
suman's Avatar
 
Join Date: Sep 2005
Location: Gurgaon
Posts: 4,589
Thanked: 256 Times
Default

Quote:
Originally Posted by tsk1979 View Post
If its tarmac(proper road), and rear wheels are not slipping at all, will engaging 4WD high help in any way?
So you don't think that additional traction has any part to play at all?

I'm wondering if you've actually tried it at all or just theoretising I've tried it & have felt a marked difference after engaging 4H.

The other thing is, I can't figure why anyone would half clutch in a 4wd vehicle - what's the purpose of engaging the 4wd then? You engage, you release the clutch & then you go. It defeats the entire purpose if you half clutch, doesn't it?

EDIT: In your Rohtang example, you can engage 4H & go along without stalling.

Last edited by suman : 1st October 2010 at 16:30.
suman is offline   Reply With Quote
Old 1st October 2010, 16:44   #149
Team-BHP Support
 
tsk1979's Avatar
 
Join Date: Feb 2005
Location: New Delhi
Posts: 22,852
Thanked: 15,406 Times
Default

At rohtang some stretches are so steep that if you let rpm come below 1200 or so, vehicle can't pick up.
It stalls.
So either you rev to 2000rpm with clutch pressed, start releasing clutch, and start climbing or engage 4L and then easily climb. I do the latter.

Regarding 4H, I was climbing the last stretch to jalori pass in 4H due to slippery terrain(ice on road).
At a hairpin. a temp trax got stuck, I had to stop. It was very steep. I then tried starting from standstill, but the vehicle rpm started falling below 800. Clutch press saved stalling.
I shifted to 4L and could easily climb as the torque is tremendous.

EDIT: On my first ladakh trip, I still had the old ECU software. I faced a lot of trouble at chang La climb, and even more trouble at Wari La climb. Wari La has very nice tarmac in some sections, and I was apprehensive engaging the 4WD at the hairpins.
After the new ECU software, this problem has reduced, but still on higher passes, esp when road is very bad and you cannot maintain rpm above 1200, vehicle tends to stall.

Last edited by tsk1979 : 1st October 2010 at 16:52.
tsk1979 is offline   Reply With Quote
Old 1st October 2010, 16:53   #150
BHPian
 
Join Date: Jul 2010
Location: New Delhi
Posts: 298
Thanked: 835 Times
Default

So i take it from the conversation that it's NOT advisable to do U-turns with 4H/4L engaged on tarmac.

However it is ok to do U-turn in 4H/4L modes on dirt-tracks. Correct?
vardhan.harsh is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
OTR & Paragliding: Palakkad Off-Road Adventure's "Off-Road Extreme 2013" JeepCaptain 4x4 Excursions 7 2nd March 2013 12:45
Drift Techniques !! varun_patra Indian Motorsport 8 7th April 2010 14:50
Any new techniques for the old gashes Speedme Technical Stuff 3 12th January 2007 19:52
Launch techniques v1p3r Technical Stuff 29 9th July 2005 22:11
rally driving techniques manticore Indian Motorsport 29 26th May 2004 17:45


All times are GMT +5.5. The time now is 09:51.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks