DEFENDER2.NET - View topic - Puma Centre Diff Lock Max Speed?

↓ Advertise on Defender2 ↓

Home · FAQ · New Posts · My Posts · PMs · Search · Members · Map · Calendar · Profile · Donate · Register · Log In

Home > Puma (Tdci) > Puma Centre Diff Lock Max Speed?

Page 2 of 3

Print this entire topic ·

David128

Member Since: 31 Jan 2010
Location: Melbourne
Posts: 30

2015 Defender 110 Puma 2.2 CSW Zermatt Silver

David128 wrote:
I use the centre diff lock at any speed provided the surface is loose, the wheels are travelling at the same speed & I going in a straight line. Generally I do not go above 80 kmh on dirt roads. I have done this with all Land Rovers.

I feel safer with both axles getting equal drive as opposed to all drive going to one wheel on a poor road surface or bad corrugations.

That’s the problem with short answers – sometimes you cannot get away from a longer response

If I am travelling on any loose surface I will lock the centre diff and I will not deliberately travel above 80kmh. Interestingly, after the fact, my average for gravel roads (courtesy of a scan gauge) is around 55kmh. However there are two scenarios that come to mind (from a recent trip) that are different. One, I was travelling on a sealed road that became gravel without warning signs. Before I hit the gravel I released the accelerator and locked the CDL whilst on the tarmac and travelling in a straight line before I hit the gravel and then naturally decelerated to a safer speed without heavy braking. Two, here in Australia we have some roads where the sealed section is just one car wide with large gravel verges each side that are sometimes a big step down from the road. As I was coming to a wide sweeping corner a road train approached, so again I released the accelerator, locked the CDL and when the light came on drifted left to the dirt. In both of these scenarios I was probably doing more that 80, closer to 100 when I locked the CDL.

So why do I lock the CDL on loose surfaces? Without trying to be too technical, several reasons: that’s how I was trained by LR both here and in the UK; it aligns with my own experience and because I believe it is safer. If the CDL is not locked on gravel there is a risk that all available drive could go to the wheel that is easiest to turn reducing the effectiveness of the other wheels to push the vehicle in the direction required and maintain control resulting in an overall loss of driving force - although in reality it is never a 100% loss (ignoring ETC at the moment). A wheel becomes easier to turn when it looses traction (far more likely on gravel than sealed) such as reduced contact with road on corrugations, or being unweighted when cornering (often the rear tyre in the inside of the curve), or a patch of gravel acting as small marbles between wheel and road, or a combination etc.

Locking the CDL automatically splits the available drive equally to the front and rear axles. Yes you can still loose traction on one wheel on each axle but it is less likely to affect two wheels at the same time in the same way as affecting one. In addition the amount of drive that can be lost to any one wheel is half the total drive - not all the drive.

With ETC the risk is reduced further. With ETC and without the CDL locked it will brake the wheel that is easier to turn that is spinning faster. The only problem is that it will transfer the drive to the next easiest wheel to turn which is…….any one of the other three wheels and if you are really unlucky it may cause ETC to “hunt the spinning wheel” - a problem with Series II Discoverys that did not have the CDL. But with CDL locked ETC will “send” the drive to the other wheel on the same axle, “redistributing the drive” not loosing it.

With a stability control equipped vehicle the risk is reduced even further. But I still lock the CDL if it is possible in the vehicle I am using.

I may reduce the life of my tyres by 10-15% because sometimes it may not be as loose for the tyres as I expect but driving on gravel chips tyres and increases wear anyway. Tyre pressures are another factor for another day. Wear on my CDL has not been an issue. I also have a 300tdi Discovery that has not had a problem with this approach to gravel and it is now 12 years old.

Good discussion.

15th Sep 2010 5:48am

Naks

Member Since: 27 Jan 2009
Location: Stellenbosch, ZA
Posts: 2620

2010 Defender 90 Puma 2.4 SW Alpine White

AndrewS wrote:
No expert and each to their own but I dont see the advantage of locking the CD or any diff at high speeds.

I suggest you go do the Land Rover Experience course.

15th Sep 2010 6:10am

AndrewS

Member Since: 10 Apr 2007
Location: Hereford
Posts: 3707

2013 Defender 130 Puma 2.2 SW Rimini Red

Naks wrote:
AndrewS wrote:
No expert and each to their own but I dont see the advantage of locking the CD or any diff at high speeds.

I suggest you go do the Land Rover Experience course.

I have

up to instructor level 130's have feeling's as well you know

15th Sep 2010 4:50pm

Naks

Member Since: 27 Jan 2009
Location: Stellenbosch, ZA
Posts: 2620

AndrewS wrote:
I have up to instructor level

And you are telling ppl not to engage CDL off tar?

15th Sep 2010 6:41pm

JoostKenya

Member Since: 31 Jan 2010
Location: Naivasha
Posts: 9

That change in tyre road friction from tarmac to gravel is exactly the situation in which switching the diff lock can potentially make it dangerous. Especially if you start braking! If your front wheels are almost locking while approaching the gravel the front axle will start transferring a brake torque to the rear axle which could affect stability when cornering. This is also why ABS and stability control systems don’t like a fully locked differential. The drive line will disturb brake forces and lateral tyre forces.

In general I would say, if the road surface is nice smooth and gravel all the way, no problem to lock. If the surface is changing all the time, better not to lock. Driving 60, 70 or 110 doesn’t make any difference for the vehicle behaviour. The only difference at 110 the safety margin is much smaller because you have to react much quicker if things get instable.

There was a quote “all available drive could go to the wheel that is easiest to turn”. As a vehicle dynamics expert I don’t know the words “available drive”. I only know things like drive torque, longitudinal or lateral drive force, tyre slip or rotating velocity. I was trying to explain that with all the diffs open the drive torque from the engine is approximately the same on all four wheels. Unlocked the drive torque will definitely not go to one wheel. This is because of the design of a differential. The wheel with the lowest friction coefficient and load is going to spin first at the same drive torque as the other wheels (it is going to run at a higher slip). This is restricting the drive toque to all wheels. Usually this is not affecting stability very much because the lateral tyre force will usually be very low as well. Anyway if you drive already 80 in a high gear the Puma engine does not have enough power to spin a wheel. Even not on snow and ice.

Look at all those modern drive trains with active differentials, electronic diff control ( Audi+ Haldex, BMW X6, WRC rally cars) . They are made for maximum traction and stability. But the active control of their diffs is not about locking a diff. Full mechanical lock would be unpredictable in terms of the amount of torque transferred from one wheel to the other. The approach for those vehicles is more about putting a certain percentage to a specific wheel. Please know that an open diff has 50/50 torque distribution. With a locked diff the torque distribution is related to the tyre grip on the road at a specific wheel. It is difficult trying to explain stability of a vehicle without being technical but maybe you can imagine that if things are getting dependent on a factor from outside the vehicle (road surface) vehicle stability is at risk.

Another reason not to lock your diffs at higher speeds: Our Defenders have the benefit of full time four wheel drive. We should not try to imitate the inferior driving of all those Toyotas and Nissans with part time four wheel drive isn’t it?
Maybe this is why some drive training instructors tell you to lock??

If somebody can give me a reason and technical explanation why to lock I would be really interested.

Joost Joost
Defender 110 Puma 2.4
Tornado TD5 Racer
Defender 110 V8
Defender 136'' 300Tdi Safaricar
SIIA V8 Hybrid

16th Sep 2010 8:28pm

AndrewS

Member Since: 10 Apr 2007
Location: Hereford
Posts: 3707

Naks wrote:
AndrewS wrote:
I have up to instructor level

And you are telling ppl not to engage CDL off tar?

Am I

I dont think so

130's have feeling's as well you know

16th Sep 2010 8:37pm

Naks

Member Since: 27 Jan 2009
Location: Stellenbosch, ZA
Posts: 2620

JoostKenya wrote:
Our Defenders have the benefit of full time four wheel drive. We should not try to imitate the inferior driving of all those Toyotas and Nissans with part time four wheel drive isn’t it?

Not exactly - on most of the Jap brands, 4WD mode is equivalent to Defender with CDL locked.

Although a Defender is touted as full-time 4WD, you can get stuck if one wheel loses traction

I think David128 explained very well the benefits of having the CDL locked off tar - that's exactly how the LR instructor explained it to us during the LRE course.

Also, with CDL unlocked, if you happen to go airborne on a gravel road, you run the very high chance of flipping over when the last wheel touches the ground - as happened to a friend of mine.

16th Sep 2010 8:42pm

custom90

Member Since: 21 Jan 2010
Location: South West, England.
Posts: 19698

This is going to sound the most thick thing ever to you lot but because I'm fairly new to the Land Rover world and never needed to use DL how do you select it?

I have only used high and low box a. to keep things running smooth and b. because i wanted the crawl ability

16th Sep 2010 8:59pm

jst

Member Since: 14 Jan 2008
Location: Taunton
Posts: 7742

2011 Defender 110 Puma 2.4 USW Stornoway Grey

the lever that you are pushing fwd to engage low can also be pushed across to the left to engage the CDL. you can do this in high, neutral or low and on the move. If engaging CDL on the move then you should be travelling at a constant speed in a straight line. Cheers

James
110 XS Utility
130 Puma Station wagon/camper (in the making)
90 Puma Hardtop

16th Sep 2010 9:48pm

custom90

Member Since: 21 Jan 2010
Location: South West, England.
Posts: 19698

jst wrote:
the lever that you are pushing fwd to engage low can also be pushed across to the left to engage the CDL. you can do this in high, neutral or low and on the move. If engaging CDL on the move then you should be travelling at a constant speed in a straight line.

Cheers

I looked it up in the manual although it wasn't greatly helpful on this topic. It did however say not to engage difflock from neutral

16th Sep 2010 10:55pm

Naks

Member Since: 27 Jan 2009
Location: Stellenbosch, ZA
Posts: 2620

konabikes11 wrote:
Cheers I looked it up in the manual although it wasn't greatly helpful on this topic. It did however say not to engage difflock from neutral

that's odd, LR instructor told us to engage CDL when driving in a straight line, clutch in and then push lever to the left.

17th Sep 2010 8:17am

Setok

Member Since: 16 Jan 2009
Location: Helsinki
Posts: 417

Quote:
Although a Defender is touted as full-time 4WD, you can get stuck if one wheel loses traction

Yes, but this is also much less likely to happen as drive is distributed to all wheels which, I believe, leads to less torque per wheel (correct me if I'm wrong here) for the same movement. With many of the Japmobiles the front wheels are not helping to drive the vehicle at all, only turn it, so the rear wheels are left to deal with all the power.

17th Sep 2010 9:27am

jst

Member Since: 14 Jan 2008
Location: Taunton
Posts: 7742

you can engage it in neutral, high or low. Cheers

James
110 XS Utility
130 Puma Station wagon/camper (in the making)
90 Puma Hardtop

17th Sep 2010 9:31am

custom90

Member Since: 21 Jan 2010
Location: South West, England.
Posts: 19698

Hmmmm, I can't understand why the manual says that then

17th Sep 2010 11:53am

Ricky Chianese

Member Since: 15 May 2009
Location: Perth
Posts: 10

2008 Defender 110 Puma 2.4 SW Stornoway Grey

Jooste

Have I opened a can of worms with this thread?

Well I suppose my original question about the difflock and speed has been answered; the banter has raised more questions and interesting reading though!

So what is your opinion ?: On a reasonable dirt road at say 80Km/hr, is it better to have CD locked or unlocked? With CD locked, in theory, there will be less wear on the CD but somewhat reduced stability in some situations. I suppose landrover may be more worried about driveline wear than stability for warranty reasons. If this is so, it helps explain the CD use instructions in the manual.

What's your take on this? Why do today what you can put off until tomorrow?

17th Sep 2010 2:35pm

Page 2 of 3

All times are GMT + 1 Hour

Jump to

< Previous Topic | Next Topic >

Posting Rules

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum