4x4 - what is really useful setup?

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Fri 25 Jan 2008 12:58
4x4 - what is really useful setup? - movilogo
Nowadays nearly all SUV type vehicles claim that they are 4x4 while in fact they are 2WD with a viscous coupling(VC)/Limited Slip Diff (LSD) for on-demand traction on rear wheels (if front ones slip).

I understand that following layouts are possible.

[1] Standard FWD with open differential (most cars nowadays)
[2] Standard RWD with open differential (Mercedes, BMWs etc, Mazda RX8 probably has a rear diff lock)
[3] FWD with viscous coupling to drive RWs if FWs lose traction (many 4x4s like Panda 4x4, Toyota RAV4, BMW X5 etc.)
[4] Permanent 4WD with a central lockable differential (Land Rovers, Daihatsu Terios)
[5] Part time 4WD - usually RWD but transmission shaft can engage FWs manually. Should not be driven on paved roads.
[6] Permanent 4WD with lockable diffs on front/rear/center (Hummer has front & rear torsen diff and a lockable central diff)
[7] Any other configuration?

Now my question is whether VC/LSD cars (in most soft roader) have any off road ability at all. Or they are just marketing gimmick?

I personally never did any off roading :( but was surprised to see what some of the true 4WD cars are capable off!

Without a lockable diff, how well cars behave off road? Also, can a car go off road if it doesn't have low range gears?

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Fri 25 Jan 2008 13:03
4x4 - what is really useful setup? - Glaikit Wee Scunner {P}
My one and only experience is with a Toyota RAV4 3 door.
Toyota demo day on a course at Oulton Park. Steep muddy bomb holes were no problem as long as we kept moving.
Even when SWMBO refused to drive any further I took over when parked at the bottom of a hole and it climbed out impressively. I think the tyres were off road types but I was still very impressed.
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Fri 25 Jan 2008 13:35
4x4 - what is really useful setup? - SteVee
>>Also, can a car go off road if it doesn't have low range gears?<<

Yes, they certainly can.
On one very muddy course, I got out of a Land Rover V8 into a little suzuki (J410?).
The Landie was hard work - the only trouble the suzuki had was that the ruts left by numerous land rovers were a different width; but uphill, downhill, traversing; in fact everything was easy in the suzuki - and it was warm and comfortable.

The suzuki was there only because we were a Land Rover short (broken -again).
The owner showed me the reason for the suzuki's great performance - excellent off road tyres :-)
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Fri 25 Jan 2008 13:35
4x4 - what is really useful setup? - doctorchris
My Panda 4x4 has, as you state, FWD with a viscous coupling to the back axle to provide varying proportions of drive to the rear. It has no transfer box but a particularly low 1st gear is provided for off-road use. It has no locking diffs, indeed the cost and weight penalty of these would make the car uneconomical to produce. However, it has a substantial sumpguard and other vulnerable parts are sensibly tucked up out of danger.
I have taken this car off-road fairly seriously and the limiting factor to its performance was ground clearance rather than traction. The guys in Landies were surprised at how it performed and I'm told many photos were taken (though I don't have them).
Only this week, I took the Panda on the military road parallel to Hadrian's wall in treacherous conditions of snow, impacted into ice in places by other vehicles. At no time did I have any problems with traction though on a couple of occasions I had problems keeping the vehicle in a straight line, probably when I became too complacent about the conditions. Cornering also gave no problems.
I feel that this vehicle has good off-road potential and is not just a marketing gimmick.
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Fri 25 Jan 2008 14:04
4x4 - what is really useful setup? - movilogo
How do you understand when the rear wheels are actually providing traction in case of viscous coupling?


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Fri 25 Jan 2008 14:45
4x4 - what is really useful setup? - doctorchris
You have no actual indication that traction is being applied through the rear wheels but if you are pulling away on a slippery surface you feel the initial slip of the front wheels then feel traction kick in as the drive to the rear is provided. In practice you don't really need to know exactly where traction is going to as long as the car moves when and where you want it to.
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Sat 1 Jan 2011 13:38
4x4 - what is really useful setup? - tmmitzzie

Hi. I'm looking at buying a smallish car with 4 wheel drive capability, rather than a 4x4. I only need the extra traction in ice/snow conditions on roads and have no intention of taking it off-road. I'm a little confused though - you state that the panda does not have a transfer box. My knowledge in this area, to be honest, is close to nil but I thought that to deliver power to the rear wheels a transfer box is necessary - or am I missing something? I've also looked into the suzuki ignis 4grip which I'm led to believe has a viscous coupling too, and this car does have a transfer box. so now I'm even more confused.

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Fri 25 Jan 2008 14:35
4x4 - what is really useful setup? - Ruperts Trooper
There are degrees of off-road - on wet grass a soft-roader on all-season tyres will outperform a 2wd car on road tyres even if it's completely outclassed by a Defender on mud terrain tyres in a swamp.

As a generalisation, many soft-roaders are bought for the school run or towing a caravan and are often not taken off tarmac nor ever need 4wd engaging. In that sense, manufacturers are pandering to the fashion without having to worry about off-road capability.

For my part, a Subaru Outback meets all my requirements - 4wd varying from 90:10 to 50:50, limited slip rear diff, no low ratio but torque converter on the autobox allows smooth starts, 200mm ground clearance and all-season tyres - copes with muddy lanes in winter as well as damp grass and towing - oh yes, it also handles nicely at speed on tarmac!!

Edited by Ruperts Trooper on 25/01/2008 at 14:36

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Sat 1 Jan 2011 16:23
4x4 - what is really useful setup? - NARU

[1] Standard FWD with open differential (most cars nowadays).

Could be a LSD instead

[2] Standard RWD with open differential (Mercedes, BMWs etc, Mazda RX8 probably has a rear diff lock)

Again, could be LSD instead

[3] FWD with viscous coupling to drive RWs if FWs lose traction (many 4x4s like Panda 4x4, Toyota RAV4, BMW X5 etc.)

Works fine, but usually cuts in only after the front wheels have lost traction and the viscous coupling can fail. But perfect for towing caravans etc.

Honda have a different variant which uses an oil pump to transmit to the rear wheels which also seems OK.

[4] Permanent 4WD with a central lockable differential (Land Rovers, Daihatsu Terios)

The centre diff can be open or LSD, and still be lockable. The front and rear diffs can also be lockable depending upon the model.

[5] Part time 4WD - usually RWD but transmission shaft can engage FWs manually. Should not be driven on paved roads.

ie. No centre diff at all. The front and rear propshafts turn at the same speed. There's nothing to stop a difflock being fitted to the rear and front diffs

[6] Permanent 4WD with lockable diffs on front/rear/center (Hummer has front & rear torsen diff and a lockable central diff)

This is [4] with locking front and rear diffs.

[7] Any other configuration?

Traction control systems are increasingly capable. Lower spec landcruiser 120s come with a locking rear diff, the higher models come with a traction control system - but are no less capable IME.

My 4x4 (a land cruiser) has a torsen centre diff, which is also lockable.

You can lock the centre diff but I've never had to off road - it has a 4-wheel traction control system (Toyota's A-TRAC) - it's phenominal off road, even detecting when a wheel is in the air. I understand that in downhill mode it even controls the pressure going to each brake individually (rather than a simple ABS type antilock)!!!

More recent 4x4s from both Toyota and Landrover use terrain selection to set up the traction control parameters.

Edited by Marlot on 01/01/2011 at 16:38

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Sat 1 Jan 2011 18:22
4x4 - what is really useful setup? - dieseldogg

Sniff

Steyr Puch is a REAL 4*4 wit selectable "on the fly" hi-lo & 4*4 plus two locking diffs.

So all four wheels can be locked together & iffen ONE gets traction one is sorted.

But normall y runs in rear wheel drive only

Cheers

M

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Mon 3 Jan 2011 07:19
4x4 - what is really useful setup? - NARU

Just remembered a very unusual full time (ish) 4x4.

The very early (1949) landrover series 1s had the most unusual full time 4x4. Before the war, rover had a freewheel option on their cars, and they used it to transmit power to the front propshaft in the first year of production. So you had full time 4x4 (I believe no central diff) on normal driving, but on the over-run (eg. going downhill) the front wheels freewheeled). Not quite sure how it worked in reverse, but I believe the freewheel could be locked for offroad use.

It obviously wasn't that great as it was dropped very quickly.

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