part time 4wd vs full time 4wd

[Froon]

Hopefully someone can explain to me why my front tyres seem to chirp on full lock with my Jeep Grand Cherokee. (Runs rings around GU and 80 Series )

I took my front tail shaft out and it still did it. I am thinking it is because of the tight limited slip combined with a very tight turning circle.

I thought the Nissan limited slips were tight but they must have nothing on the Jeep or is it because of the different front steering design.

Sorry to go off topic.
Shane

I've got no idea where to start with this one... its all so very very wrong.

[lay80n]

Totally random though, the Dana solid axles under your jeep have uni joints, not CV's. So just like in your driveshafts they have an acceleration and deceleration phase. Maybe a possibility. Or it could be the ackerman angle is not perfect, making the tyres scrub, or it could be the toe-in/toe out variation on the wheel alignment. There may be a million and one things. Many cars will start to chirp/scrub the edges of tyres at full lock.

Layto....

[RN]

After 2 high performance front wheel drive road cars I can tell you exactly why I drive a full time 4WD (STi WRX) It's as fast and sticky on a wet road than a front wheel drive in the dry.

Steve.

Fast and Sticky.

2 things full time 4WD's are not.

AWD's, well, that's a whole other kettle of fish

AWD and 4WD. Isn't the official difference that AWD does not have an option for low gearing via the transfer case, whilst 4WD do.

Full time 4WD have a centre diff, Part time don't???

My mate has had GQ and GU Nissan Patrols and has just purchased a L/Cruiser V8 T/T diesel. He reckons he will never purchase a part time 4WD again due to the stability and traction he gets out of the Toyota.

When he had the Nissans, he would whack it down to 4WD if the bitumen road was wet but realises that he would have been loading up his transfer case in doing so and wonders why he never broke one.

[Suspension Stuff]

Totally random though, the Dana solid axles under your jeep have uni joints, not CV's. So just like in your driveshafts they have an acceleration and deceleration phase. Maybe a possibility. Or it could be the ackerman angle is not perfect, making the tyres scrub, or it could be the toe-in/toe out variation on the wheel alignment. There may be a million and one things. Many cars will start to chirp/scrub the edges of tyres at full lock.

Layto....

I spoke to Hammond 4WD (Jeep Specialist) about it and they say it's normal because it has a tighter turning circle and different design. It's normal isn't a good enough explanation for me though.

Shane

[jessie928]

FWIW - I use them all. 2wd most of the time on-road, "full time" 4wd occasionally in wet weather or on high speed dirt, rarely use "part time" 4wd (locked centre diff) in high range, but centre diff locks automatically in low range.

gotta love super select

yeah, thats one thing ( the only thing) that i like about the pahero

[jessie928]

After 2 high performance front wheel drive road cars I can tell you exactly why I drive a full time 4WD (STi WRX) It's as fast and sticky on a wet road than a front wheel drive in the dry.

Steve.

Fast and Sticky.

2 things full time 4WD's are not.

AWD's, well, that's a whole other kettle of fish

AWD and 4WD. Isn't the official difference that AWD does not have an option for low gearing via the transfer case, whilst 4WD do.

Full time 4WD have a centre diff, Part time don't???

My mate has had GQ and GU Nissan Patrols and has just purchased a L/Cruiser V8 T/T diesel. He reckons he will never purchase a part time 4WD again due to the stability and traction he gets out of the Toyota.

When he had the Nissans, he would whack it down to 4WD if the bitumen road was wet but realises that he would have been loading up his transfer case in doing so and wonders why he never broke one.

he never broke anything because ita s patrol

[Suspension Stuff]

After 2 high performance front wheel drive road cars I can tell you exactly why I drive a full time 4WD (STi WRX) It's as fast and sticky on a wet road than a front wheel drive in the dry.

Steve.

Fast and Sticky.

2 things full time 4WD's are not.

AWD's, well, that's a whole other kettle of fish

AWD and 4WD. Isn't the official difference that AWD does not have an option for low gearing via the transfer case, whilst 4WD do.

Full time 4WD have a centre diff, Part time don't???

My mate has had GQ and GU Nissan Patrols and has just purchased a L/Cruiser V8 T/T diesel. He reckons he will never purchase a part time 4WD again due to the stability and traction he gets out of the Toyota.

When he had the Nissans, he would whack it down to 4WD if the bitumen road was wet but realises that he would have been loading up his transfer case in doing so and wonders why he never broke one.

he never broke anything because ita s patrol

No argument from me. The Patrol is good for a beginner, just put on some 33's, a small lift and drive it.

[jessie928]

After 2 high performance front wheel drive road cars I can tell you exactly why I drive a full time 4WD (STi WRX) It's as fast and sticky on a wet road than a front wheel drive in the dry.

Steve.

Fast and Sticky.

2 things full time 4WD's are not.

AWD's, well, that's a whole other kettle of fish

AWD and 4WD. Isn't the official difference that AWD does not have an option for low gearing via the transfer case, whilst 4WD do.

Full time 4WD have a centre diff, Part time don't???

My mate has had GQ and GU Nissan Patrols and has just purchased a L/Cruiser V8 T/T diesel. He reckons he will never purchase a part time 4WD again due to the stability and traction he gets out of the Toyota.

When he had the Nissans, he would whack it down to 4WD if the bitumen road was wet but realises that he would have been loading up his transfer case in doing so and wonders why he never broke one.

he never broke anything because ita s patrol

No argument from me. The Patrol is good for a beginner, just put on some 33's, a small lift and drive it.

the simple things in life, are often the best my friend..

Jes

[Suspension Stuff]

Fast and Sticky.

2 things full time 4WD's are not.

AWD's, well, that's a whole other kettle of fish

AWD and 4WD. Isn't the official difference that AWD does not have an option for low gearing via the transfer case, whilst 4WD do.

Full time 4WD have a centre diff, Part time don't???

My mate has had GQ and GU Nissan Patrols and has just purchased a L/Cruiser V8 T/T diesel. He reckons he will never purchase a part time 4WD again due to the stability and traction he gets out of the Toyota.

When he had the Nissans, he would whack it down to 4WD if the bitumen road was wet but realises that he would have been loading up his transfer case in doing so and wonders why he never broke one.

he never broke anything because ita s patrol

No argument from me. The Patrol is good for a beginner, just put on some 33's, a small lift and drive it.

the simple things in life, are often the best my friend..

Jes

True, like Cornflakes.

I do rate the Patrol higher for most people but I like more comfort, in fact I need more comfort for a pinched nerve in my neck. Anyone want to buy a 98 GU TI low K's. Priced at $19,900 but open to offers.

Shane

[Steve F]

Totally random though, the Dana solid axles under your jeep have uni joints, not CV's. So just like in your driveshafts they have an acceleration and deceleration phase. Maybe a possibility. Or it could be the ackerman angle is not perfect, making the tyres scrub, or it could be the toe-in/toe out variation on the wheel alignment. There may be a million and one things. Many cars will start to chirp/scrub the edges of tyres at full lock.

Layto....

The Grand Cherokee runs CV's not Unis, would make sense otherwise though as I can get this in my Cherokee (Running Unis) on very tight turns.

And for the Poll, I have both in the Cherokee but vary rarely bother running in fulltime on the road as it's a Jeep not a sports car and handles just fine in 2WD even in the wet as long as I remember that

Cheers
Steve

[jessie928]

AWD and 4WD. Isn't the official difference that AWD does not have an option for low gearing via the transfer case, whilst 4WD do.

Full time 4WD have a centre diff, Part time don't???

My mate has had GQ and GU Nissan Patrols and has just purchased a L/Cruiser V8 T/T diesel. He reckons he will never purchase a part time 4WD again due to the stability and traction he gets out of the Toyota.

When he had the Nissans, he would whack it down to 4WD if the bitumen road was wet but realises that he would have been loading up his transfer case in doing so and wonders why he never broke one.

he never broke anything because ita s patrol

No argument from me. The Patrol is good for a beginner, just put on some 33's, a small lift and drive it.

the simple things in life, are often the best my friend..

Jes

True, like Cornflakes.

I do rate the Patrol higher for most people but I like more comfort, in fact I need more comfort for a pinched nerve in my neck. Anyone want to buy a 98 GU TI low K's. Priced at $19,900 but open to offers.

Shane

you need a pahero


JEs

[Suspension Stuff]

I'm really happy with the Jeep Grande Cherokee because it is more comfortable then a Patrol, handles better, flexes better, fits into carparks without having to reverse back and is more enjoyable to drive.

The draw backs are there though. Not as strong as a Patrol in a lot of areas and can't fit as much gear in it.

Series 1 Rangie's are too dated. Disco Series 2 was a serious contender but I hate the high roofs. Could do a chop of the roof and will do if my Jeep breaks too much. I would have to strengthed the Disco 2 up a lot also.

Shane

[Hekta]

FWIW - I use them all. 2wd most of the time on-road, "full time" 4wd occasionally in wet weather or on high speed dirt, rarely use "part time" 4wd (locked centre diff) in high range, but centre diff locks automatically in low range.

gotta love super select

FTW

[dogbreath_48]

Harder to lock brakes in a full time 4WD, is it not?

[KiwiBacon]

Harder to lock brakes in a full time 4WD, is it not?

Still easily achievable, but it may make it harder to lock individual wheels due to the rotating mass.

[cloughy]

Harder to lock brakes in a full time 4WD, is it not?

And these are the people voteing

[dogbreath_48]

Harder to lock brakes in a full time 4WD, is it not?

And these are the people voteing

I didn't vote The question wasn't specific enough.

If one wheel is locked, then other wheels will be forced to change speed (i.e. they may be required to break traction) - hence that wheel may be less likely to lock. Obviously locking all four wheels will take no more or less effort compared to a part time 4x4.

My thinking may be way off though - i'd happily stand corrected if someone can explain it better

I also don't think a full time 4x4 drives much better in the dirt (center diff open), than a rear-drive 4x4. Personal opinion though - possibly because i've mostly driven part time 4x4's.

[lay80n]

Totally random though, the Dana solid axles under your jeep have uni joints, not CV's. So just like in your driveshafts they have an acceleration and deceleration phase. Maybe a possibility. Or it could be the ackerman angle is not perfect, making the tyres scrub, or it could be the toe-in/toe out variation on the wheel alignment. There may be a million and one things. Many cars will start to chirp/scrub the edges of tyres at full lock.

Layto....

The Grand Cherokee runs CV's not Unis, would make sense otherwise though as I can get this in my Cherokee (Running Unis) on very tight turns.

And for the Poll, I have both in the Cherokee but vary rarely bother running in fulltime on the road as it's a Jeep not a sports car and handles just fine in 2WD even in the wet as long as I remember that

Cheers
Steve

Learn somthing new every day, though they still used uni's. Though the other ideas i floated are still porbably close. Many cars will start to scrub a bit at full lock, and there quite a few differnt variables related to it.

Layto....

[dogbreath_48]

On 2nd/3rd/4th/5th thoughts, i think i do stand corrected. Serves me right for trying to think.

But don't at me in future cloughy, or i'll get all internet-tough-guy on ya

edit: on 6th thoughts, i'm still not sure.

[bad_religion_au]

As Dougal said - no difference to economy. Anyone who says otherwise probably thinks hiclones give better economy too.

i dont' know about this at all. every gear mesh causes drivetrain loss. drivetrain loss = less power making it to the wheels for every litre of fuel burnt.

everything i've ever read about AWD cars states that they have a higher drivetrain loss than RWD counterparts (that AWD HSV, and the Turbo territory spring to mind as cars that are directly comparable to a RWD counterpart).

your not just churning the diff oil, your keeping the whole front drivetrain spinning, from output shaft to stub axle on the CV. something that a part timer ISN'T doing.

[KiwiBacon]

i dont' know about this at all. every gear mesh causes drivetrain loss. drivetrain loss = less power making it to the wheels for every litre of fuel burnt.

everything i've ever read about AWD cars states that they have a higher drivetrain loss than RWD counterparts (that AWD HSV, and the Turbo territory spring to mind as cars that are directly comparable to a RWD counterpart).

your not just churning the diff oil, your keeping the whole front drivetrain spinning, from output shaft to stub axle on the CV. something that a part timer ISN'T doing.

If you're putting a vehicle on a 2 wheel dyno then of course it's going to show more power, it's not accelerating the front wheels. But when you're driving you are and you are with a 4wd on a 4 wheel dyno.

The steady state (i.e. flat road cruising) difference is only the drag lost in the bearings and oil in the front diff. The front wheels are still turning, you're putting half the power through the back wheels and half through the front.
When accelerating, yes you've got more rotating mass to spin up. But you've also got more traction. When you've got enough power to spin up 2 wheels then 4 wheels driving gives you faster acceleration.

My original point was that no-one had quantified the fuel economy loss between a part time 4wd with the hubs out and a fulltime 4wd. It's easy to find vehicles which have fulltime 4wd and 2wd variations, but that's not the comparison we want.

A hilux in 2wd can get stuck on wet grass.

[vSAHARAx]

A hilux in 2wd can get stuck on wet grass.

Simple, get out flick the hubs in, select 4H and continue.

And who ever is too lazy to do that or winge about it, Then by the sounds of it they need all the exercise they can get!

[bad_religion_au]

If you're putting a vehicle on a 2 wheel dyno then of course it's going to show more power, it's not accelerating the front wheels. But when you're driving you are and you are with a 4wd on a 4 wheel dyno.

The steady state (i.e. flat road cruising) difference is only the drag lost in the bearings and oil in the front diff. The front wheels are still turning, you're putting half the power through the back wheels and half through the front.
When accelerating, yes you've got more rotating mass to spin up. But you've also got more traction. When you've got enough power to spin up 2 wheels then 4 wheels driving gives you faster acceleration.

My original point was that no-one had quantified the fuel economy loss between a part time 4wd with the hubs out and a fulltime 4wd. It's easy to find vehicles which have fulltime 4wd and 2wd variations, but that's not the comparison we want.

A hilux in 2wd can get stuck on wet grass.

power output at the wheels measured on a 4wheel dyno in AWD is still less than the same engined 2wd.

no one is arguing the increase in traction... more the economy loss.

the power lost through the bearings may be significant, considering your counting all that loss through the Uni's and everything. However, no gearing is 100% efficient in transmitting power. that extra diff is chewing some power out, converting it to heat in the front diff oil.


BUT most driving involves accellerating fairly often, so greater rotating mass = more load on motor = more fuel use.

[KiwiBacon]

power output at the wheels measured on a 4wheel dyno in AWD is still less than the same engined 2wd.

Of course it is, an AWD has a more complex drivetrain. But we need comparisons of fulltime 4wd and part time 4wd. AWD vs 2WD comparisons will not help us.

[bad_religion_au]

power output at the wheels measured on a 4wheel dyno in AWD is still less than the same engined 2wd.

Of course it is, an AWD has a more complex drivetrain. But we need comparisons of fulltime 4wd and part time 4wd. AWD vs 2WD comparisons will not help us.

why??? a part time 4wd is a 2wd when driven on road when it comes to economy figures.

i'm not disputing complexity, traction gains or anything else, JUST the claim that AWD's/full time 4wd don't use more fuel on the road.

[cloughy]

power output at the wheels measured on a 4wheel dyno in AWD is still less than the same engined 2wd.

Of course it is, an AWD has a more complex drivetrain. But we need comparisons of fulltime 4wd and part time 4wd. AWD vs 2WD comparisons will not help us.

why??? a part time 4wd is a 2wd when driven on road when it comes to economy figures.

i'm not disputing complexity, traction gains or anything else, JUST the claim that AWD's/full time 4wd don't use more fuel on the road.

I don't think you get he's not really disputeing that, just pointing out its miniscule and not worth giving a fark about

[ISUZUROVER]

As Dougal said - no difference to economy. Anyone who says otherwise probably thinks hiclones give better economy too.

i dont' know about this at all. every gear mesh causes drivetrain loss. drivetrain loss = less power making it to the wheels for every litre of fuel burnt.

everything i've ever read about AWD cars states that they have a higher drivetrain loss than RWD counterparts (that AWD HSV, and the Turbo territory spring to mind as cars that are directly comparable to a RWD counterpart).

your not just churning the diff oil, your keeping the whole front drivetrain spinning, from output shaft to stub axle on the CV. something that a part timer ISN'T doing.

OK - how about empirical testing???

Many years ago I had a PT 4x4 (Land Rover) with free wheeling hubs. Whenever I engaged the FWHs - the car felt more sluggish, but that was only for the first few hundred m until everything was re-lubricated.

I did a few fuel economy tests with the FWH free and locked (locked is really equivalent to a full-time 4x4 - maybe 1 bearing less is turning). Economy was consistently low 18s (4 cyl petrol), with no significant difference either way.

Think of it this way - you are still moving the same mass around, which takes the same amount of Work. The ONLY difference is that there are couple of bearings fewer that are turning (and like Dougal said a bit of oil).

In a vacuum it might make a difference, but not the real world.

[ROGQ]

I read a few people saying that full times are better for dirt roads. But isnt it true that if you own a full time 4wd that you should lock the centre diff in this situation. I have heard that the actual center diffs themselves aren't the strongest things and on loose traction surfaces such as dirt roads they spin like crazy causing premature wear. If this is true then they dont really offer an advantage over part time on the dirt.

[-Scott-]

But isnt it true that if you own a full time 4wd that you should lock the centre diff in this situation.

No, it's not true.

I have heard that the actual center diffs themselves aren't the strongest things and on loose traction surfaces such as dirt roads they spin like crazy causing premature wear.

That's wrong. The only way the centre diff can "spin like crazy" is if the front and rear driveshafts are at massively different speeds. If all four wheels are travelling at roughly the same speed, how will that happen?

If this is true then they dont really offer an advantage over part time on the dirt.

It's not true, there's no problem, they really can offer an advantage over part time on the dirt.

When a vehicle travels around a bend, all four tyres travel a slightly different distance. A part time 4wd (or locked centre diff) needs a tyre to slip to "correct" for this difference. In a full time 4wd (with unlocked centre diff) the differentials allow for the difference, and no tyres need to slip. That sounds good to me.

FWIW, on soft sand on a beach, I find it easier to drive with the centre diff unlocked - the car seems happier to follow existing wheel ruts and doesn't throw from side to side as much.

[me3@neuralfibre.com]

As Dougal said - no difference to economy. Anyone who says otherwise probably thinks hiclones give better economy too.

i dont' know about this at all. every gear mesh causes drivetrain loss. drivetrain loss = less power making it to the wheels for every litre of fuel burnt.

everything i've ever read about AWD cars states that they have a higher drivetrain loss than RWD counterparts (that AWD HSV, and the Turbo territory spring to mind as cars that are directly comparable to a RWD counterpart).

your not just churning the diff oil, your keeping the whole front drivetrain spinning, from output shaft to stub axle on the CV. something that a part timer ISN'T doing.

OK - how about empirical testing???

Many years ago I had a PT 4x4 (Land Rover) with free wheeling hubs. Whenever I engaged the FWHs - the car felt more sluggish, but that was only for the first few hundred m until everything was re-lubricated.

I did a few fuel economy tests with the FWH free and locked (locked is really equivalent to a full-time 4x4 - maybe 1 bearing less is turning). Economy was consistently low 18s (4 cyl petrol), with no significant difference either way.

Think of it this way - you are still moving the same mass around, which takes the same amount of Work. The ONLY difference is that there are couple of bearings fewer that are turning (and like Dougal said a bit of oil).

In a vacuum it might make a difference, but not the real world.

And this is the key statement.

Take your part time 4wd, and drive it with the hubs in. You are now turning all the same parts as an AWD. What's the diff in acceleration and economy? I'll place a pretty solid bet it's 3/10 of stuff all, and the ppl I know that tried it reported same.

How many part time 4wd cars don't even have free wheeling hubs on many variants? Pajero etc? My surf had the Toyota ADD - it simply split one axle on the front left. This left the planetrys and axles and cv's spinning, and the crown wheel stationary.

The assumption that much changes is pretty vague.

Also - for the less wear argument cause it's not spinning. How many rear diffs / bearings / seals do you hear of being replaced - next to none. Now how many front? Lots. It's cause ball bearing are designed to spin, sitting in one spot - they vibrate, pit the races, unevely wear the seals etc. It's not the lack of lube, it's the stationary vibration. Presto - leaking noisy fornt diff that's "never been really used".

Finally, my AWD 105 is MUCH better for towing and in the wet or on dirt. Puts the power down so much more effectivley when traction is low. I used to have to use real 4wd in the Surf on the bitumen to tow in the rain around Bardon, could move from lights otherwise.

Paul