[Dr_Snapid]

I have been giving thought to how a locker could affect your final drive ratio.

Open diff: Each wheel will turn at the same speed as the centre on average OR to put another way, the speed of the 2 wheels added together will ALWAYS equal twice the speed of the centre.

Auto locker: Inner/slower wheel will always match the centre. Outer/faster wheel can overrun this speed if on the ground or simply turn at same speed if in the air. So combined ratio may be faster than the centre, and will only be correct when in a straight line. (ratio can vary with driving conditions, particularly in corners of course)

Now consider what running different ratios in front compared to rear would do... Rear auto locker and front open diff = varying ratio rear, fixed front = drivetrain strain (at least) or lost traction due to rear trying to push the front faster that it wants to go on corners

Just an observation

I can see autolockers being a problem in sand (on a beach) where you'll be in 4wd and def not want to be pushing your front end

I came to this conclusion after my cousin just replaced his hilux diff centre from a wreckers. Went to frazer and spent all week getting frustrated at being bogged places he should not be bogged. Came home and figured out his new front ratio was wrong.

I was thinking about an autolocker for my jimny at the time, but then I realised that an autolocker might have the same effect on the beach.

[Zook_Fan]

Dr_Snapid wrote:

I have been giving thought to how a locker could affect your final drive ratio.

Open diff: Each wheel will turn at the same speed as the centre on average OR to put another way, the speed of the 2 wheels added together will ALWAYS equal twice the speed of the centre.

Auto locker: Inner/slower wheel will always match the centre. Outer/faster wheel can overrun this speed if on the ground or simply turn at same speed if in the air. So combined ratio may be faster than the centre, and will only be correct when in a straight line. (ratio can vary with driving conditions, particularly in corners of course)

Auto locker works in reverse to that. The inner wheel ratchets and goes slower than the outer wheel.

Dr_Snapid wrote:

Now consider what running different ratios in front compared to rear would do... Rear auto locker and front open diff = varying ratio rear, fixed front = drivetrain strain (at least) or lost traction due to rear trying to push the front faster that it wants to go on corners

Just an observation

I can see autolockers being a problem in sand (on a beach) where you'll be in 4wd and def not want to be pushing your front end

I came to this conclusion after my cousin just replaced his hilux diff centre from a wreckers. Went to frazer and spent all week getting frustrated at being bogged places he should not be bogged. Came home and figured out his new front ratio was wrong.

I was thinking about an autolocker for my jimny at the time, but then I realised that an autolocker might have the same effect on the beach.

Different ratios are not just going to effect cornering, you will get drivetrain strain in a straight line as well.

[JrZook]

ZookFan you are wrong. On a Detroit (no spin) auto locker the inner clutch is driven and thus remains locked, the external clutch is thus over driven and is disengaged. Inside driven axle is therefore at crown wheel speed. So if a turn if the crown wheel rotates 10 times the inner axle will also turn 10 times. The outer axle will turn how ever many times determined by the corner radii. Lets assume wheel circumference was 1m, then the vehicle moved 10m along the arc from the inside wheel.

With a standard differential the crown wheel speed will equal the average of the axle speeds. So in a turn the inside axle has to spin less than the crown and the outer axle. As an example if the crown turned 10 times and the inner axle turned 9 times the outer axle will have to turn 11 times. Using the same circumference the vehicle moved 9m along the arc from the inside wheel. Here we can see that the vehicle will always move less per crown wheel rotation regardless of corner radii compared to the above example and therefore I guess you could say that the effective final drive ratio is numerically higher with the diff compared to the locker.

Back to your question. So what is the actual issue of having say a numerical different drive ratio fore and aft when turning? The vehicle already has this issue as front wheels will always turn at higher speeds to the rear and thus the front crown wheel will want to out run the rear crown but you have in effect a locked centre diff therefore this cannot occur therefore the rear will already try to push the front. This will be exaggerated by having different diff ratios such that the front is numerically higher than the rear. This will also have an effect in a straight line as you will always have the rear trying to push the front in which either the front has the slip resulting in very poor steering control or the rear slips resulting in bogging down.

On sand this would suck as you have seen! Added to this the torque split between the wheels on the same axle will seldom be the same on this surface resulting with the least traction wheel getting the most torque which again will end up in digging and eventually bogging.

A locker on the other hand used on a low traction surface will provide torque and speed evenly to both wheels on the same axle resulting in greater overall traction. Turning radius will be increased due to slip at the wheel required as both axles are at the same speed. With the torque split evenly and same wheel speeds you will have lesser chance of unloading both wheels, digging and bogging down.

Ughhh its too late and too many bundys for this thinking stuff!! Correct my rum-goggled thoughts where required.

[jdk81]

Your friend installing wrong ratio diff... rookie mistake.

You will find an auto locker, wont get enough traction to unlock (basically will be like a spool on the sand).

In the event the auto locker does unlock, the ever so slight variations in wheel speed are not really a concern on low traction surfaces anyway. Unless its a parking lot etc with lots of tight turns its not really a concern. Last I checked the beach driving on fraser was damn near straight (been 15 years since I was 4wding there).
The ever so slight variation you are considering, is no where near the stupidity of unmatched diff ratios a 4.11/4.3/4.8 etc where the other is different (unless its done for a purpose i.e. mudrunners).

The slight changed in front difff speed to rear diff speed has always been an issue present on centre diff locked/trasnfer case 4wd selected 4wd, due to turning radii. Which I tried to explain where you asked a similiar question earlier.

http://auszookers.com/forum/viewtopic.php?f=17&t=3447&start=30


tyre pressures are far more important.

Be more concerned about what an auto locker does to your road handling.

EDIT: added more

[SierraDan]

Auto lockers suck in the sand. From my experience.

[evski]

Ive had the opposite experience, had a front lockrite in my old ln106 hilux and it was great in the sand. You could use it to turn into dunes sharper and it kept the truck going straight on rough beaches where it would normally get thrown about side to side. Honestly I couldnt find a bad point to using it on sand, but I guess the old diesel didnt have enough power to notice any issues. Im a amassive fan of front lockers as well, especially in swb trucks where the weight and most flex is in the front. Rear lockers tend to dig you in, or lift the front off the ground making the truck very unstable. Just my findings, but I wont be locking the rear of my zook unless the front is locked first.

[SierraDan]

Why wouldnt you want the rear locked first?

[31zook]

Why have oodles of traction and not be able to steer it? I would lock the front first every time.

Plus for a rookie the rear driving under itself is allot more dangerous. Then the front pulling over rock shelves....

[got_bar_work]

Rear locker only suck
The ass tries to over take the front all the time
It makes the front unload and lift wheel all the time when trying to climb

[SierraDan]

Once the front was locked in mine it started doing huge wheel lifts. Just rear locked used to wheel lift then lose traction and spin wheels.

Like this. Wheel up, and wheelspin going nowhere.

[Dr_Snapid]

Thats a great image SierraDan LOL (not very ladylike, i can see up your skirt)
So in this image, is the front locked or the rear?

SierraDan wrote:

Once the front was locked in mine it started doing huge wheel lifts. Just rear locked used to wheel lift then lose traction and spin wheels.

In this situation is the front or rear that 'lose traction and spin wheels'?

I am assuming that the general consensus is that a locked diff does affect the final drive enough to be noticable. Now I think I can see why people will pay more for the air locker. It means you get the best of both worlds.

[SierraDan]

Rear locked.

Bcause that one in the air would spin, it made the rear ones want to spin so there wasnt enough grip to cause a backflip. but once the front was locked also, it started backflipping

[atari4x4]

buy an air locker, it will be money well spent you don't loose the on road driveability & have the option & control of when you want to use it... unlike the auto/welded option where it will do what ever it wants as per SierraDan fully sick wheelies.

[monley]

Air lockers FTW

[SierraDan]

atari4x4 wrote:

buy an air locker, it will be money well spent you don't loose the on road driveability & have the option & control of when you want to use it... unlike the auto/welded option where it will do what ever it wants as per SierraDan fully sick wheelies.

Haha, if i had more money to waste i would go air for sure. Maybe not in the rear though.. i don't feel right in open diff RWD cars anymore haha.

[atari4x4]

Dr_Snapid wrote:

I am assuming that the general consensus is that a locked diff does affect the final drive enough to be noticable. Now I think I can see why people will pay more for the air locker. It means you get the best of both worlds.

only when turning

[JrZook]

atari4x4 wrote:

Dr_Snapid wrote:

I am assuming that the general consensus is that a locked diff does affect the final drive enough to be noticable. Now I think I can see why people will pay more for the air locker. It means you get the best of both worlds.

only when turning

That's what I concluded

Doubt it is noticeable tho

[jdk81]

We agreed with the theory, but who said its enough to be noticeable on low traction surfaces?
The tyres will be ever so slightly different diametre too, same effect.
Even open diffs the final drive of the front diff will be at a different speed, due to turning radii.


The change in distance through the turn is significant enough to make the locker go click, or click click, or even multiple clicks.
each click is 360 degrees/16 or 22.5 degrees.
If you do a circle of 10m in diam (based on inside rear), the outside rear travels almost 60 revs more.
Refer to the picture, the front diff combined will travel further.
This is noticeable on hard surfaces, which is why its in 2wd.

You are being concerned about locker properties only in 4wd (or centre diff locked) whilst on hard surfaces.
Completely irrelevant to driving on sand (low traction surfaces).
Obviously an open diff will be better on sand when turning, but this isnt the issue you are raising.

These two properties of where one locker is installed, is not relevant on the issue you are raising (remember, these are low traction surfaces).
The ass trying to overtake the front is more to do with traction generated by a locked diff, in the rear.
If you lock the front it will make it much harder to steer (it will want to go straight), and it pull the rear.

You are concerned about something you will only notice on high traction surfaces, where it is supposed to be in 2wd anyway.

Be more concerned about turning in sand with an auto locker, where it wont unlock.

EDIT: More info
A bit of further explanation.

If you are doing a 10m diam turn (based on inside rear), with using standard wheel base and track etc on 31" tyres
Revs
rear inside 12.7
rear outside 16.2
front inside 13.7
front outside 17.2

If you are running an auto in the rear, the rear ring gear will do 12.7 revs, whilst the front will do the average (13.7+17.2)/2 = 15.45 revs
If you run open diffs, they both do the average
front = 15.45
rear = (12.7+16.2)/2 = 14.45

Prior to this, the concept of the average of the rear if locked was used, which is incorrect. It is the minimum number of revs which is driven, not the average.
If you jack one wheel with an auto locker up, while in gear, you can spin the wheel manually.
If you jack one wheel with an open diff up, with it in gear, you cant freely spin the wheel.

[Dr_Snapid]

Yes all true I'm sure. Having never driven on a locker I'm happy to take advice.

it's on sand that I'm concerned about. Almost all other situations I think the pros outweigh the cons.

For example, on Sandon beach where I go a bit, you have to do a u turn at the sandon end to head up the headland. The sand there is sometimes very chopped up. If you cant choose to keep your rear unlocked perhaps the locker might cause trouble.

I also wheel a bit at Glenugie and Coaldale and the creek crossings are sandy, where you have to turn up the creek bank. Another case where I worry about not having control of the locker. I now wonder about this fellas locked LC80 I went there with once. He was hopelessly bogged, I put it down to the weight, the locker may have contributed also. But no way to know really.

[jdk81]

After last post i realised theres an error,
Auto locker... Wheel with the least revs is the revs of the ring gear.
Open diff.... average of both wheels rpm is the rpm of the ring gear.
Hence a locker on rear diff wil be under driven through a corner.