Is the system on a scoob the same setup as a off road vehicle,but without the difflock? The reason i ask is that ive read on here that some people complain of wheel spin acting the same as a 2 wheel drive if they get one of their wheels on some wet grass(or similar).
If this is the case,what are scoobs like in the snow?

 

on large low profile rubber.................crap!!

 

there is a limited slip diff between front and rear (visous coupled) so the rear wheels wont spin relative to the front for very long.

the rear diff on some cars is limited slip also. Never had this clarified. Apparently all turbos are limited slip rear, which will again be a viscous unit. this should stop the left to right relative spin of the rear wheels.

the type r and later type ras have a clutch type rear lsd, so again this should prevent spin across the rear axle.

 

You may find, that untill, the viscous differential "locks up", then you can have the vehicle unable to move untill the diff coupling "reacts", so, even one tyre on a patch of ice, or very wet grass, and you can get the scenario you are concerned with.
it does not matter what tyre size, its the type of diff's fitted which dictate how the 4wd system works, so if no diff lock available, then it can send the majority of the power to the offending corner, untill it starts to work. Saying that, diff locks only equalise the power split 50/50.

 

Out of my league, but on a UK car, with the open front diff, if one of the front wheels start to spin, all power goes to that helplessly spinning wheel.

It's very easy to get stuck in the mud with a UK car... I know, I've seen it & still feel the backpains trying to get the thing moving again And that was happening to a certain rally driver that occasionally posts on here LOL.

 

EvilBevel-surely some of the power should go to the rear wheels-is it showing up a problem?-or if this is normal, whats the point in having 4 wheel drive?

 

Yeah I'd reckon so as well. Only time the open front diff is likely to be an issue is high speed cornering because then you're not getting power to the front wheels which can help pull the car into line if one of the fronts lifts off the ground slightly.

On normal driving, if one front wheel slips then most of the torque will transfer to the back since there is little load on the front meaning the centre diff will lock. As long as either of the back two wheels has traction that will transmit the power to the road and the car will be able to move off.

The only time I can imagine you'd stand still and spin the wheels is when both back wheels and one front wheel is on a slippy surface, in that case the two back wheels and one front wheel will spin, leaving the single front wheel with grip standing doing nothing.

This applies to turbo cars with an LSD in the centre and rear. New model STis have a suretrac diff on the front as well so none of the wheels will be able to spin freely.

 

ER, as I said, I'm not really familiar with how the diffs work. But I saw what I saw.

I always thought that torque would go to the wheel of least "resistance". With an open front diff, that would be the spinning front wheel. The centre diff will eventually do something I guess, but it didn't after 15 minutes in the case I'm describing

Agree that the STi7 would be another ball game. Also, bear in mind I'm talking about mud/bad conditions, but the question that was asked surely has some relation to those ?

AWD is great out of corners. The rest is bull****.

 

The front has to turn at the same rate as the back. All the power at the front will go to the wheel with least resistance, but unless the centre diff was shagged as soon as that wheel started slipping the centre would lock and transfer torque to the rears. Assuming it's got a LSD on the rear as well then both rears would then need to slip so that both axles are turning at the same time (centre locked) and both rear driveshafts at the same time (rear locked). The only diff that will allow one output shaft to turn while the other is stopped is the front.

If you're crazy enough to try it jack one front wheel off the ground and try and drive off! It will turn at first then the diffs will lock and the rears will push the car off the jack! Nah on second thoughts better not that ain't a good idea

 

BTW think of it this way as well... if it only takes one front wheel to lose grip for the AWD to fail then why can a scooby launch with the full force of 250+ BHP effectively whereas a 150BHP FWD car with an open front diff will just smoke the tyres? With the FWD what happens is that one wheel starts losing traction first, the diff diverts the power to that wheel which makes the situation worse until that wheel just spins freely with the other doing nothing and the car hardly moving.

Doesn't happen with AWD, you're more likely to destroy the clutch because the wheels transmit most of the grip to the road meaning the clutch takes the brunt of the abuse.

 

Well, i've seen it happening on two occasions, although not for very long. Once trying to tow a boat from a beach and another time having fallen sideways at 45 deg with one side of the car on a muddy road and the other side 70cm further down on a plowed field. Apparently, 4WD works, as i got out from both instances intact, but with "thinner" cluch disk. Both cases were initiated with a front wheel spin folowed by a real wheel spin, immobilization, and then only front wheel spin. It is my understanding that the center diff gives up after while as the standard item (not STI) is only a 4KG part(i think), and 4kg of torque is not enough to move a stuck car on one wheel (worst case)although is adequate on the road. But if you get FW spin then applying the brakes, while hitting the gas or lifting a bit the handbrake in RW spin helps a lot to get you moving again. In my case, on the plowed field, selecting reverse did the trick, as it seemed to had fully engaged the rear diff and the car started digging on the ditch banks so i was able to lower the whole car onto the field and drive away afterwards. I was amazed whow i got away that day, cause considering the location i was stuck then, not even my bones whould exist there today. However, i'm going to fit a quaiffe on the fronts shortly and i'm taking any offers for an adj center diff (with harness).

Regards,

George