AWD impreza and snow
06 January 2010, 11:00 AM
#31
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Not sure what all the fuss is about over abs. I've done over 1000 miles in the past week or so and not once has the abs caused me any issues.
Had one small slide as the back came round bouncing in an ice rut but a but of opposite lock and leave off the power sorted it in a second. I'm driving very carefully and using gears to slow down etc too, helps a lot.
5t.
Had one small slide as the back came round bouncing in an ice rut but a but of opposite lock and leave off the power sorted it in a second. I'm driving very carefully and using gears to slow down etc too, helps a lot.
5t.
06 January 2010, 12:47 PM
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tyre pressure also makes a huge diffrence! I pumped mine up to 35 from 34 rear just before we got the snow,and it's a lot lot slippier than the last lot of snow we had.
06 January 2010, 02:29 PM
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Locking the centre diff means exactly that - the electromagnets try and stick it together so it effectively becomes a solid shaft, giving you 50:50 front to rear torque distribution by default, but almost completely removing the diff's ability to compensate for different axle speeds (which is why the car will understeer on turn-in).
If the diff is open, the limited slip part is (almost) switched off.
06 January 2010, 02:41 PM
#38
+1 for earlier poster's comment about choice of tyres. I'm running brand new Dunlop WinterSport 3D's on my spare 16" rims, and the difference in controlability and stopping power on slidy surfaces is almost unbelievable compared with the all-season Toyos I had on my 17"s before. Even with AWD I think I would have hesitated to go very far in the 5 inches of snow we had here this morning (Surrey/West-Sussex border).
06 January 2010, 02:53 PM
#39
What are you talking about? There's no such thing as "lock to rear". That makes about as much sense as saying you've just locked the door open. The opposite of locking the diff is "opening" it, not "locking it to the rear".
Locking the centre diff means exactly that - the electromagnets try and stick it together so it effectively becomes a solid shaft, giving you 50:50 front to rear torque distribution by default, but almost completely removing the diff's ability to compensate for different axle speeds (which is why the car will understeer on turn-in).
If the diff is open, the limited slip part is (almost) switched off.
Locking the centre diff means exactly that - the electromagnets try and stick it together so it effectively becomes a solid shaft, giving you 50:50 front to rear torque distribution by default, but almost completely removing the diff's ability to compensate for different axle speeds (which is why the car will understeer on turn-in).
If the diff is open, the limited slip part is (almost) switched off.
I always leave mine in auto, so is the diff locked as soon as you turn it off from auto n move the dial up or down then? And open is when the dial is fully pushed forward or back when the dial clicks? Sorry for my ignorance. My car is an 05 STi btw.
06 January 2010, 06:19 PM
#40
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+1 for earlier poster's comment about choice of tyres. I'm running brand new Dunlop WinterSport 3D's on my spare 16" rims, and the difference in controlability and stopping power on slidy surfaces is almost unbelievable compared with the all-season Toyos I had on my 17"s before. Even with AWD I think I would have hesitated to go very far in the 5 inches of snow we had here this morning (Surrey/West-Sussex border).
06 January 2010, 06:36 PM
#41
I fitted some Winter tyres other day, can't fault erm in this weather. I'm going to do the same, winter tyres on my standard rims buy some 17s with some good summer rubber. Job done max grip all yr round.
Last edited by scooby1doo1; 06 January 2010 at 06:41 PM.
06 January 2010, 07:28 PM
#42
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06 January 2010, 10:23 PM
#44
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They are a legal requirement when driving in "winter conditions" between November and March, although the definition of "winter conditions" is open to interpretation. The general feeling is that if its above 4 degrees and dry then you're ok on summer tyres, otherwise you're running a risk of a fine and points on your license. They also have random road blocks to check for drink drivers and the like, so there is quite a high risk of being caught if you don't have the right tyres.
06 January 2010, 10:51 PM
#46
Open diff = Although both wheels are driven only one gets all the torque so in snow the driven wheel does all the spinning as well.
LSD = can completely lock the diff so both wheels are driven at the same time as if it were one solid locked axle, or it can transfer torque to the slowest moving wheel so e.g. in snow whichever wheel isn't slipping gets the most power.
So in effect WRX's are 3WD where as STi's are 4WD
Just to confuse you even more....The center diff is locked all the time so it sends torque to the front and rear in a 50:50 split. In the case of a WRX with an open front diff it might be better to have more torque going to the rears and less to the fronts but Subaru know what they are doing and i trust they did it that way for a good reason.
Not knowing something doesn't make you a loser. asking a question and getting the right answer makes you a winner
Last edited by scoobiewrx555; 06 January 2010 at 10:57 PM. Reason: More confusion :)
07 January 2010, 12:41 AM
#47
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First thing to understand is the need for a differential. During cornering, the inside wheels travel less distance than the outside wheels, so if the axle was fixed, both wheels would spin at the same speed which would result in the inside wheel slipping. A differential contains a set of pinion gears that allow the wheels to travel at different speeds when cornering which prevents the inside wheel slipping.
In an open differential, the same amount of torque is always applied to both wheels, however the amount of torque applied is limited by the amount of traction available. If one wheel has less traction than the other, then it is this wheel that limits the amount of torque to both wheels. On ice, very little torque is required to make a wheel spin, therefore very little torque (the same small amount) is applied to the other wheel which has traction which is often not enough torque to move the car, so one wheel will spin on the ice while the other wheel remains stationary and the car won't move!
In cars with a "Diff lock" the pinion gears in the differential can be locked thus effectively creating a solid axle in which case all available torque from the engine is applied to both wheels regardless of traction, so even if one wheel has no traction, the other wheel will still be driven and the car will move. However while the diff is locked, you still have the problem during cornering where the inside wheel will spin, so a diff lock should only be used to get you moving and then the diff should be re-opened.
A limited slip differential is kind of like an automatic locking differential. There are two main types of LSD, clutch types and torque sensing (torsen). Their operation is different, but the result is basically the same. When the amount of torque available (due to amount of traction) drops below a preset minimum level, then the limited slip mechanism becomes effective and locks the differential to that amount of torque, thus both wheels still be driven with a limited amount of torque when one wheel loses traction. Obviously the amount of torque must be enough to move the car. When traction is regained, then the limited slip mechanism disengages and the differential continues to operate like an open differential.
As for the centre diff, that is a Viscous Coupled differential which consists of two (actually more) plates connected to the end of the front and rear drive shafts. Between the two plates is a thick (viscous) liquid. In the Subaru, the rear shaft is driven by the engine, this shaft then causes the liquid in the diff to rotate which in turn causes the front shaft to rotate. The viscosity of the liquid determines the amount of torque which is transferred from the rear to the front. Therefore the rear drive would normally receive more torque than the front and the front drive can never be more than 50%. Generally the torque distribution is set to around 40/60 (Front/Rear). However, the liquid in the differential is is designed to change its viscosity (very quickly) with temperature. During normal operation, the liquid remains cool, giving the required torque distribution. When the rear wheels loose traction, then this will cause the rear drive to spin faster relative to the front, which in turn causes the liquid in the diff to heat up and decreases its viscosity (becomes more solid) which causes more torque to be transferred to the front drive (up to max 50/50). When traction returns to the rear wheels then the liquid will cool again and the normal torque distribution will be restored.
07 January 2010, 01:15 AM
#48
Very true statement, shame the rest of your post has so many errors
First thing to understand is the need for a differential. During cornering, the inside wheels travel less distance than the outside wheels, so if the axle was fixed, both wheels would spin at the same speed which would result in the inside wheel slipping. A differential contains a set of pinion gears that allow the wheels to travel at different speeds when cornering which prevents the inside wheel slipping.
In an open differential, the same amount of torque is always applied to both wheels, however the amount of torque applied is limited by the amount of traction available. If one wheel has less traction than the other, then it is this wheel that limits the amount of torque to both wheels. On ice, very little torque is required to make a wheel spin, therefore very little torque (the same small amount) is applied to the other wheel which has traction which is often not enough torque to move the car, so one wheel will spin on the ice while the other wheel remains stationary and the car won't move!
In cars with a "Diff lock" the pinion gears in the differential can be locked thus effectively creating a solid axle in which case all available torque from the engine is applied to both wheels regardless of traction, so even if one wheel has no traction, the other wheel will still be driven and the car will move. However while the diff is locked, you still have the problem during cornering where the inside wheel will spin, so a diff lock should only be used to get you moving and then the diff should be re-opened.
A limited slip differential is kind of like an automatic locking differential. There are two main types of LSD, clutch types and torque sensing (torsen). Their operation is different, but the result is basically the same. When the amount of torque available (due to amount of traction) drops below a preset minimum level, then the limited slip mechanism becomes effective and locks the differential to that amount of torque, thus both wheels still be driven with a limited amount of torque when one wheel loses traction. Obviously the amount of torque must be enough to move the car. When traction is regained, then the limited slip mechanism disengages and the differential continues to operate like an open differential.
As for the centre diff, that is a Viscous Coupled differential which consists of two (actually more) plates connected to the end of the front and rear drive shafts. Between the two plates is a thick (viscous) liquid. In the Subaru, the rear shaft is driven by the engine, this shaft then causes the liquid in the diff to rotate which in turn causes the front shaft to rotate. The viscosity of the liquid determines the amount of torque which is transferred from the rear to the front. Therefore the rear drive would normally receive more torque than the front and the front drive can never be more than 50%. Generally the torque distribution is set to around 40/60 (Front/Rear). However, the liquid in the differential is is designed to change its viscosity (very quickly) with temperature. During normal operation, the liquid remains cool, giving the required torque distribution. When the rear wheels loose traction, then this will cause the rear drive to spin faster relative to the front, which in turn causes the liquid in the diff to heat up and decreases its viscosity (becomes more solid) which causes more torque to be transferred to the front drive (up to max 50/50). When traction returns to the rear wheels then the liquid will cool again and the normal torque distribution will be restored.
First thing to understand is the need for a differential. During cornering, the inside wheels travel less distance than the outside wheels, so if the axle was fixed, both wheels would spin at the same speed which would result in the inside wheel slipping. A differential contains a set of pinion gears that allow the wheels to travel at different speeds when cornering which prevents the inside wheel slipping.
In an open differential, the same amount of torque is always applied to both wheels, however the amount of torque applied is limited by the amount of traction available. If one wheel has less traction than the other, then it is this wheel that limits the amount of torque to both wheels. On ice, very little torque is required to make a wheel spin, therefore very little torque (the same small amount) is applied to the other wheel which has traction which is often not enough torque to move the car, so one wheel will spin on the ice while the other wheel remains stationary and the car won't move!
In cars with a "Diff lock" the pinion gears in the differential can be locked thus effectively creating a solid axle in which case all available torque from the engine is applied to both wheels regardless of traction, so even if one wheel has no traction, the other wheel will still be driven and the car will move. However while the diff is locked, you still have the problem during cornering where the inside wheel will spin, so a diff lock should only be used to get you moving and then the diff should be re-opened.
A limited slip differential is kind of like an automatic locking differential. There are two main types of LSD, clutch types and torque sensing (torsen). Their operation is different, but the result is basically the same. When the amount of torque available (due to amount of traction) drops below a preset minimum level, then the limited slip mechanism becomes effective and locks the differential to that amount of torque, thus both wheels still be driven with a limited amount of torque when one wheel loses traction. Obviously the amount of torque must be enough to move the car. When traction is regained, then the limited slip mechanism disengages and the differential continues to operate like an open differential.
As for the centre diff, that is a Viscous Coupled differential which consists of two (actually more) plates connected to the end of the front and rear drive shafts. Between the two plates is a thick (viscous) liquid. In the Subaru, the rear shaft is driven by the engine, this shaft then causes the liquid in the diff to rotate which in turn causes the front shaft to rotate. The viscosity of the liquid determines the amount of torque which is transferred from the rear to the front. Therefore the rear drive would normally receive more torque than the front and the front drive can never be more than 50%. Generally the torque distribution is set to around 40/60 (Front/Rear). However, the liquid in the differential is is designed to change its viscosity (very quickly) with temperature. During normal operation, the liquid remains cool, giving the required torque distribution. When the rear wheels loose traction, then this will cause the rear drive to spin faster relative to the front, which in turn causes the liquid in the diff to heat up and decreases its viscosity (becomes more solid) which causes more torque to be transferred to the front drive (up to max 50/50). When traction returns to the rear wheels then the liquid will cool again and the normal torque distribution will be restored.
It's easy to copy and paste from other websites. Just copy and paste parts of your own post into google or yahoo and see what comes up!!
What a ****!!
07 January 2010, 01:52 PM
#50
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I bought my first subaru only a few months ago, its also my first 4wd car.
Last winter i was driving a 120d bmw, an luckily i think i had to drive in frosty conditions maybe twice.
I can't remember the last time we had a decent amount of snow in Ireland. (I'm 25)
To say now that i'm glad i bought the sti would be an understatment! It is by far better at going and cornering than a fwd or rwd car, but obviously not stopping.
I live on a fairly steep hill and also took pleasure in coasting up past 3 bmw's, 2 s-class mercs and a GS300 lexus who were all stuck in the snow. Only 1 5-series was still trying (in vain) to get up the hill, the rest had literally been deserted still on the road with the hazard lights on, and no sign of an owner near by!
The limited slip diff, DCCD control of torque, dab of handbrake and gentle application of throttle make cornering (in empty places) the most fun you can have with your clothes on! (even with the heating its prob too cold to drive naked
)
I love my scooby!!
Last winter i was driving a 120d bmw, an luckily i think i had to drive in frosty conditions maybe twice.
I can't remember the last time we had a decent amount of snow in Ireland. (I'm 25)
To say now that i'm glad i bought the sti would be an understatment! It is by far better at going and cornering than a fwd or rwd car, but obviously not stopping.
I live on a fairly steep hill and also took pleasure in coasting up past 3 bmw's, 2 s-class mercs and a GS300 lexus who were all stuck in the snow. Only 1 5-series was still trying (in vain) to get up the hill, the rest had literally been deserted still on the road with the hazard lights on, and no sign of an owner near by!
The limited slip diff, DCCD control of torque, dab of handbrake and gentle application of throttle make cornering (in empty places) the most fun you can have with your clothes on! (even with the heating its prob too cold to drive naked
)I love my scooby!!
07 January 2010, 02:10 PM
#51
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as said the AWD is great for getting up hills, i put it to good use today by crawling up a hill that others demeaned inpassable. but it doesn't matter how many driven wheels you have it won't help you stop any quicker and it won't save you if you hit black ice in a bend so still take it easy.
that is EXACTLY why I need a AWD car ,I have 20mins of untreated country lanes. with a hill to tackle too before I get to my house, my sisters 4.2 A8 can cope with it when it is like this, BUT my car (FWD) is useless...
...I didn't live out here when I bought/chose it
great thread
I cant wait until next winter once I've got my hands on a better suited car
07 January 2010, 02:13 PM
#52
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that is EXACTLY why I need a AWD car ,I have 20mins of untreated country lanes. with a hill to tackle too before I get to my house, my sisters 4.2 A8 can cope with it when it is like this, BUT my car (FWD) is useless...
...I didn't live out here when I bought/chose it
great thread
I cant wait until next winter once I've got my hands on a better suited car
...I didn't live out here when I bought/chose it
great thread
I cant wait until next winter once I've got my hands on a better suited car
It'll be another 20 years before we get another one like this....
07 January 2010, 02:22 PM
#53
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I need to sell my quad and current car first, also can't sell the Quad until this snow has gone, otherwise I'd be stranded with just a FWD car that I cant get further than 100yds from my house in until the snow thaws
I've never been one to rush into things blindly, I need to read up on the Imprezas anyway to make sure I know as much as possible ahead of looking for the right one to buy
sounds like you are enjoying yours (I've never owned a AWD car before either, have driven a good few but only in the summer months)
Last edited by y2blade; 07 January 2010 at 02:24 PM.
07 January 2010, 04:04 PM
#54
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It is an awesome car, even on dry tarmac, but doesn't stand out to be MILES better than the re-mapped 120d that i had before. (Dyno'd at 480 nm and 218bhp) Obviously the scooby is quicker in a straight line and A-B but cruising on M-way and fast but good B-roads, the BMW was a fairly capable match and used half the fuel!
If I have to keep commuting so far, i'll be looking at getting rid of the scoob unfortunately, as its just to dear to run over those distances.
07 January 2010, 04:46 PM
#55
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The LSD
Just to confuse you even more....The center diff is locked all the time so it sends torque to the front and rear in a 50:50 split. In the case of a WRX with an open front diff it might be better to have more torque going to the rears and less to the fronts but Subaru know what they are doing and i trust they did it that way for a good reason.
Just to confuse you even more....The center diff is locked all the time so it sends torque to the front and rear in a 50:50 split. In the case of a WRX with an open front diff it might be better to have more torque going to the rears and less to the fronts but Subaru know what they are doing and i trust they did it that way for a good reason.
if the diff was locked -- you would get transmission wind up when turning a corner as the front and rear wheels travel at different speeds (and a locked diff does not allow this to happen)
so -- in really sippery conditions (in a standard wrx) is is possible to spin one wheel i.e if one wheel looses traction -- all power will go to it
in a car that can lock the centre diff, like old Land Rovers and part time 4 wheel drive SUV's -- you can in the above scenario lock the centre diff this will transfer 50% to the rear -- but you still loose tracton if one wheel on each axle looses traction
for more info see
DIFFLOCK.com - 4x4 Explained
diff explained
Last edited by hodgy0_2; 07 January 2010 at 04:57 PM.
07 January 2010, 05:06 PM
#56
this is not true I am afraid -- a normal non DCCD subaru has an open centre diff which means on dry tarmac in optimal conditions you do indeed have 25% of the torque going to each wheel i.e. AWD (or 50% front to rear) -- but the diff is not locked --- the important thing is what happens when a wheel or wheels encounter slip
if the diff was locked -- you would get transmission wind up when turning a corner as the front and rear wheels travel at different speeds (and a locked diff does not allow this to happen)
so -- in really sippery conditions (in a standard wrx) is is possible to spin one wheel i.e if one wheel looses traction -- all power will go to it
in a car that can lock the centre diff, like old Land Rovers and part time 4 wheel drive SUV's -- you can in the above scenario lock the centre diff this will transfer 50% to the rear -- but you still loose tracton if one wheel on each axle looses traction
for more info see
DIFFLOCK.com - 4x4 Explained
diff explained
if the diff was locked -- you would get transmission wind up when turning a corner as the front and rear wheels travel at different speeds (and a locked diff does not allow this to happen)
so -- in really sippery conditions (in a standard wrx) is is possible to spin one wheel i.e if one wheel looses traction -- all power will go to it
in a car that can lock the centre diff, like old Land Rovers and part time 4 wheel drive SUV's -- you can in the above scenario lock the centre diff this will transfer 50% to the rear -- but you still loose tracton if one wheel on each axle looses traction
for more info see
DIFFLOCK.com - 4x4 Explained
diff explained
My apologies for that and i will now go and sit in the corner!!
07 January 2010, 06:37 PM
#57
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07 January 2010, 07:58 PM
#59
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now now you two - behave
I think in a standard WRX Scooby i.e. without the fancy DCCD stuf the centre diff is just an open diff
but read those articles -- both explain it very well
I think in a standard WRX Scooby i.e. without the fancy DCCD stuf the centre diff is just an open diff
but read those articles -- both explain it very well