4WD 50/50 or 35/65 ?
17 October 2003, 11:25 AM
#1
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Probably a stupid question so no flaming ;-)
Are all wrx/sti's 35/65 4wd as in more drive to the rear or is it just the RA model i have ? any have 50/50 permanent ?
Are all wrx/sti's 35/65 4wd as in more drive to the rear or is it just the RA model i have ? any have 50/50 permanent ?
17 October 2003, 11:49 AM
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Pretty sure mines 50/50 permenant (03 WRX) although i stand to be corrected on it...
It was my understanding that they were all 50/50 unless they had a variable diff.
It was my understanding that they were all 50/50 unless they had a variable diff.
17 October 2003, 12:22 PM
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Non-RA models are roughly 50:50- unsure of the exact figure tho.
The RA's and R's are roughly 65:35 (rear to front), some with driver adjustable centre to 50:50
The RA's and R's are roughly 65:35 (rear to front), some with driver adjustable centre to 50:50
18 October 2003, 11:33 AM
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sg is closest.
its 67:33 or 2:1 and as stated its only dccd equipped cars.
This is continuously variable by means of a variable coupling up to 50:50, but the switch in torque distribution comes at the expense of the freeness of the diff, so at 50:50 in the fully locked position, there is no differential effect, and no relative motion is allowed between the front and rear axles without the driving train kicking up a stink.
This is only on dccd equipped cars. All other imprezas have a viscous coupled 50:50 torque split, but be aware that this is only the static calculation, when both wheels start to slip, that axle is transmitting no torque to the ground, but since it presents no resistance to the drivetrain, all the torque will go into driving these wheels and they will simply spin and spin. In other words, even though the diff is a 50:50 torque split, 100% of the torque will go to one axle, and it will be wasted in tyre smoke as none of the torque can be transmitted to the road.
(this is in an extreme case - ie, consider the front wheels are on ice).
For this reason the standard 50:50 diff is a LSD, meaning that it will tolerate a certain degree of slip between the axles, in the situation that the front wheels are spinning there is a large speed differential or slip across the diff, the limited slip mechanism (in this case viscous coupling) will not allow this, and will partially "lock" the axles together, transmitting some of the torque to the wheels which can make use it since they are not slipping.
In this situation it will be somewhere between 100:0 and 50:50.
It is entirely possible it could go to 0:100, but this is less likely due to weight transfer to the back meaning they tend to get more grip, and therefore are less likely to slip. When all axles are totally gripping, they will be apportionaed 50:50 torque distribution, and it is the weight transfer on acceleration which causes the front to lose traction first.
On the dccd, when all wheels are gripping fully, the rear wheels are receiving two thirds of the torque due to ratio of the radii of the planet gear carrier and sun gear in the epicyclic centre diff. The rear wheels are therefore more likely to let go, even with the weight transfer to them on acceleration.
Its because of this, that a dccd equipped car should be better for the quarter mile.
This can be further improved by locking the diff manually instead of relying on limited slip effect of viscous coupled diff, the locking characteristics of which may be too slow to get the most of the traction available.
This is what is meant by the aggressiveness (agression?) of a limited slip diff.
It also should partially account for the handling charcateristics of different cars, eg, an agreesive R180 plated rear lsd has a more aggressive lock up than say a viscous coupled R160 in a uk turbo or normal sti. Whereas replacing the diff with a quaife atb can produce a predicatble and progressive "lock up". (not strictly speaking a lock up in the quaife - but dont want to complicate things).
As always, usual disclaimers, one thing I have learned from scoobynet, is that andy f always knows more than me so I have to leave myself open for being picked up on the things I don't fully understand.
its 67:33 or 2:1 and as stated its only dccd equipped cars.
This is continuously variable by means of a variable coupling up to 50:50, but the switch in torque distribution comes at the expense of the freeness of the diff, so at 50:50 in the fully locked position, there is no differential effect, and no relative motion is allowed between the front and rear axles without the driving train kicking up a stink.
This is only on dccd equipped cars. All other imprezas have a viscous coupled 50:50 torque split, but be aware that this is only the static calculation, when both wheels start to slip, that axle is transmitting no torque to the ground, but since it presents no resistance to the drivetrain, all the torque will go into driving these wheels and they will simply spin and spin. In other words, even though the diff is a 50:50 torque split, 100% of the torque will go to one axle, and it will be wasted in tyre smoke as none of the torque can be transmitted to the road.
(this is in an extreme case - ie, consider the front wheels are on ice).
For this reason the standard 50:50 diff is a LSD, meaning that it will tolerate a certain degree of slip between the axles, in the situation that the front wheels are spinning there is a large speed differential or slip across the diff, the limited slip mechanism (in this case viscous coupling) will not allow this, and will partially "lock" the axles together, transmitting some of the torque to the wheels which can make use it since they are not slipping.
In this situation it will be somewhere between 100:0 and 50:50.
It is entirely possible it could go to 0:100, but this is less likely due to weight transfer to the back meaning they tend to get more grip, and therefore are less likely to slip. When all axles are totally gripping, they will be apportionaed 50:50 torque distribution, and it is the weight transfer on acceleration which causes the front to lose traction first.
On the dccd, when all wheels are gripping fully, the rear wheels are receiving two thirds of the torque due to ratio of the radii of the planet gear carrier and sun gear in the epicyclic centre diff. The rear wheels are therefore more likely to let go, even with the weight transfer to them on acceleration.
Its because of this, that a dccd equipped car should be better for the quarter mile.
This can be further improved by locking the diff manually instead of relying on limited slip effect of viscous coupled diff, the locking characteristics of which may be too slow to get the most of the traction available.
This is what is meant by the aggressiveness (agression?) of a limited slip diff.
It also should partially account for the handling charcateristics of different cars, eg, an agreesive R180 plated rear lsd has a more aggressive lock up than say a viscous coupled R160 in a uk turbo or normal sti. Whereas replacing the diff with a quaife atb can produce a predicatble and progressive "lock up". (not strictly speaking a lock up in the quaife - but dont want to complicate things).
As always, usual disclaimers, one thing I have learned from scoobynet, is that andy f always knows more than me so I have to leave myself open for being picked up on the things I don't fully understand.
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18 October 2003, 11:41 AM
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Thanks for all the replies.
The reason i asked is that i have just bought a MY00 RA and first impression was it felt like a rear wheel drive car which is not what i expected. With the DCCD i assume it can be locked to 50/50 the majority of the time ? i've heard it makes an awful sound sometimes...is this only at slow speeds when parking etc ??
The reason i asked is that i have just bought a MY00 RA and first impression was it felt like a rear wheel drive car which is not what i expected. With the DCCD i assume it can be locked to 50/50 the majority of the time ? i've heard it makes an awful sound sometimes...is this only at slow speeds when parking etc ??
18 October 2003, 12:54 PM
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NO!
Leave it on open.
Only move towards lock,when conditions are less than dry grip.
IE. Wet/loose surface
If you move towards lock.You start relying on the interface between tyre and road surface,to provide slip,
so grippy tyres on a dry flat road and you may understeer into a hedge.
Leave it on open.
Only move towards lock,when conditions are less than dry grip.
IE. Wet/loose surface
If you move towards lock.You start relying on the interface between tyre and road surface,to provide slip,
so grippy tyres on a dry flat road and you may understeer into a hedge.
18 October 2003, 04:27 PM
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only makes a noise if it is even slightly locked and during tight turns/manouverings.
will only be rear wheel drivey if you have the dccd, normally only sti ras and rs which do. wrxs tend not to have dccds.
will only be rear wheel drivey if you have the dccd, normally only sti ras and rs which do. wrxs tend not to have dccds.
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