tarmac/gravel/snow
Evolving Member
Joined: Nov 2004
Posts: 473
Likes: 0
From: Maple Shade NJ - All ur base r belong to us
i may be wrong, but i think in sti the switch changes the actual torque split from 50/50 to 65/35 f/r? But in the evo, like mr. wong from hong kong said, it changes the duration of locking, that's why it locks for a short period on tarmac setting, since you have lots of grip and don't have to worry about stability as much.
The STi diff is mechanically geared to 35/65 F/R, but as the clutch plates lock and limit the differential action it approaches 50/50. Of course the magic is in the details (the programming and actual capability of the clutch packs) so there's no way to know which system is 'superior'.
I would be very interested in seeing an 04RS vs an 05RS on a road course (on the same day) to see what advantages the ACD confers on tarmac. I suspect not that much in expert hands. From the SAE doc posted before, it seems like the primary advantage of ACD is in split Mu situations where the front and rear axles have significantly different amounts of traction, in which case the ACD can lock up nearly completely whereas the VLSD allows more slip to the axle with less traction.
I would be very interested in seeing an 04RS vs an 05RS on a road course (on the same day) to see what advantages the ACD confers on tarmac. I suspect not that much in expert hands. From the SAE doc posted before, it seems like the primary advantage of ACD is in split Mu situations where the front and rear axles have significantly different amounts of traction, in which case the ACD can lock up nearly completely whereas the VLSD allows more slip to the axle with less traction.
Last edited by osunick; Feb 16, 2005 at 09:38 AM.
Originally Posted by raywong
Tarmac: 50/50
Snow: 50/50
Gravel: 50/50
The center diff has a fixed ratio gearing, which is 50/50.
The ACD mode varies the diff's lock state duration and locking power only. In the entrance of a turn, the diff change from open to lock to provide lateral stability. In the middle of the turn, the diff opens to induce turnning. In the exit of the turn, ACD locks the diff again to provide maxium exit stability.
Tarmac: the ACD stay lock for short duration
Gravel: the ACD stay lock for medium duration
Snow: the ACD stay lock for long duration, lowest locking power.
Snow: 50/50
Gravel: 50/50
The center diff has a fixed ratio gearing, which is 50/50.
The ACD mode varies the diff's lock state duration and locking power only. In the entrance of a turn, the diff change from open to lock to provide lateral stability. In the middle of the turn, the diff opens to induce turnning. In the exit of the turn, ACD locks the diff again to provide maxium exit stability.
Tarmac: the ACD stay lock for short duration
Gravel: the ACD stay lock for medium duration
Snow: the ACD stay lock for long duration, lowest locking power.
Evolving Member
Joined: Aug 2007
Posts: 358
Likes: 1
From: BRATISLAVA (SLOVAKIA)
its simple to find out.
try when is really snow on the road and you have lots of space.
try tarmac ,turn the wheel full on right or left and accelerate (try harder than ussual)-youll see it feel like rear wheel drive and you get right away understeer .
and then go for snow do the same thing and you wont get understeer,you will go straight through front wheels,and the gravel is something in between.
try when is really snow on the road and you have lots of space.
try tarmac ,turn the wheel full on right or left and accelerate (try harder than ussual)-youll see it feel like rear wheel drive and you get right away understeer .
and then go for snow do the same thing and you wont get understeer,you will go straight through front wheels,and the gravel is something in between.
Newbie
Joined: May 2007
Posts: 92
Likes: 0
From: Oregon
I am no expert, but somewhere on this great site I remember reading something very much like what ringmeister described above. I understood it as the clutch pack inside the acd, which is controlled electronically by a cpu, is enabled and disabled at different timed intervals depending on what position the acd switch is set to.
When I got my car I wondered how it would react while driving. So I drive the same road home every day, it was raining here in Oregon like it does, so in this same corner I had it on tarmac and about half way through I accelerated, turbo spooled up and I was 4 wheel drifting. Front and rear breaking loose at the same time. Gravel setting the next day had the rear breaking loose first, slide was predictable, snow didn't have as much difference. I felt the front end pull, but not push as much as I thought it would do. I know, not much of a scientific explanation, but I wanted the "simple" way to find out as dino above said. I have an 06 mr.
When I got my car I wondered how it would react while driving. So I drive the same road home every day, it was raining here in Oregon like it does, so in this same corner I had it on tarmac and about half way through I accelerated, turbo spooled up and I was 4 wheel drifting. Front and rear breaking loose at the same time. Gravel setting the next day had the rear breaking loose first, slide was predictable, snow didn't have as much difference. I felt the front end pull, but not push as much as I thought it would do. I know, not much of a scientific explanation, but I wanted the "simple" way to find out as dino above said. I have an 06 mr.
its simple to find out.
try when is really snow on the road and you have lots of space.
try tarmac ,turn the wheel full on right or left and accelerate (try harder than ussual)-youll see it feel like rear wheel drive and you get right away understeer .
and then go for snow do the same thing and you wont get understeer,you will go straight through front wheels,and the gravel is something in between.
try when is really snow on the road and you have lots of space.
try tarmac ,turn the wheel full on right or left and accelerate (try harder than ussual)-youll see it feel like rear wheel drive and you get right away understeer .
and then go for snow do the same thing and you wont get understeer,you will go straight through front wheels,and the gravel is something in between.
I am no expert, but somewhere on this great site I remember reading something very much like what ringmeister described above. I understood it as the clutch pack inside the acd, which is controlled electronically by a cpu, is enabled and disabled at different timed intervals depending on what position the acd switch is set to.
When I got my car I wondered how it would react while driving. So I drive the same road home every day, it was raining here in Oregon like it does, so in this same corner I had it on tarmac and about half way through I accelerated, turbo spooled up and I was 4 wheel drifting. Front and rear breaking loose at the same time. Gravel setting the next day had the rear breaking loose first, slide was predictable, snow didn't have as much difference. I felt the front end pull, but not push as much as I thought it would do. I know, not much of a scientific explanation, but I wanted the "simple" way to find out as dino above said. I have an 06 mr.
When I got my car I wondered how it would react while driving. So I drive the same road home every day, it was raining here in Oregon like it does, so in this same corner I had it on tarmac and about half way through I accelerated, turbo spooled up and I was 4 wheel drifting. Front and rear breaking loose at the same time. Gravel setting the next day had the rear breaking loose first, slide was predictable, snow didn't have as much difference. I felt the front end pull, but not push as much as I thought it would do. I know, not much of a scientific explanation, but I wanted the "simple" way to find out as dino above said. I have an 06 mr.
All the info in this thread is wrong because it from 04-05, right when the ACD got to the US and people didnt know anything about it. There is a sticky in one of the sub forums here that properly describes how the ACD works.
Newbie
Joined: Jun 2012
Posts: 6
Likes: 0
From: chile
Hello! it seems like you know alot about ACD...
i have an JDM evo VII, and got the 3 lights failure and no trouble code on scaner... do you know what could be the problem???... i live in chile and my mechanic is very lost... thanx!
i have an JDM evo VII, and got the 3 lights failure and no trouble code on scaner... do you know what could be the problem???... i live in chile and my mechanic is very lost... thanx!
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