Strange Driving Characteristic on EVO9: Is that LSD? ACD?
Jan 21, 2006 | 04:12 PM
#16
Makes sense to me, im not saying im right, i just put together the info i saw/read/heard before. cheers to figuring it out
but bottom line, you gotta drive another 06 and recreate the situation thats the only way that you can kno if there is something wrong w/ yours
but bottom line, you gotta drive another 06 and recreate the situation thats the only way that you can kno if there is something wrong w/ yours
Originally Posted by ShiftySVT
I edited out the my statement about torque distribution. Strictly speaking, I think it DOES control torque distribution.
Imagine that the front tires are on a theoretical surface with a coefficient of friction of zero (no traction at all) and the rears are in sand. If the differential is completely open, it must send equal torque to the front and rear. If we ignore the effects of the moment of inertia of the wheels, there will be no torque transferred to the front wheels (refer to Newton's 3rd law - you can't push on something if there is nothing to push back). Consequently the rear tires will receive no torque, so you're stuck.
Now consider that the ACD locks up the center diff. Now the front and rear tires must spin at the same speed, which forces the rears to receive ALL of the torque.
I'm not saying this is exactly how the ACD works, but it shows that strictly speaking, the process of locking and unlocking the center diff does change the way torque is distributed.
Imagine that the front tires are on a theoretical surface with a coefficient of friction of zero (no traction at all) and the rears are in sand. If the differential is completely open, it must send equal torque to the front and rear. If we ignore the effects of the moment of inertia of the wheels, there will be no torque transferred to the front wheels (refer to Newton's 3rd law - you can't push on something if there is nothing to push back). Consequently the rear tires will receive no torque, so you're stuck.
Now consider that the ACD locks up the center diff. Now the front and rear tires must spin at the same speed, which forces the rears to receive ALL of the torque.
I'm not saying this is exactly how the ACD works, but it shows that strictly speaking, the process of locking and unlocking the center diff does change the way torque is distributed.
Last edited by shiftdsm E; Jan 21, 2006 at 04:23 PM.
Jan 21, 2006 | 04:17 PM
#17
Originally Posted by zstryder
All the ACD does is control the speed at which the center diff locks/open depending on a variety of inputs. It does NOT work like Subaru's DCCD system, which, IIRC, actually does control torque distribution from front to rear. The torque distribution in an Evo is always 50/50.
Jan 21, 2006 | 04:23 PM
#19
Originally Posted by shiftdsm E
Right!!! but what is the result of the differential locking???
Jan 21, 2006 | 04:26 PM
#20
Evolving Member
Joined: Oct 2004
Posts: 254
Likes: 0
From: Edison New Jersey
Originally Posted by xtnct
I just switched from EVO 8 to EVO 9. 9 has the LSD & ACD. I noticed a strange driving characteristic or behaviour with the new car that was not there on the EVO 8.
Assume you are crusing on a straight road. Ahead is a long constant radious bend in the road. Once you turn the steering wheel, holding it in the same position would take you around the bend. However, on the EVO 9, once I had my steering angle for the entire curve I have to readjust it if I either apply more throttle or get off the throttle. If I apply throttle, the car ends up wanting to go straight, so I need to compensate with the steering wheel (just a tiny bit). If I let off the throttle, the car wants to turn into the turn and I have to compensate again with the steering. This is a very weary subtle feeling that I would not want to experience at higher speed (kind of like a twich). Could this be the ACD or LSD in action even when miles away from the car's actual limits?
I had a FWD car with LSD and it did not have that behaviour. I can tell you definitely what it is NOT:
- not oversteer or understeer,
- does not feel like an alignment issue
- it is not a weight trasfer characteristic
- it is not new tire break in as they are the ones I trasfered from my 8.
Changing ACD setting makes no difference. It feels more like something mechanical is happening, like something is steering the rear wheels for me...
Note that I did not WOT it around the bend. This was just cruising @ 50mph around 3K rpm and just applying moderate throttle in 5th and then easing off before full boost kicks in. I have 40 miles on the odomoter so I have not experimented with what happens at WOT and full boost.
So, would this be ACD and or LSD behavior or should I get my new car checked out?
Assume you are crusing on a straight road. Ahead is a long constant radious bend in the road. Once you turn the steering wheel, holding it in the same position would take you around the bend. However, on the EVO 9, once I had my steering angle for the entire curve I have to readjust it if I either apply more throttle or get off the throttle. If I apply throttle, the car ends up wanting to go straight, so I need to compensate with the steering wheel (just a tiny bit). If I let off the throttle, the car wants to turn into the turn and I have to compensate again with the steering. This is a very weary subtle feeling that I would not want to experience at higher speed (kind of like a twich). Could this be the ACD or LSD in action even when miles away from the car's actual limits?
I had a FWD car with LSD and it did not have that behaviour. I can tell you definitely what it is NOT:
- not oversteer or understeer,
- does not feel like an alignment issue
- it is not a weight trasfer characteristic
- it is not new tire break in as they are the ones I trasfered from my 8.
Changing ACD setting makes no difference. It feels more like something mechanical is happening, like something is steering the rear wheels for me...
Note that I did not WOT it around the bend. This was just cruising @ 50mph around 3K rpm and just applying moderate throttle in 5th and then easing off before full boost kicks in. I have 40 miles on the odomoter so I have not experimented with what happens at WOT and full boost.
So, would this be ACD and or LSD behavior or should I get my new car checked out?
Jan 21, 2006 | 04:33 PM
#21
Evolving Member
Joined: Oct 2004
Posts: 254
Likes: 0
From: Edison New Jersey
Originally Posted by shiftdsm E
so then, what would be the function of the ACD? if not to adjust torque split front/rear it certainly cant do side to side
Jan 21, 2006 | 05:12 PM
#22
The ACD springs into action, distributing all of the 4G63 engine's raw power through a hydraulic multi-plate clutch. It adjusts front and rear torque output for maximum traction based on numerous inputs like steering angle, throttle input, wheel speed and slip angle.
This is from the US evoIX brochure that I picked up when getting my oil changed the other day.
This is from the US evoIX brochure that I picked up when getting my oil changed the other day.
Jan 21, 2006 | 07:43 PM
#23
Evolving Member
Joined: Mar 2005
Posts: 269
Likes: 0
From: north jersey (15 min from nyc)
ive heard so many different renditions of how the awd system of the evo works, i confused myself and dont even know anymore...all i know is that its bada$$...
but whenever i get confused i go to the website and find the official explanations for it from mitsu themselves, if im still confused, i search here and look for credible answers
but whenever i get confused i go to the website and find the official explanations for it from mitsu themselves, if im still confused, i search here and look for credible answers
Jan 21, 2006 | 09:06 PM
#24
Evolving Member
Joined: Oct 2005
Posts: 106
Likes: 0
From: oregon
in long sweeper corners i have experienced the same twitchy type of feel in my IX and i am also coming from a fwd lsd car. maybe the car will feel more balanced after the ride hieght comes down some. has alot of body roll in long turns maybe the valving on the shocks could have something to do with it. just a thought, because the car feels tighter around a quick radius.
Jan 21, 2006 | 10:28 PM
#25
Evolving Member
Joined: Oct 2004
Posts: 254
Likes: 0
From: Edison New Jersey
Originally Posted by 501
in long sweeper corners i have experienced the same twitchy type of feel in my IX and i am also coming from a fwd lsd car. maybe the car will feel more balanced after the ride hieght comes down some. has alot of body roll in long turns maybe the valving on the shocks could have something to do with it. just a thought, because the car feels tighter around a quick radius.
I'm not going to promote trying to test your car on public roads but I can assure you that the evo IX is anything but twitchy. In the long sweepers is when its at its best. Try looking deeper into the turns instead of directly infront of you. I honestly don't think that you have any idea of how much grip and the amount of cornering speed you can carry around the wider sweepers.
Again, please do be careful out there.
Jan 21, 2006 | 11:11 PM
#26
Evolving Member
Joined: Oct 2005
Posts: 106
Likes: 0
From: oregon
yea it could be just getting used to the steering as it is sensitive. havent had the oppurtunity to really get a chance to drive aggressivly in corners autox season hasnt started and the weather is wet around here. but it has been slightly wierd that the car would feel unbalanced in the corners, compared to my last one which had suspension mods done to it.
Jan 21, 2006 | 11:59 PM
#27
[QUOTE=xtnct]If I apply throttle, the car ends up wanting to go straight, so I need to compensate with the steering wheel (just a tiny bit). If I let off the throttle, the car wants to turn into the turn and I have to compensate again with the steering.QUOTE]
What you just described is completely normal behavior for any car.
What you just described is completely normal behavior for any car.
Jan 22, 2006 | 03:18 PM
#30
Originally Posted by Maron
That is a first, a stock evo that feels twitchy?
Originally Posted by Maron
Try looking deeper into the turns instead of directly infront of you. I honestly don't think that you have any idea of how much grip and the amount of cornering speed you can carry around the wider sweepers.
Originally Posted by sponge bob
What you just described is completely normal behavior for any car.
Originally Posted by 501
yea it could be just getting used to the steering as it is sensitive.
Maybe I'll get a passenger and try to make a short vid of the behavoiur...then I will not have to describe it and you can all see.... I'll attempt that this week...