Rear Diff Options - Power Oversteer Found Here
Two questions come up in the last few posts:
Jarrod, you said that you ran Diaqueen along with some Redline LSD additive to reduce the locking... then drained and filled with Redline xx/xxx and increased both the noise and the lock. Any reason not to just refill with Diaqueen, and NOT add the LSD additive? (so you do NOT reduce the locking)? Curious here for sure..
Dave Buschur: Your point is taken, most any AWD or FWD car can be made to rotate WITHOUT adding a rear diff. I agree. However, what I have seen is the limited camber, and likely a bit of toe out in the rear to acheive this works great to make a car loose. However what alot of long standing suspension engineers have shown as well is that with the rear diff upgrade, one can more camber back to the rear, this will allow for better grip in long steady state corners, where a loose car can well... let loose, then you stomp the gas to catch it. The diff allows for a more neutral steady state cornering, and to get back to the throttle quicker.
Take all this as a simple statement of opinion, but just what I have read/experienced/driven...
Jarrod, you said that you ran Diaqueen along with some Redline LSD additive to reduce the locking... then drained and filled with Redline xx/xxx and increased both the noise and the lock. Any reason not to just refill with Diaqueen, and NOT add the LSD additive? (so you do NOT reduce the locking)? Curious here for sure..
Dave Buschur: Your point is taken, most any AWD or FWD car can be made to rotate WITHOUT adding a rear diff. I agree. However, what I have seen is the limited camber, and likely a bit of toe out in the rear to acheive this works great to make a car loose. However what alot of long standing suspension engineers have shown as well is that with the rear diff upgrade, one can more camber back to the rear, this will allow for better grip in long steady state corners, where a loose car can well... let loose, then you stomp the gas to catch it. The diff allows for a more neutral steady state cornering, and to get back to the throttle quicker.
Take all this as a simple statement of opinion, but just what I have read/experienced/driven...
bassicfun, I agree, 100%. I was only trying to be helpful in my first post, with my experiences, that is all.
This thread has made me pull apart my original RS rear diff actually. I swapped it in the spring with another good used one because it was noisy. Since my plans with my car don't involve just drag racing it and it would surely handle BETTER with a different alignment and such, the rear diff makes sense. It also makes sense for the 1/4 mile, which I still need to get the car to run the 8 second pass I set out to do. Anyway, I pulled apart the original diff that was in the car to give it to Dan to make it lock up. What I found was shocking. The drivers side portion of the diff that actually holds the bearing was BROKEN completely off. I guess that's where my noise was coming from! So we have a junk diff, good thing I didn't sell it to anyone. I was amazed that after the abuse the car saw that the ring and pinion literally look like new.
This thread has made me pull apart my original RS rear diff actually. I swapped it in the spring with another good used one because it was noisy. Since my plans with my car don't involve just drag racing it and it would surely handle BETTER with a different alignment and such, the rear diff makes sense. It also makes sense for the 1/4 mile, which I still need to get the car to run the 8 second pass I set out to do. Anyway, I pulled apart the original diff that was in the car to give it to Dan to make it lock up. What I found was shocking. The drivers side portion of the diff that actually holds the bearing was BROKEN completely off. I guess that's where my noise was coming from! So we have a junk diff, good thing I didn't sell it to anyone. I was amazed that after the abuse the car saw that the ring and pinion literally look like new.
Yeah you can make an Evo oversteer with more rear weight transfer than front (ie, big rear bar) but that's not what we want. I like a touch of corner entry oversteer usually dialed in with rear rebound, mid corner neutral, and controllable corner exit oversteer. I say controllable as I want to control it with throttle. To be able to do that, it sounds like the Diff is the answer.
I personally haven't gotten it for the evo yet, but autocrossing my buddy's STi I can tell a massive difference on the throttle out of corners. So much more progressive than my car. The tail will wag more with more throttle and less with less. Also, were doing this with basic car at maybe 300hp so were definitely aren't rotating by just completely overpowering the tires.
I personally haven't gotten it for the evo yet, but autocrossing my buddy's STi I can tell a massive difference on the throttle out of corners. So much more progressive than my car. The tail will wag more with more throttle and less with less. Also, were doing this with basic car at maybe 300hp so were definitely aren't rotating by just completely overpowering the tires.
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Joined: Sep 2009
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From: seattle
Dave,
I'm very familiar with Eric Urness' EVO suspension/diff development during the last three months.
When Eric says that the car understeers, he's comparing it to the 450lb (w/o driver) autocross car we built at college for Formula SAE - that car reacted faster than most drivers could think about applying inputs. Also, the course which he most commonly raced the car on, is a series of 30-40mph corners - tighter than most autocross courses and very, very much tighter than any road course corner. The EVO's balance is markedly different in 100'+ radius sweepers and 50' radius small corners, moving more toward understeer as the corner gets tighter.
There are people in the Motorsports forum here and on other boards, who have widespread experience setting up many brands/platforms as autocross cars, and every once in a while, you will see them point out that the ~1000lb front corner weights of EVOs are an enormous problem.
My message is simply that unless you have been running 285 Hoosiers and running super tiny courses as part of your experience, then Eric's EVO and your EVO are apples and oranges. Eric's EVO was always great fun on the street with enough rotation to go to jail, or agricultural. Once he slapped on the big wheel/tire setup, and tried to race a track with 12 U-turns, the understeer started slowing down his lap times.
Eric knows who I am and can vouch.
Matt
I'm very familiar with Eric Urness' EVO suspension/diff development during the last three months.
When Eric says that the car understeers, he's comparing it to the 450lb (w/o driver) autocross car we built at college for Formula SAE - that car reacted faster than most drivers could think about applying inputs. Also, the course which he most commonly raced the car on, is a series of 30-40mph corners - tighter than most autocross courses and very, very much tighter than any road course corner. The EVO's balance is markedly different in 100'+ radius sweepers and 50' radius small corners, moving more toward understeer as the corner gets tighter.
There are people in the Motorsports forum here and on other boards, who have widespread experience setting up many brands/platforms as autocross cars, and every once in a while, you will see them point out that the ~1000lb front corner weights of EVOs are an enormous problem.
My message is simply that unless you have been running 285 Hoosiers and running super tiny courses as part of your experience, then Eric's EVO and your EVO are apples and oranges. Eric's EVO was always great fun on the street with enough rotation to go to jail, or agricultural. Once he slapped on the big wheel/tire setup, and tried to race a track with 12 U-turns, the understeer started slowing down his lap times.
Eric knows who I am and can vouch.
Matt
bassicfun, I agree, 100%. I was only trying to be helpful in my first post, with my experiences, that is all.
This thread has made me pull apart my original RS rear diff actually. I swapped it in the spring with another good used one because it was noisy. Since my plans with my car don't involve just drag racing it and it would surely handle BETTER with a different alignment and such, the rear diff makes sense. It also makes sense for the 1/4 mile, which I still need to get the car to run the 8 second pass I set out to do. Anyway, I pulled apart the original diff that was in the car to give it to Dan to make it lock up. What I found was shocking. The drivers side portion of the diff that actually holds the bearing was BROKEN completely off. I guess that's where my noise was coming from! So we have a junk diff, good thing I didn't sell it to anyone. I was amazed that after the abuse the car saw that the ring and pinion literally look like new.
This thread has made me pull apart my original RS rear diff actually. I swapped it in the spring with another good used one because it was noisy. Since my plans with my car don't involve just drag racing it and it would surely handle BETTER with a different alignment and such, the rear diff makes sense. It also makes sense for the 1/4 mile, which I still need to get the car to run the 8 second pass I set out to do. Anyway, I pulled apart the original diff that was in the car to give it to Dan to make it lock up. What I found was shocking. The drivers side portion of the diff that actually holds the bearing was BROKEN completely off. I guess that's where my noise was coming from! So we have a junk diff, good thing I didn't sell it to anyone. I was amazed that after the abuse the car saw that the ring and pinion literally look like new.
Dave,
I'm very familiar with Eric Urness' EVO suspension/diff development during the last three months.
When Eric says that the car understeers, he's comparing it to the 450lb (w/o driver) autocross car we built at college for Formula SAE - that car reacted faster than most drivers could think about applying inputs. Also, the course which he most commonly raced the car on, is a series of 30-40mph corners - tighter than most autocross courses and very, very much tighter than any road course corner. The EVO's balance is markedly different in 100'+ radius sweepers and 50' radius small corners, moving more toward understeer as the corner gets tighter.
There are people in the Motorsports forum here and on other boards, who have widespread experience setting up many brands/platforms as autocross cars, and every once in a while, you will see them point out that the ~1000lb front corner weights of EVOs are an enormous problem.
My message is simply that unless you have been running 285 Hoosiers and running super tiny courses as part of your experience, then Eric's EVO and your EVO are apples and oranges. Eric's EVO was always great fun on the street with enough rotation to go to jail, or agricultural. Once he slapped on the big wheel/tire setup, and tried to race a track with 12 U-turns, the understeer started slowing down his lap times.
Eric knows who I am and can vouch.
Matt
I'm very familiar with Eric Urness' EVO suspension/diff development during the last three months.
When Eric says that the car understeers, he's comparing it to the 450lb (w/o driver) autocross car we built at college for Formula SAE - that car reacted faster than most drivers could think about applying inputs. Also, the course which he most commonly raced the car on, is a series of 30-40mph corners - tighter than most autocross courses and very, very much tighter than any road course corner. The EVO's balance is markedly different in 100'+ radius sweepers and 50' radius small corners, moving more toward understeer as the corner gets tighter.
There are people in the Motorsports forum here and on other boards, who have widespread experience setting up many brands/platforms as autocross cars, and every once in a while, you will see them point out that the ~1000lb front corner weights of EVOs are an enormous problem.
My message is simply that unless you have been running 285 Hoosiers and running super tiny courses as part of your experience, then Eric's EVO and your EVO are apples and oranges. Eric's EVO was always great fun on the street with enough rotation to go to jail, or agricultural. Once he slapped on the big wheel/tire setup, and tried to race a track with 12 U-turns, the understeer started slowing down his lap times.
Eric knows who I am and can vouch.
Matt
Well put Matt.
David, read my posts in here and I would bet you should rethink your stance on the topic as my initial thoughts were nearly identical to your current thoughts.
My car on low grip 235 street tires is what I would love to have on race tires (lots more grip though, obviously). I would compare it to my old BMW, which being 50/50 and RWD is a far stretch from the EVO. VERY neutral and predictable, but the back end always steps out first. Trail braking or under power, the back end is going to step out a little but the car doesn't want to spin out with the slightest error and can be managed easily with the throttle.
Toss on the 275 stickies and all that went out the window. TONS of understeer. I would bet my car has A LOT more rear bias then yours as well with the spring rates I am running. Put on some big stickies and subject it to 30-60mph corners, truly at the limit of adhesion, let us know how tail happy it is...
My car on low grip 235 street tires is what I would love to have on race tires (lots more grip though, obviously). I would compare it to my old BMW, which being 50/50 and RWD is a far stretch from the EVO. VERY neutral and predictable, but the back end always steps out first. Trail braking or under power, the back end is going to step out a little but the car doesn't want to spin out with the slightest error and can be managed easily with the throttle.
Toss on the 275 stickies and all that went out the window. TONS of understeer. I would bet my car has A LOT more rear bias then yours as well with the spring rates I am running. Put on some big stickies and subject it to 30-60mph corners, truly at the limit of adhesion, let us know how tail happy it is...
Definately. Correct me if Im wrong but I beleive this thread started by Kyooch which actually came from a discussion on another thread about the ACD flash. Just like the rear diff mod, it was a discussion about another way to look at modifying the behavior of the evo to reduce understeer, without having to resort to tuning it like a fwd car (swapping in a huge rear bar). Although a larger rear bar is effective, I think that this is just more of another way to look at it. I now have plenty of mid corner, and corner exit throttle oversteer, and Im still on stock swaybars. I see what your saying though, it is more cost effective and less time consuming to swap in a larger rear bar.
Two questions come up in the last few posts:
Jarrod, you said that you ran Diaqueen along with some Redline LSD additive to reduce the locking... then drained and filled with Redline xx/xxx and increased both the noise and the lock. Any reason not to just refill with Diaqueen, and NOT add the LSD additive? (so you do NOT reduce the locking)? Curious here for sure..
Jarrod, you said that you ran Diaqueen along with some Redline LSD additive to reduce the locking... then drained and filled with Redline xx/xxx and increased both the noise and the lock. Any reason not to just refill with Diaqueen, and NOT add the LSD additive? (so you do NOT reduce the locking)? Curious here for sure..
I assume the TRE rear diff would perform similarly.
weirddd - my cusco's locking so hard it shakes my car at low speeds.. about to switch to amsoil 75w110 svg gear though
Definately. Correct me if Im wrong but I beleive this thread started by Kyooch which actually came from a discussion on another thread about the ACD flash. Just like the rear diff mod, it was a discussion about another way to look at modifying the behavior of the evo to reduce understeer, without having to resort to tuning it like a fwd car (swapping in a huge rear bar). Although a larger rear bar is effective, I think that this is just more of another way to look at it. I now have plenty of mid corner, and corner exit throttle oversteer, and Im still on stock swaybars. I see what your saying though, it is more cost effective and less time consuming to swap in a larger rear bar.
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Joined: Oct 2006
Posts: 56
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From: Taos
Modena diffs are great. Been using them for a while.
http://www.modenaengineering.com.au/
http://www.modenaengineering.com.au/