| Mykl | 06-21-2006 10:32 PM |
1.5 way rear diff in an STi, beneficial or a waste of money?
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The OEM rear LSD is 2-way, for those that aren't familiar with it.
If I had one complaint about how my car drives around a track, or at autocrosses it would be that it's very difficult to make the car rotate in a controlled manner while off the throttle.
I've been searching like crazy and I can't seem to find any STi owners who can comment on what happens to the car when you go with a 1.5-way rear differential. Theoretically it should loosen the car up some and push the car closer to neutral. But I'm hesitant... because a Cusco RS 1.5-way differential isn't exactly cheap, and installing it is a bit of a pain. But if it will loosen the car up a bit during lift throttle situations I'll be more than happy to deal with it.
If I had one complaint about how my car drives around a track, or at autocrosses it would be that it's very difficult to make the car rotate in a controlled manner while off the throttle.
I've been searching like crazy and I can't seem to find any STi owners who can comment on what happens to the car when you go with a 1.5-way rear differential. Theoretically it should loosen the car up some and push the car closer to neutral. But I'm hesitant... because a Cusco RS 1.5-way differential isn't exactly cheap, and installing it is a bit of a pain. But if it will loosen the car up a bit during lift throttle situations I'll be more than happy to deal with it.
| OneArmedScissor | 06-21-2006 11:34 PM |
why would you want it to be looser?
| Mykl | 06-22-2006 12:43 AM |
[QUOTE=Milin]why would you want it to be looser?[/QUOTE]
Because I like it better that way? :confused:
If the rear tires will break away with less effort than they do now around an autocross course the car will be a lot easier to drive fast. Also, a car that maintains nice, smooth, and controllable break-away is a lot more fun to drive pretty much everywhere.
I also feel that if the STi was a little looser on deceleration the car would be a lot more flexible.
Because I like it better that way? :confused:
If the rear tires will break away with less effort than they do now around an autocross course the car will be a lot easier to drive fast. Also, a car that maintains nice, smooth, and controllable break-away is a lot more fun to drive pretty much everywhere.
I also feel that if the STi was a little looser on deceleration the car would be a lot more flexible.
| XeviousR | 06-22-2006 12:59 AM |
What you need isn't a 1.5 way, its a 2 way. A 2 way is locked under accel and decel. A 1.5 way is locked under accel only. The OEM 2 way is garbage. The Cusco unit is much better. I run the Cusco 2 way in the rear of my STi and it helped tremendously. If you want more info about Cusco diffs, talk to my friend Chad at [URL=http://www.napsusa.com]Nukabe Automotive[/URL]. My understanding though is that the 2 way Cusco units can be reassembled to serve as 1.5 ways, so they are 2 in 1.
| Mykl | 06-22-2006 01:06 AM |
[QUOTE=XeviousR]What you need isn't a 1.5 way, its a 2 way. A 2 way is locked under accel and decel. A 1.5 way is locked under accel only. The OEM 2 way is garbage. The Cusco unit is much better. I run the Cusco 2 way in the rear of my STi and it helped tremendously. If you want more info about Cusco diffs, talk to my friend Chad at [URL=http://www.napsusa.com]Nukabe Automotive[/URL]. My understanding though is that the 2 way Cusco units can be reassembled to serve as 1.5 ways, so they are 2 in 1.[/QUOTE]
In your setup what do you have the lock plates adjusted to? 60%, 80%, or 100%?
I read on Cusco's site that their 1.5 way diffs can be reassembled to work as a 2 way diff... and vice versa.
Why do you think I need to stick with a 2-way diff? Wouldn't this promote off throttle understeer? How exactly did it help your car? You're the first person I've found who's actually swapped out the OEM diff in his car. I'm really curious to hear what you've got to say about it.
In your setup what do you have the lock plates adjusted to? 60%, 80%, or 100%?
I read on Cusco's site that their 1.5 way diffs can be reassembled to work as a 2 way diff... and vice versa.
Why do you think I need to stick with a 2-way diff? Wouldn't this promote off throttle understeer? How exactly did it help your car? You're the first person I've found who's actually swapped out the OEM diff in his car. I'm really curious to hear what you've got to say about it.
| XeviousR | 06-22-2006 01:33 AM |
The problem I was experiencing with my STi was that the inside rear wheel would lift off the ground during hard cornering. When this occured, I would loose power to the hovering wheel. The 04 STi comes with a rear LSD, but it did not work well for me. When you loose power to the hovering wheel, you essentially loose all power to the rear, and you are front wheel drive. This is until you loose enough momentum to drop the inside rear again, and if you are accelerating it is likely to jump up again, and can cause an unsettling pogo action. I don't know if you are experiencing this or not. Regardless, a 2 way rear diff will give you more control under accel and decel. The OEM STi less predictable. Unfortunately I can not comment on the effect on installing the 2 way rear diff alone, as I installed a 1.5 way front diff at the same time to combat understeer. I believe my lock plates are adjusted to 80% becuase it is used primarily at the track.
| Mykl | 06-22-2006 07:59 AM |
[QUOTE=XeviousR]The problem I was experiencing with my STi was that the inside rear wheel would lift off the ground during hard cornering. When this occured, I would loose power to the hovering wheel. The 04 STi comes with a rear LSD, but it did not work well for me. When you loose power to the hovering wheel, you essentially loose all power to the rear, and you are front wheel drive. This is until you loose enough momentum to drop the inside rear again, and if you are accelerating it is likely to jump up again, and can cause an unsettling pogo action. I don't know if you are experiencing this or not. Regardless, a 2 way rear diff will give you more control under accel and decel. The OEM STi less predictable. Unfortunately I can not comment on the effect on installing the 2 way rear diff alone, as I installed a 1.5 way front diff at the same time to combat understeer. I believe my lock plates are adjusted to 80% becuase it is used primarily at the track.[/QUOTE]
What kind of coilovers do you have? Spring stiffness? Swaybars?
What kind of coilovers do you have? Spring stiffness? Swaybars?
| Turn in Concepts | 06-22-2006 08:07 AM |
When we lift the inside wheel it spins like mad. the diff doesn't work when one wheel is in the air.
| Mykl | 06-22-2006 08:15 AM |
[QUOTE=Turn in Concepts]When we lift the inside wheel it spins like mad. the diff doesn't work when one wheel is in the air.[/QUOTE]
Can this behavior not be tuned out with different swaybars?
If the diff doesn't work when one wheel is in the air then what difference does it make if it's 1.5 way or 2 way? Also, I was under the impression that only mechanical torsen type diffs like Quaiffes and the OEM Suretrac stopped working entirely when one side was in the air, but the clutch type diffs would still lock.
Can this behavior not be tuned out with different swaybars?
If the diff doesn't work when one wheel is in the air then what difference does it make if it's 1.5 way or 2 way? Also, I was under the impression that only mechanical torsen type diffs like Quaiffes and the OEM Suretrac stopped working entirely when one side was in the air, but the clutch type diffs would still lock.
| 10th Warrior | 06-22-2006 08:54 AM |
[QUOTE=Mykl]Can this behavior not be tuned out with different swaybars?
If the diff doesn't work when one wheel is in the air then what difference does it make if it's 1.5 way or 2 way? Also, I was under the impression that only mechanical torsen type diffs like Quaiffes and the OEM Suretrac stopped working entirely when one side was in the air, but the clutch type diffs would still lock.[/QUOTE]
no, even if you run no sways you'll still get inside rear lift. Its just the way it is.
As for the diff not working or should be working with a wheel in the air, you are correct. However, the OE diff isn't very good, and there is enough torque stock to overcome its resistance (it is a [I]limited[/I] slip, after all). The Cusco diff (I co-drive with James) is much, much stronger, better designed unit and actually does what its supposed to. The car is considerably more predictable and faster. As an example of how good the Cusco diff is, with a broken half-shaft, it chirped the unbroken side on the shift. It was pretty amazing. Even drove onto the trailer no problem. Its well worth the money, IMHO.
If the diff doesn't work when one wheel is in the air then what difference does it make if it's 1.5 way or 2 way? Also, I was under the impression that only mechanical torsen type diffs like Quaiffes and the OEM Suretrac stopped working entirely when one side was in the air, but the clutch type diffs would still lock.[/QUOTE]
no, even if you run no sways you'll still get inside rear lift. Its just the way it is.
As for the diff not working or should be working with a wheel in the air, you are correct. However, the OE diff isn't very good, and there is enough torque stock to overcome its resistance (it is a [I]limited[/I] slip, after all). The Cusco diff (I co-drive with James) is much, much stronger, better designed unit and actually does what its supposed to. The car is considerably more predictable and faster. As an example of how good the Cusco diff is, with a broken half-shaft, it chirped the unbroken side on the shift. It was pretty amazing. Even drove onto the trailer no problem. Its well worth the money, IMHO.
| Mykl | 06-22-2006 10:05 AM |
[QUOTE=10th Warrior]no, even if you run no sways you'll still get inside rear lift. Its just the way it is.
As for the diff not working or should be working with a wheel in the air, you are correct. However, the OE diff isn't very good, and there is enough torque stock to overcome its resistance (it is a [I]limited[/I] slip, after all). The Cusco diff (I co-drive with James) is much, much stronger, better designed unit and actually does what its supposed to. The car is considerably more predictable and faster. As an example of how good the Cusco diff is, with a broken half-shaft, it chirped the unbroken side on the shift. It was pretty amazing. Even drove onto the trailer no problem. Its well worth the money, IMHO.[/QUOTE]
Awesome endorsement, then a Cusco diff will be put right at the top of my shopping list. Now it's really just a matter of finding the time to actually install it.
Back to the rear wheel lift scenario...
Clutch type mechanical differentials still function when one wheel is lifted and the other isn't and torsen types don't, correct? So basically the lesson here is to run a clutch type diff and not a torsen type in the rear.
What I don't understand is why we're talking about lifting the rear wheel in the first place. A 1.5-way (or even 1-way) diff is going to maintain the same lockup ratio when you get on the throttle as a 2-way will. So why does it matter? Any quality clutch type LSD is going to solve the acceleration issue that occurs when a rear wheel is lifted, it doesn't seem to matter what the deceleration lockup ratio is.
As for the diff not working or should be working with a wheel in the air, you are correct. However, the OE diff isn't very good, and there is enough torque stock to overcome its resistance (it is a [I]limited[/I] slip, after all). The Cusco diff (I co-drive with James) is much, much stronger, better designed unit and actually does what its supposed to. The car is considerably more predictable and faster. As an example of how good the Cusco diff is, with a broken half-shaft, it chirped the unbroken side on the shift. It was pretty amazing. Even drove onto the trailer no problem. Its well worth the money, IMHO.[/QUOTE]
Awesome endorsement, then a Cusco diff will be put right at the top of my shopping list. Now it's really just a matter of finding the time to actually install it.
Back to the rear wheel lift scenario...
Clutch type mechanical differentials still function when one wheel is lifted and the other isn't and torsen types don't, correct? So basically the lesson here is to run a clutch type diff and not a torsen type in the rear.
What I don't understand is why we're talking about lifting the rear wheel in the first place. A 1.5-way (or even 1-way) diff is going to maintain the same lockup ratio when you get on the throttle as a 2-way will. So why does it matter? Any quality clutch type LSD is going to solve the acceleration issue that occurs when a rear wheel is lifted, it doesn't seem to matter what the deceleration lockup ratio is.
| 10th Warrior | 06-22-2006 12:27 PM |
[quote]Clutch type mechanical differentials still function when one wheel is lifted and the other isn't and torsen types don't, correct?[/quote]
Correct. A torsen type diff requires resistance, the clutch packs in a clutch type provide that resistance even if nothing else (the ground and resultant friction) is removed from the scenario.
[quote]basically the lesson here is to run a clutch type diff and not a torsen type in the rear.[/quote]
also correct. Just make sure the clutch packs have enough resistance to shift the torque when one wheel has total slip. The cusco obviously does :)
[quote]A 1.5-way (or even 1-way) diff is going to maintain the same lockup ratio when you get on the throttle as a 2-way will. So why does it matter?[/quote]
A good question. I think you are mostly right that there won't be a difference between the 1.5 and the 2. However, with big stickies, we do tend to first lift the inside before we're back on the throttle. In that situation, the 2 way might help in keeping everything spinning as it should. One could envision a similar situation in a long sweeper where you balence with the throttle; a little on, a little off. Ultimately though, I don't know. As you know, they aren't cheap and not exactly a picnic to swap, so it makes testing different diff settings beyond the reach of most of us, present company included :) Thus I can't say for sure. What I do know, is that the Cusco 2-way is a huge improvement over stock. Whether there is a significant difference between the 1.5-way and the 2-way, I don't know. I would imagine they would be similar, but can't say for sure. Either would be better than stock.
Hope this helps!
Correct. A torsen type diff requires resistance, the clutch packs in a clutch type provide that resistance even if nothing else (the ground and resultant friction) is removed from the scenario.
[quote]basically the lesson here is to run a clutch type diff and not a torsen type in the rear.[/quote]
also correct. Just make sure the clutch packs have enough resistance to shift the torque when one wheel has total slip. The cusco obviously does :)
[quote]A 1.5-way (or even 1-way) diff is going to maintain the same lockup ratio when you get on the throttle as a 2-way will. So why does it matter?[/quote]
A good question. I think you are mostly right that there won't be a difference between the 1.5 and the 2. However, with big stickies, we do tend to first lift the inside before we're back on the throttle. In that situation, the 2 way might help in keeping everything spinning as it should. One could envision a similar situation in a long sweeper where you balence with the throttle; a little on, a little off. Ultimately though, I don't know. As you know, they aren't cheap and not exactly a picnic to swap, so it makes testing different diff settings beyond the reach of most of us, present company included :) Thus I can't say for sure. What I do know, is that the Cusco 2-way is a huge improvement over stock. Whether there is a significant difference between the 1.5-way and the 2-way, I don't know. I would imagine they would be similar, but can't say for sure. Either would be better than stock.
Hope this helps!
| Mykl | 06-22-2006 01:06 PM |
[QUOTE=10th Warrior]Hope this helps![/QUOTE]
Absolutely. I've been obsessing over this for the last few days and every bit of useful information I can get my hands on is good. At first I was having a difficult time separating the useful info from the not so useful info. But now that I have a solid understanding of how clutch type differentials work I feel that I can make an informed decision.
stretch over on iwsti.com pointed me to this...
[quote]Contrary to what manufactures want you to believe, TRD-Toyota Technocraft, Mugen-Honda Racing, RalliArt-Mitsubishi Rally Operations, MazdaSpeed-Mazda, [b]STI-Subaru Technica Int.[/b], NISMO- Nissan Motorsports, all have their LSD's made by the same supplier, a Hitachi subsidiary. This is because the majority of the normal differential gears are supplied by them. They use the cheap factory casing and re-work the inside. This limits the size and number of the gears, and clutches thereby sacrificing true potential. They claim 4 pinions but have only 3 or 4 small clutches on one side. They use very high cam profile to put high loads on the clutches so that it can achieve high lock up. [b]The problem with this approach is that the pre-load on the clutches are higher and tires have constant drag.[/b] Also, since the clutches are small and few, the load is larger per given surface area, translating into higher operating temperatures and fast wear. [b]Another major disadvantage to this type of LSD has to be the abrupt lock-up, making on-off conditions less predictable and controllable.[/b] [/quote]
[url]http://www.club4ag.com/faq%20and%20tech_pages/limited_slips_differential_101.htm[/url]
That seems to be a good explanation for why our OEM clutch diffs are so crappy.
Another problem I was encountering was early in my research I assumed that our OEM rear diffs were normal, healthy functioning 2-way differentials. Which they are not. So the question isn't so much whether or not an aftermarket 1.5 way or 2 way is better for the STi, it's a matter of knowing that either is a lot better than stock, as you've said.
With this in mind, the 1.5 way versus 2 way thing seems to be a relatively insignificant question. I'm under the impression that the choice comes down to your personal driving style and preferences and really doesn't affect the overall performance limits of the car.
Absolutely. I've been obsessing over this for the last few days and every bit of useful information I can get my hands on is good. At first I was having a difficult time separating the useful info from the not so useful info. But now that I have a solid understanding of how clutch type differentials work I feel that I can make an informed decision.
stretch over on iwsti.com pointed me to this...
[quote]Contrary to what manufactures want you to believe, TRD-Toyota Technocraft, Mugen-Honda Racing, RalliArt-Mitsubishi Rally Operations, MazdaSpeed-Mazda, [b]STI-Subaru Technica Int.[/b], NISMO- Nissan Motorsports, all have their LSD's made by the same supplier, a Hitachi subsidiary. This is because the majority of the normal differential gears are supplied by them. They use the cheap factory casing and re-work the inside. This limits the size and number of the gears, and clutches thereby sacrificing true potential. They claim 4 pinions but have only 3 or 4 small clutches on one side. They use very high cam profile to put high loads on the clutches so that it can achieve high lock up. [b]The problem with this approach is that the pre-load on the clutches are higher and tires have constant drag.[/b] Also, since the clutches are small and few, the load is larger per given surface area, translating into higher operating temperatures and fast wear. [b]Another major disadvantage to this type of LSD has to be the abrupt lock-up, making on-off conditions less predictable and controllable.[/b] [/quote]
[url]http://www.club4ag.com/faq%20and%20tech_pages/limited_slips_differential_101.htm[/url]
That seems to be a good explanation for why our OEM clutch diffs are so crappy.
Another problem I was encountering was early in my research I assumed that our OEM rear diffs were normal, healthy functioning 2-way differentials. Which they are not. So the question isn't so much whether or not an aftermarket 1.5 way or 2 way is better for the STi, it's a matter of knowing that either is a lot better than stock, as you've said.
With this in mind, the 1.5 way versus 2 way thing seems to be a relatively insignificant question. I'm under the impression that the choice comes down to your personal driving style and preferences and really doesn't affect the overall performance limits of the car.
| crystalhelix | 06-22-2006 01:14 PM |
Stupid Q maybe....when moving to a clutch type do you not use fluid in the rear diff or are they wet-type clutch paks? Just curious as I know my MC used a wet clutch. I am just wondering if you have to clean out the rear housing etc....
| Mykl | 06-22-2006 01:29 PM |
[QUOTE=crystalhelix]Stupid Q maybe....when moving to a clutch type do you not use fluid in the rear diff or are they wet-type clutch paks? Just curious as I know my MC used a wet clutch. I am just wondering if you have to clean out the rear housing etc....[/QUOTE]
Our OEM rear differentials are a clutch type, so yeah... they're wet-type clutch's. Aftermarket differentials are no different.
Our OEM rear differentials are a clutch type, so yeah... they're wet-type clutch's. Aftermarket differentials are no different.
| Mykl | 06-22-2006 01:55 PM |
One more question for the guys with Cusco diffs...
Do you feel that the car is easier to coax into rotation when you're going into, and going through a turn? Does it eliminate some of the understeer that occurs on turn-in when you're driving at the limits of the car?
You guys tell me it's an improvement, but in what way? Can you describe how it changes the characteristics of the car?
Do you feel that the car is easier to coax into rotation when you're going into, and going through a turn? Does it eliminate some of the understeer that occurs on turn-in when you're driving at the limits of the car?
You guys tell me it's an improvement, but in what way? Can you describe how it changes the characteristics of the car?
| crystalhelix | 06-22-2006 02:02 PM |
Mykl - what kind of suspension and adjustments do you have? Are you referring to a stock STi? I have corrected most of those issues but I am nowhere near stock..but I do need a pimpy rear diff as well.
J
J
| Mykl | 06-22-2006 02:09 PM |
[QUOTE=crystalhelix]Mykl - what kind of suspension and adjustments do you have? Are you referring to a stock STi? I have corrected most of those issues but I am nowhere near stock..but I do need a pimpy rear diff as well.
J[/QUOTE]
I have a Cobb front swaybar, otherwise I'm stock. I'm still in the process of putting together a good shopping list because I plan to have '05 hubs on my '04 STi before this season is over. I'll be going with KW V3 coilovers and Whiteline front and rear swaybars.
I'll probably run 255 width Toyo RA1's for tires starting next season. I'd go with V710's, but I want a tire that's flexible enough for track days and I don't want to have eleventy billion spare wheels sitting around my apartment. I'm not really looking to be terribly competitive in Solo II anyway, I autocross mostly because it's a fun.
J[/QUOTE]
I have a Cobb front swaybar, otherwise I'm stock. I'm still in the process of putting together a good shopping list because I plan to have '05 hubs on my '04 STi before this season is over. I'll be going with KW V3 coilovers and Whiteline front and rear swaybars.
I'll probably run 255 width Toyo RA1's for tires starting next season. I'd go with V710's, but I want a tire that's flexible enough for track days and I don't want to have eleventy billion spare wheels sitting around my apartment. I'm not really looking to be terribly competitive in Solo II anyway, I autocross mostly because it's a fun.
| AUTOwrXER | 06-22-2006 03:41 PM |
[QUOTE=10th Warrior]no, even if you run no sways you'll still get inside rear lift. Its just the way it is.[/QUOTE]
It doesn't have to be that way. Add front spring, rear droop, and zzyzxmotorsports.com ;)
It doesn't have to be that way. Add front spring, rear droop, and zzyzxmotorsports.com ;)
| AUTOwrXER | 06-22-2006 03:47 PM |
[QUOTE=Mykl]One more question for the guys with Cusco diffs...
Do you feel that the car is easier to coax into rotation when you're going into, and going through a turn? Does it eliminate some of the understeer that occurs on turn-in when you're driving at the limits of the car?
You guys tell me it's an improvement, but in what way? Can you describe how it changes the characteristics of the car?[/QUOTE]
If you're trying to tune out understeer, the rear diff is one of the last places I would turn to. The rear diff is important, but it is important for delivering power (i.e. the last 1/3rd of the corner). The center diff is a bigger factor when it comes to the diffs' effect on balance, but there are other things that you can do to change balance that don't involve swapping parts. My suggestion is to try raising your rear ride height by 1/4" - 1/2" for starters.
Do you feel that the car is easier to coax into rotation when you're going into, and going through a turn? Does it eliminate some of the understeer that occurs on turn-in when you're driving at the limits of the car?
You guys tell me it's an improvement, but in what way? Can you describe how it changes the characteristics of the car?[/QUOTE]
If you're trying to tune out understeer, the rear diff is one of the last places I would turn to. The rear diff is important, but it is important for delivering power (i.e. the last 1/3rd of the corner). The center diff is a bigger factor when it comes to the diffs' effect on balance, but there are other things that you can do to change balance that don't involve swapping parts. My suggestion is to try raising your rear ride height by 1/4" - 1/2" for starters.
| AUTOwrXER | 06-22-2006 03:50 PM |
[QUOTE=Mykl]I'll be going with KW V3 coilovers and...[/QUOTE]
Why would you want to buy coilovers that gave you no droop in the rear? If you don't know what we're talking about when it comes to spinning the inside rear wheel, you soon will.
Why would you want to buy coilovers that gave you no droop in the rear? If you don't know what we're talking about when it comes to spinning the inside rear wheel, you soon will.
| Mykl | 06-22-2006 04:04 PM |
[QUOTE=AUTOwrXER]If you're trying to tune out understeer, the rear diff is one of the last places I would turn to. The rear diff is important, but it is important for delivering power (i.e. the last 1/3rd of the corner). The center diff is a bigger factor when it comes to the diffs' effect on balance, but there are other things that you can do to change balance that don't involve swapping parts. My suggestion is to try raising your rear ride height by 1/4" - 1/2" for starters.[/QUOTE]
I'm trying to reduce understeer, not increase oversteer. How would raising the rear of the car help? I've never heard anybody offer this solution to the issue so I'm not entirely sure how it would work.
What does the center diff have to do with this? On the brakes the DCCD controller is mostly unlocked.
[QUOTE=AUTOwrXER]Why would you want to buy coilovers that gave you no droop in the rear? If you don't know what we're talking about when it comes to spinning the inside rear wheel, you soon will.[/QUOTE]
This conflicts with pretty much everything I've read about the KW's. I was under the impression that they had quite good droop travel in the rear.
What coilovers would you recommend? I haven't started ordering parts, so I'm open to suggestion.
I'm trying to reduce understeer, not increase oversteer. How would raising the rear of the car help? I've never heard anybody offer this solution to the issue so I'm not entirely sure how it would work.
What does the center diff have to do with this? On the brakes the DCCD controller is mostly unlocked.
[QUOTE=AUTOwrXER]Why would you want to buy coilovers that gave you no droop in the rear? If you don't know what we're talking about when it comes to spinning the inside rear wheel, you soon will.[/QUOTE]
This conflicts with pretty much everything I've read about the KW's. I was under the impression that they had quite good droop travel in the rear.
What coilovers would you recommend? I haven't started ordering parts, so I'm open to suggestion.
| AUTOwrXER | 06-22-2006 04:27 PM |
So here's the thing. The handling balance of a car is either understeer (aka push, aka plow, etc.), neutral, or oversteer (aka loose, aka super dorifto, etc.). Understeer and oversteer aren't seperate quantities that you increase or decrease, they are just terms that describe the car's balance. If you are trying to get rid of understeer, you can do so by increasing front grip or reducing rear grip. Given that you haven't started building the car yet, what you need to do is maximize front grip with the new suspension, wheels, tires, alignment, etc. and then revisit this conversation.
The center diff affects a car's handling balance both in steady-state and power-on situations. During steady state cornering the front wheels and rear wheels describe a different arc. In other words the rear wheels are moving along a smaller diameter circle than the front wheels. The difference between front and rear axle speeds is handled by the center diff. If that diff resists the difference in speed, then it resists the car's ability to turn, and therefore it creates understeer. When the driver starts to pick up the throttle, the center diff controls the distribution of torque. A center diff that favors the front wheels (like in the Evo) will cause throttle-on understeer. A center diff that favors the rear wheels will cause throttle-on oversteer. The center diff is very critical in the way an AWD car handles.
If you want a second opinion on the KW coilovers, talk to Courtney Cormier or Junior Johnson. They tried to campaign a car nationally last year with the race DA KWs. They had issues with rear droop. Maybe KW has come out with a significantly longer shock for use in the rear, but a minor change to the shock housing will not fix the problem that Courtney and Junior had. If you want my recommendation, it is to spend the money and do it right the first time. I've had 4 suspensions on 2 different WRXs, and I would have saved a lot of money in the long run (and gone faster) if I bought the zzyzxmotorsports coilovers instead of doing it over, and over, and over again.
The center diff affects a car's handling balance both in steady-state and power-on situations. During steady state cornering the front wheels and rear wheels describe a different arc. In other words the rear wheels are moving along a smaller diameter circle than the front wheels. The difference between front and rear axle speeds is handled by the center diff. If that diff resists the difference in speed, then it resists the car's ability to turn, and therefore it creates understeer. When the driver starts to pick up the throttle, the center diff controls the distribution of torque. A center diff that favors the front wheels (like in the Evo) will cause throttle-on understeer. A center diff that favors the rear wheels will cause throttle-on oversteer. The center diff is very critical in the way an AWD car handles.
If you want a second opinion on the KW coilovers, talk to Courtney Cormier or Junior Johnson. They tried to campaign a car nationally last year with the race DA KWs. They had issues with rear droop. Maybe KW has come out with a significantly longer shock for use in the rear, but a minor change to the shock housing will not fix the problem that Courtney and Junior had. If you want my recommendation, it is to spend the money and do it right the first time. I've had 4 suspensions on 2 different WRXs, and I would have saved a lot of money in the long run (and gone faster) if I bought the zzyzxmotorsports coilovers instead of doing it over, and over, and over again.
| Mykl | 06-22-2006 04:42 PM |
[QUOTE=AUTOwrXER]So here's the thing. The handling balance of a car is either understeer (aka push, aka plow, etc.), neutral, or oversteer (aka loose, aka super dorifto, etc.). Understeer and oversteer aren't seperate quantities that you increase or decrease, they are just terms that describe the car's balance. If you are trying to get rid of understeer, you can do so by increasing front grip or reducing rear grip. Given that you haven't started building the car yet, what you need to do is maximize front grip with the new suspension, wheels, tires, alignment, etc. and then revisit this conversation.[/quote]
Fair enough. I had the thought that perhaps taking the approach of doing my drivetrain modifications first, and then tuning the suspension around it would be a good idea. If you think it's a better idea to get my suspension sorted and then consider the differential upgrade, I'll put more consideration into that route.
[QUOTE=AUTOwrXER]The center diff affects a car's handling balance both in steady-state and power-on situations. During steady state cornering the front wheels and rear wheels describe a different arc. In other words the rear wheels are moving along a smaller diameter circle than the front wheels. The difference between front and rear axle speeds is handled by the center diff. If that diff resists the difference in speed, then it resists the car's ability to turn, and therefore it creates understeer. When the driver starts to pick up the throttle, the center diff controls the distribution of torque. A center diff that favors the front wheels (like in the Evo) will cause throttle-on understeer. A center diff that favors the rear wheels will cause throttle-on oversteer. The center diff is very critical in the way an AWD car handles.[/quote]
As you know, the STi has a variable locking center differential. During steady state cornering and braking, the center differential is mostly unlocked. As the driver starts to throttle out of a turn the DCCD controller begins ramping up the lock ratio, and of course inducing understeer... which is neutralized when power overwhelms the rear tires. At least that's how my STi drives out of turns, I'm not sure about yours.
But my issue isn't with post apex behavior. I love the way the STi drives out of turns. It's going into turns that I'm not so happy about. This is why I do not simply want to increase oversteer, because the car is already pretty loose when you're on the throttle. I don't want my post-apex drive to suffer because I wanted a car that would rotate more easily pre-apex.
Perhaps my initial impression was incorrect. I thought that perhaps the 2-way action on the OEM rear differential had a strangle hold on the car. The theory was that it provided enough extra grip at the rear under deceleration that it overwhelms the front tires.
[QUOTE=AUTOwrXER]If you want a second opinion on the KW coilovers, talk to Courtney Cormier or Junior Johnson. They tried to campaign a car nationally last year with the race DA KWs. They had issues with rear droop. Maybe KW has come out with a significantly longer shock for use in the rear, but a minor change to the shock housing will not fix the problem that Courtney and Junior had. If you want my recommendation, it is to spend the money and do it right the first time. I've had 4 suspensions on 2 different WRXs, and I would have saved a lot of money in the long run (and gone faster) if I bought the zzyzxmotorsports coilovers instead of doing it over, and over, and over again.[/QUOTE]
I want as many opinions as I can get. How much are these xxyzxmotorsports coilovers?
Fair enough. I had the thought that perhaps taking the approach of doing my drivetrain modifications first, and then tuning the suspension around it would be a good idea. If you think it's a better idea to get my suspension sorted and then consider the differential upgrade, I'll put more consideration into that route.
[QUOTE=AUTOwrXER]The center diff affects a car's handling balance both in steady-state and power-on situations. During steady state cornering the front wheels and rear wheels describe a different arc. In other words the rear wheels are moving along a smaller diameter circle than the front wheels. The difference between front and rear axle speeds is handled by the center diff. If that diff resists the difference in speed, then it resists the car's ability to turn, and therefore it creates understeer. When the driver starts to pick up the throttle, the center diff controls the distribution of torque. A center diff that favors the front wheels (like in the Evo) will cause throttle-on understeer. A center diff that favors the rear wheels will cause throttle-on oversteer. The center diff is very critical in the way an AWD car handles.[/quote]
As you know, the STi has a variable locking center differential. During steady state cornering and braking, the center differential is mostly unlocked. As the driver starts to throttle out of a turn the DCCD controller begins ramping up the lock ratio, and of course inducing understeer... which is neutralized when power overwhelms the rear tires. At least that's how my STi drives out of turns, I'm not sure about yours.
But my issue isn't with post apex behavior. I love the way the STi drives out of turns. It's going into turns that I'm not so happy about. This is why I do not simply want to increase oversteer, because the car is already pretty loose when you're on the throttle. I don't want my post-apex drive to suffer because I wanted a car that would rotate more easily pre-apex.
Perhaps my initial impression was incorrect. I thought that perhaps the 2-way action on the OEM rear differential had a strangle hold on the car. The theory was that it provided enough extra grip at the rear under deceleration that it overwhelms the front tires.
[QUOTE=AUTOwrXER]If you want a second opinion on the KW coilovers, talk to Courtney Cormier or Junior Johnson. They tried to campaign a car nationally last year with the race DA KWs. They had issues with rear droop. Maybe KW has come out with a significantly longer shock for use in the rear, but a minor change to the shock housing will not fix the problem that Courtney and Junior had. If you want my recommendation, it is to spend the money and do it right the first time. I've had 4 suspensions on 2 different WRXs, and I would have saved a lot of money in the long run (and gone faster) if I bought the zzyzxmotorsports coilovers instead of doing it over, and over, and over again.[/QUOTE]
I want as many opinions as I can get. How much are these xxyzxmotorsports coilovers?
| maxQ | 06-22-2006 04:42 PM |
[QUOTE=AUTOwrXER]
If you want a second opinion on the KW coilovers, talk to Courtney Cormier or Junior Johnson. They tried to campaign a car nationally last year with the race DA KWs. They had issues with rear droop. Maybe KW has come out with a significantly longer shock for use in the rear, but a minor change to the shock housing will not fix the problem that Courtney and Junior had. If you want my recommendation, it is to spend the money and do it right the first time. I've had 4 suspensions on 2 different WRXs, and I would have saved a lot of money in the long run (and gone faster) if I bought the zzyzxmotorsports coilovers instead of doing it over, and over, and over again.[/QUOTE]
Surprisingly enough, on that exact car, I disconnected the rear swaybar and the rears stay planted... at least on street tires.
If you want a second opinion on the KW coilovers, talk to Courtney Cormier or Junior Johnson. They tried to campaign a car nationally last year with the race DA KWs. They had issues with rear droop. Maybe KW has come out with a significantly longer shock for use in the rear, but a minor change to the shock housing will not fix the problem that Courtney and Junior had. If you want my recommendation, it is to spend the money and do it right the first time. I've had 4 suspensions on 2 different WRXs, and I would have saved a lot of money in the long run (and gone faster) if I bought the zzyzxmotorsports coilovers instead of doing it over, and over, and over again.[/QUOTE]
Surprisingly enough, on that exact car, I disconnected the rear swaybar and the rears stay planted... at least on street tires.
| Mykl | 06-22-2006 04:45 PM |
[QUOTE=maxQ]Surprisingly enough, on that exact car, I disconnected the rear swaybar and the rears stay planted... at least on street tires.[/QUOTE]
How big was the swaybar and how stiff were the springs? Is it possible that the bar was too stiff for the springs?
Is the Impreza prone to this or can be tuned out? It seems like anybody with any large amount of grip is having this issue.
How big was the swaybar and how stiff were the springs? Is it possible that the bar was too stiff for the springs?
Is the Impreza prone to this or can be tuned out? It seems like anybody with any large amount of grip is having this issue.
| maxQ | 06-22-2006 04:52 PM |
I believe it's a Perrin 14mm. The rear springs were/are 9k.
No, I believe the front (10k) isn't stiff enough for the rear stiffness the rear had with the swaybar connected. I have some 11k springs I'm going to put in the front once I get the car running again.
No, I believe the front (10k) isn't stiff enough for the rear stiffness the rear had with the swaybar connected. I have some 11k springs I'm going to put in the front once I get the car running again.
| AUTOwrXER | 06-22-2006 05:05 PM |
[QUOTE=maxQ]Surprisingly enough, on that exact car, I disconnected the rear swaybar and the rears stay planted... at least on street tires.[/QUOTE]
Have you jacked up the rear of the car and measured droop travel?
Have you jacked up the rear of the car and measured droop travel?
| Whiteghost 2.5 | 06-22-2006 05:13 PM |
I have been trying to contact zzyzx motorsports and have gotten no response from them. Does anyone have a phone number.
| maxQ | 06-22-2006 05:16 PM |
[QUOTE=AUTOwrXER]Have you jacked up the rear of the car and measured droop travel?[/QUOTE]
Yep. Just over 2", IIRC.
I'll check my notes tonight if I remember.
Yep. Just over 2", IIRC.
I'll check my notes tonight if I remember.
| jjameson | 06-22-2006 05:25 PM |
I think this belongs in the 'Transmission and Driveline Forum. ' and should be moved......
There are several recent threads in that form that talk about clutch Diffs, fluids, oversteer, understeer, 1.5 way, 2 way, welded, etc
Here are a couple....
[URL]http://forums.nasioc.com/forums/showthread.php?t=1020337[/URL]
[URL]http://forums.nasioc.com/forums/showthread.php?t=995327[/URL]
There are several recent threads in that form that talk about clutch Diffs, fluids, oversteer, understeer, 1.5 way, 2 way, welded, etc
Here are a couple....
[URL]http://forums.nasioc.com/forums/showthread.php?t=1020337[/URL]
[URL]http://forums.nasioc.com/forums/showthread.php?t=995327[/URL]
| zzyzx | 06-22-2006 06:56 PM |
I just put the rear 1.5-way Cusco in the rear of my RS. It certainly helped decrease wheel spin. It changed the on-throttle balance of the car:
1) Steady state (on street tires), you can fell it induce massive understeer.
2) On slicks in a sweeper, the additional power to the ground at the rear makes the rear end step out, providing a little oversteer.
This is with the stock center diff - 50/50. I'll soon be installing the Cusco 35/65 center tarmac diff.
Joel hit the nail in that the center diff plays a much larger role in the balance of the car then the rear diff. You only need to change the rear diff when power loss due to wheel spin becomes a problem.
In a well set up STi in STU, you shouldn't need to change the rear diff.
In *SP and up, you will.
Sufficient front roll stiffness is critical to reducing rear wheel lift. You can get there with appropriate spring rates or a combination of a bar and springs. I don't do bars. My RS has so much grip and roll resistance that I'm far beyond body roll and into weight jacking. With serious increases in grip come equally serious setup challenges on our Subarus.
Reducing rear wheel lift can include:
1) Sufficient front roll stiffness (springs, swaybar, bump damping).
2) No rear swaybar.
3) Very little rear rebound damping.
[QUOTE=Whiteghost 2.5]I have been trying to contact zzyzx motorsports and have gotten no response from them. Does anyone have a phone number.[/QUOTE]
You have an email. :)
1) Steady state (on street tires), you can fell it induce massive understeer.
2) On slicks in a sweeper, the additional power to the ground at the rear makes the rear end step out, providing a little oversteer.
This is with the stock center diff - 50/50. I'll soon be installing the Cusco 35/65 center tarmac diff.
Joel hit the nail in that the center diff plays a much larger role in the balance of the car then the rear diff. You only need to change the rear diff when power loss due to wheel spin becomes a problem.
In a well set up STi in STU, you shouldn't need to change the rear diff.
In *SP and up, you will.
Sufficient front roll stiffness is critical to reducing rear wheel lift. You can get there with appropriate spring rates or a combination of a bar and springs. I don't do bars. My RS has so much grip and roll resistance that I'm far beyond body roll and into weight jacking. With serious increases in grip come equally serious setup challenges on our Subarus.
Reducing rear wheel lift can include:
1) Sufficient front roll stiffness (springs, swaybar, bump damping).
2) No rear swaybar.
3) Very little rear rebound damping.
[QUOTE=Whiteghost 2.5]I have been trying to contact zzyzx motorsports and have gotten no response from them. Does anyone have a phone number.[/QUOTE]
You have an email. :)
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