OK that makes much more sense now. I had no idea the rear diff was modified from an evo III. Learn something new everyday.

So I am really temped to upgrade my rear diff. The Cusco seems like a nice piece however I feel as though I would get the same results with a TRE upgraded diff for much less.

So do you have the 1.5 installed in your car? What made you decide on that one over the other options? I really need to get in touch with someone on the phone to discuss my options however I cannot find the time...so its much easier for me to ask questions on this forum.

My car is my daily driver so I am looking for a unit that will not compromise the driveablity of the car. I would be getting it to obviously help the car rotate however I do not want to turn the thing into a death trap if you know what I mean. On top of that the car is driven in the snow occasionally so I do not want to loose its ability to trek though that stuff confidently.

 

i would guess that snow traction is improved with the TRE upgrade.

Since reading this thread I'm really eager to try this.

 

I never had issues with traction in the snow. I could get my car to oversteer with ease in that stuff. I am just wondering if itll now kick out like crazy as that may not be ideal. Id imagine during an auto-x however the car would respond so much better to my inputs.

 

if it is improving overall grip then snow traction would improve. There is not too much difference between driving at the limit in the snow/wet or on dry tarmac. The car should have the same tendency to over-steer/under-steer. Once past the "limit" the snow allows greater yaw angles, without sacrificing as much momentum.

My thinking was that if the diff upgrade is just creating a tendency to over-steer rather than under-steer under power, without improving the overall grip, than it is simply a band-aid for poor technique.

From what I have read it will improve grip, therefore snow traction will improve.

 

https://www.evolutionm.net/forums/ev...ml#post8556044

here's another thread, and there are many others reviewing the rear differential. it creates power on oversteer. it's not like just adding a big sway bar or something

 

^I have read through that thread a couple of times as I found it to be very related to my situation with regards to understeer. I thought a larger bar in the rear would help but it really didnt do much aside from lift my inside wheel more. Both that and lots or tire pressure in the rear are more of a band aid whereas the diff would be an actual solution.

I know this has been covered in some other threads however I am wondering if we could get into a discussion regarding the different options for rear diffs. Explaining both the benefits and drawbacks to each. I'd imagine a harsher locking rear diff would limit turn in response whereas moer of an open diff would really allow the car to react. Am I correct with this assumption?

 

i did a bunch of searching before and i found the main options to be the tre, shep, cusco and carbonetics.

i hadn't heard of the shep at the time, and i was having trouble getting a hold of jon@tre. i also didn't want to pull the rear diff out myself and ship it and have the car down for that amount of time. if you look through the later part of the tre rear diff review thread, there's a post or two that suggests the cusco does 'more' of what the tre does. i got mine for a fairly good deal, had it shimmed properly (very important for the cusco), and had it installed by a professional shop. i heard the carbonetics is also very good.

though i will say i'm not experienced enough to comment about the reactions of harsher locking rear differentials, the type i got, specifically the cusco 1.5 way type rs seems to address this issue by using springs to allow for more gradual/delicate response

http://www.cusco.co.jp/en/parts_prod...rs_typemz.html

Also, just found this thread here

https://www.evolutionm.net/forums/ev...l-options.html

that i actually made it didn't take off very well, i may ask some people to post reviews and get the thread going a bit

 

I have the TRE rear diff and have noticed no issues with turn-in response. IMO it has been the best $400 I've spent on my car.

l8r)

 

Cured my understeer issues.

Its a compromise of hardware settings and driving techniques. Try adjusting the tire pressure, maybe 32-34 psi in front and 36-40psi in rear. As far as the sway bar goes, set it to the softest setting. Your alignments looks on par for auto-x and street.

 

That's exactly what I do, run between 2 and 4psi more in the rear depending on surface. I'm on Kumho v710s and run about 30-32psi front, 33-35psi rear. On concrete I lean more toward the 4 psi differential, but if it's a more gravelly surface I'm usually at 1-2psi more in the rear.

What I've also found to help with turn-in is adding toe-out in the front. I have a friend who's got a nationals level subaru (his codriver took 1st in DSP-L last year) and he runs as much as 1/4" toe out in the front. I've gotten good results with 1/8" out on my car, along with -3.5* camber in front. (If you look at nationally prepared Evo's they're typically running mid 3's in front and mid 2's in the rear in terms of negative camber).

 

^^ i'm telling you guys, its all about the rear diff - then you can work on optimizing your settings for maximum grip rather than getting rid of plow

https://www.evolutionm.net/forums/ev...l-options.html

 

Kyooch, the nationally prepped cars I'm talking about run that aggressive of an alignment WITH an aftermarket rear diff. Just ask Marshall

 

oh i dont doubt that at all - just saying i think the point is it to do the rear diff first to fix corner exit and then make suspension and alignment adjustments around it

 

I loosened up my rsb and will hopefully test it out on Sunday. I had it on the stiffest setting and now its set in the middle. Assuming I decide to wake up on Sunday instead of sleeping in I will be able to see how differently the car reacts to this change.

When you mention those tire pressures are they the cold pressure or with some heat in the rubber? I have had about 2-3lbs more in the rear and it has indeed helped. Also are those pressures with R-comps or street tires? My car is on star specs for the record.

You said I should put the RSB on the softest setting. Contemplating doing that instead of the middle setting however I think the middle will be a good compromise.

So I was thinking about this whole situation in the shower(yes the shower is where I have most of my brilliant thoughts) Anyway, I never thought of understeer in different perspectives. My original thought was hey I hear a rsb will help induce oversteer so I should get one. When it comes to the initial turn in it helps to take grip away from the rear tires so in that regard it will induce oversteer.

On the other hand upon corner exit when I get back on the gas I need the rear wheels to be down in order to put the power down and force the back end out. With the bar too tight it isnt able to transfer the power to the tarmac so therefore the front tires have to put the power down thus the push.

What I am getting at is that it appears everything is a compromise. A larger bar will help induce oversteer when turning in however it limits oversteer coming out of the corner.

 

His recommendations seem to be more for street tires. I run my r-compounds in the low 30s (warm).

Just to make you even more indecisive I noticed that when I put my 27mm rear bar on full soft (from full stiff) the car seemed to a) have more grip and b) rotate way better.