Tre Rear Differential Upgrade Service
TRE is doing exactly the right thing with the rear diff. We've been doing it in the Evo race car for over two years now, and it works perfectly. The reason it works is because you apply torque to the outside rear wheel which promotes oversteer and better turning.
Most guys resort to taking all the camber out of the rear tires, jacking up the rear ride height, or using way too stiff rear springs to attempt to get Evos to rotate properly, but these are all band aids that don't truly solve the problem.
Some people claim they fix the center diff to solve this problem, but that still doesn't get the torque to the outside rear wheel. Even with a modified center diff, you still need a tightened rear diff to get good balance. Balance past the apex is not a problem with front to rear torque split, as many think. It is a problem of inside to outside rear torque split as even in stock form there is plenty of torque going to the rear tires.
Keeping the stock 1.5 way diff open with on proload under deceleration preseves good turn in, while coming off the the turn you want as much lock as possible in the rear diff.
Most guys resort to taking all the camber out of the rear tires, jacking up the rear ride height, or using way too stiff rear springs to attempt to get Evos to rotate properly, but these are all band aids that don't truly solve the problem.
Some people claim they fix the center diff to solve this problem, but that still doesn't get the torque to the outside rear wheel. Even with a modified center diff, you still need a tightened rear diff to get good balance. Balance past the apex is not a problem with front to rear torque split, as many think. It is a problem of inside to outside rear torque split as even in stock form there is plenty of torque going to the rear tires.
Keeping the stock 1.5 way diff open with on proload under deceleration preseves good turn in, while coming off the the turn you want as much lock as possible in the rear diff.
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I have this in my race car as well and as Jon/David said, it is basically unnoticeable on turn in but does help the car rotate once the power is put down. I am able to straighten the wheel out sooner and rely on the go pedal to point me in the right direction (the less you use the steering wheel to turn the better). You will not have to worry about your car spinning out on you, however, if you are used to trying crazy things to "kick" the rear end out, youll want to refrain from doing that until you get used to the new feel. If you end up bringing the rear end around too much once you install this piece, just unwind the wheel a bit more next time around and let the rear help you rotate. Also, remember to squeeze that pedal down and not slam it to the floor, this will result in a nice controllable corner exit.
Oh and in case you are wondering how it does in the rain, it was not an issue and the car was very controllable even in a full drift.
Oh and in case you are wondering how it does in the rain, it was not an issue and the car was very controllable even in a full drift.
Last edited by Galant VR-4 #34; Dec 17, 2007 at 05:59 PM.
From what I've seen here I assume this mod is effectively a 1 way, zero preload diff with shallow ramp angles. My question is, how effective is the diff at putting power to the outside rear tire when the inside rear is in the air (or lightly loaded)? I would expect a 'zero' preload diff to perform poorly in that situation.
Marshall,
Your car doesn't lift wheels does it?? Watching it at Nats it seemed pretty flat. From watching a video of our car this year it seems ours only lifts when trail braking hard into a fairly sharp corner, and then it only a little bit. What have you experienced?
Your car doesn't lift wheels does it?? Watching it at Nats it seemed pretty flat. From watching a video of our car this year it seems ours only lifts when trail braking hard into a fairly sharp corner, and then it only a little bit. What have you experienced?
Marshall,
Your car doesn't lift wheels does it?? Watching it at Nats it seemed pretty flat. From watching a video of our car this year it seems ours only lifts when trail braking hard into a fairly sharp corner, and then it only a little bit. What have you experienced?
Your car doesn't lift wheels does it?? Watching it at Nats it seemed pretty flat. From watching a video of our car this year it seems ours only lifts when trail braking hard into a fairly sharp corner, and then it only a little bit. What have you experienced?
Thus my question about diff locking ability with wheel in the air.
From what I've seen here I assume this mod is effectively a 1 way, zero preload diff with shallow ramp angles. My question is, how effective is the diff at putting power to the outside rear tire when the inside rear is in the air (or lightly loaded)? I would expect a 'zero' preload diff to perform poorly in that situation.
Jon@TRE
This is sounding like a good alternative to the bump steer and roll center kits. The cost ends up about the same considering you don't need bushings pressed out or alignments done.
Jon@TRE
I wouldn't consider the rear diff upgrade a replacement for the bump steer correction kit, and definitely not for the roll center kit, which is mostly used to get the front suspension geometry back in-line if your Evo's suspension has been lowered.
Jon, my diff is on its way.
l8r)
Jon, my diff is on its way.
l8r)
I got my rear diff back from the TRE re-build a few weeks ago, and as promised, I'm posting my impressions of it so far. Note that I'm in the NorthEast, with snow tires on, so I haven't been able to try it in racing conditions yet (where an inside rear wheel would be off the ground).
First of all, my car is almost 5 years old (it's one of the 1st Evo's in the country -- March '03), and the factory rear diff was worn out, almost completely open. Especially after upgrading to the LSD in the front, the car felt completely like a FWD car. It was impossible to get on-throttle oversteer under any conditions except deep snow.
The first thing I noticed with the diff rebuild was when I turned in a tight radius at low speed in a wet parking lot. Whenever I was on the throttle slightly (in 1st gear) I could hear the tread blocks of my rear Blizzaks making skittering noises on the pavement, as the inside tire tried to go farther than the outside tire in the turn. But as soon as I would lift throttle, the diff would open up and the tread noise went away. This is exactly what you expect and indicates the limited slip is working as it should.
Another thing I noticed is that when I pressed down the throttle agressively in a second-gear sweeper turn, the car tried to rotate in a little more (on my big squishy Blizzak tread blocks, the car could actually rotate noticeably without skidding). A good sign.
The next level of testing was a full throttle left turn from a stopped position, in 1st gear, on a dry road. Whooeeeh! We have throttle over-steer! Oh ****! Counter-steer and save the paint job! Great God almighty, now I remember why I bought the car!
I then did several tests of 2nd-gear braking and cornering at the limit, and there is no sign of any understeer caused by the diff.
My final test will be to take the car out to my abandoned parking-lot skid-pad, where I can do a 100-ft-radius circle at high autocross speeds in 2nd gear. I want to see which end breaks loose when I'm cornering at the limit and suddenly floor the throttle. Before this upgrade it would always be the front end. I'll report on that later.
Oh, I should also say that there is no extra noise from the diff. I have all the same gear-train noise I had before, loud and clattering as you back off the throttle, but nothing new from the diff rebuild.
Anyway, good work, Jon. I'm a satisfied customer so far!
First of all, my car is almost 5 years old (it's one of the 1st Evo's in the country -- March '03), and the factory rear diff was worn out, almost completely open. Especially after upgrading to the LSD in the front, the car felt completely like a FWD car. It was impossible to get on-throttle oversteer under any conditions except deep snow.
The first thing I noticed with the diff rebuild was when I turned in a tight radius at low speed in a wet parking lot. Whenever I was on the throttle slightly (in 1st gear) I could hear the tread blocks of my rear Blizzaks making skittering noises on the pavement, as the inside tire tried to go farther than the outside tire in the turn. But as soon as I would lift throttle, the diff would open up and the tread noise went away. This is exactly what you expect and indicates the limited slip is working as it should.
Another thing I noticed is that when I pressed down the throttle agressively in a second-gear sweeper turn, the car tried to rotate in a little more (on my big squishy Blizzak tread blocks, the car could actually rotate noticeably without skidding). A good sign.
The next level of testing was a full throttle left turn from a stopped position, in 1st gear, on a dry road. Whooeeeh! We have throttle over-steer! Oh ****! Counter-steer and save the paint job! Great God almighty, now I remember why I bought the car!
I then did several tests of 2nd-gear braking and cornering at the limit, and there is no sign of any understeer caused by the diff.
My final test will be to take the car out to my abandoned parking-lot skid-pad, where I can do a 100-ft-radius circle at high autocross speeds in 2nd gear. I want to see which end breaks loose when I'm cornering at the limit and suddenly floor the throttle. Before this upgrade it would always be the front end. I'll report on that later.
Oh, I should also say that there is no extra noise from the diff. I have all the same gear-train noise I had before, loud and clattering as you back off the throttle, but nothing new from the diff rebuild.
Anyway, good work, Jon. I'm a satisfied customer so far!
How significant have you guys found this to be?
I am just putting a ralliart front diff in and want to be able to modulate the angle of the car with the throttle as much as possible, think the upgrade is a easy way dollar for impact?
Scorke
I am just putting a ralliart front diff in and want to be able to modulate the angle of the car with the throttle as much as possible, think the upgrade is a easy way dollar for impact?
Scorke
In all other respects I totally agree with point&shoot, although I have not had the opportunity to really push the car yet. Turn-in is as good, if not slightly better, and even in my limited street driving so far, I can tell that the car behaves differently coming out of a corner. If we get some warmer temps or more snow, I'll take it out on a parking lot to see how it does.
l8r)