Diff Fluid and Oversteer
 

I made several changes to my BRZ at once, and now I have a slight oversteer problem. Mods:

-dampers changed to Koni Yellow
-rear springs swapped to OE FRS (stiffer)
-Aligned to -1.5 camber and 0 toe all around.
-Diff fluid changed to Amsoil 75w-90 GL-4
-No change to the sways. I'm on OE BRZ

I Think the component changes are pretty conservative, so I'm surprised how much more oversteer I have. It's fun, but I'm not a drifter so I want grip.

Could this be caused by the diff locking early because of the fluid I'm using? I think I should have used GL-5.

If you have -1.5 camber front and rear I'm surprised you have oversteer. I'd start with a little toe-in in the rear. Maybe 1/8” total.

Is this a street only car?

No, the fluid has nothing to do with it.

Also, torsens don't lock anyway.

Shock and rear spring change (and maybe alignment) are probably the cause. Also lots of time perceived handling ills are driver induced...

e1: Thanks for the advice.

Redlined: I do track days. The car actually feels loose mid corner now. Pre-mod, the car was locked down at the rear. More power resulted in more push. Kind of boring, but probably faster.

Your fluid choice have nothing to do with your oversteer, as others have stated. Stock Torsen doesn't care about what fluid you use.

-alex

...did you get an alignment? Sounds like it could be a toe problem. Did you check your tire pressure recently?

Add a bigger front sway bar and 1/8 toe in the rear. That should sort it out.

Also to answer your question:
1) one (or more) of your original shocks may have been bad
2) stiffer rear spring = oversteer

Assuming your alignment was done correctly, both of those could have been major contributing factors to your current oversteer "problem"

I am never a fan of changing more than one item at a time, especially if I drive the car daily or track it often. Wholesale changes are only necessary to fix something...

-alex

Diff Fluid and Oversteer
 

What tire is it? Size& width? Or it's still stock?

Other then that maybe frs spring, tiny adjustments can still change the feel on this car a bit.


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make the front dampers stiffer and/or soften the rear dampers. it's more of an experimental phase now so just try one change and drive it to see how you like it before making any more changes.

Q: Why do you install FR-S rear springs?

A: To induce oversteer.

The stiffer FR-S rear springs will induce oversteer, as will the hefty increase in front camber (stock is roughly zero) and the decrease in rear toe (stock is roughly 0.05 degrees). Add rear toe (OEM spec is good) and recheck. If still no good, change the springs back to BRZ.

Set the dampers in the front harder or the rear softer. Or more negative camber in the front.

The other way round.

Agreed on the slight rear toe in being helpful.

Damper changes (stiffer front, softer rear) would be helpful on corner entry and exit.

- Andrew

Sorry to disagree. Koni yellows have adjustable _rebound_ damping only.

In this case, a stiffer front setting induces more oversteer on corner exit and a softer rear induces corner entry oversteer.

reason for edit: typo

wait, diff fluid causes oversteer? well I'll be damned :bonk:

If it's on the track rather than in the diff it might...

Why do drifters lock their axles together? Why do McLaren and lotus resist using mechanical diffs? Why can't forum contributors answer honest questions or just stay out of the thread?

Yes my car was aligned by a professional shop, and I have the final readouts.

OE tires.

I chose FRS rear springs in an attempt to balance the car. Same for the alignment specs. I just have trouble believing the changes I made moved the grip so far forward.

I count three changes you made that would contribute to more oversteer.

Individually they're not drastic changes but done all at once, they would have a pretty noticeable effect. I think people have made useful suggestions.

First try playing with damper settings since it's free. Here's a flow chart for dealing with oversteer (keeping in mind that Koni single adjustables appear to alter rebound only):

https://robrobinette.com/images/S200...steerFixes.jpg

If that doesn't solve your issue, try adding slight rear toe-in (and/or more rear camber). Alignments are relatively cheap.

And if that fails, try an adjustable front sway bar.

One thing to keep in mind is that if you change to track tires, your opinion on the car's balance might change as well.

I feel like flaming someone , but i dont want a temp ban. So I'll keep my mouth shut.

I seriously don't get the point of this. That you even feel the need to "flame someone" aka be a douche. Do you get internet troll "brownie points" or something? lmao :lol:

I've personally ran BRZ front and FRS rear springs with factory dampers and im a bit surprised you are getting oversteer. My alignment was a bit different though. The result was a bit of understeer at entry. Maybe those Konis along with your alignment has something to do with your resulting oversteer.

My alignment with the set up (apporx with camber bolts and rear lower control arms):

-3 camber 0 toe front
-2.5 camber 1/16" toe rear

No, but pointing out the defense has holes in it about diff fluid from OP...I would have probably chosen less than nice words for stupid questions haha.

Why do drifters lock their axles together?
Because drifters care very little about handling, they want both wheels locked together so they spin at the same time and at the same speed. Alternatively they may go for 2 way LSDs

Come on dude, you're pushing it, in what world would the Diff fluid effect over-steer on this car? have you owned other cars that induced over-steer because of the fluid? What led you to that conclusion?

Also your mclaren and lotus examples don't even apply here

McLaren P1: They use frictional balancing with brakes/electric motors so they don't need an LSD system as they can be more precise without it.

Mclaren MP4,670s, 570 etc: Use brakes on the inner wheels at times moments, also the suspension is adjusted on the fly, they also have NO sway bars everything is connected electronically or hydraulically and adjusted in split second intervals (this is in the P1 as well)

For the lotus: A limited slip differential matters more in wider, heavier cars than it does in narrow lightweight cars, FYI, because the different radius paths of travel are smaller, and the distribution of weight left-right during a corner is smaller as well. They are famous for saying it here:
http://www.lotustalk.com/forums/f25/...06/#post552007

This is very helpful, thanks.
I will definitely experiment with the damper settings. I have been adding "stiffness" to the front to get traction at the rear, but now I see I've been going at it backwards!

I'm also due for tires, so I'll try something stickier. The extra roll will get me some camber at the back which should help.

We have almost identical setups. The Koni's seem to have far less compression damping than OE, which may be allowing the front to drop with corner loads.

Your alignment is more aggressive than mine, but you don't seem to be having any trouble. What tires are you running?

LOL changes springs and doesn't understand that it will affect handling characteristics.

Your brain fluid needs to be changed.

Look, from the fact that you know the FRS springs are stiffer and you changed them on the rear it should be no surprise to you that it would induce oversteer.

Why would you even think that its related to the fluid ?

Because you made a TON of changes all at once... that's where I would start.

I have no problems with oversteer on my car, and my alignment is

F -3.6 camber, 0 toe
R -2.7 camber, 1/16" toe in

-alex

How plain do I need to be...

The point of my rhetorical questions was that differential behavior affects chassis balance. I think the oil you run in your diff will affect the way it reacts, and therefore the car's balance.

I used Amsoil GL-5 in my transmission, and it sucked. My bad, switching to Redline GL-3 made a huge difference.

I used Amsoil in my diff .... and I have oversteer.

You don't know how a Torsen diff works, hence the misunderstanding.

[ame="https://www.youtube.com/watch?v=JEiSTzK-A2A"]Torsen Differential, How it works ? - YouTube[/ame]

Of course I knew FRS springs would move grip to the front. Because I'm using BRZ fronts (also stiff), I'm still softer (relatively speaking) at the rear than the FRS.

If you're not contributing to the discussion, go troll another thread.

That video is awesome! Thank you. This is just the response I needed. I guess as long as the diff fluid 'lubricates', I'm good. I wonder why there are different specs for transmission and Diff oil. Must be materials ...

Im sorry if what you dont want to hear is critism and you assume its trolling. Welcome to the internet.

My problem with this thread (and thread title) is that I spent more time (~15 seconds) researching the problem online than you did.

And found the solution you wanted faster than you were able to type responses to trolls, which is to be expected given the noob nature of the thread title.

-alex

This is the type of person I wouldn't want modding the car, does everything all at once and then blames the wrong thing for oversteer.

Not nessecarily blaming, but just misinformed. Then draws conclusions based off of, well I dont know. The way he worded the OP was a matter of fact kind of statement rather than conceding that he may be wrong in his assumptions. Regardless, I was there at one point but I also googled and googled when I was younger. I only asked questions when I was 100% confused and had exhausted my research capabilities, which does extend to the search function on this forum (not to say this topic has already been covered, but theres a whole heap of topics that have).

You seem convinced, and I'm not saying you're wrong. change the fluid back and see if it corrects the oversteer.

I'm no longer using this set up. I did run hankook rs3 tires in 215/45/17 and 225/45/17 as well as Goodyear F1 assimetrical 245/40/17 with that set up.

Even though the shock is still from your brz, you put in a stiffer spring. This is what changed your handling characteristics. What did you think was going to happen ? What was your planned outcome from this ?

Don't confuse traction control with a "simulated electronic limited-slip differential"