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