Diff Fluid and Oversteer - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

ansibe · 05-09-2016, 10:02 PM

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.

redlined600 · 05-09-2016, 10:14 PM

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?

e1_griego · 05-09-2016, 10:16 PM

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...

ansibe · 05-09-2016, 10:28 PM

Quote:

Originally Posted by e1_griego

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.

mav1178 · 05-09-2016, 10:33 PM

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

Tor · 05-09-2016, 10:50 PM

Quote:

Originally Posted by ansibe

I made several changes to my BRZ at once...

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

smg1138 · 05-09-2016, 10:53 PM

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

mav1178 · 05-09-2016, 10:56 PM

Quote:

Originally Posted by ansibe

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

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

chaoskaze · 05-10-2016, 12:53 AM

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.

Sent from my iPhone using Tapatalk

ryoma · 05-10-2016, 01:50 AM

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.

NissanGuy · 05-10-2016, 02:28 AM

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.

tyler_win_photo · 05-10-2016, 06:51 AM

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

freerunner · 05-10-2016, 11:30 AM

Quote:

Originally Posted by tyler_win_photo

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

The other way round.

Racecomp Engineering · 05-10-2016, 11:42 AM

Agreed on the slight rear toe in being helpful.

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

- Andrew

05-09-2016, 10:02 PM	#1
ansibe Member Join Date: Jun 2013 Drives: White BRZ Location: Toronto Posts: 60 Thanks: 9 Thanked 32 Times in 18 Posts Mentioned: 3 Post(s) Tagged: 0 Thread(s)	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.

05-09-2016, 10:14 PM	#2
redlined600 Senior Member Join Date: Nov 2014 Drives: Fr-s Location: MN Posts: 774 Thanks: 139 Thanked 555 Times in 288 Posts Mentioned: 5 Post(s) Tagged: 0 Thread(s)	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? __________________ Build log

05-10-2016, 12:53 AM	#9
chaoskaze The Fail Boat Join Date: Aug 2011 Drives: CWP S.B. Location: LasVegas Posts: 3,028 Thanks: 4,720 Thanked 1,294 Times in 874 Posts Mentioned: 19 Post(s) Tagged: 0 Thread(s)	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. Sent from my iPhone using Tapatalk

05-10-2016, 01:50 AM	#10
ryoma Senior Member Join Date: Mar 2015 Drives: 2015 Subaru BRZ Limited CWP Location: SoCal Posts: 1,561 Thanks: 34 Thanked 669 Times in 469 Posts Mentioned: 13 Post(s) Tagged: 0 Thread(s)	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. __________________ My 2015 CWP BRZ Build

05-10-2016, 02:28 AM	#11
NissanGuy Senior Member Join Date: Feb 2014 Drives: Strangely. Location: Burbank, CA Posts: 390 Thanks: 104 Thanked 142 Times in 100 Posts Mentioned: 6 Post(s) Tagged: 0 Thread(s)	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. __________________ My FR-S has a build thread! (It's mostly full of Nissans)

05-09-2016, 10:16 PM	#3
e1_griego Senior Member Join Date: Jul 2015 Drives: Many Location: Independence, Ore. Posts: 721 Thanks: 231 Thanked 409 Times in 246 Posts Mentioned: 9 Post(s) Tagged: 2 Thread(s)	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...

05-09-2016, 10:33 PM	#5
mav1178 Senior Member Join Date: Apr 2013 Drives: 2005 Toyota Camry Location: 91745 Posts: 6,562 Thanks: 493 Thanked 6,099 Times in 3,030 Posts Mentioned: 95 Post(s) Tagged: 3 Thread(s)	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

05-09-2016, 10:53 PM	#7
smg1138 Senior Member Join Date: Jan 2014 Drives: 2013 Raven FR-S Location: Nashville Posts: 775 Thanks: 968 Thanked 213 Times in 136 Posts Mentioned: 3 Post(s) Tagged: 2 Thread(s)	Add a bigger front sway bar and 1/8 toe in the rear. That should sort it out.

05-10-2016, 06:51 AM	#12
tyler_win_photo Senior Member Join Date: Dec 2013 Drives: 2014 Scion FRS (Asphalt) Location: Redmond, WA Posts: 559 Thanks: 39 Thanked 173 Times in 143 Posts Mentioned: 6 Post(s) Tagged: 2 Thread(s)	Set the dampers in the front harder or the rear softer. Or more negative camber in the front.

05-10-2016, 11:42 AM	#14
Racecomp Engineering Join Date: Nov 2011 Drives: 2016 BRZ, 2012 Paris Di2 & 2018 STI Location: Severn, MD Posts: 5,520 Thanks: 3,542 Thanked 7,415 Times in 3,033 Posts Mentioned: 311 Post(s) Tagged: 9 Thread(s)	Agreed on the slight rear toe in being helpful. Damper changes (stiffer front, softer rear) would be helpful on corner entry and exit. - Andrew

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