Unstable during braking carbotech xp10/xp8
 

Did my first track day last weekend on a proper race pads. I went with recommended xp10 fronts and xp8 at the rear for track days. Also have front z1 2 piece slotted rotors and stoptech sport rotors at the rear also slotted. Ever since changed to this setup, the car is very unstable during hard braking. I could feel it the first time I tried them during bedding on the street. It almost feels like the rear wants to step out in either direction. The bite is superb but I had to back off during braking because I totally lost confidence that I can keep it under control. For non track days I use nismo pads all around and do not get that sensation under hard braking whatsoever. The car stays and behaves as it should. I tried to search but could not find anyone else with similar issue. Is it possible that the brake bias is too much up front due mixed pads? My next step is to try same compound all around instead going step lower in the rear. Just not sure whether to go with xp10 or xp8. Any feedback is very welcome.
My current setup:
Front brakes air cooling ducts
Stock nismo shocks with swift springs
Front and rear whiteline swaybars
2.5 neg camber with zero toe up front, 1.5 neg camber with slight toe in at the rear
hankook rs3 275/305
os giken rear diff

You could try running XP8's all the way around. And adding a little toe in, in the front. How much toe in do have in the rear?

2nd the motion...going with xp8 all around.

I have, a similar set up with no issues during braking. I am running -2.6 front and -2.0 rear with a touch of toe on for both.

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I have the same "unstable" feeling, moving a little side to side on the hardest braking points. I think it's more to do with the very good pad+stock suspension with a side of abs kicking in. XP8s and XP10s all around didn't change it for me, still on the stock nismo suspension and springs.

Add more weight in the trunk. Keep spare tire and full tank of gas.

Not sure how much toe in at the rear but as far I can remember it wasn't much. It's been awhile since I did an alignment so I will do one this Saturday and see if anything changed. Still running stock toe bolts so maybe something moved. I will start with that before anything else.

Maybe little more camber in the rear would help. I get to do my own alignments so I could play with it with no extra cost. Also been thinking that possible extra brake bite causes more aggressive weight transfer towards the front which stock suspension can't handle. I see you upgraded to coilovers which I am sure could be a factor for more stable braking. I'm planning track day in two weeks so would love to figure this out before I get back on the track.

It could be a contributing factor you spun out during the rain at the thunderbolt. I could definitely feel it more loose during wet sessions. Very scary and no fun. What pads are you running now?

Did my fuel starvation fix so I can run less fuel!

Definitely think its an extreme weight transfer issue. I have the same carbotech set up, and since raising the front a bit to help with nose dive the issue is less apparent. Unrelated to this particular issue, I'm increasing my spring rates soon to a stiffer set up and think it should help by resisting nose dive as well.

That was just plain old going to fast, ran out of talent. Getting XP10/8 combo and trying out FrozenRotors blanks. Used up my current XP10/10 and Z1 slotted rotors last weekend.

I think that is the issue as well. It seems like I am not the only one so it makes me slightly less irritated. Just need to figure it out the proper setup. It seems like it's a nismo thing! :rolleyes:

If i recall correctly Zs have more weight up front than rear, so hard braking, especially with good pads, will do that. I now (after tracking) see why I was recommended 16/9 spring rates for the car back when I ordered my suspension.

Nonetheless conditions were horrible. Are you still planning for another track day this season? Im going most likely the 29th at thunderbolt. Let me know if you're interested. I'll send you the link.