I was doing HPDE 3 at summit point this weekend in my Turbo II, and the car ran fantastically all weekend, with one minor glitch. I had a really good run out of turn 10, setting me up for a very fast run down the front straight into turn one. Those of you who have run at Summit know that turn one can be pretty greasy. I braked hard coming to the turn, and realizing that I wasn't on the brakes quite as hard as I needed to be, I gave it a little more pressure, not stabbing the pedal, just adding pressure. The rear rapidly let go, stepping out to the left and whipping around quickly, sending me backwards to the inside, just into the grass. I was able to get first gear and get the hell out of there, nothing was damaged when I went in to the pit.

The guy behind me said he had no idea what happened, no tire smoke from locking up the rears, and he said it looked like I was braking perfectly in a straight line and then boom.

Any ideas what happened? I have a bit of static rear toe-in, but is it possible that the rear is getting toe-out when unloaded under the brakes? I don't think I have uneven rear brakes, both calipers are very new, and freshly bled before the event.

Suspension is the K2RD kit that was sold eons ago, I also have the RB front swaybar, stock rear swaybar, and BGF-R1 track tires in 225/50R16 in front and 245/45R16 in the rear. (These tires are awesome, btw)

 

Sounds like the rear tires locked up under breaking and just lost grip. That extra braking pressure may have been just too much at that point.

 

Yep, just sounds like a snap spin with no time for tires to really give off smoke.

IIRC isn't that braking area pretty bumpy on the line? I seem to remember it having some waves and you were better off in the middle of the track in the braking zone. Its been over tens years since I've been there so its probably been repaved since then.

 

Turn one isn't bumpy, just greasy... everyone brakes way to the left, on the line for entry to the right turn. You might be thinking of the braking zone at the bottom of the hill in turn 4 (big right hander) leading into turn 5 (sharp left), there are some bumpy spots at the bottom that can make braking interesting there.

 

Yep, it was repaved in 1999. It was extremely bumpy before that.

 

Ah, that predates my career.

 

What kinda brakes (pads?) were you running?


-Ted

 

Hey Gene!

The same thing happened to me at Shenandoah this March. I had been locking the rears up most of the weekend and I chalked it up as the cause of my spin. I was running Hawk Blues in the front and blacks in the back. I changed the rears to Hawk HP+ and still got lockup. I'm now using HPS on the rear w/ blues in the front and it seems to be the right bias.

 

patfat hit it - the stock brake bias on the FC makes the rear lock up first - right rear on my car. When one of the rears locks up, it pulls the car to one side, which is less than desirable.

 

Carbotech Panther Plus front and rear. Stock calipers and rotors.

 

Pat - this was in your 993, right?

I just curious because I'm trying out blues(f)/blacks(r) for the first time this weekend and am a little concerned about too much brake in the rear. I don't have a bias-adjust installed.

I was running HP+ in the rear (w/ blues in the front), but had to replace the pads.

Any thoughts from anyone?

-b

 

My impression was that the FC is overbiased to the front brakes in stock form, which is why Mazdatrix sells their rear rotor upsize kit. (I don't have this, however)

Forgot to mention, I do not have ABS on the car. It was broken when I bought it and after having one cheap forum-bought used unit fail also, I opted to delete it rather than keep messing around.

 

I don't know squat about FCs, but bias is a moving target. Add sticky tires & pads, and the extra weight transfer can make the rears lock up first.

 

Bill,

No, this is in my 87 FC. I'm trying to sort it out for track duty. I tend to take the FC to Summit and leave the Porsche for the big tracks. WGI, VIR, and such. I think you'll be fine w/ the HP+ in the rear and blues in the front. How did it go this weekend w/ the brakes?

 

Not bad. I had a couple very light lockups in back, and quite a few times i felt a little squirrelly in heavy braking, so I think that the blacks may be a little too much pad w/o a proportioning valve.

I'm not 100% sure though, because by the time I started working on my braking zones, it was Sunday and places like the entry to T1 and T14 were getting really greasy.

-b

 

I'm gonna bring this thread back from the dead because the same thing just happened to me again at VIR this weekend at turn 1 and I have a couple of new thoughts on the matter...

Alignment may be off in a couple of ways:

The original post was the first run with the heavier front swaybar installed, and I wonder if my corner weights are messed up because of preload on the bar, as we didn't redo the corner weights after installing it.

Also, the rear is all crazy. The car had been in a sideways-into-curb crash with a previous owner, and things were bent. I have the AWR camber adjusters to put things back to normal (or -2 degrees anyway) but one is cranked all the way to positive and one is cranked all the way to negative. There may be other things out of whack as well, and dynamic alignment may be changing unevenly when the rear gets light under the brakes.

Aero:

Before the first event I had installed the Shine Auto Project front lip in a bid to get more air into my heat exchangers. I wonder if it is creating enough front downforce at speed to lighten the rear, especially when the car dives under the brakes and the AOA increases.

 

dunno about the aero, but it sounds like something in the rear is still bent