Stoptech C43 front BBK

[elbert]

It's on 700/800 spring rate, valved to whatever True Choice Koni set it at when they rebuilt them to this spring rate. We've tried to dial down the rear rebound to help unbind the front on turn in and mid corner, but a small increase might just be enough to help the brake dive without affecting the front on turn in. That's the other puzzle of this car, the damn thing lifts the front inside tire on every corner. Wondering if roll correction control arms will help out.

My WAG is you probably won't need to make too much of a change, maybe a 1/4 to 1/2 turn. But if you're doing a 1:37 at MidOhio with the chicane, I not sure I would mess with anything!

As for the inside front tire lifting, the PTG M3 did that too:

[CrookedCommie]

What sway bars are you running?

Hotchkis front+rear, front set to full stiff, rear to full soft. More variables to play with, but I'm guessing turning down the front sway bar will probably induce understeer holding other things constant.

[r4dr]

What sway bars are you running?

[CrookedCommie]

Oh, definitely increase it then. Which valving did you get, and what spring rates are you using?
edit: I probably should add to my previous post that the amount of rebound adjustment might depend on both front and rear spring rates. If you're doing that flat ride business, you might need to increase the rebound a bit more.

It's on 700/800 spring rate, valved to whatever True Choice Koni set it at when they rebuilt them to this spring rate. We've tried to dial down the rear rebound to help unbind the front on turn in and mid corner, but a small increase might just be enough to help the brake dive without affecting the front on turn in. That's the other puzzle of this car, the damn thing lifts the front inside tire on every corner. Wondering if roll correction control arms will help out.

[elbert]

Awesome thank you. Will test this as well - my custom valved TCK setup is on full min rebound in the rear.

Oh, definitely increase it then. Which valving did you get, and what spring rates are you using?
edit: I probably should add to my previous post that the amount of rebound adjustment might depend on both front and rear spring rates. If you're doing that flat ride business, you might need to increase the rebound a bit more.

[CrookedCommie]

I had the same issue in the past -- tail wagging in deep brake zones coming off the main straight.
I corrected it by increasing the rear rebound, which helps slow the weight transition to the front. I didn't need to change it by much -- just one click on my Motons.

Awesome thank you. Will test this as well - my custom valved TCK setup is on full min rebound in the rear.

[elbert]

I had the same issue in the past -- tail wagging in deep brake zones coming off the main straight.
I corrected it by increasing the rear rebound, which helps slow the weight transition to the front. I didn't need to change it by much -- just one click on my Motons.

[CrookedCommie]

It's hard to tell from the video, more of an in-car feeling. Big wang will help, and is next. I've driven myself in circles (literally) trying to get this car to brake like the newer gen stuff (front or rear engine) and it just isn't happening.

Here's the brake zone in question, 0:51:

https://www.youtube.com/watch?v=1iPq6KZeqNQ

[mrgizmo04]

Yes r4dr

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[eacmen]

It's been a long day but my theory is: braking while going downhill simulates moving the car bias forwards in regards to weight transfer. So the rears lock up sooner because that end is lighter and the front end is heavier in weight (though car mass is obviously the same). This would have the same effect on lockups as shifting the bias to the rear right?

Am I making sense? That's not a rhetorical question, I'm genuinely talking myself into a circle here.

So if we go back to your original question, your brake bias is probably ok unless you want to dial it in more for downhill braking.

The 911 doesn't see that because it has the majority of its weight on the rear axle. That's why it squats instead of dives even when you're braking on flat ground. You could try putting the S54 behind your seat.

This.

Put a big wang on the back. Should alleviate some of the rear end stability under downhill braking.

Downhill braking is also more sensitive to smooth application of the brakes, you don’t want that sudden weight shifted forward when the front is already loaded. Not saying this is the case here but i’ve been victim to it myself.

[r4dr]

It's been a long day but my theory is: braking while going downhill simulates moving the car bias forwards in regards to weight transfer. So the rears lock up sooner because that end is lighter and the front end is heavier in weight (though car mass is obviously the same). This would have the same effect on lockups as shifting the bias to the rear right?

Am I making sense? That's not a rhetorical question, I'm genuinely talking myself into a circle here.

So if we go back to your original question, your brake bias is probably ok unless you want to dial it in more for downhill braking.

The 911 doesn't see that because it has the majority of its weight on the rear axle. That's why it squats instead of dives even when you're braking on flat ground. You could try putting the S54 behind your seat.

[mrgizmo04]

but I don't hear too good after seeing the price tags.

LOL 👍


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[CrookedCommie]

Try another zone/track to compare/confirm. There are some sections at Sonoma where I have trouble with rear, thinking my brakes are having issues. A lot of elevation changes with poor pavement/grip. Adjust the approach to start braking earlier and less violently to keep it planted, and then you have confidence to properly trail brake with rear planted. Don't have issues on any other norcal tracks.

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The 7GT3 throws the anchor out, no issues. I do agree though, slower smoother initial weight shift on the E46's will manage it, but, ain't nobody got time for that 😂.

This is the worst brake zone, at other tracks, brakes work mostly fine. Mostly. They keep telling me to get the big boy kit, but I don't hear too good after seeing the price tags.

[mrgizmo04]

Mid Ohio, back straight from ~135mph to turn in China Beach. I have to manage the rear first before reaching maximum threshold. The stopping power just isn't there compared to the 6-7GT3 on DH's (stock calipers, 1.11's).

This is probably a bad brake zone example btw - it's a slight downhill and MO is notorious for having low grip.

Try another zone/track to compare/confirm. There are some sections at Sonoma where I have trouble with rear, thinking my brakes are having issues. A lot of elevation changes with poor pavement/grip. Adjust the approach to start braking earlier and less violently to keep it planted, and then you have confidence to properly trail brake with rear planted. Don't have issues on any other norcal tracks.

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[CrookedCommie]

When you say full braking zones, are you borderline triggering ABS at maximum threshold braking? What locks up first, front or rear?

I'm guessing rears based on the sideways feel you described? I'd imagine front lockup would just induce under steer and plow forward.

Mid Ohio, back straight from ~135mph to turn in China Beach. I have to manage the rear first before reaching maximum threshold. The stopping power just isn't there compared to the 6-7GT3 on DH's (stock calipers, 1.11's).

This is probably a bad brake zone example btw - it's a slight downhill and MO is notorious for having low grip.