Track forum general chit chat.

[tsk94]

Originally Posted by roastbeef

i see the point you're trying to argue. if you're overwhelming the front grip levels, i'd agree- understeer. but front brake bias and a high bite, high torque pad up front doesn't cause understeer. we all have front brake bias. everyone i know of consciously runs a more aggressive pad up front.
lets take it off the deep end and imagine a car with no rear brakes at all. at turn-in, with proper trail braking, they car would want to oversteer. right?

i don't think we're actually disagreeing about anything as long as front grip isn't exceeded though too much input from the driver.

For your example; actually no. And the situation I provided explains exactly why that's the case. If you had no rear brakes the only job the rear tires have is to provide lateral grip and the front tires are tasked with doing 100% of the braking and then if you try to add lateral load as well, it's going to understeer. Your situation is actually an excellent example of exactly why very high front bias would lead to/increase turn in understeer.

>but front brake bias and a high bite, high torque pad up front doesn't cause understeer.

Yes it does, if we're looking at it from just the brakes perspective. If by understeer we are referring to the handling of the car while trail braking. Other aspects of the car setup affect this entry phase of the corner as well. So you can tune out this inherent trail brake understeer caused by 'very high front bias' other ways. But if we're speaking solely of the affect of brake bias, then yes, high front bias does cause understeer (while trail braking).

Of course we all have front brake bias. And that amount of brake bias can vary depending on what pads you run front and rear. Even in my scenario where I mention a street pad up front and a race pad in the rear, the brake bias is very likely still front 'biased' simply due to the mechanical torque advantage of the larger front brakes.

What I'm trying to say is; increasing front brake bias, leaving the rest of the cars setup constant, will increase understeer while trail braking. This increase in understeer may be minimal, but it WILL understeer more. Does that mean a highly front biased braking setup will understeer at turn-in? No. Because there are many many factory in a cars setup that contribute to how the car behaves in the entry phase, the brakes being just one of many.

The only thing we seem to disagree on is you don't believe me that increasing the front brake bias introduces more understeer into a car while trail braking. But I can assure you that is the case. Hopefully this explanation clarifies it a bit?
If you have a sim rig, that's a great and easy way to test this yourself.

[roastbeef]

i think we're just going to have to agree to disagree. i have experienced different.

[tsk94]

Originally Posted by roastbeef

i think we're just going to have to agree to disagree. i have experienced different.

How so? I'm curious.

I've played around on this platform running higher torque rear pads (compared to the front) and much higher torque front pads relative to the rear. I've driven race cars with in car adjustable bias. All my experiences and experimentation are in line with that I can find in setup books and documentation online; that increasing front bias will increase understeer while trailing braking. If you've experienced the exact opposite I'm very curious as to the details of your experience.

You can find online plenty of reputable sources on car setup that confirm the same affects for increasing front bias.

[StripclubDJ]

I just press the brake pedal with more foot force so car stops lot faster and more harder.

That's my theory .

[roastbeef]

i'm ok with a friendly debate and i'll continue.

the whole purpose of trail braking is to gently transition off of the brakes while keeping just a little weight over the front axle. this is a good thing and helps with turn-in as long as you're not exceeding grip limits.

when trail braking, the weight is already pivoted over the front axle. if you were to jab the brakes mid corner, i suppose you could exceed the slip angle and induce understeer for a short time. but the rear has such little grip, the brake jab and sudden further weight shift could unsettle the car enough to influence the rear two swing out.

imagine an rc car with one "stuck" right front wheel. when trying to drive it straight, would it pull to the right?
this is the influence the front tires have, even when grip is exceeded. the front tires exceeding the slip angle can still have more grip than the rears during a trail brake.

i have always ran a higher bite/torque pad up front. for a long time, i just had the front half of my ap kit with dsuno pads. i ran pfc08 pads on the rear oem brakes with this setup for a while. during heavy braking, the rear end always had some squirm that was heavily influenced by the slightest angle of the front wheels. i had to incorporate this into which way i wanted to turn to set the car. if i tried to just go straight, i was fighting the car and wasn't sure which way the car was going to want to turn. so i just worked with it and had the car pointed ever so slightly into the corner as i began my hard press. as the rear started to rotate, i began my trail brake and steering input.

another scenario is coming up on another car in a high speed sweeper. before i was outside enough for comfort to make the pass, the other driver must have lifted. me being faster already and him lifting throttle caused me to have to brake mid corner. even braking slightly in this scenario was enough to loosen up the rear end. a brake jab would have for sure caused a spin.

[Ximian]

Sounds like you're both saying the same thing but still disagreeing.

If you have a higher torque pad in the front on your next lap and you brake at the same pressure for the same duration, I think we should all be able to agree that brake bias has increased to the front.

If a car starts to squirm under braking, it typically indicates a rear bias for braking. This is one of those "common knowledge" things. This doesn't necessarily mean that the rear brake pads are better or higher torque, it could be caused by the rear tires having much better grip relative to the front.

If your rear starts to step out under any sort of braking while cornering, your front tires have more grip than the rear you are below the limit for the steering grip. It's a tiny bit contradictory to the previous sentence on the face of it, but as there is a lateral component, the behavior is a bit different.

roastbeef - in your example of a brake jab causing a spin, that's correct but doesn't really show what tsk94 is saying is incorrect. The point tsk94 is making is that under braking with everything else being equal (e.g. comparing two identical laps), a higher torque pad will cause more understeer since there is more of the available grip being used by braking as opposed to cornering.

In practice, this isn't an issue as we typically use less braking force for the same stopping distance with a higher torque pad in corners where there is low to medium braking needed.

[rhyary]

@dparm or anyone,

The C5 brakes commended my attention.
First, the brakes were fine at stopping the car.
But they felt like more like on or off.

In my car, and what I am used to, the soft part of the travel does a lot. So I can modulate the the brakes in pretty precise way from 50psi to 800 were my ABS kicks in.

So on that C5 I had a hard time getting to the apex on the trail brake.

So what controls that? Where do you look to get the brake to be more progressive rather than on/off?

[Bartledoo]

I’ve always used the same compound front and rear. The only reason I would consider going less aggressive in the rear would be that I wasn’t getting the rears into their ideal temp range…

Adjusting brake bias to be less front biased will reduce entry understeer all else being equal. Case closed. I’m not sure how this is an argument since it’s pretty well known.

It seems like someone’s intuition is having them imagine a car going straight with only front brakes, such that the rear end wants to overtake the front, but this is ignoring the dynamics of corner entry. For example, you are releasing brakes while you turn in, and you are also adding front braking by lateral grip while you turn the wheel to enter. These have combined effects when paired with changes in bias. More rear bias means you are releasing relatively more rear brake on entry. Also, think of throttle steering, where moderate longitudinal slip of the rears causes rotation. Longitudinal slip also occurs under heavy braking. Then you also have to take lsd locking under decel and its transition into account. Lots of variables, but change towards more rear bias equals less entry understeer / more oversteer.

P.S. I wrote this all while my Tesla autopiloted me to the track, so take it with a massive grain of salt lol.

[rhyary]

>> P.S. I wrote this all while my Tesla autopiloted me to the track, so take it with a massive grain of salt lol.


Do you mean you were going for breakfast, but the car knew where you really wanted to go?

[Kelse92]

Originally Posted by b4hand

Explain please

For me anyway, I tend to over slow the car so the less friction pad stops me less. Also, less temp needed to heat them up on a cooler day

[torrque]

Track Night in America Price : 160.

Overtaking a Corvette C6 with slicks when you run All seasons ? Priceless

[dparm]

He's gapping you on the straights but his cornering is awful. Missing the apexes by several feet, sudden steering inputs, no trailbraking...your driving is MUCH better. Looked to be a Grand Sport, so in the right hands I would expect that thing to be quite formidable.

[roastbeef]

Originally Posted by Bartledoo

I’ve always used the same compound front and rear. The only reason I would consider going less aggressive in the rear would be that I wasn’t getting the rears into their ideal temp range…

Adjusting brake bias to be less front biased will reduce entry understeer all else being equal. Case closed. I’m not sure how this is an argument since it’s pretty well known.

It seems like someone’s intuition is having them imagine a car going straight with only front brakes, such that the rear end wants to overtake the front, but this is ignoring the dynamics of corner entry. For example, you are releasing brakes while you turn in, and you are also adding front braking by lateral grip while you turn the wheel to enter. These have combined effects when paired with changes in bias. More rear bias means you are releasing relatively more rear brake on entry. Also, think of throttle steering, where moderate longitudinal slip of the rears causes rotation. Longitudinal slip also occurs under heavy braking. Then you also have to take lsd locking under decel and its transition into account. Lots of variables, but change towards more rear bias equals less entry understeer / more oversteer.

P.S. I wrote this all while my Tesla autopiloted me to the track, so take it with a massive grain of salt lol.

i'm going to have to experiment with this. the last time i talked with my brake pad guy (cobalt friction) who makes and tests pads himself, i asked about going with a more aggressive pad in the rear. he advised against that, citing the rear brakes don't see as high of temperatures or get as much load when the weight shifts. triggering rear abs at turn-in doesn't sound like a great idea if you exceed threshold braking.
up front, i'm running xr1 pads, and i was going to go with xr2 pads in the rear, but he strongly suggested xr3 pads for the rear.

so if i used xr1 pads (high torque, high bite) in the rear, i'd reduce understeer?

[tsk94]

Originally Posted by roastbeef

so if i used xr1 pads (high torque, high bite) in the rear, i'd reduce understeer?

If that pad is a higher torque pad then what you're currently using, then yes. You'll have more rotation under trail braking with the XR1s.

[roastbeef]

its not higher torque, it would be matching the front compound.

[tsk94]

Originally Posted by roastbeef

its not higher torque, it would be matching the front compound.

I meant higher torque compared to what you're currently using in the rear

[k_mann]

Woah glad I sparked some discussion! Lots of information thanks guys! I ended up ordering the 11's so I'll see how the combo goes. Luckily the 08's have probably a weekend left in them so if I like these 11's I'll go matching all around.

Sounds like I need to assess my alignment with the shop, it's a mild track/street friendly setup. Maybe I should go a little more track focused.

[SonnyJack]

The new pumps are in at Summit Point Main and quite an improvement over the splitter destroyer they previously had!

[k_mann]

While we're on the topic of brakes, I was curious on rotors for stock calipers. Mainly OEM vs girodisc. Would OEM from fcp make more sense until going bbk?

Or does girodisc add some braking benefit? My only guess would be heat capacity/longer life than stock rotors

[bigjae1976]

Originally Posted by roastbeef

i'm going to have to experiment with this. the last time i talked with my brake pad guy (cobalt friction) who makes and tests pads himself, i asked about going with a more aggressive pad in the rear. he advised against that, citing the rear brakes don't see as high of temperatures or get as much load when the weight shifts. triggering rear abs at turn-in doesn't sound like a great idea if you exceed threshold braking.
up front, i'm running xr1 pads, and i was going to go with xr2 pads in the rear, but he strongly suggested xr3 pads for the rear.

so if i used xr1 pads (high torque, high bite) in the rear, i'd reduce understeer?

Awhile back, Turner used to sell pagids with a more aggressive rear pad. This was to help the stock front brakes which will work on track but require management.

If you want reliable braking throughout a session at just about any track, a 4 wheel Stoptech BBK is the starting point.

I've seen a less aggressive rear pad used. Not sure that is necessary or helpful.

[bbnks2]

My personal experience was that more rear bias was better. Trail-braking felt better and the rear felt more stable. I think the general rules of thumb can't really be debated without knowing the exact car and scenario because we are all running different springs, pads, aero, tires, etc. More front bias = more understeer is true. However, maybe you have a suspension issue inducing understeer and therefore more front bias might help during trail braking to keep more weight over the front wheels thus reducing understeer? It's all real complicated it makes my head hurt.

Keep in mind these cars have EBD... I ran the M3 rear-end on my 135i with the stock 135i front Brembos... so significantly more rear bias. The car felt great. I never locked up the rear tires ever. The rear felt more stable under trail braking. Seems counter-intuitive based upon what I read online about how more rear bias = more oversteer tendency but that was my experience.

With the current M3 front brakes the rear feels like it wants to kick out on me. I think it is not because of too much rear bias locking up the rears but rather the rear-end getting light. You read things like "weight transfer doesn't change just how the car behaves due to it." That also seems counter-intuitive to me and I don't think looking at static formulas that prove that statement really matches up with the type of dynamic situations we are talking about. My front wheels turn black with brake dust possibly evidencing the over-working of the front brakes relative to the rear.

[dparm]

Originally Posted by aututto

While we're on the topic of brakes, I was curious on rotors for stock calipers. Mainly OEM vs girodisc. Would OEM from fcp make more sense until going bbk?

Or does girodisc add some braking benefit? My only guess would be heat capacity/longer life than stock rotors

GiroDisc is immensely better but a BBK is probably the better long-term choice. You can usually get them at a discount via contingency/membership discounts with NASA and other organizations. I think I got mine for 15% off.

GiroDisc advantages:

1. Floating design -- better for heat and radial float reduces knockback
2. Tons of directional cooling vanes
3. Higher quality steel which wears more slowly and is less prone to cracking
4. Lighter than stock (not sure how much, but usually a few pounds per corner)