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    Thread: Brake Bias

    1. Member Light on Fuel's Avatar
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      05-22-2012 03:40 PM #1
      Has anyone on here ever adjusted their brake bias for autoX'ing?

      I'm trying to get the rear to rotate a little quicker when I tap the brakes while not losing too much momentum through the turn. My thinking is that being able to adjust to rear bias would enable me to do this without the front brakes grabbing too much and scrubbing too much momentum.

      I'll concede that it may be a matter of driving technique, but if being adjusting the bias is beneficial, then please let me know. If that's not the case, then I'm more than willing to receive some useful tips from a more experienced driver.

      Any comments, suggestions or precedents would be extremely welcome. thx

    2. Member redneckdzl's Avatar
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      05-22-2012 03:47 PM #2
      Never played with the brake bias, but mk4 are rear biased braked already, from what I've read and seen

      Best bet if you want some rotation is add a rear swaybar

    3. Member Roadkilled78's Avatar
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      05-22-2012 04:39 PM #3
      When I was autocrossing the Golf I did not mess with brake bias, however trail-braking was essential to getting it to rotate well. This was coupled with the rear shocks adjusted to nearly full-stiff.

      Not sure how new you are, but here goes, if you need a quick lesson: Trailbraking refers to continuing to brake as you turn in, rather than getting all your braking done in a straight line. Maintaining the forward weight transfer helps the front grip better and the 'lighter' rear end is more eager to come around.

      It may also catch you by surprise and cause a spin. Or, you waited too long to begin braking and plow straight thru the corner. Or you already slowed enough going straight, then continued braking into the corner, and are by then just going slow . It can be hard to get the hang of.
      Last edited by Roadkilled78; 05-22-2012 at 04:41 PM.
      Quote Originally Posted by Hogan View Post
      What kind of ass backwards world do you live in where your Miata is broken and your Alfa is your reliable source of transportation?

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      05-22-2012 06:18 PM #4
      Quote Originally Posted by redneckdzl View Post
      Never played with the brake bias, but mk4 are rear biased braked already, from what I've read and seen

      Best bet if you want some rotation is add a rear swaybar
      I noticed that. My pads in the rear are worn more than my fronts even though I installed them a month after my fronts.

      I have a larger bar on the rear. It's on the middle adjustment point so I guess I'll try it on full (closest to the beam, that is) and see how that feels.

      Quote Originally Posted by Roadkilled78 View Post
      When I was autocrossing the Golf I did not mess with brake bias, however trail-braking was essential to getting it to rotate well. This was coupled with the rear shocks adjusted to nearly full-stiff.

      Not sure how new you are, but here goes, if you need a quick lesson: Trailbraking refers to continuing to brake as you turn in, rather than getting all your braking done in a straight line. Maintaining the forward weight transfer helps the front grip better and the 'lighter' rear end is more eager to come around.

      It may also catch you by surprise and cause a spin. Or, you waited too long to begin braking and plow straight thru the corner. Or you already slowed enough going straight, then continued braking into the corner, and are by then just going slow . It can be hard to get the hang of.
      I'm know the concept although execution is another matter. I've already had a tank slapper that put me into a spin: I came into a turn too hot, had my right rear fully loaded, tapped the brakes (bad move), over-corrected, then found my rear sliding past me.

      I guess the hard part is figuring out the exact braking points at a given speed. I'm headed to my 4th event in 2 weeks so the advice on getting the rear to rotate properly is greatly appreciated. I placed 2nd in my 2nd ever event, but I really want to up my game, so to speak.

      I just installed coilovers (I'll follow your advice and set them to almost full stiff on the rear: how about the front?) and got a new set of V12's for the event. Now, I just need the skills. I am registered for an autoX school: hopefully that'll help. We'll see.

      I'm open to more pointers if anyone has them. thx

    5. Member Roadkilled78's Avatar
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      05-23-2012 08:25 AM #5
      The car may feel very different with the new shocks and springs, don't go out and make drastic changes to your driving style on the first run. Find out how the shocks/springs have changed the car, see if shock adjustments alone make it handle the way you want.
      Quote Originally Posted by Hogan View Post
      What kind of ass backwards world do you live in where your Miata is broken and your Alfa is your reliable source of transportation?

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      05-23-2012 08:51 AM #6
      Quote Originally Posted by Roadkilled78 View Post
      The car may feel very different with the new shocks and springs, don't go out and make drastic changes to your driving style on the first run. Find out how the shocks/springs have changed the car, see if shock adjustments alone make it handle the way you want.
      That makes sense. I can already feel the difference in my morning commute. Prior to my Koni install, I had FK (F-in Krap) springs and shocks. They were only supposed to provide a 1.25" drop, but when it settled it was closer to 2" and there was a lot of body roll (to the point where my tires were rubbing on my inner fender lining). The tires I used were V4's (all weather) so I'm sure that the V12's will also add to the different feel of the car.

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      05-23-2012 06:41 PM #7
      One trick to adjusting brake bias without adding a lot of hardware (and, in my case, running afoul of Street Touring rules) is to mix and match brake pads front and rear. Our Miatas have a tendency to be overly front-biased, so the fix for that is to run more aggressive pads in the rear. In my car I run regular old Napa pads up front with Hawk HPS in the rear.
      Parsimonious Racing - autocrossing Miatas in the Washington DC area and beyond

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      05-23-2012 09:48 PM #8
      Quote Originally Posted by Claff View Post
      One trick to adjusting brake bias without adding a lot of hardware (and, in my case, running afoul of Street Touring rules) is to mix and match brake pads front and rear. Our Miatas have a tendency to be overly front-biased, so the fix for that is to run more aggressive pads in the rear. In my car I run regular old Napa pads up front with Hawk HPS in the rear.
      Wow. That is very clever. I think that once I have a little more seat time under my belt, I will try to mix and match pads also. Thanks for the advice.

    9. Member Roadkilled78's Avatar
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      05-24-2012 08:25 AM #9
      Yeah, that's a good Miata trick. I was thinking OP had rear drums.

      "next event in 2 weeks" = NNJR on the 3rd? I may be there too, usually run in Philly but have been wanting to try a Meadowlands event.
      Quote Originally Posted by Hogan View Post
      What kind of ass backwards world do you live in where your Miata is broken and your Alfa is your reliable source of transportation?

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      05-24-2012 09:04 AM #10
      Quote Originally Posted by Roadkilled78 View Post
      "next event in 2 weeks" = NNJR on the 3rd? I may be there too, usually run in Philly but have been wanting to try a Meadowlands event.
      Yes, but it's on the 2nd (I didn't see an event on MREG for a June 3rd event). I'm registered for that event, the autoX school on the 8th followed by the event that same afternoon. Although I have nothing to compare it to in terms of attending events elsewhere, the events at Meadowlands are really fun with great turnouts and very long courses. And the people there are pretty chill with lots of great cars (a few exotics usually attend as well).

      If you decide to make the drive over, come by and say hi: I love picking the brains of the more experienced drivers. I drive the GTi #393. My sig has a link to a pic of the car. I should be easy to find considering that I have yet to see a Mohavi colored GTi at these events.
      -Manny

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      05-24-2012 10:16 AM #11
      Another thing you can do is to play with your rear tire pressures. We found on the scirocco, when we were in the sweet spot on them, as little as a 1-2# change would have a large effect on how the rear would follow or lead. Increasing press will tend to increase oversteer, it may take some experimenting to find the sweet spot and then you can adjust accordingly for the type of course.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      05-24-2012 11:22 AM #12
      Quote Originally Posted by ps2375 View Post
      Another thing you can do is to play with your rear tire pressures. We found on the scirocco, when we were in the sweet spot on them, as little as a 1-2# change would have a large effect on how the rear would follow or lead. Increasing press will tend to increase oversteer, it may take some experimenting to find the sweet spot and then you can adjust accordingly for the type of course.
      That makes sense. Last time out I ran 48# on all four corners. It was a small run group so after my 2nd run the pressures shot up to 52-54#. What would be good pressure front and rear to use as a base point?

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      05-24-2012 11:56 AM #13
      That is totally dependent on the car and your setup and tires. Like I said, we were in an 80 scirocco with Kumho 710's, on 13X8 wheels. We ran no front bar and a big rear bar setup and pressures were mid to low 30's front and mid to upper 20's rear. And car prolly weighed around 2000#'s or less.

      We used tire temps to get the front pressures figured and the rears took many spins before we figured those out. Cause when it went, it went quick and was seldom catch-able, but once we figured them out, it was great fun.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      05-24-2012 12:25 PM #14
      Quote Originally Posted by ps2375 View Post
      That is totally dependent on the car and your setup and tires. Like I said, we were in an 80 scirocco with Kumho 710's, on 13X8 wheels. We ran no front bar and a big rear bar setup and pressures were mid to low 30's front and mid to upper 20's rear. And car prolly weighed around 2000#'s or less.

      We used tire temps to get the front pressures figured and the rears took many spins before we figured those out. Cause when it went, it went quick and was seldom catch-able, but once we figured them out, it was great fun.
      Gotcha. I'm on Koni coilovers (1150) with Honkook V12's (17x7.5) and a BRB. I guess my best bet is to invest in a tire temp guage and start experimenting. I'm not sure what the temp range should be on those skins so it'll definitely be trial and (much) error situation.

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      05-24-2012 12:44 PM #15
      actual temps are not the issue, the target is even temp across the tread, inside/middle/outside.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      05-24-2012 09:34 PM #16
      Quote Originally Posted by ps2375 View Post
      actual temps are not the issue, the target is even temp across the tread, inside/middle/outside.
      The even temp across the face of the tire I'm aware of: learned through some of the books I've read, a decade watching F1 religiously, and of course, playing Forza. But I always thought that there was a certain temp range where the tires have their max grip. Is this a concept that only really applies to road racing and not so important on short autoX sprints? Thanks for all the tips (and patience).

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      05-24-2012 09:39 PM #17
      You can over heat tires at an auto-x, especially street tires, but it generally takes two drivers (or one driver) with a short time between runs. I don't know if it's actual heat at the tread or just heat in general causing excess tire pressure.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      05-25-2012 07:00 AM #18
      Quote Originally Posted by ps2375 View Post
      You can over heat tires at an auto-x, especially street tires, but it generally takes two drivers (or one driver) with a short time between runs. I don't know if it's actual heat at the tread or just heat in general causing excess tire pressure.
      That was pretty much the case at the last event I attended. Since it was a PCA event and I don't drive a Porsche I was in a very small run group. I barely had enough time to check my pressures between runs. All of the more experienced drivers had spray bottles with them and were cooling down their tires between runs. I guess knowing when that's necessary will come with more experience.

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      05-26-2012 12:27 AM #19
      Another (rather advanced) driving technique which I don't think anyone else mentioned yet is left foot braking. The basic concept as I understand it, is that by braking with your left foot and keeping your right foot on the throttle the front wheels will keep rotating while momentarily locking the rear wheels. While I have heard of using left foot braking for continuous braking and momentary tapping/jabbing, I was initiated to it via the latter. I read about it in a book (porsche driving handbook i think) and taught it to myself in the snow. My basic parking lot approach was: maintain speed in a circle approaching understeer, then begin to tap/jab the brake pedal with the left foot. Sure enough with a bit of practice I was able to rotate the car with this technique. It definitely requires some fancy footwork and developing sensitivity in the left foot. You can develop your left foot just by using it to slow down on the street when you are clear of traffic or other hazards.
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      05-30-2012 06:37 AM #20
      ^That's what I do whenever I go karting. I first heard about the technique in F1, especially when the teams all made the switch over to semi-automatic gearboxes. The only problem with that method for me is that my left foot is mashed against the dead pedal when I drive a course: It's the only thing that prevents my skinny ass from sliding off my seat.

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      05-30-2012 08:53 AM #21
      I like to set the car up to be neutral or with very slight over steer with the rear tire pressures, then a slight tap of the brakes can induce the rotation I need and still keep the rear "catch-able".
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      05-30-2012 08:59 AM #22
      That's pretty much what I'm looking for. What pressures do you run or are you on slicks?


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      05-30-2012 09:54 AM #23
      "R" comps will be much diff that street tires. I posted the pressures back in post #13.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      05-30-2012 12:17 PM #24
      Quote Originally Posted by ps2375 View Post
      I posted the pressures back in post #13.
      Oops. I forgot. Please disregard.


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      06-04-2012 01:21 PM #25
      Not seeing a mk4 gti in the results...did you make it out to that event? How'd it go with the new suspension?
      Quote Originally Posted by Hogan View Post
      What kind of ass backwards world do you live in where your Miata is broken and your Alfa is your reliable source of transportation?

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