Brake Bias

[Light on Fuel]

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

[redneckdzl]

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

[Roadkilled78]

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.

[Light on Fuel]

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.

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

[Roadkilled78]

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.

[Light on Fuel]

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.

[Claff]

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.

[Light on Fuel]

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.

[Roadkilled78]

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.

[Light on Fuel]

"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

[ps2375]

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.

[Light on Fuel]

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?

[ps2375]

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.

[Light on Fuel]

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.

[ps2375]

actual temps are not the issue, the target is even temp across the tread, inside/middle/outside.

[Light on Fuel]

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).

[ps2375]

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.

[Light on Fuel]

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.

[Brianjk]

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.

[Light on Fuel]

^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.

[ps2375]

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".

[Light on Fuel]

That's pretty much what I'm looking for. What pressures do you run or are you on slicks?


Sent from my iPhone using Tapatalk

[ps2375]

"R" comps will be much diff that street tires. I posted the pressures back in post #13.

[Light on Fuel]

I posted the pressures back in post #13.

Oops. I forgot. Please disregard.


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[Roadkilled78]

Not seeing a mk4 gti in the results...did you make it out to that event? How'd it go with the new suspension?

[Light on Fuel]

Not seeing a mk4 gti in the results...did you make it out to that event? How'd it go with the new suspension?

I didn't make it out. I was hearing a front end clunk whenever I went over a speed bump or loaded up the front at low speeds. I checked my LCA bushings and saw that they were completely shot.
So I used that day to replace both LCA's. As much as I wanted to hit up the event, I decided that it might be a really bad idea considering the condition they were in. Also, I'm registered for a morning autoX school this Friday 8th, followed by an afternoon event. Since that means I'd be getting 50-60 runs in total for the day, I had to sacrifice the last event to get my car sorted for this Friday. Now, I can go to the event having a very crisp handling car that I can be confident in.


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[Light on Fuel]

So I did the school and event yesterday. I got a trophy for 3rd place which isn't too bad when you consider that everyone in my class were on slicks! But now I'm thinking that the thread should be renamed to "how to get the car to rotate." lol

The new suspension and tires felt great and there were several runs where I could feel the rear rotate perfectly, which is a very rewarding feeling. But there's one big problem: I'm not sure "how" I got it to rotate so well sometimes and not others. I don't think that I fully understand the physics involved in getting the rear to rotate. If you look at my times I was very consistent, enough so that I got the highest consistency points in my class. But I wasn't consistently getting the rear to rotate when I wanted it to. Any advice?

Also, I noticed several times that when the front was loaded up under hard cornering, when I would try to give it some juice, it felt almost as if the trans was binding up. Was this because I was asking too much of the car in those instances; is it because I need a better diff; or is it just crappy driving? Thx.


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[2003 golfer]

Were you getting the car to rotate well in certain corners and not in others, or was it different run-to-run in the same corners? If it was in different corners then it's possible that the pavement in those areas had more/less grip or perhaps had some gravel/debris on them (not sure if the event swept the track beforehand, we used to when testing our Formula SAE car at school)

Did the car's rotation change somewhat continually through the day? It's possible that the track temp was changing and effecting grip.

Did you wind up getting a tire gauge? What were your readings like?

Take my comments with a grain of salt, as you may actually have more experience than me

I'm not sure what you meant by your transmission binding, but maybe you want to invest in a stiffer transmmssion bushing? I got the ECS dogbone bushing upgrade a few weeks ago and really like it except when I'm idling, and especially when idling with AC on.

[Light on Fuel]

Thanks for the reply. I Have less than 6 events under my belt, so I will check for some of the above mentioned conditions on my next outing (which isn't for at least another month since I currently have a broken foot).

I bought a good gauge and tried different pressures throughout the day at the school. I settled on 48psi on the rear tires: I didn't land on anything conclusive for the front tires though. But they were still rolling a bit on the sidewalls at 46psi. So I'm not sure what to do about that.

It terms of getting the rear to rotate; it was always a hit or miss affair. For example: the rear would rotate beautifully through the first slalom on one run, but not every run, or the rear rotates well through turn two sometimes, but not all the time. I always check my pressures between runs, so it's not due to changing tire pressure. Which leads me to believe that it may be my lack of experience/knowledge with the physics behind the car.



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[babarber]

what kind of tires are you using? because if they cant hold up at that kind of pressure then something is wrong
if your running really high performance street tires like hankook rs-3 or toyo r1r then you should be running mid 30s front low 30s rear mid 30s as well in the rear if you want a bit less grip for rotation
if running regular street tires you want up 30s to low 40s rear and low 40s front

mark your tire sidewall with chalk, etc
you should be rubbing the chalk off down to the tip of this triangle

[flyinglizard]

Stock suspension stuff may need 40- 50 front and up to 55 rear. If the car is inconsistent, you are probably gettting on the edge , per above post.
Or you may be trail braking into some sections only part of the time. Trail braking and/ or left foot brake can loossen up the car enough to go faster.
Sometime the car needs more air for the "turn around" , if your track has one. Many solo courses have a single pin of of some sort and really hurts the outside tire. , add air for this turn ,as it may help and long slow turn.

Optimal air may not be the same for all of the tires., or even left to right.

[Light on Fuel]

I'm running Hankook V12's. I used Moroso Race Write and marked all four corners. The rears were fine in terms of rolling onto the sidewalls. It was the front that rolled past the triangle and across both those raised lines beneath it. At that point, I raised the pressure up to 46psi at the fronts.

I considered the idea that it may be a setup issue, but if that were the case then I wouldn't be getting the rear to rotate at all. I think that it's down to my driving and lack of consistency.

So I'm wondering: how should I be entering a turn and/or slalom? What are some the rule of thumbs to keep in mind when driving a FWD car with a rear beam? Any advice would be greatly appreciated.


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[babarber]

when entering a turn i brake hard right before the turn then gradually let off the brakes during turn in this puts alot of the load on the front tires which helps the front grip and the rear rotate

in slaloms i stay as close to the cones as possible so i dont have to make big turns which will quickly overwhelm the fwd

[Light on Fuel]

when entering a turn i brake hard right before the turn then gradually let off the brakes during turn in this puts alot of the load on the front tires which helps the front grip and the rear rotate

in slaloms i stay as close to the cones as possible so i dont have to make big turns which will quickly overwhelm the fwd

I'll try that at my next event: Which probably won't be for at least another month unfortunately due to my broken right foot. But that's a really good tip.

I had tried doing something like that at my last event but found that my brakes were slightly inadequate. I worked the first heat and noticed during my run group that it was taking me a lot longer to drop speed at the corner I had been working than the previous cars had needed. I initially thought that it may be that I had more speed than them, but that's not the case cos I'm sure some of the Evo's were carrying way more speed than I was. So I may try getting Hawk pads and braided lines front and rear.


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[babarber]

im running stock brake setup with oreilly's 20$ pads i want to upgrade the pads but the courses we run on are sealed asphalt and is very slick as far as track surfaces go so even with my star spec tires brakes keep up with the tires grip