Trail braking, rear brake bias?

[armyav8tor]

Originally Posted by Dascamel

Army, I'm not an expert but before even thinking about trail braking get some real instruction. I'm talking a day or two with real advanced drivers that are used to providing training at a high level. You have a very high natural level of talent, but your line and other things can still be improved. DCSTEP mentioned a few things like turning in too early in a few places, everytime you did it slowed you down. Trail braking can help, but you can shave time in so many other areas first w/o even turning MDM off.

As I have mentioned before, I don't condone trail braking. I've seen way too many accidents as people brake late into the corners to include one of my guys who drove his Evo right into the Armco. I now realize that I may have been doing some trail braking myself from watching the above mentioned youtube video. If that is trail braking then it feels natural to me and at no time did I feel I did not have full control of the car.

When I'm driving on the Ring, I focus most of my attention to the corners, especially my exit speed. I say this because the corners are the only places you can put over 90% of your skills into on public track days. It is far too dangerous to push it in the straights because the Ring is full of blind corners and you never know if there is a disabled car or an oil spill on the other side of that corner. So, you'll hear me back off the gas on the straights but I try to attack the corners the best I can because the car is not going that fast even if I was to hit something on the other side.

I had to alter some of my lines in the last weekend because my tires and brakes were done. The tires had ~40 laps on the Ring and the brakes were "warped" beyond believe (I stopped by the local dealer to find out they didn't have any tires/ rotors in stock). But for the most part, the lines are by the book. I actually memorized all the corners while I was in Iraq on my off time by watching an instructional video I acquired and I would drive the track in my head over and over again (I'm driving it as I write this... :P). Here's a little secret if you guys ever go to the Ring. The turn-in point and apexes are marked with white lines. If you watch my video, you'll know what I'm talking about. The instructors painted those lines there to help their students as it is difficult to remember what to do in each corner when you first drive there.

As far as traction control goes, I would never go DSC off on a public track day there. MDM is the best bet. DSC full on is also dangerous when it decides to cut power when you are trying to power out of a corner. I found that out in the wet.... Its unfortunate I never got to drive the Scuderia Hanseat, I'll be stationed in Germany again someday!

[dcstep]

Let's talk about what "trail braking" really is.

Trail braking is where you intentionally brake and turn the car at the same time. Braking adds weight to the front of the car and as you begin to turn it that transfers weight to the outside front tire, allowing the tire to maintain grip and turn in at a speed higher than it would without the added braking load. If you tried to turn in at the same speed without trail braking the car would push to the outside of the corner, perhaps even off course.

It's usually used on smaller track than the Ring, where there's a long, high speed straight followed by a slow, neautral turn (often a u-turn). It's used to go faster and school such as Skip Barber in the US actually teach it. As the car speed drops and the steering angle increases, you must very finely adjust the brake pressure to avoid over braking or getting off the brakes too soon and pushing. With a little practice it can become a very solid, repeatable technique.

It can also be a "rescue" technique, where you've missed your apex or carried too much speed into a corner. Realizing that the car will turn in better with weight on the front might just save your butt or, at least, keep the car on the asphalt. Of course, when used this way it's NOT the fast way around. Still, being aware of what it can do for you may pay off where you least expect it.

Dave

[dcstep]

Originally Posted by armyav8tor

... I've tried left foot braking just on the street with regular driving and noticed that I was not smooth at all and usually step on it way too hard. I didn't think it would be wise to try that at the Ring and I didn't have enough time left in Germany for me to learn to be smooth with my left foot and go to the Ring to try out the technique so I just said screw it. My right foot is very accurate with the gas and brakes though. My left foot is used to stepping fast and hard into the clutch's engage/disengagement point and then releasing as it grabs the gear so it is not programmed for braking at all. ...

You just need practice. Your left foot will ultimately be superior to the right foot because it'll only have one duty. Practice a little in a safe place, then start using it full time on the street. It'll fill very natural quickly.

When you get back into a car with a clutch there's no problem going back to the old way.

Dave

[armyav8tor]

Originally Posted by dcstep

Let's talk about what "trail braking" really is.

Trail braking is where you intentionally brake and turn the car at the same time. Braking adds weight to the front of the car and as you begin to turn it that transfers weight to the outside front tire, allowing the tire to maintain grip and turn in at a speed higher than it would without the added braking load. If you tried to turn in at the same speed without trail braking the car would push to the outside of the corner, perhaps even off course.

It's usually used on smaller track than the Ring, where there's a long, high speed straight followed by a slow, neautral turn (often a u-turn). It's used to go faster and school such as Skip Barber in the US actually teach it. As the car speed drops and the steering angle increases, you must very finely adjust the brake pressure to avoid over braking or getting off the brakes too soon and pushing. With a little practice it can become a very solid, repeatable technique.

It can also be a "rescue" technique, where you've missed your apex or carried too much speed into a corner. Realizing that the car will turn in better with weight on the front might just save your butt or, at least, keep the car on the asphalt. Of course, when used this way it's NOT the fast way around. Still, being away of what it can do for you may pay off where you least expect it.

Dave

Cool

[lucid]

Originally Posted by dcstep

Let's talk about what "trail braking" really is.

Trail braking is where you intentionally brake and turn the car at the same time. Braking adds weight to the front of the car and as you begin to turn it that transfers weight to the outside front tire, allowing the tire to maintain grip and turn in at a speed higher than it would without the added braking load. If you tried to turn in at the same speed without trail braking the car would push to the outside of the corner, perhaps even off course.

It's usually used on smaller track than the Ring, where there's a long, high speed straight followed by a slow, neautral turn (often a u-turn). It's used to go faster and school such as Skip Barber in the US actually teach it. As the car speed drops and the steering angle increases, you must very finely adjust the brake pressure to avoid over braking or getting off the brakes too soon and pushing. With a little practice it can become a very solid, repeatable technique.

It can also be a "rescue" technique, where you've missed your apex or carried too much speed into a corner. Realizing that the car will turn in better with weight on the front might just save your butt or, at least, keep the car on the asphalt. Of course, when used this way it's NOT the fast way around. Still, being aware of what it can do for you may pay off where you least expect it.

Dave

Good post Dave. I just got back from NHMS and there was a whole lot of discussion on trail braking. One clearly doesn't want to trail break at every turn, but some turns just demand it if you want to go through them fast. A highly advanced driver can trail brake consistently without running into trouble. And one has to try it and practice it to get to that level, and I am sure there will be mistakes during the learning process. An open track with good run-off area is the place to practice this skill. Surely not the Ring. If it is done by a novice at a fenced in track, it will surely result in poor outcomes. I have not mastered it myself; I practice it where I deem it is safe. I rode shotgun in a friend's E90 M3 at NHMS. He has years and years of racing experience, and is really fast. When you see this skill put to work on the track to rotate the car at speed by someone who has mastered it, you can't help being immensely impressed.

[JAJ]

dcstep pretty much nailed it. The performance driving school that runs the days I attend teaches trail braking (they call it "balance braking") from the very first time on the track. I don't even think about it any more, I just do it.

The point of the lessons is to go fast by keeping the car settled. Braking is about managing weight transfer as much as it's about slowing down, and the brakes and throttle allow you to move the traction forward to the front tires as you turn in and back to the rear tires as you exit the corner. Treat the braking process as a single event that starts with a strong application at the braking point and ends with a smooth release and transition to the throttle at the apex as you unwind the wheel through the exit. You can carry a LOT of speed by being smooth and keeping the car settled and balanced with the brakes.

And, as Dave also said, if you mess up and enter the corner too fast, balance braking gives you more steering ability. While you might run wide and lose momentum, you don't go slithering off into the weeds (or that pesky cement wall).

[KINGLEH]

your funny armyav8tor...... Seem to be a little comfused about the whole "track day" thing...

Against trail braking but dont really know what it is..... And telling people not to do it...


You have alot to learn but it is great you get to drive on the ring... Its like no other track... Which is why.. You have alot to learn!

[Montoya]

From Wikipedia:

"Trail braking is a motorcycle riding and driving technique where the brakes are used beyond the entrance to a turn and are gradually released up to the point of apex.

In a broader scope, trailing off the braking pressure either while straight line braking or, as above, after turn in has begun, allows for a less abrupt and more accurate final corner entry speed adjustment. Some corner entries, such as decreasing radius turns, are more adapted to the leaned over trail braking technique. In turns where a quicker steering action is more applicable, trailing the brake while turning in is unnecessary."

This broader definition is the point I was trying to make in my earlier post regarding the friction circle.

It continues...

"Usage in four wheel vehicles

In 4-wheel vehicles trail braking pertains to using the brakes past the corner entrance (as opposed to the normally taught practice of releasing the brakes before starting the turn). This practice is used for creating weight transfer towards the front tires, thus increasing their traction and reducing understeer. It works best in light vehicles that have their brake bias to the front.

In order to be properly performed, the driver must have excellent sense of the vehicle's behavior and be able to keep the braking effort within very tight limits. Excessive braking effort may result in the vehicle heavily understeering, or - if the brake bias is set to nearly neutral - in the rear wheels locking, effectively causing the vehicle to spin as in a handbrake turn.

Once a driver has mastered trail braking, it can help enter the corners at higher speeds, or avoid an accident if the driver has entered a corner at a speed exceeding the vehicle's (or driver's) capabilities."

This is a more exacting definition. Emphasis on points made by others.

[dcstep]

Originally Posted by Montoya

This is a more exacting definition. Emphasis on points made by others.

You may have confused verbosity with exactness.

Dave

[lucid]

I am still not convinced that ABS will let your rear brakes lock up due to braking torque. As the rear wheels get unloaded, they will have less traction, but ABS will detect that and should adjust hydraulic pressure to reduce braking force and prevent noticable wheel lock up.

[dcstep]

Originally Posted by lucid

I am still not convinced that ABS will let your rear brakes lock up due to braking torque. As the rear wheels get unloaded, they will have less traction, but ABS will detect that and should adjust hydraulic pressure to reduce braking force and prevent noticable wheel lock up.

I agree with this. I certainly haven't experienced any rear brake lock up, even in the rain when I did get the ABS going a time or two on all four wheels. BTW, it turned better when I modulated the brakes manually.

The OP did indicate that he might be downshifting a DCT while turning. I also did that with no ill effect, but I was not skipping any gears and the rpm match wasn't very many rpm. Also, I was well under control as I was slowing and turning at the same time.

I never tried this, but I'm led to believe that if you slow from high speed (like 140 mph) to low speed (say 50 mph) and don't run down through the gears like I do, that the DCT might jump from 5th to like 2d or 3d. If that is indeed the case, then that might be rough enough to cause the back end to get unsettled. I'd suggest not doing that and making the downshifts without skipping any gear.

Dave

[Montoya]

Originally Posted by armyav8tor

Were you on full DSC or MDM? I ask because the rear steps out much easier when DSC is on. It is exactly as you've described, the car would cut power and the back end steps out. I experimented with full DSC on a wet track and discovered it was much more dangerous for me than to leave it in MDM. The MDM will literally let you drift around a corner where as DSC will cut power as soon as it senses you are at the limits of traction and the sudden cutoff will cause the car to rotate out and you are basically in a slide at that point.

No I Drive so no MDM- Your experience is interesting, my experience was similar. In the end it was just a squiggle and I was well within the limits, but it's not a confidence raising experience to think if you are going faster when you might really need DSC to pull you back from the abyss that it actually might make it worse!

[armyav8tor]

Originally Posted by Montoya

No I Drive so no MDM- Your experience is interesting, my experience was similar. In the end it was just a squiggle and I was well within the limits, but it's not a confidence raising experience to think if you are going faster when you might really need DSC to pull you back from the abyss that it actually might make it worse!

Yeah, DSC needs to be off on the track if MDM is not available (probably very poor advise ). I turned it off at the local Autox (first one for me) today because MDM was cutting off too much power but then eating cones is a lot cheaper than eating rails.... so I don't know if you want to risk it. Oh and I was trail braking all day today now that I have a few definitions of what it is... and I had a lot of fun bringing the tail out, something that I did not dare to do intentionally on the Ring.

[KINGLEH]

ive had the rear abs only cycling before.. because of unloaded rear..... abs cant change physics.. just band aids a problem..

[lucid]

Originally Posted by KINGLEH

ive had the rear abs only cycling before.. because of unloaded rear..... abs cant change physics.. just band aids a problem..

Not sure if I understand what you mean. ABS can't give you the traction that you don't have and make you decelarate faster than the traction that you do have allows you to decelarate, but it can adjust braking forces so that the wheel does not lock up. Sounds like you got yours to lock up. That is surprising. Like dcstep, I haven't been able to do anything to the car that resulted in that. What were you doing exactly?

[KINGLEH]

yea i explained it kinda bad...


Its hard to feel the ABS cycling sometimes.. i dont call it "locking up but i guess some would.. its trying to lock up but ofcourse ABS wont let it... you can feel the rear tires pulsing through the brake pedal and feel of the car...


when it happens ---- downhill hard braking.. and hard trail braking into corner... perfect example would be downhill 270* off ramp on interstate while in the entry.. I had it with stock brakes and have Stoptechs now.. I changed the pad compounds to get a better bias on the stoptechs and it improved...

[dcstep]

I don't think I'd worry about it if it only happens when the rear is unweighted in a downhill turn. Almost any car will step out in that condition. If you adjusted brake bias such that it did NOT do that when the rear was unweighted with side force, then you would reduce your straight line braking capacity slightly. Of course any brake bias setting is a compromise and should reflect driver preference.

Of course you know the solution is not to trail brake into downhill corners OR just be prepared for it and get on the gas when the rotation gets you pointed in the right direction.

BTW, is there no brake bias adjuster for the M3s? I suppose it might mess with the DSC and ABS. I used to have a little knob on my 5.0 Mustang that allowed for magic little adjustments, but then I didn't have ABS.

Dave

[von_zoom]

I am kind of late getting into this thread, but I too have never had rear brake lock up with any car which had ABS functioning. That is the purpose of ABS, to allow all wheels to continue to turn, thereby giving you control. If the wheel is locked and sliding, you cannot turn. The wheel has to rotate. This past week end at the track, with stock pads, I experienced fade, but no lock at any time, front or rear.
vz

[dcstep]

Originally Posted by von_zoom

I am kind of late getting into this thread, but I too have never had rear brake lock up with any car which had ABS functioning. That is the purpose of ABS, to allow all wheels to continue to turn, thereby giving you control. If the wheel is locked and sliding, you cannot turn. The wheel has to rotate. This past week end at the track, with stock pads, I experienced fade, but no lock at any time, front or rear.
vz

vz, yes you are late and you're not saying anything thing that we don't already understand. This thread is well beyond what ABS is designed to do, thank you. If you'll read the thread I think you'll understand that.

Most of the people in this thread drive on the track and do these things on purpose and know how to control skids without ABS. You say that you track your car and had no lock up. I suspect conditions were dry for you. Did you trail brake late into a downhill corner? That's the condition where at least one is experiencing the condition. Most of us have not experienced it either, but apparently it happens in certain condition.

Dave

[KINGLEH]

Originally Posted by dcstep

I don't think I'd worry about it if it only happens when the rear is unweighted in a downhill turn. Almost any car will step out in that condition. If you adjusted brake bias such that it did NOT do that when the rear was unweighted with side force, then you would reduce your straight line braking capacity slightly. Of course any brake bias setting is a compromise and should reflect driver preference.

Of course you know the solution is not to trail brake into downhill corners OR just be prepared for it and get on the gas when the rotation gets you pointed in the right direction.

BTW, is there no brake bias adjuster for the M3s? I suppose it might mess with the DSC and ABS. I used to have a little knob on my 5.0 Mustang that allowed for magic little adjustments, but then I didn't have ABS.

Dave

I'm not worried about it...

I did the pad change for optimum bias...

The rear wont step out really because of the pulsing... If the rear steps out its more of a weight transfer thing...

also bias adj with ABS is not really ideal and difficult....

[KINGLEH]

i think before this goes any further we should establish what we should call this situation...

the original poster is calling it "lock up" but what i think he means is its trying to lock up.... of course ABS pulsing the tire does actually lock up for a hundredth of a sec or so.. but I personally dont call that lock up...



Noone should actually be able to LOCK UP any of their tires unless they get a ABS fault and the system fails... That still might not be the case because I'm even pretty sure i had ABS fault light on my dash after Dynoing my car and went out and tried to lock up a tire to see if it was totally off and ABS still cycled....

[dcstep]

[QUOTE=KINGLEH;5512342]...
the original poster is calling it "lock up" but what i think he means is its trying to lock up.... of course ABS pulsing the tire does actually lock up for a hundredth of a sec or so.. but I personally dont call that lock up...
[QUOTE]


Well, the OP was also talking about this happening in conjunction with downshifting, which is indeed possible to "lock up" in that condition. It could be a looseness in semantics, or something that actually happens on a downshift when the rear is light enough. Either way, it's something that's solved by being smooth and/or finishing the braking sooner and/or downshifting later.

I purposely make the rear end step out, or slide, with trailing throttle oversteer. I wonder if that's what the OP experienced. Depending on how extreme it is, it feels like the rear wheels are "locked". We know that they're not and it's the extreme side slip that we feel and hear, but the OP misinterpreted that kind of event. If you suddenly lifted off the gas while turning AND downshifted, many might mistake that as lock up. With the MDM and DSC off, it'll get sideways big if you don't manage it.

Dave