RJay

Hmmm... Four and certainly Eight I can understand. But why Bridge and Namerow? Given the relatively extreme uphill elevation change before each of these turns, why wouldn't you want to take full advantage of the free extra decel gs the hills offer and get on the gas earlier?

M758

I don't think I am on the fence at all. I trail brake and feel it is a very important especially in a 944. These cars have little hp and for some of corners you can do 60% of your braking after turn in. I do believe how much is dependant a number of factors. I rarely brake only in a straight line. I often start my braking in straight line and heel and toe in a straight line, but often do my last bits of braking well past turn in.

I am not reall sure what mitch talks about when he says heavy trail brakers.

I guess those are guys who brake in straight line and continue to brake after turn in where are too slow. Seems to me that if come to braking zone a straight line braker will strart at maybe the 100 yard marker and be finished and off the brakes at about 25 yards ready as he begins turn in.

Me I would simply brak at the 50 or 75 yard marker turn in a 25 and contine to brake to maybe 5-10 yards from the apex.

I attempeted to explain this in another thread, but will do it again here.

If you are on the throttle the weight transfer puts more grip to the rear. This in general makes turning more difficult as the car will understeer. Not a good thing when you trying to turn the car.

If you are on the braks the weight trasnfer puts more grip to the front. This in general makes the car mor willing to turn as it will oversteer. This good as it helps you turn.

By trail braking (or braking after turn in) you gain two important advantages over straight line braking.
1) Longer straight away by starting the braking point much later
2) Weight transfer helps turn in so you can be FASTER at turn in than with no weight transfer

The major drawback to trail braking is the potential for spins. The trick is manage the braking so that you are just getting the back end to slide, but it is still under control. In this case you can in exceed the stready state grip level in normal cornering.

It is very similar to braking proceedure.

If you get on the brakes hard the weight transfers to the front and you have lots of grip. Then as weight settles back you must relase some pedal since the tire may lock. So the process is hard at first slowly lessening pedal maintain and impending lock up.

By contrast if you get on the brakes soft and easy then push harder and harder you will experience lock-up long before you would had you been able to weigh down the nose of the car.

Trail braking has a similar aspect in the by weight the front the car and lessening the load on therear you can in fact corner FASTER than if you had only the purely static weigh distribution. Just like in a braking zone.

Another example is harpins in rallying. These hit the rear e-brake to break the back end loose this allowing the car to turn MUCH MUCH faster than normal methods. They obviously can control the "180 spin" and overall go much faster. The issue of corse with sliding the car around every corner is tire wear and a potential in ability to apply power on corner exit since tracition may not be regained. Trail braking is safer variation of this where the rear grip is decrease relative to the front causing a natural rotation tendancy that the driver must control mostly with brake pedal and steering input and occasional applcations of throttle if the rotates too far.

So to me it sounds like Mitch's "heavy trail brakers" are just braking too much.

Bottomline is what to brake as late and as little as possible. If I do that as I am turning it actully helps the car turn thus allowing me to corner even faster. The trick is too much brake results in an uncontrolled turning often called a spin.

RJay

I do, but I'm no expert. Certainly I find myself naturally beginning some turns with the brakes still slightly applied. This, to me is just part of being smooth and not upsetting the car. Having just come back from NHIS, turn 1 and 3 certainly to my mind demand that you finish braking, then add power to throttle steer through the turn. Athough I've certainly overcooked the entry to three and been forced to trail brake through it!

I wonder about the explanations of the advantages of TBing here at least as relates to 911s. The notion that maintaining weight on the nose of a 911 through a turn seems to me counterintuitive, particularly as any well taken corner is on three wheels anyway. For example:

http://www.vicelford.com/store/photo52big.jpg

joey bagadonuts

Sorry for the mirepresentation, M758, but I thought your reponse to the straight line braking question was also an endorsement. I've since reread your post.

M758

Well if the car naturally oversteer then you probably need to be on the throttle so the car does not over rotate (ie spin).

If the car naturally understeers then by continuing to brake you help the car turn thus allowing to achive a higher speed and still make the corner.


Ok

How about this.

At constant speed ( assume little to now accel/decel forces) a car can a certain corner at 70 mph with a perfect balance between front tire grip and rear tire grip, Basicly assume front and rear take equal cornering load.

What happens if you at 70mph apply power? Weight get transfer from the front to the rear causing more grip in rear than in front. So this means understeer. A car in understeer simply wont turn as much thus requires a larger radius. So as you try to apply more power and go faster you start taking a larger radius. Well you don't have more space so you need to back off to help the car turn. Hmm can really go any faster can you.

What happens if you are at 70 mph and apply brakes? Weight goes to the front causing oversteer. Here the car turns on tighter radius. Hmm A tighter radius means you have more track space, but alas you are going slow it sucks, but there is way out of this.

Now enter that same coner at 85 mph. What happens if you do it with a neutral front to rear balance? Well the car drifts off track since you can't make the corner. So enter at 85 and apply a little brakes. What happens now? Well the car will tend to turn on a tigher radius and you might be able to make the corner now. This is good. So enter the corner faster and by getting the weight trasnfered just right you take the turn tighter than you could before. So may you make the corner now at 75 mph vs 70. Now you are getting somewhere.

So by braking in the corner you use the weight transfer you turn faster thus allow you corner just abit faster. Plus you entered the corner bit fast too. In fact for trail braking to in fact be faster you MUST be going faster at turn in. Else you will slower overall since you are in fact slowing the car some.

Hmm,
If you are used to braking at 100 yards slowing to 60 mph and accelerating after you turn so that you exit at 75 mph then must change you entry speed to make trail braking work. If you turn in at 60 still you will be going slower at the apex (may be 55) and probably only 65 at turn exit. If however you use less brake and turn in at 80 mph you can slow to 75 for the mid coner and accell to 85 on the way out. DE logic teachs slow in fast out. Similar to the first model 60 mph at turin in 65 at mid corner and 75 at exit. To trail brake you go fast in 80 mph at turn in use brakes and weight transfer at to make the car turn at 75 at mid corner then accel 10 mph to 85. Fast in and faster out!
If you trail brake with slow in fast out it becomes slow in and slower out.

PS...
I hope this is clear.

M758

No problem. I guess I should have added wink to that one as my tougue was definitaly in my cheek on that one.

Bob Rouleau

Rjay - I trail brake into Bridge and Namerows because they are slow turns and TB-ing helps rotate the car. If I feel really hot, I toss my car into Namerow and nail the gas. That's more of a rally technique but it works and is a lot of fun - trouble is there are too many novices watching that corner...so it's reserved for instructor days only. At Bridge I brake less but I am well into the turn as I fade off the brakes. Namerow being a "U" turn is much the same. It is trail braking to assist rotation of the car.

Best,

RedlineMan

Thanks fellows;

A good growing of my little seed here. Now all we need is a big time 914 or Boxster guy to give the "confused" chassis story (doesn't know which end is which!). And where's Cervelli and Sunday? We want/need that HIGH level input!!

I think the best description for me is when someone here (?) said TB decreases the queezies between full frontal and side load Gs. Before the suspension sets to full side load, TB helps stabilize the "floating" chassis transition. That is a style of TB I have used for quite a while, and came to it all on my own... somehow.

Probably when I was still slow in - fast out, I went in hotter than normal, had a wiggle, and instinctively did some LFB to bring it back into shape. This has turned into a ritual now. I do it almost everywhere.

What Color tried to elucidate, and what Cervelli and M758 have fleshed out is the idea of using TB to carry in otherwise unmanageable levels of entry speed, and keep things under control enough to get past the apex and onto the gas. I certainly understand the idea of more speed in = more speed out, and if one has or developes the stones, then this type of TB is mandatory... for some turns.

What I am trying to decide is whether this can indeed be applied in its more extreme form to more turns than I think. Turns that do not fit my current mold, as it were. Perhaps a listing of the turns a lot of us know, and how I do them might be food for thought?

Lots of us know Watkins Glen, so we'll start there. This is all based on my powerless 84 944, neutral chassis setup.

T1 - Heavy straightline braking (HSB) with H&T to 3rd with only momentary balance TB after aggressive turn in. Full throttle AT turn in.
I know I can carry more speed in here. Question is, does TB help or hinder, and do you just have to take it as a super flyer if TB is not the answer?

T2-3-4 - WFO!

Inner Loop - "HSB" Aggressive turn in and full throttle at turn in. Stay in 4th and drive it like a straight!
I'm imagining that moderate to heavy TB might work here.

T5 - WFO in 4th

T6 - Careful! "Moderate straightline brake (MSB) with H&T to 3rd. Balance TB. Very early throttle, before gradual steer.
Perhaps more aggressive TB would help here, but it is NOT a place to experiment too drastically!!!

T7 - HSB & H&T to 3rd. Heave the car in sharply, floor the throttle, and straighten the wheel as much and as soon as possible.
I'm not sure TB will help because of the blasted hill?! You just can't give up ANY momentum.

T8 - HSB & H&T to 3rd. Slight Balance TB (BTB). Aggressive turn in with full throttle.
Less straightline and more TB here too?

T9 - Tiptoe again! Light straightline brake (LSB) Early moderate to heavy throttle before late turn in.

T10 - Sight BTB, no lift, flat out.
Obviously no TB here!

T11 - Very light SLB with H&T to 3rd. Slight BTB. Assertive turn in with full throttle.
In my car, I just need to do it flat! I think it can be done, if the driver is willing.

ALTERNATELY - To deviate to the advanced line, I take the late apex corners (5, 6, 7 & 9) much faster with earlier turn in and longer apexes.

I was managing 2:30-35 lap times (so I'm told) with one just a tick under 2:30.

Comments anyone?

Premier Motorsp

Funny, I typed a Watkins Glen description like this last night and decided not to post it.

Comments follow:

John:T1 - Heavy straightline braking (HSB) with H&T to 3rd with only momentary balance TB after aggressive turn in. Full throttle AT turn in.
I know I can carry more speed in here. Question is, does TB help or hinder, and do you just have to take it as a super flyer if TB is not the answer?

Me: I trail brake big time here. You can then roll down to the apex much faster. Think of it this way: Brake less than you are now, so that at the turn in there is just no way the nose will point unless helped from forward weight transfer. Just be prepared to get busy on the steering. You want to maintain slight tail out from a little past turn in down to the throttle on point (early for you). The throttle on will fix the oversteer.

John:T2-3-4 - WFO!

Me: Everything I have driven here has been WFO, even the 3.8RSR. Huge fun. Must think about minimizing scrub, so the mirrors should nick the armco.

John:Inner Loop - "HSB" Aggressive turn in and full throttle at turn in. Stay in 4th and drive it like a straight! I'm imagining that moderate to heavy TB might work here.

Me: I drag the brakes all the way past the first apex. That gives a few more mph at turn in and closer to the FC for the first part. It is hairy when done to the limit (1 or 2 times/weekend for me, too much risk to do it all the time)

John:T5 - WFO in 4th

Me: Really? I must drag the brakes lightly to point the nose. Very gentle because downhill+trail braking gives really responsive steering. Sometimes too responsive.

John:T6 - Careful! "Moderate straightline brake (MSB) with H&T to 3rd. Balance TB. Very early throttle, before gradual steer. Perhaps more aggressive TB would help here, but it is NOT a place to experiment too drastically!!!

Me: Big danger here and I am a big chicken. Trail brake just to do it, I am way off the FC. It is downhill so the nose points better.

John:T7 - HSB & H&T to 3rd. Heave the car in sharply, floor the throttle, and straighten the wheel as much and as soon as possible. I'm not sure TB will help because of the blasted hill?! You just can't give up ANY momentum.

Me: Go into the toe with insane entry speed. If you are sure you can't make it, you are almost fast enough. I pass more here than anywhere. The uphill gives you automatic decel, and the upward G gives extra stick. When you do it right, you drift all the way through and track out past the white line. Also the apex is earlier than what most people do, especially with no HP. This so fun when you get it right. I saw like a 20mph difference here between me and the less experienced drivers. No where else was it so obvious.

John:T8 - HSB & H&T to 3rd. Slight Balance TB (BTB). Aggressive turn in with full throttle. Less straightline and more TB here too?

Me: The entry is over really quick and exit is big. I trail brake just enough to point in, but I don't emphasize entry speed as much here. The apex actually is late.

John:T9 - Tiptoe again! Light straightline brake (LSB) Early moderate to heavy throttle before late turn in.

Me: Much trail braking. The entry is off camber and uphill so you understeer. The apex is always hard to get to. This corner is slow and it feels weird with all the fast corners at the Glen. I don't go crazy here.

John:T10 - Sight BTB, no lift, flat out. Obviously no TB here!

Me: Nope, not enough decel to TB. BUT, if I really was a big hero, I'd brake a little later (I can't really brake less, it is the lightest possible squeeze) to eliminate the understeer I always get in the entry. Big risk here, but one of the best corners anywhere.

John:T11 - Very light SLB with H&T to 3rd. Slight BTB. Assertive turn in with full throttle. In my car, I just need to do it flat! I think it can be done, if the driver is willing.

Me: I have real decel with this corner and TB enough to get a wicked sharp turn in. I go for unusually early throttle here. I make alot of mistakes here. This corner is incredibly fast when done right. It is roomier and slower than 10, so the risk is not as high. T11 sometimes creates one of those moments I try to avoid. I call them Moments of Truth. It is when your fate is 99% sealed as soon as you turn in. The Kink at Road America is like this too. I have noticed that the faster I go, the more Moments of Truth I get. I think the Moments of Truth occur when you are really, really at the limit of the car or your ability.

I agree with early turn in and longer apexes. This comes naturally as you get fast enough to have understeer on turn-in.

The C car runs 2:08s with a single 2:07 last year (04). The 3.8RSR I ran here in 1997 ran 2:00 flat. Back then the inner loop curbs were really tall, so these days the track should be faster. In my 996 I did 2:10s. Not enough power to get flying thru the esses.

Setup wise for the B and C cars I prefer almost zero understeer. That means that with my normal heavy TB, the car goes to slight OS instantly after turn-in. For a place like the Glen I run a bit more understeer because of the fast corners.

For the fast cars I run much more understeer. I don't really enjoy the fast cars sliding with the tail-out. On the other hard, I need a stiff feeling rear end (firm damping) so I have feel for the rear's grip level. I guess I prefer this for the B & C cars as well, but it is not so crucial.

Chris Cervelli
Premier Motorsports

ColorChange

M758
I agree with everything you said about trail braking.

John, I think you have it as well. Sorry I can’t comment about the turns. No experience or data.

Chris, I know you have it in spades.

Premier Motorsp

CC,

Speaking of data, I have had a chance to look at what you sent me. I can't really analyze you or your car because I don't have any context which with to provide backdrop.

I have Motec data from the boss' Cup car but that is apples and oranges since it is about 10 secs faster.

You need to expand your data logging to get the most from this. Every control device you interact with must be logged. Here is how I set up the boss' car and how I will be doing the 3.8RSR for Road America (dash showed up today).

RPM, self explanatory, surprised you don't have it?

Speed, self explanatory

Lat G, self explanatory

Long G, will create with math, as you have. (Motec uses a 3 axis sensor, so no need to create)

Throttle Position, 3rd most important channel for driver training. I mostly watch it for aggressiveness or lack thereof.

Steering angle, 2nd most important channel for training. I watch for an appropriate amount of countersteer. No countersteer = going slow or bad understeer.

Brake Pressure, most important channel. Braking is the hardest part to do right. I find if I visualize what the graph will look like I can control my pressure much better. Plumb this in before the ABS unit. You want to know what the driver is asking for, not what ABS and PSM is giving him. You want to make sure your plumbing is bombproof, for obvious reasons. I have a nice 996 setup if you want the details.

Chris Cervelli
Premier Motorsports

ColorChange

Thanks Chris, appreciate the feedback.

I have my car only minimally wired as I am hoping they are going to write the bus interface soon so I hate to waste the cash properly wiring the car. The only data I have right now is tach, speed, and lat g. Long g is calculated as are the other numbers. I just got the system before that event so that is why there was no tach in the data I sent. I now have the tach from the OBD2.

Please give me the 996 brake details. I haven't done that in the past for fear of failure. What do you have? I absoultely agree that braking is numero uno.

mitch236

Ok, this is where I disagree. If you can trail-brake at 85, then you should be able to keep the car at 85 with neutral throttle. In your above example you say that if you enter at 85 under neutral throtle you miss the apex because of drift but if you trail-brake the car wants to turn in better (which is true) but what you left out is that now the front bites better increasing the lateral demand of the rear at a time when you are unloading the rear of the car. I would think this would increase over-rotation and spinning. Now, in a car that understeers, trail-braking is a necessity to carry speed and make the apex but an understeering car is slow, it feels safer but it is slow.

So I guess the moral is if you are driving an understeering car (many street cars, especially 996's) then more trail-braking is required then a neutral car (most track cars). You probably don't want to trail-brake an oversteering car at all.

M758

Yes it does. The oversteer helps you turn. The trick is to manage this so that it is just enough to provide enough help to turn, but not so much as to cause a spin. Tough thing to do really and that where all top level racers earn their money.

mitch236

I think what I am trying to say is that in my car, once I am turned in (which requires trail-braking) and the suspension has settled into the turn, I can keep the car neutral and if I begin to loosen up, it occurs at both ends. If I were to trail-brake at that same speed the car would spin.

Now I'm no great driver by any stetch. When I have asked professional racers why they trail-brake deep into turns I get the reply: In a race you need to protect the corners so you go in too fast and too deep, this leaves no choice but to trail-brake quite heavily just to make the turn. Of course, you sacrifice exit speed but you have maintained your position, which is more important in a race. In time trials, much less trail-braking takes place.