SundayDriver

So there are some here, including Tim, that believe that trail braking - hard (near threshold) taken to the apex (or close to it) is the fastest way through most corners. I think that Chris C agrees (at least that is my impression from posts). Tim, if I have this correct, even states this as absolute fact.

So this is a 2 part question for Tim if you are willing to provide a high character answer:
1) What is it that makes you say this is an absolute fact? There are many professional drivers and coaches who clearly do not feel this way. At best, it seems to me that this is an arguable point. So what makes it fact - what group of top level drivers say this is fact?
2) What is the logic behind this? Seems to me that hard trail braking requires a different (early apex) line to use all the available grip and I don't see how this is faster in non-aero cars.

ColorChange

Mark: In prior thread I spent an awful amount of time trying to explain it to you only to be personally attacked by you and the other LC hoodlums. Are you telling me that you will refrain from that type of conduct this time? I can assure you I will not throw the first barb (present warranted inferences excepted).

RedlineMan

... sort of.

Hey;

First let me reiterate that I draw a distinction between Balance Trail Braking and Rotational Trail Braking. I believe Color always refers to the latter. I think?

This weekend I found my first ever reason to need to rotate my car by trail braking. I was running some funky junk-yard-dog tire sets to try and burn up some old dogs lying around the shop. I had finally chorded one of my beloved 200+ heat cycle Toyos earlier this summer. A realignment showed massive toe out on the right front. It took that to kill them! So I replaced it (on the right front) with an equally worn Yok A032R. I told you it was funky!

This had worked seamlessly at Mosport, but the Yok simply did not have it at the Glen. MASSIVE understeer on the tighter left handers, most notably by far the Off Camber. I simply had to stop dead to get any grip, but then I was getting run over by the damn Cup Cars, et al.

I found myself thinking of trail braking, and it did help. I would go deeper and wider, trail brake and yank the wheel to swing the rear around, then floor it as usual, only much deeper and later. It was not easy and did not come naturally. Something about not being "flat" at the turn in makes me nauseous.

It was still slower by far than having the right grip, but I didn't have to STOP! Maybe there's a use for TB after all? I think I'll be trying it in Turn 1 and Roller Coaster (if the curb doesn't work) at VIR in November too.

SundayDriver

Don't bother.

Brian P

I have another question, and some of it is based on my personal experience...

I used to be a big believer of the "brake late, brake hard and trail brake a lot" style of driving. I didn't hook up a DAS, but I'm sure if I did, it would say that I was near the limit of the friction circle. I doubt I could have braked much more without inducing a spin, and when I got back on the gas, it was with full throttle.

The question I started to think of was "how am I going to pick up lap time?" I would compare my times against club racers and it seemed like we were driving completely different tracks - I was so much slower. If I was truly near the friction circle, the only way I could pick up time would be to brake harder for a shorter distance.

If I wasn't near the edge of the circle, I could try to go faster in the turn. How could this be done? I would again after to brake for a shorter amount of time. I.e., enter the same turn with more speed and the similar weight imbalance.

So, my questions to you CC are these...
1) How far off are you from the club racer's times?
2) I think you believe that in some turns, you are at the max speed that the car can carry (according to your DAS). Can you quantify how much time you are losing in the other turns?
3) Do you believe that the difference in those times is simply the lost time in those turns?

For example, let's say that you are 20 seconds off of the best club racer time. Let's say that you can account for 5 of those seconds due to turns that you could be taking quicker. The remaining 15 seconds suggest to me that you could be going quicker in all of the turns and that your assumption that you were at the limit was wrong.

Alternatively, let's say that you are only 5 seconds off the best time and you can account for all 5 of those seconds due to the slow turns. Then it might seem that you could make a strong point that your style of driving is the best.

Premier Motorsp

John, you are busted!


You had crappy tires and big understeer, and thus had to trail brake in order to get the car to the apex.

Isn't this exactly the same as having good tires and such high entry speed that trail braking is REQUIRED to get the car to the apex?

This is what I try to achieve in almost every corner. The entry speed is high enough that the front will not point to the apex unless helped by a little trail braking. If I make it to the apex easily, I didn't go in fast enough. If I miss the apex, I went in too fast.

Getting it right means that the car is on the edge of control (more on what this means later) right down to the apex, and getting to the apex is just barely possible. Very likely, there will be oversteer at the throttle application point. Applying the throttle cancels out the oversteer.

Edge of control: different cars are going act very differently in this situation. Modern Porsches (ABS, high locking factor in the diff on decel, multilink suspension, major rear weight bias), properly setup, will be understeering initially on turn-in. This is because the brake pressure is still quite high, possibly in ABS on 1 wheel. (ABS on all 4 wheels at turn-in may indeed be a valid technique, the understeer is really heavy though, so you must turn in MUCH earlier. This is a little too ugly, even for me) As the speed and brake pressure decrease, the understeer goes away and transitions to slight oversteer right at the throttle application point.

My point is that this is all quite controllable. Understeer increases as brake pressure increases, so all the driver has to remember is that if the car really, really won't turn, he has to let up on the brake. Not always so easy to convince the foot to do that.

This is the real beauty of ABS. It allows the driver to use all the grip the front tires can give in a totally controllable manner. This is SO much harder without ABS.

As I stated in our email exchange, this is not so easy in a semi-trailing arm car (even one with ABS), since the rear axle kinematics are almost always 100% opposite of what they need to be. I don't know what a formula car is like since I haven't driven one seriously enough to try this all out.

To answer SundayDriver's question directly:

I don't know exactly why top drivers are faster than me. I have always suspected that their speed comes in corner entry because, frankly, corner exit is not at all difficult in any normal car. Thus, I am always working on entry speed in order to decrease the lap time.

I also know that any time I spend during the lap with the car not on the limit is not optimal. If I don't trail brake, I am not on the limit from turn-in to apex.

Yes, in general faster entry speed will require an earlier turn in. If you enter fast enough that you struggle a little with understeer prior to the apex, then you are going to need more distance(track length?) to get the car down there then the guy who turns in and drives to the apex under the limit. Remember that early turn in does not automatically mean early apex.

Another thing: I think most drivers underestimate the amount of lateral G they can generate while at 100% throttle. Race cars that accelerate at over .4G are rare (for club racers anyway) so that leaves a great deal of friction circle left for cornering. This leads me to believe that unwinding the wheel just as you get on the gas is wrong.

One other random bit of data to back up my argument which favors corner speed over exit speed. Pretty much any run-of-the-mill low dollar, low hp formula car laps faster than a fast club racing Porsche. It is obvious that the formula car's advantage is cornering speed, not acceleration.

Chris Cervelli
Premier Motorsports

Larry Herman

IMHO, you have to drive the car and the turn. If you never trailbrake, you will be slow in the tight and decreasing radius turns. If you always trailbrake, you will be slow in the fast sweepers and increasing radius turns. It really depends on how your car handles, and how the turn lays out. Remember that regardless of HP, the idea to fast lap times is to maximize the time you are accelerating. That means getting on the gas, floored, as soon as possible. In many turns, that is immediately upon turn in (i.e. brake, turn-in, and floor it). If you are not doing this, you are giving away speed. Your line should allow you to do this. And as mentioned before, you need to drag the brakes into the corner in order to get the car to rotate. As soon as it does, you should be setting the car with the gas to stop the rotation and be accelerating, full throttle, past the apex and down the next straight.

Bill L Seifert

I don't trail brake because I didn't learn that way. Not that I am against it, I just don't know. One of the best quotes on trail-braking, I heard, was years ago. I believe the big proponent of trail-breaking was Mark Donahue. In the mid-70's it was talked up a lot. Some magazine asked Jackie Stewart about trail braking, and Jackie said he thought the best way was to brake in a straight line. The magazine said that Mark Donahue was the big name that said trail-braking was best. Jackie said, "Oh really, and how many Grands Prix has he won. In case you are wodering the answer is none.

Bill Seifert

1987 944S Race Car under const.

ColorChange

Chris:
Bravo. I don't think I can add much to that.

Larry:
I gerneally agree with you also on fast sweepers, maybe some decreading radius turns. I once thought that you should always trail brake at least a little (where braking beyond a breath was required) and someone came up with an example or two where you wouldn't. They corrected me.

Guys, I described this before and didn't get a lot of feedback. when I was driving my tt, I thought that I could trail brake pretty heavily, go to nuetral throttle near the apex. At this point I could often rotate the car by breathing off the throttle, the magnitude and quickness of the lift controlling the amount of rotation. When it was rotated where I wanted it, I coudl squeeze the throttle pretty quickly to settle everything back down and launch out of the corner as I went quickly to full throttle. Is this the proper (fastest) way to drive the tt or since it's not carving (pretty big slip angles for a little while anyway) is it slower than staying near optimal slip angles?

ColorChange

Bill:
Can you show me or reference that exact quote. I just can't believe that Jackie would say not to tb.

SundayDriver

Chris,

Very interesting observations. Most I agree with, some I am not sure about.
I very much agree with corner entry being the key to that extra speed. I have been able to do data overlays with quicker racers in SRF a few years ago. I was consistently matching, and sometimes beating them on exit speed. But I was 2 seconds off the fast guys and it was all before the apex.
However, the caveat for this in a DE environment is the high risk of maximizing entry speed - there is just no room for error. Great for racing but not so smart in a street car that you plan to drive home in.
Of course, corner speed is the main weapon in a formula car or sports racer but there is more to it. My car will significantly outcorner a production car. Because of the light weight I can accelerate very well up to ~120 mph. After that, I lack the HP to really overcome the drag. So what happens vs. a high HP production car is that I gain in the corner, I am starting the drag race with an extra 10-15 mph and have good acceleration for a while. I might eat a Viper aliv down a straight if I took the corner at my speed, but if I am held up by them, I can't win the drag race. So the higher cornering speed also 'wins' the drag race.

The trail braking part is what I am not sure about. I do know that in an aero car, you want to carry as much entry speed as you can to take advantage of the higher grip (assuming a corner that has a high approach speed). That means early turn-in and trail braking to get down to the min corner speed. It also implies that you make a nice geometric corner into a decreasing radius corner so that you hit the desired apex, as you point out (early entry does not have to equal early apex). Without aero, I don't see an obvious answer to what is faster. If you turn early and trail brake heavily, then you use a lot of grip for braking. When you get down to the bottom, where you are at min radius and min speed, you will have to be quite a bit slower than a brake then turn approach (or even light trail braking). The upside to the trail braking approach is higher speed during the first half of the corner at the expense of lower min speed and lower exit speed. Traditionally it was taught that you trail brake at the end of the long straights to maintain speed and go for maz exit speed on the corners leading to the straights. I 'think' that is correct based on my limited experience. I may beat someone on entry speed, but if they win the exit speed battle before a straight, they are going to walk away from me in equal cars.

Frankly, I think there are far too many real world variables to be able to really answer the question of whether trail braking is faster. It also highly depends on the driver's attitude and beliefs. A driver lacking conficence in the car or style is not going to be fast. I guess that is why it is a sport to DRIVE the freakin cars, because the computer can't do it as well (at least with our budgets).

Thanks for the interesting observations.

Bill L Seifert

Color Change,

Are you kidding me? I read that back in the 70's. I promise you I am not making it up, but to tell you exactly where I read it, ain't no way. I do remember it was obviously before Mark was killed, and I think that happened in 76 or 77. I read 5 or 6 car magazines a month, and have since 1961. That means I have read over 1800 magazines since the middle 70's. No way I can give you a direct quote, but I have no reason to make it up, I am totally neutral on trail-braking. I don't do it and am too old to learn new tricks. I just rememberd it and thought it was kind of a cool quote. People my age remember things from the old days better than we do today, but not all the details. For instance I can tell you who won the 1961 Dutch Grand Prix, and the 1961 French Grand Prix, but I sure can't tell where I read it. I also don't keep magazines, so i can't look it up. I don't have a single magazine in my house that is older than the late 90's.

Bill

mdbickell

I've been watching the friction circle / trail braking / CC debate here for a while so I know there are a lot of opinions out there. I still consider myself a novice, so I'd like to throw out the following question to hear some of the expert opinions on what I'm observing while on the track.

So here we go - Its been my understanding that any car is better settled and thus has better grip under power. Perhaps this is a flawed assumption, but given this assumption, doesn't it make sense to brake as hard as possible in a straight line where you have the most grip so that you can get back on the throttle through the turn? On most constant or increasing radius turns this seems to generate MY best lap times. In decreasing radius or particularly tight turns a bit of TB seems to work. It seems as though this approach makes more sense in lower powered cars where you don't have as much grunt to help accelerate after the apex.

If my assumption above is wrong regarding grip under power, please explain why.

A bit of background info on where I'm coming from... First, I'm no engineer so if I'm missing something in my understanding of physics please forgive me. As far as my driving experience, I've raced karts for a number of years before tracking my 81SC. I've also gone to the 3 day school at Russell. So as I said, I'm a novice, but I do have some experience to pull from.

I hope this question doesn't seem too rudimentary for this thread... I'm just a bit confused.

thanks,
Matt

Premier Motorsp

ColorChange said---

"Guys, I described this before and didn't get a lot of feedback. when I was driving my tt, I thought that I could trail brake pretty heavily, go to nuetral throttle near the apex. At this point I could often rotate the car by breathing off the throttle, the magnitude and quickness of the lift controlling the amount of rotation. When it was rotated where I wanted it, I coudl squeeze the throttle pretty quickly to settle everything back down and launch out of the corner as I went quickly to full throttle. Is this the proper (fastest) way to drive the tt or since it's not carving (pretty big slip angles for a little while anyway) is it slower than staying near optimal slip angles?"

This a more likely scenario since trail braking perfectly is really hard. Really CC should be acheiving his rotation using only the brake release, which is much more difficult. I would rather see a student use CC's technique instead of abandoning the concept entirely.

SundayDriver:

I agree that you can't ever say one technique works for all corners. But one principle remains:

You MUST maximize the Gsum through the whole corner. We have gone over the conditions required to make this statement accurately. I hope that we don't have to go over that again.

To maximize Gsum in the entry phase, significant decel is going to have to occur along with the building lateral G. It is exactly the opposite of the exit phase, where significant acceleration occurs with lessening lateral G. Nobody argues with the exit part.

Whether you get the decel in the entry phase from aero drag, tire drag or braking, the result is the same.

I 100% agree that confidence is important. It is the most important thing for club drivers.

Also, there is no doubt that this technique leaves much less room for error than slow in, fast out. I guess Stirling Moss understood that, even as he blasted into corners with wild abandon.

Larry Herman said---

"Remember that regardless of HP, the idea to fast lap times is to maximize the time you are accelerating. That means getting on the gas, floored, as soon as possible. In many turns, that is immediately upon turn in (i.e. brake, turn-in, and floor it). If you are not doing this, you are giving away speed"

This is a great way to safely realize 90% of the car's potential. As with almost everything in life, the last 10% of performance requires 90% of the effort.

Really, the idea to fast lap times is to have the car going at the highest possible speed at every point of the course. 100% throttle immediately after turn-in requires a lower-than optimal turn-in speed. I guess if the car accelerated at higher G than it cornered, your technique might work. No road racing car that I can think of can accelerate harder than it can corner and brake.

The statement : "Remember that regardless of HP, the idea to fast lap times is to maximize the time you are accelerating" is correct if you take the word accelerating to mean pulling any kind of G. Once again this presupposes that you are driving the correct line etc.

One point I have not yet made is that trail braking in no way compromises the exit speed. Larry's technique means that he will be on the gas far sooner than me, but his speed at the exit will likely be lower since his acceleration run started from a lower speed. The best way to win a drag race is to start at a higher speed than your opponent.

Chris Cervelli
Premier Motorsports

SundayDriver

Like you, I remember Jackie saying some things like that.