Brian Morris

Mitch,

I have the same question as you, and I don't think it has ever been completely been answered - but I think Chris C. kind of alluded to what's going on in one of his posts.

Everyone seems to agree on a couple of uses of trail braking but the third is giving some (many) people pause. People agree that using TB at turn-in to fight understeer and to trade-off lat g's for lon g's and to rotate the car is a good thing and all fast drivers do at least this. People also seem to agree that some corners can be heavily TB'd because of the configuration of the track - typically a decreasing radius turn where the mid corner speed is significantly lower - since the initial arc is gentle, extra grip is available so you TB down into the turn to use up the excess grip. The third situation is trailbraking deeper into a turn that could be taken at neutral throttle - at the edge of grip - not everyone agrees what to do here.

The dilemma as you describe, for me as well, is the section after balance has been established. As you described one approach would be to TB at turn-in, fading off brakes, feeding in steering, getting to max lat g's, and zero braking. During this phase you've scribed a decreasing radius as the steering is fed in. Let's say that takes 20% of the turn, and you have 30% down to the apex. Now in your beautifully balanced 944 (shameless plug) you can take the 30% to the apex at neutral throttle, and a constant radius, and constant speed, right at the edge of grip for all four tires. Then at the apex you feed in throttle, unwind the wheel, open up the arc to compensate for the accel. Beautiful, you've been on the FC the whole way.

My theory on why TBing more could be faster has to do with the line and the rotation caused by the TBing. With the more TB approach you would turn in slightly earlier - Chris C. mentioned this, and at higher speed. As he pointed out early turn in doesn't have to equal early apex, but if you turn-in early and "drive" to the correct apex you will be pointed the wrong direction - you haven't turned enough. Unless you've been rotating the car. In Chris's description, he is scribing a decreasing radius all the way towards the apex, rotating the car at a constant rate (hopefully). He will arrive at the throttle on point, going the same speed, going the same direction, but his average speed from turn-in to throttle-on has been faster because he started out faster and decreased his speed going through the turn. This is more complex than the simple "trading g's" theory.

I think the fast club racers use TB for an *initial* rotation then get on the throttle - as Larry H. described - which stops the rotation. Faster guys like Chris (semi-pro) TB more, setting up rotation - and keep it going. They dance the car into the turn, when everything goes right.

If you don't do everything right, driving as you describe will be faster, and you're less likely to crash. The heavy trail brakers you follow and are slow aren't going in fast enough and probably aren't rotating the car enough. If you just TB and "carve" a line you're not doing it right.

This is just my theory - but I can't figure out how it would work otherwise. I think this is also an area of disgreement for the experts. "Going Faster" description of trail braking is that you brake down to the throttle point, and then get on the gas. Carroll Smith believes more in a neutral throttle period but acknowledges that some disagree with him.

--Brian Morris
89 951

ColorChange

This discussion is really good.

Brian, well said. I'm also in the neutral throttle camp on many turns but as Chris taught me, if you do it right, on many turns you can use your release of tb near the apex to get the rotation started, and then stop it with the throttle. The speed of the rotation, now what you could call a rotating neutral phase (oh god have I opened up another Pandora’s box), is controllable and should be faster for shorter turns that don't have long neutral sections.

So for many turns, you could go from heavy tb, short rotating neutral phase, and throttle squeeze. This is pronounced for high hp cars.

RedlineMan

Chris -

Thanks for your input. It is MUCH appreciated. I think the most interesting part of your commentary is the Chicken part. Almost everything in life boils down to a matter of degrees. We're all the same, we just experience things to and at different levels!

I agree with much of your thinking and analysis, as it is similar to what I was working out in my mind... that I'd LIKE to be brave enough to do. Cost/Benefit, eh?

Turn 5 - YES, I'm on full throttle (with a little Balance TB in the transition) all the way through the Inner Loop to the braking zone in 6. Remember, we're only dealing with 147hp here!!

Turn 6 - You really NEED the big side G load. I must say I think I'm pretty quick through there. It is not a corner to get wrong by any means, but it has really never bothered me!?!

"The Toe" - Yes, I agree with your thinking. I am thinking of a new strategy to try here. There are a lot of good "Rally Turn" corners at the Glen, and I do it a bit in 1 7, & 8.

For the Toe, I might try going in really hot from about 10 feet from the left edge. Then, do a very gradual "shake," steering to the left edge of the track, and then back to the right hard to go into the turn. This and some TB would load the suspension to full side Gs earlier and maybe allow more entry speed. Just a theory.

Turn 10-11 - I sort of disagree with your assessment. Agreed, there is more TRACK SURFACE in 11, but there is FAR MORE RUNOFF in 10. If you blow it in 10, just steer right and go into the gravel. No such luck in 11!

Anyway, thanks a bunch for your pro input. It would be great if our paths crossed out there some day.

RedlineMan

Good show, Brian;

What has been illustrated in these TB threads is that there are indeed disctinct varieties of TB. Many of us probably do the Jackie Stewart type (more than we think) for reasons of balance in the transition phase. What Color has been driving at all along is "Radical" TB; that which is used to keep the car on the absolute edge going in, all the way to throttle time.

I think we can all see now that not only is this NOT useful in all turns, but that where it is, it is backstopped by some SERIOUS potential consequences. I myself strongly prefer staying on the pavement.

Chicken indeed!

chris walrod

Amen to that! It seems that most modern braking systems suffer from lack of rear bias, for performance driving that is... Rear bias is important for the trail braking styles of driving.

For the 993 anyhow, it is simple to install higher pressure bypass valves in the ABS controller, shifting bias aft. Wonder if this is true for the 996 based car?

Premier Motorsp

Chris W:

The bias valve situtation is similar in the 996. The 993 and 996 valves don't appear to be interchangable. The 996 Cup doesn't use a valve. I think MAYBE PSM cars also don't have them, I could be wrong.

All of them are really front heavy once the car is lowered and has a racing suspension. However, the concept of reducing the rear pressure only after a certain pressure is reached seems better than a balance bar. For sub-limit braking, there is no reason to reduce the rear pressure.

John:

I agree 10 has some decent run off room. I am pretty sure that if I were to blow it in 10 I would hit the left wall between 10 and 11. No room there!

11 seems wider if you spin to the inside.

Just to continue with an idea that CC picked up on, the neutral throttle phase is another giant point of argument. In theory, it seems like a bad idea to not have any Long G. In practice, however, a large number of turns do seem to require a pause between TB and throttle on. I am not sure what this pause really accomplishes, or if the pause really isn't just an extension of the decel phase. For me, the pause is usually 0-20% throttle only.

Chris Cervelli
Premier Motorsports

ColorChange

John, do you think I'll be diving in with mambo tb when I am moving quickly on a narrow track with nearby armco ... bgawk bgawk ... Heck no! I'll back off when I have to (I sure hope enough). But for now, I am trying to drive really safe tracks and really learn the technique. So am I a chicken by design?

Chris W: Very interesting!!!!

I changed the piston area (smaller) up front to bring some of the factory overly front biased brakes back to balanced (and a firmer pedal). If that doesn't work, I planned to run and even higher friction coefficient pad at the rear to further move the bias back there. And finally, if that doesn't work, change the bypass valve as you suggest.

Do you have any suggestions or comments?

Chris C, love to hear about your brake pressure sensor suggestions. Do you ABS brake in the 996 when at threshold (straightline) or do you try to keep just below that? Do you modulate at turn in?

ColorChange

ChrisC: I think the pause is also related to the hp/weight ratio. The higher the ratio, the more v’d the line, the shorter the pause, and vice versa for lower powered cars. Carousels obviously have long neutral phases but normal turns to longer turns do also correct?

There is an SAE article coming out on “driving the fc” soon that discusses these issues in some detail, including different and novel lines with actual data.

Premier Motorsp

CC:

I am usually in the ABS until just before turn in. The 996 offered pretty fine control of this but I still used the ABS a great deal. With the 993 the inital application is really inconsistent (master cylinder small and knockback problem) so I wind up in the ABS with that too. The 996 did a better job of turn-in under ABS, but I don't like to do that because the understeer is heavy since the fronts are so busy slowing the car.

The thing about ABS is that it does increase your slowing distance compared to perfect threshold braking, but it allows you to disregard the inside front tire which is always locking without ABS. Since you can disregard the locking inside front, you don't have to straight line brake. This opens up some possibilites you otherwise wouldn't have. At Gingerman for example, braking into the 5,6,7 complex isn't really straight. The ABS car can always go deeper there.

One thing I have learned from other people's driving coaches is that the pro's de-emphasize straight line braking. They always say don't force the car into a straight. They say the penalty from this is greater than the increase slowing distance in a curved brake zone.

Come to think of it, the one guy I am thinking of de-emphasizes all the traditional DE techniques. He wants:

Early turn in
Early apex
Huge TB, much more than I do

Also he doesn't get too concerned with the car's position on the track at the corner entry if the corner preceding puts the car on the wrong side or in the middle. I think a compromise needs to be reached in those situations, and when in doubt you have to vote for the stronger exit.

Chris Cervelli
Premier Motorsports

George A

Sorry for the OT and not meaning to change the thread but: Chris, can you please describe what you mean about the 993 braking? Please? I'm having issues right now with my 993 and it sounds like you touched on it.

TIA,
George

RedlineMan

Chris -

Sounds like he is espousing a tight entry, long apex approach. As we touched on earlier, the faster the entry speeds, the narrower the entrance angle by necessity of grip. By early apex, I'd say that translates to reaching the inside curb early, and holding a very long apex instead of a short clip on a classic DE line.

Color -

You are lucky to have Gingerman so close. Take full advantage of it to work on your heavy TB theories. As Chris has mentioned, "Chicken" very often applies to my "home track"... The Glen. LOTS of bright blue Armco!!!!

ColorChange

John:

If my home track was the Glen I probably would have been arguing the clasic line.

ChrisC: Thanks. At Gingerman on 5,6,7, do you V that or try to sweep it? I have tried both and if you V it, you can come in supper hot, trail brake way deep, brake again to turn the car at the outside apex, and then apex again and get on the throttle hard and for track out.

Haven't done segment tests on my DAS on the two different lines yet.

Premier Motorsp

George A:

I have the exact same problem you have described in your other threads. I have replaced all possible parts and nothing has helped. I have no idea what is really happening. It has to be at least partially knockback because it is the worst at the Glen after running thru the esses. Also when warming the tires the pedal will go low. A single pump always brings the pedal back up. A 993RSR, which has all the same wheel bearings etc. does not do this. The RSR has a bigger MC.

CC: What I was actually doing at 5,6,7 at Gingerman is not worth talking about. The way it should be done follows:

Brake for 5 gently in an arc that continues from the exit of 4 all the way to the turn in for the part of the turn that goes up the hill. So your brake zone will be a long decreasing radius arc. The brake pressure would start high and taper off to nothing as you turned in to go back up the hill. But you would be on the edge of the FC all the way down to the turn in point. (It would be pretty heroic to actually accomplish this) The last (only?) apex is really late since the turn tightens up so much at the end. Once you turn in and make the apex the exit is easy.

I really hated this turn. It would be SO much better if the exit opened up just a little. The low speed you must have for the final part of the corner makes the whole entry feel really odd. Plus the outside run-off at the entry of 7 (exit of 6) didn't look too friendly.

I probably would have loved that turn if I had ever done it right. 90% of the time I was way slow in the entry and made a decent exit. When I did the entry right, and clipped the apex right, for some reason the car went into huge oversteer which made the exit slow.

I'll take this opportunity to complain about the guy who designed Gingerman and Arizona Motorsports Park. Both tracks suffer from this strange no-flow problem. Almost every turn features something that prevents you from going fast in it.

Chris Cervelli
Premier Motorsports

George A

Thanks Chris,

It happens in the esses, exactly. Darn, I wonder if you can just change to a bigger MC without changing anything else.

Ok, you guys can go back to your TB discussion. There's nothing like an advanced instructor riding with you and telling you that you are braking at least 20 feet too late in some of the corners. You just kind of hope the 20 minutes goes by quickly.

George