ColorChange

Mark:

I have only been on two tracks, Gingerman hot and Road America but only rudimentary work up there.

I agree on the trail braking comment, and have said in almost all cars and almost all turns you should trail brake to some degree. I am defining trail braking as braking during or after turn in. This is the theory and it is correct. Now, does this mean sometimes you shouldn't trail brake? No. Someone mentioned on another thread, one example where you would not want to trail brake is a high speed sweeper where you had a badly oversteering car.

Now, the practical constraints should be discussed separately, as you have done. When approaching a walled turn at 120, three feet off the tarmac, you very well may not want to be at the limit. I agree with this but the theory says, the person that gets closer to the limit (trail brake in this example) will be faster than the person that doesn't. The theory does not say to do it all the time. I think too many people try to apply the theories like that blindly and that is wrong. Execution/application of the theory should always be a separate discussion, as you have pointed out, and I agree with.

Brian P

Being an engineer, you should know that theories aren't correct until they are proven correct. At that point, they become facts.

I think that was used as one example. I would bet most people on this board (and certainly most of the books I have read) would say that in general, you want to be on the gas at turn-in on high speed turns. You may want to read "Speed Secrets" and "Speed Secrets 2" by Ross Bentley. In one of them he explains why this is.

I'll paraphrase as best as my memory allows. Basically, at some point in every turn, your car takes a "set". This is the point that the suspension has settled down and you can now get maximum traction out of your tires. The good drivers get the car to take a set as quickly as possible, and bad drivers might never get the car to take a set.

In low speed turns, you know that you will be getting a lot of torque from the engine and the car will accelerate well. As this happens, the weight transfers to the back and the car's suspension works more. The advantages of taking a "set" aren't as apparent because as soon as it does take a "set", you are on the gas hard and the suspension shifts.

On high speed turns, the car can take a "set" and it will hold it for a while (high speed turns are, by definition, long turns) Also, the weight won't transfer much under acceleration because the engine won't have as much torque. This means that the driver who can get the car settled the fastest will have the most traction through the life of the turn. This, in turn, means that a fast driver wants to get on the gas as soon as possible - a trail braking driver may be faster in the first part of the turn, but will likely be slower by the end, as he has to get the car settled down before he can get maximum traction.

Ross explains it better in his book, but it gives you a bit of an idea why nearly all driving books will say that you don't trail brake every turn. Trail braking high speed turns is possible and probably everybody on this board can do it. The fast people have learned that it's slower.

Oh, and this is all IMHO.

ColorChange

Brian:

You probably were the one who found the example. I just didn't want to take credit for it because it wasn't my idea and I was too lazy to go through the old thread and find who said it first. I am a little concerned we may be hijacking this thread but I will reply. I haven’t read those two books. Are they good? If yes, I will get them.

I understand (I think) what you are talking about when the car takes a set. To me it means that the suspension is smoothly and heavily loaded and the tires are “carving” the turn near the fc limit (max lat g’s basically). And I agree the best drivers do this the earliest/fastest in a turn. Now, my point is the precisely fastest way to do this is to trail brake (assuming your good enough and have big enough cajones to do it … I’m sure I don’t).

Now I think, it the trail braker should be slightly faster and here is why. Your driver slows the car more than necessary before the turn, and then gets on the gas before turn in. The tb driver would only brake to the entry speed you wanted and then smoothly transition from brake to gas (a great lfb opportunity here so as not to induce car upset and as you say, “set” the car early).

I agree that most books say not to trail brake in all turns. While this is technically correct (you gave an example where you correctly shouldn’t), I think most books are not talking theory and do not consider very little tb at turn in to be tb. I do. They usually are much more practically oriented and from practical terms, it is much better/safer to not tb in the turn we are discussing. My point is it isn’t the fastest.

DJ

Here's a real life example that completely disproves the theory you just stated:

Turn 6, Laguna Seca.

The approach to T6 is steeply uphill, and right at the entry, the road dips ever so slightly downhill toward the apex, then transitions immediately steeply upward again. There's even a slight depression in the pavement right on the line near the apex. The FASTEST way through T6 is to brake, then go immediately back to full throttle before turn-in. Many people have tried to carry their speed longer, brake later, and trail brake very slightly after turn-in. You can see their skid marks and where they stuffed their cars into the tire wall. Same thing for those that haven't gone in at full throttle. Now, you can certainly make this turn safely with a little trail braking, or without being at full throttle before turn-in, but you WILL NOT be at the limit. If you are at the limit, and you try this, you will spin. The only way to trail brake into this corner is to be going slower, i.e., not at the limit.

The reason that this is true is because of the change in elevation. As the car transitions into the (ever so slight) downhill section at turn-in, the weight moves forward, onto the front tires, and away from the rear tires. The fronts have too much grip (in relation to the rears), and the rears have too little grip (in relation to the fronts). The car spins. Too much weight transfers to the front, leaving the rear tires without enough weight on them, and hence, not enough rear grip is also exactly what you'll get in a lot of corners if you try to trail brake where you shouldn't.

This is not theory. This is real life.

ColorChange

DJ: I didn’t say to always trail brake. This would be another example, like the high speed sweeper I mentioned earlier, where I am in complete agreement with you, you would not want to trail brake.

My quote ” in almost all cars and almost all turns you should trail brake to some degree.”

Now, this does nothing to destroy any theory. There is no logical interconnect there. The example you listed is one where you would not want to. There are quite a few more, but there are many, …, many more turns where you should trail brake than you can ever find where you shouldn’t. That’s all I’m saying.

Brian P

Color,

I'd highly recommend the "Speed Secrets" and "Speed Secrets 2" books by Ross Bentley.

I think the big underlying assumption you are making with your model is that you can trade off longitudinal G for lateral G and the car will maintain the same amount of overall traction. I'm not sure that that assumption is correct.

DJ

Color:

Pick a track, any track that you're familiar with, and list off the corners one-by-one at which you think trailbraking will be the fastest. I'm sure that there will be someone here with actual experience at that track, and we can see how well your theory that there are many, many more turns wherein trailbraking is the fastest way than not.

Tim Comeau

Color,
We're learning alot, huh? Good stuff, this learning.........
Let's clear up one point of confusion:


DOUBLE CLUTCHING IS NOT THE SAME AS HEEL AND TOE.

there's no down shifting in a street Porsche without using the clutch, or like John says, "Cha-Ching" $$$$$$.

So then, double clutching, or double de-clutching as the Brits call it, involves an extra step which might be neccessary for a race car with straight cut gears.

Our synchromesh trannies don't need that. We only push in the clutch once, select the next gear down as we're taching the engine up to match tranny speed, then releasing the clutch.
Make sense?
There's no substitute for educating YOURSELF.
2 books will get you up to speed quicker.

1. Competition Driving- Alain Prost (One of my heros, along with Niki Lauda, Stirling Moss, Jackie Ickx).
2. Driving in Competition- Alan Johnson (local Hero).

Cheers!

RedlineMan

Hey Guys;

Good show to all still involved in this. Big boys we are, eh?

I think at this juncture it is important to restate a definition. To me, the term Trail Braking refers to braking late in a corner in order to get the car to rotate because with out TB you would not make the turn. There are others forms of braking after turn in, but they ARE NOT the same as TB.

As far as I am concerned, TB is not a cornering scenario that gains you speed at exit, but keeps you ontrack and perhaps ahead of the competition.

Color - To me, your model is for racing, not lapping. You will note that a car running by itself is usually the one that sets fast lap anywhere, like when Schumi rips 3-4 fast laps when his competition pits, or when 2 or more cars behind the leader start racing eachother and thus slowing eachother down while the leader pulls away. A car in traffic is driving a different strategy (going deeper and giving up speed to maintain track position) or being held up, and will be slower.

Slow in, Fast out is NEVER wrong, but it is a function of how slow "slow" IS. For a novice this means staying safe. For an advanced driver it simply means braking early, setting the car decisively, and getting on the gas WAAAY ahead of where most people do. Entry speed may be a tad slower than the guy that goes deep and trail brakes to stay on course, but exit speed will have you sailing past with ease. How many times have you seen repasses like that in a race?

Corners are only about maximizing speed in that they lead to straightaways. The guy who carries the most speed in AND is on the gas the earliest and hardest wins the drag race on the next straight.

Think of your TB/FC model in terms of cam timing. You are doing every thing very late, closer to Top Dead Center. This is not how you make power in an engine. It just keeps them from pinging. Your timing is RETARDED... and yes this is all a most delicious pun festival!!

We who do everything much sooner are doing things much further before TDC. We are more advanced than you!! We are making more power because of this advance in our timing. Transfer that to the track, and HP gained from timing advance represents straightaway speed.

In terms of the FC, with your TB-heavy model, you are using your available friction for braking and turning simultaneously as a means of staying on the FC. Since we have already finished our braking long ago in a straight line, the rest of us "arguing against you" are using our available friction for turning and ACCELERATING.

You must see that this is faster... not accoriding to your model, but in REALITY, eh?

Bob Rouleau

John

Let's not be too harsh on CC. I believe that he restated his position to accept that a fast lap is not maximizing velocity in one turn but rather over the lap. As you and others have pointed out we sometimes compromise corner entry to favor the exit speed.

FWIW I agree with you on TB in a 911 (front engined cars can often benefit from TB more than we can, in fact they have to to try and keep up with us as we exit - applying power early which is one of the "features" of the 911 layout. I use it on almost all slow very tight turns since my car tends to understeer under those conditions. TB helps rotate the car faster so I can get on the power sooner. On the other hand, I am not brave enough to trail brake into turn 2 at Mosport to name one, or turn one at Tremblant. For those who don't know the latter, the approach is not quite straight - there is a little jog in the "straight" as well as a bit of a rise. The rise is enough to make your car light and it is followed by a downhill section leading to an uphill off camber turn. Entry speed is around 100 MPH in a well set up car with R compound tires. Making a mistake there is not an "oops" but rather an "OH, SH*T!!".

Best,

DJ

I agree with that completely, and thought it important enough to set it out again, all by itself.

Thanks, RedlineMan.

mds

DJ and RLM, this TB definition is too restrictive IMO. On an oval or on long decreasing radius turns in some cars (mid-engine open wheel for example) I want to TB to maintain speed gained from the prior straight longer. To me, this is TB but not for rotating purposes.

ColorChange

Brian: Yes, the car will maintain very similar total traction (total g’s) if you load the car smoothly in long or lat, or any combination. I will get the books. Thanks.

OK DJ, the only track I can talk about intelligently from direct experience is Gingerman, and even there I don’t have much but I do have enough to converse.
Turn 1, huge trail barker.
Turn 2, I was using a lift, brake or probably better LFB mostly (maybe tiny tb).
Turn 3 huge tb
Turn 4 flat out
Turn 5 tb
Turn 6 no braking, throttle control
Turn 7 huge tb
Turn 8 no braking, throttle control
Turn 9 no braking, throttle control
Turn 10 huge tb
Turn 11 huge tb
I can present my DAS data on any turn you want to see in my Countach.


Tim: I understand what you are saying. Before I did all of my upgrade work on my Countach it had a shot second gear synchro so I had to double clutch. I feel it is much easier on the tranny to double clutch so this is what I normally do. I also thought it would better prepare me for straight cut gears if the day ever arises, correct?

I have purposely stayed away from racing strategy based driving books as I didn’t want to frustrate/temp myself. Are these also good books for just going faster in DE’s?


John: We are using different definitions then. I am saying if you turn the wheel while you are on the brakes, it’s tb. The reason I do this is because it directly contrasts with the “get your business done first before turn in” approach beginners are taught. Maybe our views aren’t that different then.

While I agree that driving in race conditions is dramatically different thatn lapping, I am talking strictly about lapping.

While I did get a laugh out of your cam analogy, I would prefer to stick to direct facts and direct discussions of points.

In terms of the FC, with your TB-heavy model, you are using your available friction for braking and turning simultaneously as a means of staying on the FC. Since we have already finished our braking long ago in a straight line, the rest of us "arguing against you" are using our available friction for turning and ACCELERATING.

Of course I am saying get as close as possible to the fc at all times, (on braking, max lat g’s, on accelerating, or any combination of the two {or three if you’re a LFB’r}), but for a typical turn where you finished braking in a straight line, I GUARANTEE you are wrong and you are slow.

Now that we have officially hijacked this thread, I will repeat an example I gave from another thread.

If you have two cars that agree on the ideal line for a turn, and for this example, let's assume that the maximum lateral g's occurs at the apex (not the normal case, I know) at 70 mph. If both of our cars hit the apex at the same speed and track out the same way, what matters is what happens before that point. My trail braking (tb) approach is faster.

No tb vs tb car.
This notb car approaches the corner at threshold braking. His braking point has to be earlier than the tb car because he has to allow time (equals distance) for the car to drop from tb long g’s to 0 long g in preparation for turn in. My tb car blows right past him at full throttle, braking later and with no tb to 0 long g change and necessary delay for the suspension to settle before turn in. Cool so far huh?.

Now let's keep going.
The tb car hits his corner entry point at 70 mph, throws the car into the turn, and holds it at that speed until the apex. It took the tb car time to build up the lat g's to get to the max at the apex. You are correct that the notb car can turn in faster (he has more grip, or as you seem to prefer more contact patch available) than my tb car but I am turning in earlier and at a higher speed.

My car is going 75 mph at the tb car turn in point (earlier point probably than the notb car). It then passes the notb car turn in point at 73 mph (3 mph faster), and is still dropping long g’s and building up lat g’s.

We both hit the apex at 70 mph at the lat g limit of our cars, I just did it well before the notb car because I was faster through the entry section. How did I do this, I stayed closer to (on preferably) the fc for more of the time than the notb car, and I was faster.

MDS: I agree. DJ, that's not what I call trail braking, that's something quite different. I call trail braking any braking done during or after turn in. This is what most texts call tb. If we all want to agree on something else I can do that and adjust my statements accordingly. The primary reason for trail braking is to maximize g sum (brake and turn at the same time as near as possible to the fc).

Just for the record, the thread, Data Acquisition Systems - use and interpretation
Shows actual data of trail braking well past turn in.

mitch236

Maybe we should all vote on the definitions of all these terms since I always thought trail braking referred to continuing braking during turn in. It comes from the thought that one is brake turning, that is; turning while braking. Your definition sounds like trail brake oversteer. That would imply using trail braking to rotate the car.

Let's not thrash color, he is making this thread interesting. In my profession a mixture of science and art is the key as it is in racing/DE. He is trying to work out the science with limited art. With more seat time I am confident his absolute truisms will soften

Mark in Baltimore

My gosh, can someone please seance the spirit of the late Al Holbert? I think he's driven at more than two tracks...

Mitch, look at what you've started.