333pg333

Having read quite a lot on this and other forums / books, especially recently I am still somewhat mystified by the various explanations from different sources.

Apart from my own thoughts which is cause for enough confusion without anyone else's help, I have had very recent experience that just added to the mix. Did a Porsche drive experience day last week. Basically I think this is mostly aimed at current or prospective Porsche owners which gives you a day to experience many of the current or new models. So we had a new Boxter S and 991 plus 997 2/4, Cayman S, 997 GT3, 997tt, Cayenne V8 and Panamera V8. Not to labour too much on the day but they gave us a few exercises such as late braking, or Slalom etc to sample the cars before being let loose in each car around a short track for 3 laps at a time. Jumping in and out of each car didn't really help and frankly nor did sitting beside a different instructor in each car. These guys weren't the local track instructors, they're mostly existing Aussie V8 and Cup drivers, so they're a good standard of driver at least. I realise this doesn't qualify them as good instructors, but there's little time to get acquainted over only 3 laps.

Anyway, to get to my point. They really emphasise squeezing on and off the brakes. Especially the head guy who runs these days. Now this is also in line with other advice out there including Mr Bentley's fine publications. I think that partially this was also to do with the type of day they run which is aimed more at the 'enthusiast' who wants to experience these cars on a track type situation which they normally don't do. They're all street cars on street tyres too. To be honest I was simply amazed at how much grip and poise the new cars have at speed on street tyres with the PASM which was on all day. Compared to what I drive (stripped, caged, modified 944 turbo) which has nothing, not even brake booster now, these cars are just sooo different. I am more used to pressing pretty hard with the initial brake application and in fact think that I need to increase this to make a faster rate of climb on the data logs. However, when I would do this in the street cars a few of the instructors said that I am too hard initially on the brakes. That I need to squeeze them more on and off.

So this is the crux of my question. On one hand we are told to have brake logs that look like a sudden and almost vertical line followed by a sloping tail as we release or trail through the corner. I can't figure out how to do this while squeezing on the initial application?? I felt like if I did what they wanted me to do I would be braking for a longer time/distance too. Far be it for me to argue with the Pros and I'm completely willing to accept that I'm not doing it right. But the guy who did a bit of engineering for me on my own carwas actually trying to get me to brake later and harder initially so that I released the brakes and off right about the apex. His point was that you shouldn't be able to get back on the throttle earlier than the apex. He said that my logs looked like I was still used to the previous setup which had a booster but still no ABS so I tended to be a bit careful not to push too hard initially as this could lead to lockup. So according to him I was sort of doing what these drive day pros were suggesting and he wanted more time on the throttle followed by steeper initial brake lines.

Sorry for a rather long story but I have to say that I am quite confused. I think that my question is, How do you squeeze the brakes on AND create a steep initial brake line on the logs? This may seem a very amateurish question but that's what most of us are and I'm sure I'm at the lower end of the scale. The worst thing is going around the track and second guessing yourself.

Laguna_Dude

Brake as hard as you can initially and then trail off as your speed decreases. Locking up never occurs on initial braking. It occurs only when you don't trail off and your speed declines and your still too hard on the brake. In a perfect scenario, you brake as hard as possible and trail off right at the limit before locking and maintain that limit during the trail until you are off the brake and on the gas out of the turn. In a 911, you are generally on the gas before apex. By squeeze, they mean hard at first and un-squeeze (trail) at limit of grip.

333pg333

True on the locking up situation. I think there must be something between what I was doing in the new cars when they said I braked too hard and what I interpreted what they meant by Squeezing. Just can't seem to reconcile the term squeeze and brake hard initially in the same breath.
I totally understand what you mean when you describe how you brake and this is what I'm attempting. I dunno...maybe I shouldn't try and drive with rollerblades on. Must be something I'm doing or not.

RickBetterley

Squeezing is not either squeeze or not squeeze - its how hard and/or fast to squeeze. Perhaps the Experience instructors were not communicating that well in the brief time they had with each driver.
Squeeze on quickly, squeeze off slowly.
Btw, students are sometimes puzzled when I suggest squeeze off, so I explain that as unsqueezing.

67King

There's a big difference between slamming on the brakes, and squeezing them. If you have the book "Going Faster," it gives a very good explanation. By squeezing them, you are allowing the weight to transfer before applying full force. If you slam on the brakes, you can lock up the fronts (and yes it is quite possible - I've done it). The pressure should take a fraction of a second to build (I want to think the book says about 0.7 seconds, but that seems like a long time), rather than being instantaneous.

I would guess that your foot is "calibrated" to your pedal, and you apply proper brake force on your own car, but for cars with highly boosted brakes, it probably is more like slamming on them.

kurt M

I like to call it "ramping in and out" A basic braking cycle is a measure of 0 psi to some peak number and then back to 0 psi. How quickly you go from 0 to peak is the ramp in. slamming on might be 1/8 of a second but is still a rate curve. How quickly you ramp in depends on the car and corner. What might be too fast for one car might be too slow for another. I am far from an expert and have found that the newer street cars like a slower ramp in but are more stable at the higher brake pressures. .

car_slave

Funny, I went through this same conundrum myself this year after I put on some bigger brakes and couldn’t control the car. I was also under the impression that your brake curve should be a very steep ramp up which I interpreted as slamming them on. It turned out that my brake application was all wrong.
It took some good instruction from fellow lister Van Svenson to talk me back through the basics. He had me work on slowly squeezing on and building up the pressure. The change was dramatic because I could build WAY more braking force without having my street tires start to dance under the car. I started out slow and smooth, then worked back up to doing this quickly but still making it a squeeze. This came after three years of DE so I guess it might be harder to teach than you’d think. It could also be one of those things which becomes more pronounced in a street car or on a wet track.

J richard

The difference between a "squeeze" and a "slam" IMHO has less to do with your foot and more to do with how the chassis responds to the input. A stiffly sprung racecar will react faster to the input and respond better to faster inputs the street car will take more time to evenly settle the chassis. So the same speed of application will seem like too much in the softer car.

IcemanG17

many great comments.....I also agree with "squeezing" or "rolling" into the brakes, granted you do it extremely quickly at times

I look at it this way, since our cars have crappy at best ABS, we need to quickly get the tires up to their peak grip temp and hold them there.....if we instantly "slam" the brakes we overload the available friction and the car skids.....by rolling into the brakes we increase the temp which increases the peak grip.....

Don't forget Jackie Stewart....he claims he won his races by being the smoothest coming OFF the brakes!!!

ALso how is your chassis is setup is huge....how stiff is it? Are you running stock bushings? Whats your brake bias-etc.....but the bottom line is modern P-cars have excellent stability control systems-ABS which can assist the driver quite a bit

333pg333

I suppose the term 'slamming' had to be used even though that's not what I considered what I was doing. It wasn't like I hovered my right foot 18" above the pedal and literally smashed it into the middle peddle when approaching a corner..lol. So in trying to define what we're all talking about it seems that it needs to be almost brought down to a time for that initial ramp up. As in e.g. 1 second before max pedal pressure for that particular corner. Or .7 or .5 etc...

So in translating that to a line on a brake trace we are not going from flat to vertical instantly, that I understand, but how much of an initial rise on that line before going vertical should occur under track conditions?

I was also thinking that they were saying I was too hard initially as it was a road car but I tried to briefly engage the instructor about this and he was more or less saying this is on all cars.

btw Car is currently on 900/1100 springs, Motons, no rubber bushings etc...

KaiB

The slope of the line(s) will vary from car to car, from corner to corner and should change as tires heat, as the track changes and as weight is removed from the car during the session.

Van

"Squeezing" isn't necessarily "slow" - what it means is that you should be progressive. As soon as you start braking, weight transfers to the front of the car. As weight transfers to the front tires, you have more grip and can press the pedal a little harder. As more weight transfers, you can press the pedal even harder - and so-on.

This increase of pressure as the front tires load up to reach your threshold braking point is the "squeeze". And, because it's dependent on the weight transfer, it will be affected by the spring rates and suspension of the car. A very stiff track car transfers weight very quickly - and thus the "squeeze" will be quite quick. On a street car with a softer suspension, that "squeeze" will take longer in duration.

333pg333

Van, do you have some brake graphs to display your point. I do understand what you and others are saying but I've also seen brake traces which are very vertical. Perhaps it just all comes down to the car and suspension ratings.

Van

Patrick, here's a comparison for 4 different drivers - same track, same corner. This is a g-force trace.

The red and blue (me and Dave) are track cars with pretty stiff springs, and we get pretty tall slopes. The black and green are both street cars, one's a turbo and one's a GT3.

Andrei (black) has a propensity to "stab" the brakes, as opposed to "squeeze" the brakes. See how his trace is different?

I'd say that Dave (blue) has the nicest brake release - aka trail braking into the corner.

Mark (green) lets off on the brake pressure, and then gives another little stab towards the end of the braking zone, and that's why his curve has that little "shelf". And, on Mark's trace, do you see how the slope is pretty gentle at the very beginning? That's where he's lifted off the throttle and is coasting before applying the brakes.

Van

And you might like to see this one - on my new car, I log actual brake pressure.

Same corner as above, I'm the black trace and a novice driver is the green trace.

See how my "squeeze" on is much more rapid (taller slope), and after holding peak pressure I try to release gradually? Max, on the other had, applies some braking pressure, and as he goes deeper into the corner thinks, "oh crap - I'd better brake a little harder!"

That second bump is going into the left hander - just a gentle brake.