Trail Braking Revisited
08-02-2004, 04:14 PM
#3
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I was just going to post this very thing - I'm only about half through the article but very interesting reading. I don't believe the article is online - magazine is at the newsstands now for about $8
08-02-2004, 08:40 PM
#4
Burning Brakes
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Trail Braking?? Really?CC... you mean you don't just....
" STOMP ON THE BRAKES at corner entry" and use your trusty ole ABS as you turn down to apex?
Whats this World coming too? CC has changed... and Alternate racing craft methods are being EXPLORED !!!
08-03-2004, 09:31 AM
#5
Three Wheelin'
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The most interesting quote on the 7 page article is the following:
pg 62 "The message is to try to keep the force on the car at it's maximum - ride the rim of the friciton circle - but also to make sure that the force is pointing in the most useful direction at all times."
Hmmm .. I have nothing to say.
pg 62 "The message is to try to keep the force on the car at it's maximum - ride the rim of the friciton circle - but also to make sure that the force is pointing in the most useful direction at all times."
Hmmm .. I have nothing to say.
08-03-2004, 10:33 AM
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Originally Posted by ColorChange
The most interesting quote on the 7 page article is the following:
pg 62 "The message is to try to keep the force on the car at it's maximum - ride the rim of the friciton circle - but also to make sure that the force is pointing in the most useful direction at all times."
Hmmm .. I have nothing to say.
pg 62 "The message is to try to keep the force on the car at it's maximum - ride the rim of the friciton circle - but also to make sure that the force is pointing in the most useful direction at all times."
Hmmm .. I have nothing to say.
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08-04-2004, 11:41 AM
#8
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CC,
No flame intended but I grabbed a copy and felt that it was really an article about line choices as opposed to trail braking. While the byproduct of the parabolic vs classic line through a hairpin is increased speeds in the more useful directions, the article really doesn't focus on the advantages of trail braking.
A more useful comparison, IMHO, would've included segment times using various brake-throttle transition points on the same line, i.e. Am I faster when I get on the gas right after turn in or closer to the apex? The "Going Faster!" book by the Skip Barber people covers this issue in some detail and points to some of the keys for making this determination:
- The more your car tends towards understeer, the more you can trail brake
- The sharper the turn, the more you should trail brake
- The more powerful your car, the more you should trail brake
In my experience, defining the right amount of trail braking is a trial and error process. I often devote considerable track time to determining how long I can keep my foot on the brakes before switching to the throttle. In fast sweepers, that happens right after turn in; in a hairpin, it's right before the apex. Obviously, this drill is inherently risky and can result in some high-speed moments but if you limit brake use only to the straights, it's very like that you're not entering the corner at the maximum possible speed.
0.02
No flame intended but I grabbed a copy and felt that it was really an article about line choices as opposed to trail braking. While the byproduct of the parabolic vs classic line through a hairpin is increased speeds in the more useful directions, the article really doesn't focus on the advantages of trail braking.
A more useful comparison, IMHO, would've included segment times using various brake-throttle transition points on the same line, i.e. Am I faster when I get on the gas right after turn in or closer to the apex? The "Going Faster!" book by the Skip Barber people covers this issue in some detail and points to some of the keys for making this determination:
- The more your car tends towards understeer, the more you can trail brake
- The sharper the turn, the more you should trail brake
- The more powerful your car, the more you should trail brake
In my experience, defining the right amount of trail braking is a trial and error process. I often devote considerable track time to determining how long I can keep my foot on the brakes before switching to the throttle. In fast sweepers, that happens right after turn in; in a hairpin, it's right before the apex. Obviously, this drill is inherently risky and can result in some high-speed moments but if you limit brake use only to the straights, it's very like that you're not entering the corner at the maximum possible speed.
0.02
08-04-2004, 12:00 PM
#9
Three Wheelin'
Originally Posted by joey bagadonuts
I often devote considerable track time to determining how long I can keep my foot on the brakes before switching to the throttle.
08-04-2004, 12:46 PM
#10
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Yes, I know that sounds backwards but here's the context.
If you go into a tight corner (hairpin) and use only straight line braking:
1) You've overslowed the car--guaranteed!
2) You need to gently apply the throttle (coast) to avoid understeering through the corner
In a 911 with a locked differential (C4, LSD) and wide rear tires, the car ploughs in tight corners and the rear weight bias exacerbates the understeering characteristics of the car. If you get on the gas too aggressively, you push wide of the apex. By trail braking, you not only avoid this ploughing sensation but also put more weight on the front wheels which improves grip and cornering force in a light-nosed 911.
If you've ever autocrossed a 911, you'll know what I'm talking about. You can't just jump on the gas and hope to come flying out of the corner. Unless you go deep with your braking, you'll need to nurse your way up to speed to ensure the front end doesn't wash out.
So while I may still be on the brakes in a turn, I can guarantee you that it's a lot faster than overbraking in a straight line and tip toeing my way to the apex. My goal is not to be on the gas as much as possible but to maximize cornering speeds--sometimes that means using the brakes instead of the gas.
If you go into a tight corner (hairpin) and use only straight line braking:
1) You've overslowed the car--guaranteed!
2) You need to gently apply the throttle (coast) to avoid understeering through the corner
In a 911 with a locked differential (C4, LSD) and wide rear tires, the car ploughs in tight corners and the rear weight bias exacerbates the understeering characteristics of the car. If you get on the gas too aggressively, you push wide of the apex. By trail braking, you not only avoid this ploughing sensation but also put more weight on the front wheels which improves grip and cornering force in a light-nosed 911.
If you've ever autocrossed a 911, you'll know what I'm talking about. You can't just jump on the gas and hope to come flying out of the corner. Unless you go deep with your braking, you'll need to nurse your way up to speed to ensure the front end doesn't wash out.
So while I may still be on the brakes in a turn, I can guarantee you that it's a lot faster than overbraking in a straight line and tip toeing my way to the apex. My goal is not to be on the gas as much as possible but to maximize cornering speeds--sometimes that means using the brakes instead of the gas.
Last edited by joey bagadonuts; 08-04-2004 at 01:10 PM.
08-04-2004, 01:21 PM
#11
Three Wheelin'
Sure, that all makes sense - in fact its a great explanation of why trail braking can be advantageous. But you're really not seeing how long you can stay on the brakes like you said in your earlier post. You're just seeing how much of the total braking you need to make the corner you can defer until you're past the turn in point. My point is that if you can reduce the total amount of braking you do for a corner and retain more of your momentum you *will* go faster. I see a lot of intermediate students overdoing their trail braking past the point where they could have transitioned back to the throttle and easily made the corner.
08-04-2004, 01:55 PM
#12
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Originally Posted by Jim Child
Sure, that all makes sense - in fact its a great explanation of why trail braking can be advantageous.
Originally Posted by Jim Child
My point is that if you can reduce the total amount of braking you do for a corner and retain more of your momentum you *will* go faster.
BTW, Congrats on the Putnam win, Jim!
Last edited by joey bagadonuts; 08-04-2004 at 03:21 PM.
08-04-2004, 09:21 PM
#13
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The Jim & Joey Show.
Well done, gents!
I think what has stuck in all of our craws is Color's habit of dealing in Arithmetic Absolutes, which driving is not. No offense, Color!
Driving is like a cake mix with no formal recipe, not a formula on a chalk board. There are just too many variables at play with different cars, surfaces, corners... To get it right only means for one corner, maybe only for one lap. Theories are a great way to quantify for our hungry brains things that are exceedingly esoteric. We want answers. The dynamics of driving only reveal so much in absolutes. The rest is up to experience... and chance.
To say that one wants to achieve theoretically maximized G and friction loads is to state the Painfully Obvious. To try and say HOW is diametrically opposed in its complexity, to the point of being un-answerable in absolute terms.
"Whatever works!"
Well done, gents!
I think what has stuck in all of our craws is Color's habit of dealing in Arithmetic Absolutes, which driving is not. No offense, Color!
Driving is like a cake mix with no formal recipe, not a formula on a chalk board. There are just too many variables at play with different cars, surfaces, corners... To get it right only means for one corner, maybe only for one lap. Theories are a great way to quantify for our hungry brains things that are exceedingly esoteric. We want answers. The dynamics of driving only reveal so much in absolutes. The rest is up to experience... and chance.
To say that one wants to achieve theoretically maximized G and friction loads is to state the Painfully Obvious. To try and say HOW is diametrically opposed in its complexity, to the point of being un-answerable in absolute terms.
"Whatever works!"
08-04-2004, 11:14 PM
#14
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Gee we've come full circle. When this issue came up many months ago I recall posting that trail braking is very useful in slow turns in a 911 which tends to understeer and ill advisd in fast sweepers... it just goes to show you that the truth remains the truth
To be fair, CC has shown a much nicer attitude towards information which contradicts his instincts. Much nicer this way. By the way, the 996 TT has "yaw control" which cannot be turned off. It takes pre-emptive action if you try and brake and turn at the same time beyond a slight degree. This is what gave rise to the rumors that PSM turns itself back on under heavy braking (it doesn't). I tested it and the brake pedal gives you a heck of a shove - not the gentle rumble of the ABS but a real kick in the foot so to speak. No mistaking it. Porsche's way of reminding what your instructor taught you about braking
To be fair, CC has shown a much nicer attitude towards information which contradicts his instincts. Much nicer this way. By the way, the 996 TT has "yaw control" which cannot be turned off. It takes pre-emptive action if you try and brake and turn at the same time beyond a slight degree. This is what gave rise to the rumors that PSM turns itself back on under heavy braking (it doesn't). I tested it and the brake pedal gives you a heck of a shove - not the gentle rumble of the ABS but a real kick in the foot so to speak. No mistaking it. Porsche's way of reminding what your instructor taught you about braking
08-05-2004, 12:57 AM
#15
Originally Posted by Bob Rouleau
By the way, the 996 TT has "yaw control" which cannot be turned off. It takes pre-emptive action if you try and brake and turn at the same time beyond a slight degree. This is what gave rise to the rumors that PSM turns itself back on under heavy braking (it doesn't). I tested it and the brake pedal gives you a heck of a shove - not the gentle rumble of the ABS but a real kick in the foot so to speak. No mistaking it. Porsche's way of reminding what your instructor taught you about braking
My local track has one low speed 2nd gear corner where the involuntary braking activated PSM of the 996tt prevents use of trail braking to rotate the car. The PSM must be preventing the car from rotating because if I completely release the brake (momentarily before getting back on the gas) the car will rotate the moment I'm off the brake. In long corners with the PSM off, I can use a slight throttle lift to rotate the car, but it won't rotate under braking at corner entry. I've never felt a "shove" or "kick" in the foot. YMMV