Trail braking

[SWortham]

I've seen some people use trail braking when autocrossing and others who don't. I'm one of the drivers who does it often, and when I do it well I feel I can go faster.

 

Here's my simplified theory behind it, let me know what you think. To me, trail braking works best on a car with a lot of steady-state understeer (which most street cars have). Without trail braking on an understeering car, the car can only make use of 100% of its grip up front and perhaps 80% of its grip in rear. But with proper trail braking, you have 2 advantages:

1.) You can extend your braking zone slightly.

2.) You can make use of 100% of the car's grip in front and rear. Granted a portion of the front tires' grip is now being used for braking and less for cornering. But I feel that disadvantage is made up for by the fact that with the weight shifted forward, the rear tires can now reach their optimimum slip angle along with the fronts.

 

Thoughts?

[SWortham]

Just found this link. It doesn't address my theory, but it's a good article...

http://www.getfaster.com/Techtips/Physics23.html

[Xenonk]

I do it to get around cones.. more time spent on the gas, the faster you are.. compress the braking zones and maximize the grip of the tire 100% throughout the whole course, that's how you go fast..

[SWortham]

The real trick to it I think is to not let your trail braking turn into an "oh crap!" and overshoot the corner. It's one of those things that demands another level of precision in your driving. I am by no means an expert, but I'm gonna keep at it.

 

By the way, there was something I thought of awhile back. You could trail brake with your left foot, and get on the gas smoothly and let off the brake smoothly as you approach the apex. That method would actually help spool the turbo. But that would require a whole 'notha level of coordination, especially if you're also heel-toe downshifting as you approach the corner. That would take some fancy footwork.

[Xenonk]

the idea is to maximize your braking and allow the rear end to get to the point where it rotates on you.. trail braking allows your front tires to turn and brake at the same time.. it's that recipocal (sp?) effect:

 

100% max grip = 0% turning + 100% braking

100% max grip = 10% turning + 90% braking

100% max grip = 25% turning + 75% braking

etc

etc

etc

(notice the brakes are "trailing off" as you turn, it's getting less and less braking effort).

 

by the time you maxed out the amount of turning, you should be off the brakes or near that point of transitioning off the brakes on back onto the throttle, which by now you are learning open-loop driving. You can then Substitute the braking for acceleration.

 

Hence the "traction circle".

 

Left foot braking is something you will learn the use of overlapping engine power and braking power to balance out the car's grip. The bonus to left foot braking is when you are going into a turn and it's a turn that you dont need to shift.. so you can concentrate on the brake and throttle (unless your name happens to be Tim O'Neil, rally driver). Left foot braking is very beneficial to keep the turbo spooling and creating that power.. on non AWD cars, this can be beneficial for FWD to help lock up the rear a little bit or in RWD, it helps pivot the car some, both situations is to get the car be balanced and get some rotation out of the car.

[robinlsb]

I do it to get around cones.. more time spent on the gas, the faster you are.. compress the braking zones and maximize the grip of the tire 100% throughout the whole course, that's how you go fast..

 

+1 on the above Plus====

 

Trail braking can do a lot of things: It can toss out the rear end (in a RWD) so that you are pointed or drifting through and/or to the next turn. In a FWD car, this can help pull you through a turn. In a FWD , full gas and brakes at the same time (with proper modulation of the brakes can produce amazing results because he weight transfer will be to the front wheels.

 

I have never raced an AWD car but having gone "fast" through a few corners I will make the following observations ( at least in terms of a wagon with good sway bars)

 

A twitch of the steering wheel to brake the rear end lose can be very helpful (old Porsche trick)

 

Trail braking can do the same thing, but have both feet on a pedal. Once the rear end loosens, apply power. Lots of it. Instantaneously, so to speak.

[SWortham]

Left foot braking is something you will learn the use of overlapping engine power and braking power to balance out the car's grip. The bonus to left foot braking is when you are going into a turn and it's a turn that you dont need to shift.. so you can concentrate on the brake and throttle (unless your name happens to be Tim O'Neil, rally driver). Left foot braking is very beneficial to keep the turbo spooling and creating that power.. on non AWD cars, this can be beneficial for FWD to help lock up the rear a little bit or in RWD, it helps pivot the car some, both situations is to get the car be balanced and get some rotation out of the car.

Thanks Keefe, you pretty much summed up my thoughts here and reaffirmed some things. I think I'll practice left foot braking when I get a chance but combining heel-toe shifting with left foot trail braking is a bit too advanced for me to think about doing, heheh.

 

What about you Keefe? Do you use left foot braking at all when autocrossing?

[SWortham]

A twitch of the steering wheel to brake the rear end lose can be very helpful (old Porsche trick)

I've done that with my car a few times. It can be tricky though because if you flick it too hard you can wind up with more rotation than you expected and completely screw up the corner. Old-fashioned powersliding is a heck of a lot easier.

 

Trail braking can do the same thing, but have both feet on a pedal. Once the rear end loosens, apply power. Lots of it. Instantaneously, so to speak.

That makes sense. I'll have to work up to that once I get the hang of left foot braking (it feels awkward now).

[robinlsb]

. I think I'll practice left foot braking when I get a chance but combining heel-toe shifting with left foot trail braking is a bit too advanced for me to think about doing, heheh.

 

If you have a big enough foot, use one half for the brake and one half for the throttle. If you have small feet, add a block to the gas pedal so that by pushing either side of your right foot you can brake or throttle. That leaves you left foot hovering between either of two pedals. A slight movement of your right foot allows you left foot to use hard braking. Or in extreme cases, both feet for the brakes

[robinlsb]

I've done that with my car a few times. It can be tricky though because if you flick it too hard you can wind up with more rotation than you expected and completely screw up the corner. Old-fashioned powersliding is a heck of a lot easier.

 

Thats why a lot of Porsches are in junk yards:icon_mrgr Off course/road backwards!

[Xenonk]

Thanks Keefe, you pretty much summed up my thoughts here and reaffirmed some things. I think I'll practice left foot braking when I get a chance but combining heel-toe shifting with left foot trail braking is a bit too advanced for me to think about doing, heheh.

 

What about you Keefe? Do you use left foot braking at all when autocrossing?

 

 

actually, either you are left foot braking OR you are doing heel-toe.. (it's not properly sound to have BOTH feet on the brake pedal). You dont do both. You are left foot braking ONLY if you know that you are not going to shift.. if you are going to shift, just heel-toe it. Heel toe is done before you make the turn.. Left foot braking can be before, during and sometimes after a turn (used for type-2 turns, where a turn leads into another turn).

 

Tim O'Neil is the USA Rally driver (he has a school up in New Hampshire) which he teach the "O'Neil" shift. It's left foot braking with a down shift.. or in other words, it's a clutchless downshift while left-foot braking. Kinda confusing aint it?

 

I only done it a few times in the wet pavement because it's a whole new skill level that I have yet to master coming into a turn with LFB while add a downshift in the process.. tarmac really has a lot of grip and could screw something up if you plan to do the O'Neil shift.. it's a really advance technique.

 

I left foot brake (LFB) now and then.. I HAVE to do it during karting with single gears, it's only natural to do. I still practice some LFB at autox events if I see a long sweeper that I need to keep it tight on the inside, especially the decreasing radius type turns where you just have to tighten up the car.. the brakes will help you tighten up the car, while you can still be on the gas with near full boost.

[Xenonk]

I've done that with my car a few times. It can be tricky though because if you flick it too hard you can wind up with more rotation than you expected and completely screw up the corner. Old-fashioned powersliding is a heck of a lot easier.

 

a little "scandinavian flick" is what it's really called if you exaggerate the input motion to unload the side that you are turning It's how I normally get the car sideways (on purpose or by accident through the slaloms) at autox events.. quick transitions usually kill me since my cars are usually setup really loose.. I just have to balance the car better and not flick so hard and be on the gas longer and harder.

 

http://www.team-oneil.com/press1.htm

[robinlsb]

it's not properly sound to have BOTH feet on the brake pedal). You dont do both.

 

Unless of course, you are racing a Shelby GT350:lol: :lol:

[SWortham]

a little "scandinavian flick" is what it's really called if you exaggerate the input motion to unload the side that you are turning It's how I normally get the car sideways (on purpose or by accident through the slaloms) at autox events.. quick transitions usually kill me since my cars are usually setup really loose.. I just have to balance the car better and not flick so hard and be on the gas longer and harder.

 

http://www.team-oneil.com/press1.htm

Yeah, it can be tricky. I got about 120 degrees of rotation in the rain once when I was only wanting about 40 degrees.

[SWortham]

I left foot brake (LFB) now and then.. I HAVE to do it during karting with single gears, it's only natural to do. I still practice some LFB at autox events if I see a long sweeper that I need to keep it tight on the inside, especially the decreasing radius type turns where you just have to tighten up the car.. the brakes will help you tighten up the car, while you can still be on the gas with near full boost.

Thanks, good to know. I like to know what you seasoned turbo AWD drivers do to get those fast times.

 

This car was a big change for me but I feel I've improved quite a bit since my first event with it. The stock suspension and stock alignment isn't the greatest but it's been fun adjusting my driving to suit the car. I'm not so much trying to be competitive yet (if I was I'd adjust the alignment) but I'm getting closer to the STU times after every event.

[Xenonk]

it's not properly sound to have BOTH feet on the brake pedal). You dont do both.

 

Unless of course, you are racing a Shelby GT350:lol: :lol:

 

AND shift AND rev-match???

[Xenonk]

Thanks, good to know. I like to know what you seasoned turbo AWD drivers do to get those fast times.

 

I could go faster, but it's not always necessary to use left-foot braking.. it all comes down to always using 100% of the grip you have.. or better drivers will purposely drive at 98% and if they drive a smidge too much, they will only hit 100% worth of grip.. that's the tough part about going fast, you are always at the edge at 99% to 100%, sometimes it's 101% if you got the balls to do that.

[Th3Franz]

I rode along in an Integra Type R with race tires at Gingerman with a very good driver behind the wheel. I think it's at turns 4 and 5 where one can mesh them together to become one turn when trail braking is used. The driver got the car a little sideways the first time and had to correct. The next time, he nailed the trail braking perfect and it was awesome. I need to get better at this technique.

[Xenonk]

trail braking isn't so much of a technique, but it's just a part of a transition of overlapping the turning with the braking.. I know instructors always tell new driving students "BRAKE STRAIGHT! or you'll spin out" but as you progress later and learn to trail brake, you as the driver, are learning how to maximize the grip level of the tires and understand what "open loop driving" is really for and thus becomes a second nature action..

[robinlsb]

AND shift AND rev-match???

__________________

 

Of course not! But first, you had to drag it down. And unless the brakes were really ( and I mean really) hot, It took both feet to slow it down! Never had fade thou! Besides, it was a heavy car, you could use momentum to your advantage:)