scofa

i have heard lots about it but i don't know really what it is.. could someone explain?

.RJ

Trail braking differs from the traditional approach of "brake (straight line), turn, accelerate". It generally means the driver brakes later into the turn, turning while still braking and releasing the brakes as the car settles into the turn, gently rolling onto the throttle while releasing the brakes (to maintain weight balance). When used skillfully, the driver can use the brakes to rotate the car faster around the turn, thus braking later (and carrying more speed in the straight leading up to the turn). In hard braking, sharp turns it can be worth a half second when done right - when done wrong you'll lose time. By wrong, i mean locking up the brakes, getting off line, sliding the car around - all contribute to slow corner exit speeds (bad).

-Ryan

Crack Monkey

It's something you shouldn't do on the street.

The best way for 99% of drivers to brake is in a straight line. I've tried trail braking in my RX-7 a few times and it never quite works out. The last time I tried, I busted a control arm and a steering box on the curbing at Summit Point Raceway. Doh!

phat-S

As Al and Ryan have eluded, trail braking and trailing throttle lift is not for an inexperienced driver and in some cars is a detriment. Trail braking means that you are loading the front suspension into a turn thus making the rear end light. You want to think of the weight shift you experience when driving normally (throttle throws weight to the rear end (FWD/AWD/RWD), braking or lifting off the throttle shifts weight forward, turning left shifts weight right and turning right shifts weight left - just think of how it feels on your body). So if you are coming down a straight chute and are going to turn left (personally, I say - straight line brake, ease into the throtte while turning in - i.e. turn in under throttle) for example; you move your braking zone out which will require that you hold your brakes down into turn-in. Because you want to have the throttle down at that point to keep the rear end tracking in relation to the front, you have loaded the front (actually front right) and unloaded the rear (most importantly, right rear - left rear is already unloaded) and the rear will want to step out (further right) creating an oversteer condition. You will need to be on the throtte almost as soon as you've done this less you will loop the car. If that doesn't make sense, don't try it and if you have an instructor in the car and plan to do it, warn them first. This has no, zero, zip, nada, nichevo application on the street.

Knestis

Some distinction needs to be made between "trail braking" and "left foot braking".

To be on the throttle as you are still on the brakes, you would have to be using your left foot on the throttle. Trail braking is simply maintaining any braking force during or after turn-in.

A driver may or may not be doing both of these things at the same time - that is to say, it is possible to left-foot brake and finish braking before turning in. It is also possible to trail-brake w/o left-foot braking.

Finally, it is possible to do both - left-foot trail-braking - and to complicate things EVEN MORE, you may or may not be applying throttle while the brakes are still on!

The two longer explanations above - if I am reading correctly - seem to suggest that this is happening. What happens in this case is that the "turn-in" effect that they describe MAY be amplified, depending on brake bias (the balance of braking forces between the front and rear wheels), the rotational inertia of the car (the tendency of the car to continue to rotate, established by the balance of the car, its mass and length, and the inputs by the driver), and a bunch of other variables.

Having only raced cars that really wanted me to use the clutch, the only time that I left-foot brake (besides with karts, of course!) is into corners that do not require a downshift. In a British Touring Car or something else with a dog-type gearbox (with which clutch use is not required), I would want to do it all the time - great example on this evening, in-car video of Yvan Muller BTCC @ Snetterton, I think... Left-foot braking, as a driver input, is pretty much the same for front- and rear-drive cars, as is trail-braking before throttle application. The dynamics of on-throttle behavior are going to be pretty different between front- and rear-drivers, particularly if the brakes are still on...

I would suggest that a LOT of people use trail braking on the street and don't even know it. This is not to say that they are using it WELL and I don't have any scientific data to support my theory but, just for fun, try humming when you press the brake pedal. It will make you more aware of when and how much you are using it and I'll bet that at least some of you are already turning in on the binders.

To summarize?

1. "The Classic" - Brake and downshift in a straight line, off the brakes, even throttle at turn-in, accelerate past the apex and out of the corner. This may also be done with left foot braking, particularly if you don't have to shift (kart, automatic, no real slowing for the corner required).

2. "Front Drive Understeer Band-Aid" - Downshift and right-foot brake beyond the point of turn-in, transition off brakes and onto throttle, accelerate through corner.

3. "Touring Car" (requires dog box, front drive/4wd?) - Left foot brake and downshift beyond turn-in, transition off brakes and onto throttle, accelerate through corner.

4. "Swedish Massage" (requires dog box, front drive/4wd, big clankers) - Left foot brake and downshift beyond turn-in, continue to brake, apply throttle, balance car on the brakes to control direction, off brakes, go like heck.

Good question!

Kirk

Crack Monkey

Knestis - did you ever decide on a car for next year? I remember you were asking about the 92-95 DX. Over at improvedtouring.com somebody said the weight was gonna be 2300lb+, which is more the EX in ITS. Where do they come up with that garbage? Oh well.

Al

Chris

A great place to read up on all these roadracing terms is TurnFast.com. Link in my sig.

Hracer

Knestis, great post!!

Trail braking is especially useful in FWD cars to get them to turn. The degree that you have to use it also varies a lot depending on the car and setup. In some corners driving my friend's MR2, the tail can come around on entry by not even carrying the brakes into turn-in. Just being off the gas during turn-in is enough to get it to rotate.

grippgoat

Whether your car is trail-brake friendly depends on setup a lot, too.

At Road America for NSXPO this year, all the instructors at the driver's meeting said "brake in a straight line, do NOT be on the brakes when the car is turning" yadda yadda, and they drove that way, too. So, either they all suck (possible, actually), or it's because the stock NSX can get tail-happy under trail braking (my car had a modified suspension when I bought it, so I really don't know exactly how a stock NSX handles).

However, I just couldn't get the car to feel right without trailbraking it. I'm sure some of it was because of my shocks not being quite right letting the car feel a little vague in transitions without having the suspension loaded. That is, trying to turn in while the shocks were still recovering from letting off the brakes felt really weird. However, trail braking and gradually easing weight from the inside front to the outside rear felt a lot better. I've also got proportionally wider tires in the rear compared to stock (stock is 205/255, I've got 215/255), and I've also get less rake (I think that's the right word, talking about front ride height vs. rear ride height), not to mention big differences in spring rate and alignment from stock.

Anyway, I had no problems with the rear end trying to step out under trail braking. So either my car was set up well for it, or I just have mad skillz y0. Heh.

Another thing is, I learned how to drive fast in an integra, and I was used to having weight on the front wheels. So I just feel better having weight on the front wheels when going into a turn. It also makes it easier to deal with oversteer... If you're over-steering because you're trail braking too much, then you simply ease off the brakes and it'll usually tuck the back end in again, then you can roll onto the throttle.

Whether it's faster, I have no idea, really.

But anyway, when thinking about trail-braking, it's also important to consider your traction circle. If you're still using some of your front wheel traction for braking, there's a little less there for cornering. And if you try to trail-brake too agressively, you'll end up overloading the front tires and you'll just understeer off the track.

-Mike

Crack Monkey

More than likely, they didn't want to deal with inexperienced drivers spinning at the end of every straight. I dunno about the NSX, but both my RWD cars get very unhappy when trailbraked (Caprice, RX-7).

The RX-7 just snaps around. Chock that up to a poorly designed rear suspension and a solid axle. The car is VERY prone to snap oversteer, so smoothness is quickly becomes the driver's mantra.

The Caprice is a different story. Although it doesn't display the same propensity towards snap oversteer, it just doesn't feel comfortable in trailbraking. Maybe it's the solid axle bouncing and skipping around. I dunno.

Anybody ever drive a Camaro or other RWD, solid axle car at the track? Just curious if you tried trailbraking or not.

krshultz

It's been many years ago but yes. The Mustangs at Bondurant back in 1996. They responded to trailbraking with pretty substantial rotation. Our instructors encouraged us to play with it. Certainly wasn't anything uncontrollable or even weird feeling - actually quite effective.

phat-S

Whereas I would agree with you in the definition of the term but as for the intent of trail-braking (my view is; to create rotation in a car that is lacking in either balance, front end grip or some other factor), I would contend that braking on an off-ramp or through an intersection is "going to work" or "picking up groceries" and so on - the individual is doing it not for rotation but because they have no reason whatsoever to think that what they are doing is changing the balance of the car. Even on track, if someone is going through a turn at "half" speed and they are on the binders (say there is a waving yellow and they are way backed off), I wouldn't call that trail-braking either. Moreso, the comment "This has no, zero, zip, nada, nichevo application on the street." was a disclaimer toward creating rotation via trail-braking on the street.

For clarification's sake, I was simply referring to moving your braking zone down (or out, whatever term preferable) so that that it would be impossible to turn-in under throttle but rather still on the brakes. What I was suggesting was that the transition from brake to throttle be in real quick succession (not letting the car slide until it grips) or else the rear end is going to go away. I would agree 100% that trail-braking can be done with the left foot but sans book knowledge - I would have called creating rotation at corner entry by braking as trail-braking and creating rotation anytime later in the turn with the left foot as left foot braking. Is this an incorrect translation?

All of this might simply be my own **** poor vocabulary, was just trying to clear up what I was trying to get across and apologies if my comments were/are misleading.

Knestis

Yup - 2330 lbs, and they didn't list the Coupe. I am actually not going to be done with the new degree until the end of this coming summer, so my plans don't really need to come on-line until this time next year. I'm not too worried but I am disappointed by the Comp Board's decision on this. It just seems like such a waste of thousands of affordable, reasonably zoomy cars...

True, as far as that goes but don't forget that the "diameter of your circle" - the total grip available for any given wheel - is dependent on the vertical load placed upon it. As you shift weight onto the front wheels, they increase their over grip potential, laterally and longitudinally. Spring rates and shock valving control weight transfer so the effect of this will vary a LOT between cars.

Also a good point but this is why it is important to get the car rotating before applying any of these techniques - and is why it takes so much commitment to make them work!

No worries, Adam. I TOTALLY understood what you were talking about. Functionally, drivers who are familiar with the practice use the term "trail braking" to describe the action that the car goes through, rather than the actions (inputs) of the driver. It's just the old junior high teacher and coach in me trying to be specific
about terms, for those who might not be as up-to-speed as you seem to be. Yes on all counts to your last post - I said people were trail braking on the street, not that they were making a darn bit of difference to how their cars behaved.

Best to all,

Kirk

fsp31

I guess I use the "swedish massage" without the downshift.

For autocross, I'm constantly trail-braking. I co-drove a friends CSP CRX for a few events and trail-braking was even more effective in his car than in my FSP Civic. I expected the shorter wheelbase to be more of a handful, but in his car I didn't even have to be all that gentle. Just trail-brake until the car rotates about where you want it (regardless of the direction of travel ;-) then stomp on the gas and shoot through the turn. It was a real blast. I haven't been able to duplicate that feel in my car yet. I imagine it's hopeless. CRX's just feel better...


[Modified by fsp31, 6:18 PM 1/14/2002]

siisgood00

About the traction circle...

The best way its been described to me was imagine a string connected between your foot and the steering wheel. When the wheel is striaght ahead, you are on full brake. As soon as you start to turn in, lift the same amount off the brakes as you are turning in. Make it smooth! Then when you go to straighten out the wheel and track out (apex), string is still connected but slide foot over to the gas and apply gradually as wheel is straightened. Kinda hard to put down into words.... Hope this helps at all on how to actually perform the maneuver, not what its good for.

Knestis

Try a little toe out on the rear wheels...

Kirk

MechE00

Forgive me for being a weeny, but is that a typo, or am I misunderstanding something.. I'm pretty sure I understand the various forms of braking pretty well.. I'm just trying to figure out when the left foot ever ends up on the throttle..

Sorry if that's a typo and I'm being too much of a weenie..

Ahh.. maybe that was supposed to be brake, not throttle.. umm.. sorry.. it's early, and I'm dense..

Knestis

Ummm. I had my middle foot on the keyboard when I typed that. OOPS. You would have to have your left foot on the BRAKE pedal. Left-foot throttling is ONLY for the very experienced, the very drunk, or idiots with those pesky unintended acceleration Audis. I also recommend against...

* Using your hands on ANY of the pedals
* Holding the steering wheel in your teeth or lips
* Left hand shifting (unless in Japan, Australia, NZ, GB, or the Bahamas, of course)
* Adjusting the radio with your dangly bits while at speed - this is OK if the car is not moving

Sorry for the error!

K

fsp31

>>
--------------------------------------------------------------------------------
...I haven't been able to duplicate that feel in my car yet. I imagine it's hopeless. CRX's just feel better...
--------------------------------------------------------------------------------

Try a little toe out on the rear wheels...
<<

Thanks, I'll give that a try. Haven't played with the rear toe much. Alignment shops like to put in a tiny bit of toe-in for tire wear, but I had them set mine to zero. Maybe just a tad bit toed out will be the ticket.

scofa

wow thanks for all the great replies.. i really appreciate it.. this place is great..

Black96Cobra

Gotta be careful with a Mustang though, you can bind up the rear pretty easily and pitch yourself around suddenly. How hard were you pushing it (7/10s, 8/10s, etc)? Near the limit the stock rear end is pretty crappy, trailbraking is a risky maneuver. I try not to do it with my car if I can help it.

Hracer

Just be very easy with the rear toe out on a CRX. We run 0 toe out in the rear and just under 1/8th toe out front and even so it is still twitchy in hard braking zones. I once had to drive the car for qualifying with a terrible alignment (we didn't have time to reset it after we had an off in practice), so it had 1/4th toe out in the back, 1/2 in the front. That was by far the longest 15 mins I had so far driving something and came so close to putting the car off the track a number of times because we couldn’t afford to be too far off the pace of the leaders. With so much rear and front toe the car simply has a mind of its own and that's not good around road atlnata in the wet (but it was the wet conditions that actually saved us since we somehow still got pole and 5th overall out of 72 cars?! Yeah we’ll take that! But in the dry we would have lost a lot of time with this setup). Lesson learned: if you ever go over hard bumps in an off, always check your alignment since it could be off. And just like Tom F. told us, we've found that having rear toe out in the back only destroys the car's stability. Play with the front toe to get the car to turn in better, which kind of serves the same purpose as trail braking. But too much will make the car unstable, especially during braking. Right now with just under 1/8th toe out in the front, the car turns in really great but you can feel it weave slightly on the straights at higher speeds. For autox, try 1/8th or more toe out for the front and experiment with rear toe, but on the track be very careful with rear toe out because it can really damage the car's stability.

Knestis

Yup. Lack of stability = turn in. BUT my suggestion was in the context of autocrossing, which (I hope) was part of the original question. We used toe-out on rally cars and solo stuff but, particularly with a short-wheelbase car, please don't simply generalize my suggestion to circuit racing or other road course activities!

Thanks for reminding us of this...

Kirk


[Modified by Knestis, 4:33 PM 1/16/2002]