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> FF Trail Braking, A bit of Oversteer with your understeer, sir?
DigiBunny
  Posted: Aug 30 2010, 08:52 AM


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So I whored the the track for a while today, and just thought I'd share my experience.

Now for those who are unaware, I'm running a 4AGE Corolla Sedan, with basically nothing but the Chassis justifying me calling it a sedan. Suspenion's from a Levin, Brakes are from a Corona, The tires are Maxis All seasons, I've got bigger alloy wheels than the car would have normally come with, etcetera, etcetera!

But I think that's beside the point.
Now for the real inquiry.

I've noticed that on a decreasing radius turn that if I jam the brake just before I turn in harder, I can turn the car a bit faster than if I just used the normal method of cornering with an FF; i.e. keeping my foot on the gas and hoping I don't understeer into the tire barrier. This also seems to work to a lesser degree when I'm on a hairpin or a 90 degree curve.

The general effect of this quicker turn in seems to be due to what I theorize is:

1.) The weight of the car shifting forward once I start turning. Since I was accelerating all throughout the curve, it makes logical sense that with all the weight in the back, my drive wheels have less traction to cope with me trying to accelerate out of the curve.

2.) The brake causes a slide. Now since the car is already NOT straight, it's going to make it jolt, however much, more into that bias.

Doing my homework tells me that I'm performing some form of trail braking, do correct me if I am mistaken.


However, The effect isn't really all that... ah, noticeable if I just tap the brake while I've got the wheel turned. At best, I could describe the difference from that and simply accelerating without the brake tap as negligible. Were I to brake harder or longer, the car would then either understeer due to a four wheel skid without twisting, or just bog down and make me lose momentum.

Given that I'm still fairly new to racing at all, I wonder if there's more laws of physics I can manipulate to refine my technique?
Kiroshino
Posted: Aug 30 2010, 01:05 PM


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From the little I do know, it sounds like weight/load shifting to me. Basically, when you jam the brakes before a turn, you're shifting the weight onto the front tires, giving yourself better traction for turning.

There was a good picture in Speed Secrets: Professional Race Driving Techniques that gave an idea of when to release the brakes and start pressing on the gas for optimum speed during turns. The most important part about this is the timing for when you release the brakes during the turn.

I've never raced so take this with a grain of salt.

http://www.speedsecrets.com/PRODUCTS/Speed...99/Default.aspx
MetalMan777
Posted: Aug 30 2010, 02:03 PM


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Yep, Load shifting, trail braking, etc.

It's a big thing in FWD rally cars. Left foot braking is awesome in the right car. If you're on a loose surface, all you have to do to swing that rear end out is brake while turning, all the weight shifts forward, sometimes the rears even lock, and they fly to the outside of the turn.
DigiBunny
  Posted: Aug 30 2010, 03:45 PM


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the problem is I don't think I'm using it to it's potential, especially for 90 degree bends. That's more of a hit and miss. Sometimes I get a jump in grip, sometimes it just slows me.

I've been thinking of using the handbrake to give it that extra mobility, but the handbrake on my car isn't too keen on locking the rear. Since the handbrake is still slowing the car greater than letting it glide out, I suppose there would be some ( but less) weight shift. That tells me it's more effective.

So about the handbrake. If I'm running all wheel discs already, how do I improve it's bite?
MetalMan777
Posted: Aug 30 2010, 05:50 PM


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Convert it to a hydraulic handbrake like they have in rally cars. Also you could try moving your footbrake's bias rearward, so that you could get that same weight shift with your foot, rather than your hand.
MattW
Posted: Aug 30 2010, 06:18 PM


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Get something better than all-seasons.
DigiBunny
  Posted: Aug 30 2010, 07:02 PM


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QUOTE (MattW @ 44 minutes, 1 seconds ago)
Get something better than all-seasons.

Naturally, that would be a step at some point. However, I'd like to focus on only my braking technique.

----------------

A hydraulic system makes me a little nervous. Isn't the whole point of a mechanical brake system to work when your foot brake ( which is a hydraulic ) fails?

The rear bias sounds relatively riskless, save for changing my brake feel. How would one go about doing that? The most I know about the brakes on my car is how to change the fluids.
Spaz
Posted: Aug 30 2010, 07:41 PM


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You would replace the brake proportioning valve.
flohtingPoint
Posted: Aug 30 2010, 07:50 PM


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-Dont touch your hand brake, it serves no purpose on a circuit.
-Worry less about trail braking, work on slow in/fast out.

What you're describing is very jerky driving, which is the product of driving on terrible tires (look at any of my videos from last year when I was on terrible tires due to saving my budget for the off season). Get some much better tires and work on the fundamentals. Look at getting some Toyo RA1's (if they're available in your region), they're not bad track tires at all (they're the Spec Miata mandated tire for National competitions) and they're fairly cheap.

This post has been edited by flohtingPoint on Aug 30 2010, 07:59 PM
sideways
Posted: Aug 30 2010, 08:46 PM


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What the man there said. I cant think of a situation on a track where youd want to use the hand brake, unless were talking about a corner so tight it exceeds the turning radius of your vehicle and you need to rotate around it. But Im assuming were not.

Try working on your transition, never "jab" the brakes, never "jab" the gas, never "dart" the wheel in, and the opposite is just as true. When coming off the brakes and turning in dont side step the pedal and point at the exit of the turn, "release" the brakes in proportion to how much youre turning in. They key to going fast is being smooth, the smoother you are the better.
DigiBunny
  Posted: Aug 30 2010, 09:15 PM


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My tires are actually due for a swap already; that last run burned off whatever cornering ability was left in them. Though I must ask, why the emphasis on my tires? Would one not be able to perform the technique regardless?

I guess the challenge in being smoother is pulling it off within the small, small timeframe I have then. Point acknowledged.

Slow in fast out seems to be counter intuitive to going fast. I've been taught to keep my cornering speeds up and constantly stay on the limits of the tire traction.
flohtingPoint
Posted: Aug 30 2010, 09:27 PM


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QUOTE (DigiBunny @ 11 minutes, 42 seconds ago)
Slow in fast out seems to be counter intuitive to going fast. I've been taught to keep my cornering speeds up and constantly stay on the limits of the tire traction.
Möbius
Posted: Aug 31 2010, 12:32 AM


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QUOTE (flohtingPoint @ 3 hours, 5 minutes ago)
http://www.soloperformance.com/Secrets-of-...tts_p_1226.html

Read and understand.

I was going to link this one, but I am a bit biased. cool.gif
DigiBunny
  Posted: Aug 31 2010, 03:14 AM


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Okay! So after alot of mathematical justification, the conclusion is that an earlier acceleration point is more effective than a traction challenging wheel lock in one direction. Just to clarify, this applies for all cars, regardless of drive wheels and power, yes?

Another thing I end up doing on the track is purposely understeering as I exit a corner and then letting off enough so that grip returns when I straighten. My reasoning is that by doing this, I build up momentum for the wheels to get going on the straight that follows, but I have a feeling this is in the same category as drifting; i.e. Useless tire smoking.
flohtingPoint
Posted: Aug 31 2010, 04:24 AM


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QUOTE (Möbius @ 3 hours, 51 minutes ago)
I was going to link this one, but I am a bit biased. cool.gif

Secrets to Solo is like "See Jane Run" for driving. It should be everyone's first stop before trying to tackle "War and Peace".

QUOTE
Okay! So after alot of mathematical justification, the conclusion is that an earlier acceleration point is more effective than a traction challenging wheel lock in one direction. Just to clarify, this applies for all cars, regardless of drive wheels and power, yes?


Seriously, read the book. I wasn't joking or being a dick. It's a great source for beginners.

If you're lapping without an official timer (done via transponder), you're not getting much useful high-level driving. You need those times (and splits if available) to understand if what you're doing is genuinely faster or not. Becoming faster is a lot of boring methodical and mechanical process involving lots of math and analysis. Video definitely helps you out too so you can see what you're doing between splits.
Rudy
Posted: Nov 21 2010, 03:11 PM


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sideways
Posted: Nov 21 2010, 03:25 PM


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Youve got a weird definition of "fun" awesome.gif

This post has been edited by sideways on Nov 21 2010, 03:37 PM
Rudy
Posted: Nov 21 2010, 03:30 PM


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sideways
Posted: Nov 21 2010, 03:37 PM


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Adding sarcasm to sarcasm doesnt usually work. Let me go edit that post
Rudy
Posted: Nov 21 2010, 03:42 PM


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Type 100
Posted: Jun 21 2011, 01:38 AM


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QUOTE (DigiBunny @ Aug 30 2010, 08:52 AM)
The general effect of this quicker turn in seems to be due to what I theorize is:

1.) The weight of the car shifting forward once I start turning. Since I was accelerating all throughout the curve, it makes logical sense that with all the weight in the back, my drive wheels have less traction to cope with me trying to accelerate out of the curve.

2.) The brake causes a slide. Now since the car is already NOT straight, it's going to make it jolt, however much, more into that bias.

Doing my homework tells me that I'm performing some form of trail braking, do correct me if I am mistaken.


However, The effect isn't really all that... ah, noticeable if I just tap the brake while I've got the wheel turned. At best, I could describe the difference from that and simply accelerating without the brake tap as negligible. Were I to brake harder or longer, the car would then either understeer due to a four wheel skid without twisting, or just bog down and make me lose momentum.

Given that I'm still fairly new to racing at all, I wonder if there's more laws of physics I can manipulate to refine my technique?

Hi. First post, although I've been lurking in here ever since IDAS4 was popular.

I've been participating in trackdays for two years now and I figured I should let you pick my brains. My real-life ride's a GD1 Honda Jazz 1.3S, all stock except for some spiffy seats.

First of all, DigiBunny, yes you picked up on a fundamental racing concept, weight transfer. Any discussion of trail braking however has to involve another fundamental racing concept which is the limit of tire grip.

Imagine you have three interconnected strings, each called "throttle", "brake" and "steering." Pulling on one string means you can't do as much of the other two. That's the inherent limitation of tires' grip - so you have to be smart about how you use them.

In a strictly ideal/orthodox sense, you would pick your actions one at a time to maximize the grip of the tires for that particular action. When driving on public roads, it's usually a bad idea to turn in while braking, for instance, because your cornering just gets corrupted. When you brake hard and turn in hard, your front tires become overworked due having to deal with the forces of steering and the sudden weight transfer to the front due to braking.

Also, if you turn hard while adding max brake input too suddenly, you can spin out - regardless of drivetrain layout - because your car's rear end is unweighted in a sudden-braking scenario. (So many people have spun out at Subic International Raceway's Turn 1 driving FF cars because they braked too suddenly and too late, while trying to suddenly turn left. FAST IN, SPIN OUT!)

Usually the best thing to do is to
1. perform all your braking in a straight line, scrubbing off all excess speed before you initiate the turn
2. apply steering lock and turn in, while gently applying the throttle
3. straighten out and balance the car as you apply more throttle to WOT exiting the corner.
This assumes that you know how to dissect a corner into braking area, apex and exit - which is something you can gain with practice.

Trail braking, however, is an advanced technique and flies in the face of such orthodox wisdom. Basically trail braking is a compromise, expending the tires' total grip between two separate tasks you're not doing 100% of. In this case you could do 50% max brake effort while applying 50% of your orthodox steering input - it really depends where you do it.

The key to successful trail braking is all in the execution. For example, this is how one would attack the banked, double-apex R-Bend at Batangas Racing Circuit.

1. When you approach the turn, do most of your max braking in a straight line as normal.
2. As you approach your turn-in point, gradually reduce your braking pedal pressure while applying some steering lock into the turn at the same time.
3. Once your car is settled mid-turn, gently apply even more steering lock and roll back on the throttle.
4. Perform corner exit, straightening out and application of throttle to WOT toward corner exit as normal.

A auto-crossing friend of mine has a quote I love using:
"Slow is smooth. Smooth is fast. Therefore SLOW IS FAST."
The key to real-life motorsport technique is smoothness - no sudden jerking of the controls. You don't want to introduce more weight transfer than is necessary, because it stunts your progress and you'll waste more time trying to contain your car's added body motions when you could've spent that time accelerating.

Hope this helps. It would be great if you could enroll yourself in a performance driving course.

Just in case anyone busts me for not knowing my stuff...this is my car attacking the chicane at BRC, where understeer means getting up close and personal against the tire wall.

user posted image
RickkyyP
Posted: Apr 24 2013, 03:22 PM


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QUOTE (Type 100 @ Jun 21 2011, 01:38 AM)


1. When you approach the turn, do most of your max braking in a straight line as normal.
2. As you approach your turn-in point, gradually reduce your braking pedal pressure while applying some steering lock into the turn at the same time.
3. Once your car is settled mid-turn, gently apply even more steering lock and roll back on the throttle.
4. Perform corner exit, straightening out and application of throttle to WOT toward corner exit as normal.

This is my favourite way to corner, to me it just seems a better use of grip, because as you reduce the pressure on the brake pedal you gradually apply the steering. And as you unwind the steering you apply the the throttle

With conventional brake and then turn, the moment you release the brake pedal is extremely important, thats when you need to turn in to take advantage of the weight transfer to the front. If you release the pedal too early you'll have a dull turn in because you'll have less grip from the front. Release it to late and you'll miss the apex, have to scrub speed mid corner and have a horrible exit.

With the first method you can modulate your braking or throttle as the situations demands. As for which method is faster in the hands of a pro I have no idea, but for someone who can't regularly practice on tracks etc I find trail braking easier.

P.s. Loving the bouncing over the curb, thats commitment!

This post has been edited by RickkyyP on Apr 24 2013, 03:23 PM
Meteor
Posted: Apr 24 2013, 04:39 PM


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^From a time-attack perspective, the first method will always be faster so long as the car can handle it (and most cars generally can). Trail-braking allows you to brake a little later than normal without overshooting your preferred turn-in points, and while the time gained from this is marginal, it adds up corner after corner and makes for a significant decrease in lap times. From a racing perspective though, braking in a straight line and then turning in makes conserving the tires over several laps easier.
Banken
Posted: Apr 24 2013, 10:36 PM


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Jabbing the brakes in the turn would basically be a very low-level form of trail braking. By taking weight off the rear and putting it on the front, you have increased grip in the front and decreased grip in the rear, which will make the car turn better.

But what you should have done was ride the brakes into the corner, reducing brake pressure gradually while turning into the corner until you reach the apex. By doing this you can force the car to turn without upsetting it's balance, which lets you take the corner at a higher speed.

Secondly, you do not need a hydraulic handbrake!!! Any stock handbrake in good condition, properly adjusted and with fresh wires/cables, and decent rear brakes (good pads and clean rotors) can turn a car 180! Especially with all-season tires.

My MR2 wouldn't do a 180 with high-grip street tires on it, but that was because one of my cables was bad. Once I replaced it I could do 180's just fine.

Now, if you have rear drums connected to a pedal-activated parking brake, that's another story. In that case you would need to install a hand brake from another car.
Rudy
Posted: Apr 25 2013, 02:32 PM


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