Braking in a turn explained. - ZX6R Forum
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post #1 of 50 Old 12-13-2012, 12:38 PM Thread Starter
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Braking in a turn explained.

I was curious about what actually causes a bike to right itself when you brake while turning, found this on All Things (Safety Oriented) Motorcycle - Front Brake Stands Up Bike:

If your bike's front-end is designed with a rake angle greater than zero (they all do), then use of the front brake while in a turn results in a significant tendency to straighten the bike up while widening that turn in the process. I will show why shortly.

The rear brake does the same thing, but with much diminished effect than use of only the front brake. That, because there is less weight transfer occurring with the use of the rear brake than with the front brake. Again, I will demonstrate that shortly.

Because of that rake angle, when you turn your handlebars, say 10 degrees to the left or right, the direction of travel is NOT changed by that same number of degrees - it is changed LESS than 10 degrees. Instead, some portion of the changed handlebar position is translated into shifting the contact patch forward relative to the body of the motorcycle. Furthermore, because your motorcycle is not a unicycle, when you change the steering angle it must travel some distance before that change of steering angle becomes the desired change of direction. The longer the wheelbase, and the greater the rake angle, the 'slower' your steering is.

Observe that as we turn the handlebars in these two diagrams a full 90 degrees that the center of the contact patch has moved forward from point 'B' to about 'C' (and that the front-end has lowered).






Had there been no rake angle (if the forks had been vertical) there would have been no forward displacement and the direction of change from a 10 degree turn would have been 10 degrees after the motorcycle had moved a sufficient distance for the body of the motorcycle to catch up with your intention.

What happens when weight transfer is added to the picture is that the forks compress and as a result become more vertical - the rake angle gets smaller!. In other words, the steering becomes 'faster'. Now a 10 degree turn of the handlebars results in a change of direction that is closer to 10 degrees than without any weight transfer.

Said differently, if you had already dialed in a 10 degree steering angle and then applied the brakes, you would have effectively turned your front tire slightly INTO the turn and that, as any fan of counter-steering knows, diminishes the lean angle and the track widens.

So now we go on to front brake vs. rear brake effects.

Of course there is weight transfer when you use either. However, the amount of weight transfer is a function of the height of the CG as compared to the length of the wheelbase (and the deceleration rate, of course). Use of only the front brake maximizes weight transfer because as the front forks compress, as shown earlier, the rake angle diminishes and so, too, does the length of the wheelbase along with the height of the CG.

But by using only the rear brake you tend to straighten out the swing arm which lengthens the wheelbase and lowers the CG. Those things reduce the amount of weight transfer for any given rate of deceleration. As a result, the amount of weight transfer for any given rate of deceleration is less when using the rear brake than when using the front brake.

With less weight transfer, it follows that the front fork compression is also less and that, in turn, means that the tendency to go wide in a turn (and move toward vertical) is less.

Finally, let's look at that issue of 'steering speed' based on length of wheelbase.




By 'travel distance' I mean, of course, the front tire must move that distance to the left or right. Thus, the longer the wheelbase, the 'slower' the steering is.
-James R Davis
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Last edited by Hamsack; 12-13-2012 at 03:25 PM.
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post #2 of 50 Old 12-13-2012, 01:01 PM
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On a related note:

Braking by Nick Ienatsch

Stole this from another forum. Read it!


"If you have to stop in a corner, one of two things will happen. One, you will stand the bike up and ride it off the shoulder and into whatever is over there. Or two, you will lay the bike down and slide off the shoulder of the road. Braking is done before, or after a corner. The best thing to do before taking a corner is to grind the thought "I'm going to turn this corner" into your mind."

Hiya FZ1 lovers.
I’ve stewed for two days about the above quote taken from another FZ1OA thread...and finally decided to launch this thread. In past years I would have just rolled my eyes and muttered, “Whatever”…but not anymore. I want to tell you that there are measureable, explainable, repeatable, do-able reasons that make great riders great. And brake usage is at the very tippity-top of these reasons. It’ll save your life, it’ll make you a champion. It will save and grow our sport.
I’ll ask this one favor: Would you open your mind to what I’m about to write, then go out and mess around with it?
To begin: Realize that great motorcycle riding is more subtle in its inputs than most of us imagine. I bet you are moving your hand too quickly with initial throttle and brakes. Moving your right foot too quickly with initial rear brake. The difference between a lap record and a highside is minute, almost-immeasureable differences in throttle and lean angle. The difference between hitting the Camaro in your lane and missing it by a foot is the little things a rider can do with speed control at lean angle. Brakes at lean angle. Brakes in a corner.
Yes, a rider can brake in a corner. Yes. For sure. Guaranteed. I promise. Happens all the time. I do it on every ride, track or street. Yes, a rider can stop in a corner. In fact, any student who rides with the Yamaha Champions Riding School will tell you it’s possible. Complete stop, mid-corner…no drama. Newbies and experts alike.
There are some interesting processes to this sport, mostly revolving around racing. But as I thought about this thread, putting numbers on each thought made more sense because explaining these concepts relies on busting some myths and refining your inputs. Some things must be ingrained…like #1 below.

1)You never, ever, never stab at the brakes. Understand a tire’s grip this way: Front grip is divided between lean angle points and brake points, rear grip is lean angle points and acceleration points, lean angle points and brake points. Realize that the tire will take a great load, but it won’t take a sudden load…and so you practice this smooth loading at every moment in/on every vehicle. If you stab the brakes (um...or throttle...) in your pickup, you berate yourself because you know that the stab, at lean angle on your motorcycle (and bicycle, btw), will be a crash.

2)Let’s examine tire grip. If you’re leaned over at 95% (95 points in my book Sport Riding Techniques and fastersafer.com) of the tires’ available grip, you still have 5% of that grip available for braking (or accelerating). But maybe you only have 3%!!! You find out because you always add braking “points” in a smooth, linear manner. As the front tire reaches its limit, it will squirm and warn you…if that limit is reached in a linear manner.
It’s the grabbing of 30 points that hurts anyone leaned over more than 70 points. If you ride slowly with no lean angle, you will begin to believe that aggressiveness and grabbing the front brake lever is okay…and it is…until you carry more lean angle (or it’s raining, or you’re on a dirt road or your tire’s cold…pick your excuse). Do you have a new rider in your life? Get them thinking of never, ever, never grabbing the brakes. Throttle too…

3)If you STAB the front brake at lean angle, one of two things will happen. If the grip is good, the fork will collapse and the bike will stand up and run wide. If the grip is not-so-good, the front tire will lock and slide. The italicized advice at the beginning was written by a rider who aggressively goes after the front brake lever. His bike always stands up or lowsides. He’s inputting brake force too aggressively, too quickly...he isn't smoothly loading the fork springs or loading the tire. He may not believe this, but the tire will handle the load he wants, but the load must be fed-in more smoothly…and his experience leads to written advice that will hurt/kill other riders. “Never touch the brakes at lean angle?” Wrong. “Never grab the brakes at lean angle?” Right!
But what about the racers on TV who lose the front in the braking zone? Pay attention to when they lose grip. If it’s immediately, it’s because they stabbed the brake at lean angle. If it’s late in the braking zone, it’s because they finally exceeded 100 points of grip deep in the braking zone…if you’re adding lean angle, you’ve got to be “trailing off” the brakes as the tire nears its limit.

4) Radius equals MPH. Realize that speed affects the bike’s radius at a given lean angle. If the corner is tighter than expected, continue to bring your speed down. What’s the best way to bring your speed down? Roll off the throttle and hope you slow down? Or roll off the throttle and squeeze on a little brake? Please don’t answer off the top of your head…answer after you’ve experimented in the real world.
Do this: Ride in a circle in a parking lot at a given lean angle. That’s your radius. Run a circle or two and then slowly sneak on more throttle at the same lean angle and watch what your radius does. Now ride in the circle again, and roll off the throttle…at the same lean angle. You are learning Radius equals MPH. You are learning what throttle and off-throttle does to your radius through steering geometry changes and speed changes. You are learning something on your own, rather than asking for advice on subjects that affect your health and life. (You will also learn why I get so upset when new riders are told to push on the inside bar and pick up the throttle if they get in the corner too fast. Exactly the opposite of what the best riders do. But don’t believe me…try it.)
Let me rant for a moment: Almost every bit of riding advice works when the pace is low and the grip is high. It’s when the corner tightens or the sleet falls or the lap record is within reach…then everything counts.
“Get all your braking done before the turn,” is good riding advice. But what if you don’t? What if the corner goes the other way and is tighter and there’s gravel? It’s then that you don’t need advice, you need riding technique. Theory goes out the window and if you don’t perform the exact action, you will be lying in the dirt, or worse. Know that these techniques are not only understandable, but do-able by you. Yes you! I’m motivated to motivate you due to what I’ve seen working at Freddie’s school and now the Champ school…
I’m telling you this: If you can smoothly, gently pick-up your front brake lever and load the tire, you can brake at any lean angle on and FZ1. Why? Because our footpegs drag before our tires lose grip when things are warm and dry. It might be only 3 points, but missing the bus bumper by a foot is still missing the bumper! If it’s raining, you simply take these same actions and reduce them…you can still mix lean angle and brake pressure, but with considerably less of each. Rainy and cold? Lower still, but still combine-able.

5)So you’re into a right-hand corner and you must stop your bike for whatever reason. You close the throttle and sneak on the brakes lightly, balancing lean angle points against brake points. As you slow down, your radius continues to tighten. You don’t want to run off the inside of the corner, so you take away lean angle. What can you do with the brakes when you take away lean angle? Yes! Squeeze more. Stay with it and you will stop your bike mid-corner completely upright. No drama. But don’t just believe me…go prove it to yourself.

6)Let’s examine the final sentence in the italicized quote. The best thing to do before taking a corner is to grind the thought "I'm going to turn this corner" into your mind.
No, that’s not the best thing. It’s not the worst thing and I’m all for positive thinking, but we all need to see the difference between riding advice and riding techniques. This advice works until you enter a corner truly beyond your mental, physical or mechanical limits. I would change this to: The best thing to do before taking a corner is to scan with your eyes, use your brakes until you’re happy with your speed and direction, sneak open your throttle to maintain your chosen speed and radius, don’t accelerate until you can see your exit and can take away lean angle.
7)Do you think I’m being over-dramatic by claiming this will save our sport? Are we crashing because we’re going too slowly in the corners or too fast? Yes, too fast. What component reduces speed? Brakes. What component calms your brain? Brakes. What component, when massaged skillfully, helps the bike turn? Brakes. If riders are being told that they can’t use the brakes at lean angle, you begin to see the reason for my drama level. When I have a new rider in my life, my third priority is to have them, “Turn into the corner with the brake-light on.”

I’ve said it before: This is the only bike forum I’m a member of. I like it, I like the peeps, I like the info, I love the bike. Could we begin to change the information we pass along regarding brakes and lean angle? Could we control our sport by actually controlling our motorcycles? If we don’t control our sport, someone else will try. Closed throttle, no brakes is “out of the controls”. Get out there and master the brakes.
Thanks, I feel better.

Nick Ienatsch
Yamaha Champions Riding School
Fastersafer.com
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post #3 of 50 Old 12-13-2012, 01:21 PM Thread Starter
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Great read. I will say the intent of my post was not to say that you should never brake in a turn, but to understand the physics of why a bike rights itself while braking in a turn.
I often find myself braking in a turn, and from the start I didn't buy the "never ever brake in a turn" crap that they tell you in the safety course, it just didn't make sense to me.
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post #4 of 50 Old 12-13-2012, 02:18 PM
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Sorry, didn't mean to make it sound like I was refuting anything you posted, just suplimenting it. It just happened to get posted on a local forum I am on earlier this morning and thought it was a good read.

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post #5 of 50 Old 12-13-2012, 02:55 PM Thread Starter
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That's how i took it, just wanted to emphasize my point. It supplements quite well
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post #6 of 50 Old 12-13-2012, 03:06 PM
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Physics homework.
Will be read later.

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post #7 of 50 Old 12-13-2012, 03:12 PM
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Both great reads... This why I love this forum...
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post #8 of 50 Old 12-13-2012, 03:12 PM
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Great information should be the main focus of any real forum - and this definately qualifies. Well worth reading a couple of times.

Anyone can go fast in a straight line...
Better to ride a slow bike fast than a fast bike slow.
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post #9 of 50 Old 12-13-2012, 03:22 PM Thread Starter
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double post

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post #10 of 50 Old 12-13-2012, 03:24 PM Thread Starter
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Quote:
Originally Posted by ArrhythmiA View Post
Physics homework.
Will be read later.
Rake Angle, Center of Gravity, Wheel base, and weight transfer are the key points. I bolded the two most important sentences for ya.
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post #11 of 50 Old 12-13-2012, 03:49 PM
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Iv got Nick's book, He & Code differ slightly on some points.

But Yeah its best to get most or all of your braking done before the corner.
If you still need to adjust your speed bit, Use the rear. thats right I said the rear.
Slight pres is good for adjusting your line, Not for stopping.

Slow/smooth in is faster out, Get your braking & down shifting done,
set your line & it will be much easer to keep that line without trying to brake & downshift while worrying about over loading the brakes @ the same time.

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post #12 of 50 Old 12-13-2012, 04:43 PM
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Good reads, thanks both of you for posting. I'm a firm believer of front brake while leaning and trail braking. My rule of thumb is, if I'm in the twisties, front brake only. That's mainly because I trust my right hand and because my foot is never near the pedal anyway.

Also, I know my bike will stand up if I use front brake so I just add more body lean as I'm braking.
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post #13 of 50 Old 12-13-2012, 04:45 PM
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Quote:
Originally Posted by oldninjadude View Post
Iv got Nick's book, He & Code differ slightly on some points.

But Yeah its best to get most or all of your braking done before the corner.
If you still need to adjust your speed bit, Use the rear. thats right I said the rear.
Slight pres is good for adjusting your line, Not for stopping.

Slow/smooth in is faster out, Get your braking & down shifting done,
set your line & it will be much easer to keep that line without trying to brake & downshift while worrying about over loading the brakes @ the same time.
How do you use your rear brake if you're cranked over to the right?
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post #14 of 50 Old 12-13-2012, 05:28 PM
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I use both brakes in the corners. I paid good money for them I'm going to use them. I probably use a lot more front though because I'm already getting a little braking on the rear from the engine. How much depends on if I leave the throttle cracked a little.

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post #15 of 50 Old 12-13-2012, 05:31 PM
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man, a lot of good info in this thread.....

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