Jump to content
asic_ridah

Braking Vs Acceleration. Bike Physics

Recommended Posts

Hi All

   I have a group of riders who actually believe that the act of braking causes the bike to stand up!   

PLEASE HELP!!!  I need a forum moderator or an accredited expert to respond.  Please explain away this myth!

Someone PLEASE help!!! 🤦🏽‍♂️🤦🏽‍♂️🤦🏽‍♂️

1. What action causes the bike to stand up braking or acceleration.

2. Is accelerating while adding lean angle a good thing?

3.  Does accelerating make the bike harder to lean?

4. Does brakin or coming off throttle make the bike easier to lean?

 

Share this post


Link to post
Share on other sites

I am neither a forum moderator nor an accredited expert but here's my understanding:

1. "Standing-up" the bike, or reducing lean angle, is done by pushing on the outside handlebar -- countersteering in the opposite way the turn was initiated. Acceleration will cause the bike to straighten out its path of travel, but the throttle doesn't affect lean angle. 

2. No. It's best to complete the steering action before adding throttle. Adding throttle and lean angle simultaneously is asking a lot of the rear tire and traction limits can be exceeded with little or no warning.

3. Yes because as the bike accelerates, the front suspension is unloaded. This changes rake/trail and makes the bike harder to steer. Also, the faster the engine is spinning, the more resistance to leaning because of its gyroscopic inertia.

4. Yes, for the same reasons as above.

 

However, I remember being taught that if a rider were to chop the throttle mid-corner, the bike will stand up initially. A sudden increase in friction on the inside of the front tire from chopping the throttle has the effect as a turning force towards the inside, which tends to stand the bike up. 

I, too, look forward to the expert responses so I can know if I'm completely mistaken.

Share this post


Link to post
Share on other sites

Some bikes will straighten up dramatically if the front brake is applied mid-corner, other bikes are mostly unaffected. The cause is, AFAIK, debated.

Share this post


Link to post
Share on other sites
14 hours ago, trueblue550 said:

I am neither a forum moderator nor an accredited expert but here's my understanding:

1. "Standing-up" the bike, or reducing lean angle, is done by pushing on the outside handlebar -- countersteering in the opposite way the turn was initiated. Acceleration will cause the bike to straighten out its path of travel, but the throttle doesn't affect lean angle. 

2. No. It's best to complete the steering action before adding throttle. Adding throttle and lean angle simultaneously is asking a lot of the rear tire and traction limits can be exceeded with little or no warning.

3. Yes because as the bike accelerates, the front suspension is unloaded. This changes rake/trail and makes the bike harder to steer. Also, the faster the engine is spinning, the more resistance to leaning because of its gyroscopic inertia.

4. Yes, for the same reasons as above.

 

However, I remember being taught that if a rider were to chop the throttle mid-corner, the bike will stand up initially. A sudden increase in friction on the inside of the front tire from chopping the throttle has the effect as a turning force towards the inside, which tends to stand the bike up. 

I, too, look forward to the expert responses so I can know if I'm completely mistaken.

My point is brake pressure or rather braking force does NOT stand the bike up!  It’s impossible, the front tire under hard braking at a shallow lean angle may (due a dramatic increase in resistance from the ground) be snapped back straight thus straightening the bike up!  However it is NOT the braking force that is doing it, in reality it’s dumb luck!!

Acceleration will ALWAYS (if you have traction) pull the bike back up, this is why we can roll on throttle out of a corner and also the reason why “accelerating” will ALWAYS increase your turning radius!!

This is basic physics no way braking force will decrease lean angle on its own, if that was the case the old adage “when in doubt gas it out” would have no meaning!  That adage comes from the fact the stability and balance comes from the throttle, NOT the brake!  You can’t  brake your way out of a lean, and acceleration will, increase the gyroscope forces that balance and keep the bike up! 

Im not say you don’t have to counter steer I’m simply talking about the affects of braking force and acceleration (gyroscope force)  braking will make you fall over acceleration will stand you up!  Any school  kid’s toy top will prove this.

“Acceleration will cause the bike to straighten out its path of travel, but the throttle doesn't affect lean angle.“

Thats EXACTLY how you straighten out your path of travel!  You have to change your lean angle!  You CANT do it ANY other way!

This is why slowing down while turning or using the rear brake “tightens” up your turning radius because you are affecting lean angle you “are” leaning lower ever so slightly!

 

 

Share this post


Link to post
Share on other sites

BTW the reason I came here is because Keith’s video on Twist Wrist actually says that dramatic braking while cornering will make the bike straighten up dramatically.  

Its leading individuals I know to think that braking in corners is the safest way out of jam or a method of picking the bike up if you LOOSE traction!!!

Thats why I want a Expert here to explain away this misinterpretation of what Keith was saying!

 

THIS IS INSANE!!!

Share this post


Link to post
Share on other sites

I disagree. Steering input changes lean angle, not throttle. I think that if a rider was turning in a circle of a constant radius providing no steering input, acceleration by rolling on the throttle would cause the circle to become larger, i.e., a wider line, but the motorcycle would maintain it's lean angle. Braking would have the opposite effect of tightening the turn radius except for the aforementioned front-tire friction increase that actually causes a steering action and initially stands the bike up.

Share this post


Link to post
Share on other sites
5 hours ago, trueblue550 said:

I disagree. Steering input changes lean angle, not throttle. I think that if a rider was turning in a circle of a constant radius providing no steering input, acceleration by rolling on the throttle would cause the circle to become larger, i.e., a wider line, but the motorcycle would maintain it's lean angle. Braking would have the opposite effect of tightening the turn radius except for the aforementioned front-tire friction increase that actually causes a steering action and initially stands the bike up.

What you are saying is “impossible” if the lean angle is static!! It’s simple impossible to increase or decrease a radius without changing the diameter of the circle, the ONLY way to change the diameter of the circle on a bike is to change the lean angle! 

NO OTHER WAY!!!!

When you are leaned over the front wheel DOES NOT STEER THE BIKE.  Only the rear wheel can do that!  The front only controls lean, the rear steers the bike, and if you increase throttle (and there is sufficient traction) the rear wheel will pull/push the bike upward, you have to counter steer after releasing throttle to lean the bike further to to turn tighter.

 

Share this post


Link to post
Share on other sites

Ironically I watched TOTWII DVD again just this last week and I caught that part too. What was said is that the braking action deforms the tire, creating a countersteering action that has a tendency  to stand the bike up.

Many riders are too tense on the bars and they resist or are insensitive to this tendency. Bike geometry, road surface, tire profile and pressure can all affect how much of the tendency is fed back to the rider.

(edit: I did take a little creative license for effect of clarifying the point)

Edited by Jaybird180

Share this post


Link to post
Share on other sites
On 10/2/2019 at 8:20 PM, asic_ridah said:

What you are saying is “impossible” if the lean angle is static!! It’s simple impossible to increase or decrease a radius without changing the diameter of the circle, the ONLY way to change the diameter of the circle on a bike is to change the lean angle! 

NO OTHER WAY!!!!

When you are leaned over the front wheel DOES NOT STEER THE BIKE.  Only the rear wheel can do that!  The front only controls lean, the rear steers the bike, and if you increase throttle (and there is sufficient traction) the rear wheel will pull/push the bike upward, you have to counter steer after releasing throttle to lean the bike further to to turn tighter.

 

This isn’t entirely true; or the hook turn wouldn’t work and body position would be far less important. Rake and wheel base can change line fairly notably at the same speed and lean. To a lesser extent, moving the center of gravity to the inside helps too but I think it’s mostly overwhelmed by the other factors (especially on a heavier bike)

Share this post


Link to post
Share on other sites
On ‎10‎/‎2‎/‎2019 at 8:24 AM, asic_ridah said:

BTW the reason I came here is because Keith’s video on Twist Wrist actually says that dramatic braking while cornering will make the bike straighten up dramatically.  

Its leading individuals I know to think that braking in corners is the safest way out of jam or a method of picking the bike up if you LOOSE traction!!!

Thats why I want a Expert here to explain away this misinterpretation of what Keith was saying!

 

THIS IS INSANE!!!

Hello, I'm glad you found our forum and came here to look for some additional understanding, and you bring up some VERY interesting topics, about which there can be a lot of confusion - as you have seen. I'm happy to help out, as are many other very friendly and very knowledgeable riders here on the forum, but first I respectfully ask that we calm down a little on the caps and exclamation points, this is a friendly and informative forum and discussions can and should be calm and productive. As I'm sure you know, typing in all caps and using a lot of !!!! is the internet version of "shouting" and we can have a very lively and interesting discussion without that. :) 

Share this post


Link to post
Share on other sites
On ‎10‎/‎1‎/‎2019 at 7:28 AM, asic_ridah said:

Hi All

   I have a group of riders who actually believe that the act of braking causes the bike to stand up!   

PLEASE HELP!!!  I need a forum moderator or an accredited expert to respond.  Please explain away this myth!

 

 

Braking, with the front brake, while leaned over in a turn, can definitely cause the bike to stand up noticeably - assuming the braking is hard enough to shift significant weight to the front and NOT so hard that the wheel actually slides, the braking forces cause a friction drag of the contact patch against the pavement that makes the front wheel want to turn to the inside, which creates a countersteering effect and stands the bike up. So when braking while leaned over, the rider has to resist that turn of the front wheel by pushing on the opposite bar to counteract it, to keep the bike on line (i.e., if in a left hand corner the rider would have to push on the left bar to offset the countersteering effect of the braking). This can get tricky to manage, as the rider is restricting movement of the bars, and placing additional load on the front end, so braking TOO hard while leaned over can exceed the limits of traction of the front tire.

If braking verrrrry gently the counter steering effect is so slight that the rider may not feel any tendency of the bike to stand up, and the fact that the bike is slowing down will eventually decrease the radius of the turn, so a rider who only brakes very gently while leaned over (or uses just rear brake - which can also be tricky) may not ever notice any tendency of the bike to stand up. But braking harder or more abruptly makes it much more noticeable. Or, a rider who has a lot of experience with using the front brake while leaned over may be so accustomed to automatically pressing on the opposite bar to counteract the countersteering effect may not be aware of the bike's tendency to stand up, and a rider like that would have to go out and consciously try to relax the arms and observe what happens if he or she ADDS front brake in a corner while leaned over.

 

  • Like 2

Share this post


Link to post
Share on other sites
On ‎10‎/‎1‎/‎2019 at 7:28 AM, asic_ridah said:

Hi All

1. What action causes the bike to stand up braking or acceleration.

2. Is accelerating while adding lean angle a good thing?

3.  Does accelerating make the bike harder to lean?

4. Does brakin or coming off throttle make the bike easier to lean?

 

1) Braking, while leaned over, can cause the bike to stand up, see my more detailed answer above. On a properly set up sport bike, accelerating does NOT cause the bike to stand up. Accelerating WILL increase the radius of a circle but WITHOUT changing lean angle. A rider who thinks the bike stands up because of the throttle is unconsciously steering it up with the bars. Note - a bike with a more extreme, non-neutral setup - like a chopper with a stretched out front end, or a bike with a serious suspension problem - may act differently.

2) No. You are adding load to the rear tire in two different ways at once and that can easily overload it and lead to a rear tire slide, without a lot of warning to the rider or time to correct it. Doing one at a time is a much safer approach.

3) Yes, the front forks are more extended which makes it more difficult to steer the bike and there is less weight on the front tire which affects traction - the most extreme example would be accelerating so hard that the front tire is off the ground, obviously at that point there is no traction at all on the front tire.

4) Coming off the throttle makes it easier to lean the bike. It compresses the front end which steepens the steering angle and makes the bike easier to steer. Braking lightly can do the same, however on many bikes braking REALLY HARD can make the bike harder to steer; I'm not sure all of the reasons for that but I think it has to do with overloading the front tire (deforming it) and suspension, not to mention the difficulty for the rider of keeping enough pressure off the bars to steer effectively under hard braking. 

 

  • Like 1

Share this post


Link to post
Share on other sites
On ‎10‎/‎2‎/‎2019 at 8:20 PM, asic_ridah said:

What you are saying is “impossible” if the lean angle is static!! It’s simple impossible to increase or decrease a radius without changing the diameter of the circle, the ONLY way to change the diameter of the circle on a bike is to change the lean angle! 

NO OTHER WAY!!!!

When you are leaned over the front wheel DOES NOT STEER THE BIKE.  Only the rear wheel can do that!  The front only controls lean, the rear steers the bike, and if you increase throttle (and there is sufficient traction) the rear wheel will pull/push the bike upward, you have to counter steer after releasing throttle to lean the bike further to to turn tighter.

 

Well, it IS true that it is impossible to decrease a radius without changing the diameter of the circle. :)

Above, you said that "when you are leaned over the front wheel does not steer the bike". So, when you ride through a left-right chicane, you lean the bike left, and then when you need to turn the bike back to the right, how do you accomplish that? Are you saying you use the throttle ALONE to change the bike's direction of travel?

Share this post


Link to post
Share on other sites

Is it possible that this topic would be better served in the Cornering section of the site?

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...