Rear Brake Usage during Braking

Discussion in 'The Perfect Line and Other Riding Myths' started by ParaMud, Dec 11, 2012.

  1. Barry

    Barry Just Beastly

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    this ^^^^^^

    And...

    GP bikes with thumb brakes for the rear, cause nobody needs a rear brake??? Right... so they added the weight and complexity just cause. OMG. REALLY??? Yes, they use the rear brake.

    Barry
    #81
  2. Ronin ADV

    Ronin ADV Gear addict

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    This thread reminds me of the old saying that it's cornering and braking that separate the men from the boys.
    Good braking is definitely a learned skill.
    I think it's generally a mistake to apply "absolute" rules to anything.
    Telling someone to never use the rear on the street is about as silly as saying never use the front in the dirt.

    Disclaimer: the above is just my opinion. I don't pretend to be an expert. So nobody get your panties in a twist. :lol3
    #82
  3. ParaMud

    ParaMud Been here awhile

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    I never said that motogp never use their rear brake or it never should be used of course they use it. Control wheelies, tighten a turn and some do use it when slowing down, but not all of them.

    I know people who have lap records at race courses and never touch the rear brake. Most brake by downshifting.

    Now lets talk about locking up the rear brake.


    Will locking it up slow you down faster than not touching it?
    #83
  4. farmerstu

    farmerstu Been here awhile

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    little touchy are we. but sorry, i did a poor job of seperating my statement.
    1. lots of bad advice (in general on this topic,not directed at you)
    2.most bikes and stoppies responding to your post.
    3.klr and op what i said.
    #84
  5. ParaMud

    ParaMud Been here awhile

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    #85
  6. crofrog

    crofrog Long timer

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    Last time I checked when I have 100% weight transfer during stopping my back brake is supplying 0% of the braking power.

    Assuming your riding a bike that can lift the rear wheel (aka not a harely). If you don't have 100% weight transfer (or damn close to it) then you're doing a bad job of "emergency" braking.
    #86
  7. crofrog

    crofrog Long timer

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    There's a huge difference between using the rear brake as a "control" to help the bike do something specific versus using the brakes to stop.

    You want to back it in sure you're going to need a bit of rear brake to make it slide smoothly, you want to take up some chain torque and control wheel spin out of a corner rear brake time...

    If you're coming into a stop at full braking, if you'e doing it right the rear tire is either barely on the ground or not on the ground at all.

    Even off road I routinely lift the back wheel using the front brake.


    You don't always use the rear brake for stopping
    #87
  8. catweasel67

    catweasel67 Honda XRV 750 RD04

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    But you understand that a newbie won't break as aggressively as you so would benefit from learning to use both to maximise their braking until they get close to your declared skill level?
    #88
  9. crofrog

    crofrog Long timer

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    Not really, doing the same wrong thing for 300k miles is no different than doing the same wrong thing for 5 miles (not saying what your doing is wrong per se)

    How do clutch plates wear when they are fully engaged?

    I'd love to see some side by side test done with riders using both brakes versus just the front with repeated stops I think you'll find that adding the rear removes very little stopping distance while the chance of getting it wrong while stopping with the rear brake is allot more. You fuck up and lock both brakes you're going to have a much worse time than just locking the front.
    #89
  10. ParaMud

    ParaMud Been here awhile

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    Isnt that why you practice? Tons of people are saying to go out and practice. Why start teaching the wrong thing?

    :freaky

    Thanks guys for keeping this civilized, its hard to do that on the internet.
    #90
  11. catweasel67

    catweasel67 Honda XRV 750 RD04

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    The maximum braking

    The maximum braking allows to achieve the maximum deceleration, that is: <CENTER>
    [​IMG]</CENTER>
    The deceleration is a function of the wheelbase p, of the vertical h and horizontal position of the center of gravity and of the coefficients of friction, not of the vehicle mass.

    The ratio between the front wheel braking force and the total available braking force depends only from the geometrical properties and the coefficients of friction: <CENTER>
    [​IMG]
    [​IMG]
    Figure 6. Deceleration lines and braking ratio
    wheelbase p=1.4 m; height of the center of gravity h=0.7 m; horizontal position of the c.o.g. b=0.7 m</CENTER>
    The above figure shows that the deceleration increases with the coefficients of friction. Due to the load transfer the front wheel braking force is bigger than the rear wheel braking force.
    The braking ratio between the front and the rear wheel are expressed by the red lines.
    The horizontal axis represents a rear wheel only braking condition; the vertical axis a front wheel only braking condition.
    If the coefficients of friction are low, the importance of the rear braking force is not negligible, as in high friction condition.
    The maximum deceleration before the forward tilting is 1 g.
    As an example consider braking a vehicle with a deceleration equal to 0.5g; it is possible to reach the desiderate decelerationusing different ratio braking. Braking using the front wheel only, requires a front coefficient of friction equal to 0.68 (point A).
    If the used braking ratio is 80% on the front wheel, 20% on the rear wheel, the same 0.5g deceleration requires a front coefficient of friction equal to 0.55 and equal to 0.4 on the rear wheel (point B).
    Which is then the optimum braking to achieve the 0.5g deceleration?
    If the maximum coefficients of friction are the same for both the wheels, Figure 7 shows that the maximum deceleration is achieved when both the tires are used in the same way.
    As an example consider a coefficient of friction equal to 0.8 for both the tires; the maximum deceleration (0.8g) is achieved with a braking ratio equal to 90:10.
    Using the front brake only, the maximum deceleration is equal to 0.67g; using only the rear brake is equal to 0.29g.
    In slipping condition the coefficient of friction is equal to 0.4, the maximum deceleration is equal to 0.4g and the optimum braking ratio is 30:70.
    Se il fondo stradale è più scivoloso e i coefficienti di aderenza di entrambe le ruote risultano pari a 0.4 la frenata ottimale si ha con una diversa ripartizione (30/70) e fornisce una decelerazione pari a 0.4 g.<?XML:NAMESPACE PREFIX = O /><O:p></O:p>

    The 45° line represents the condition mf= mr and is the optimum braking; this line intersects different braking ratio lines as function of the desiderated deceleration. <CENTER>
    [​IMG]
    Figure 7. Braking action of dry(0.8) and wet(0.4) surfaces</CENTER>
    Figure 8 shows that the optimum braking line is tangent to the 50:50 braking ratio; it do not intersect the ration curves with the rear wheel braking force bigger than the front wheel braking force.
    The above consideration is valid even if the static load is bigger on the rear wheel.
    The optimum braking line is always tangent to the ratio curve having the same values of the static loads ratio.

    As an example, if the static loads ratio is 45:55 (45% on the front wheel, 55% on the rear wheel), the optimum ratio curve is the 45:55 and is tangent in the origin to the optimum braking line. <CENTER>
    [​IMG] Figura 8. Braking action of dry(0.8) and wet(0.4) surfaces
    wheelbase p=1.4 m; height of the center of gravity h=0.7 m; horizontal position of the c.o.g. b=0.7 m


    or. put another way.

    use both brakes to maximise braking.
    </CENTER>
    #91
  12. crofrog

    crofrog Long timer

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    My thoughts on why rear brake usage during panic stops is bad.

    1. You're added _twice_ the amount of task for stopping you now need to manage 2 separate brakes systems and tire level tractions.
    2. The majority of the bike's stability is coming from the gyro of the running engine and the spinning wheels. If you lock the front and the engine is still spinning and the rear tire is still turning you have a very good chance of reducing pressure and riding out of it because the bike is still stable and tracking straight.

    You lock the rear which is very easy to do while hard on the front and kill the engine you've lost much of your stability and your ability to re-accelerate and if you then lock the front on top of that the bike is completely unstable. To avoid killing the engine you now need to manage a 3rd control.

    The nature of an emergency is that you aren't planning for it. It's hard to properly modulate 7 controls (front brake, rear brake, clutch, steering, body position, throttle) during a full on stop when doing planned full on stop, like on a race track.

    It's going to be damn near impossible to pull it off when you didn't except it, because face it. If you where in a position to do it all right you'd not be in an emergency stop because you'd have seen it coming and already taken action to avoid the situation.
    #92
  13. Red9

    Red9 Been here awhile

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    ^ this....
    #93
  14. bwalsh

    bwalsh UUU, UUU!!!

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    Bullshit!

    You do not need to assign a false fixed percentage to it...
    Sound familiar?
    #94
  15. cybrdyke

    cybrdyke In the Dark

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    Let me try this from a different angle for ya...
    If you were 100% sure that you were doing the exact right thing by teaching your girlfriend to brake this way, you wouldn 't have posted up asking for everyone's opinions (unless you were just trying to stir the pot). You've heard many opinions, most of them telling you that you are wrong, but some that agree with you. Since you're not going to get any consensus here, and since you're not 1000% sure....my recommendation to you is to quit teaching your girlfriend and let a professional instructor do it.
    Good luck.
    #95
  16. Assero

    Assero Classic Adventurer

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    Thanks. This is really educational and useful. And I think it ends the argument. :rogue
    #96
  17. crofrog

    crofrog Long timer

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    Yeah, except it's not the entire story and because of it's over simplification ends up being basically wrong.

    http://dinamotoweb.dimeg.unipd.it/d...DF format/2009_05 Adherence ICMEM Beijing.pdf

    "Figure 3 (a) shows that the optimal braking maneuver (dash line), which uses also the rear brake, is able to reach the
    ellipse of adherence, except when stoppie condition occurs. There is a net gain in the maneuver performance which is
    quantified by the highlighted yellow area in the Figure. However, the optimal braking strategy acts to the tire limits and
    including the fact that the load torque of the engine in many cases is high enough to lock the rear wheel, only few racing
    riders are able to put into practice this optimum braking strategy. The same cannot be said for acceleration maneuvers
    since traction force is only available at the rear wheel."

    Now make sure you properly read figure 3a because for straight up and down braking it shows stoppies occurring meaning there is no gain from rear brake usage.
    #97
  18. crofrog

    crofrog Long timer

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    From http://www.elsevierscitech.com/pdfs/CEP_Corno.pdf

    Pro-racers have problems accurately modulating both brakes but n00bs in a 2 day program can learn it easily right?

    So which is it MSF the program is so basic and the riders skills are so low that you don't have time to teach things like trail braking.

    Or the program is so good that it can teach "advanced skills" like accurate rear brake usage?

    Or your program is so cruiser oriented that it's under serving the sport bike community.


    The study shows that both brakes provide .3 seconds better braking performance from 300km/h which is about 23ft. That's entirely because at high speeds aerodynamic forces. The cross over point occurs at 200km/h above 200km/h the aerodynamic forces keep the rear down and front tire traction is the limiting factor, below that speed rear wheel lift is the limiting issue.
    #98
  19. ParaMud

    ParaMud Been here awhile

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    So I should send my girlfriend to what? What type of training? MSF? As what the instructors say at the end of the class "Congrats you can now ride around a parking lot.". Send her to a track school? At the school she will learn to use the front brake....
    #99
  20. PhilB

    PhilB Long timer

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    Yes. Braking without locking it up provides the most stopping power, but locking it up does provide some braking power as well. The problem with locking it up is the loss of control and potential for falling down. Which is why (a) using it is good, and (b) PRACTICING using it so you know how to use it is important.

    PhilB