maximum braking while standing up?

[NoHeat]

When maximum braking, what's the limit to:

* how much weight you can put on your pegs instead of seat (and wrists) when maximum braking

* if it's possible to get all your weight off the seat, what's the limit to how much you can stand up

[tobyzusa]

what's the limit to how much you can stand up

Can you clarify for me why anyone would want to raise the center of gravity while undergoing maximum braking? Maybe I don't understand your question.

[Ken H.]

"Maximum braking" implies some sort of a situation where you need all the stopping power you have, which seems to me to be a poor time to be affecting the stability of the bike by changing body position.

 

But to your question; as long as you can operate the braking controls with the same amount of exact control needed for the particular moment in question (a daunting task it seems to me), standing up, sitting down, bouncing up and down for that matter, shouldn't effect the braking envelope of the bike at all.

[NoHeat]

Sorry that I wasn't clear: my question doesn't require changing your body position.

 

You might already be in a position where you are weighting both pegs or even standing a little, when the need suddenly arises to brake hard. It's not the usual case when you brake hard, but I can imagine that it could happen.

 

There's a physics element to the problem and a human element.

 

The physics element is this: Maximum braking means an acceleration of 0.6 - 1.0 g, depending on the bike and rider skill, so that a 200 lb rider experiences a forward force of 120 - 200 lb. Moreover, if you are standing up so that your CG is above your grips, then that force would apply a torque that would tend to lift your body up and forward over the grips. All that is really a statics problem. Your body is in a certain position and it experiences forces and torques during braking.

 

The human element is my question: can you stay in control despite that much forward force (and the torque I mentioned) if you're partly or even fully on your pegs.

 

Maybe the answer is that you just lose control and fly over your bars if you are even 1% weighted on your pegs. Or maybe the answer is that you don't even if you are 100% weighted on the pegs and fully standing up. Or maybe it's somewhere in between. I don't know because I haven't tried, and I haven't read it anywhere, either. So I thought I'd see if anybody here knows.

[Misti]

Hmmmm,

 

That is an interesting question. I didn't even make it though one week of my physics 11 course so I'll answer it from experience instead... When riding I generally have a little bit of weight on the pegs, when I'm racing it tends to be more as I want to be fast and agile when moving from side to side as well as light in the saddle to help the suspension work better (like a jocky on a horse) When I brake hard (whether fully seated or with some weight on the pegs) it feels like the same push forward. I tend to squeeze the tank to prevent myself from slamming against the tank or moving in the seat at all. If you are stiff on the bike and not connected to it (by squeezing your legs into the tank) then you will move more, and with more force then if you are relaxed and connected to the bike.

 

I've also seen guys stopie thier bikes while standing up so there has to be some way to control the "flying over the handlebars" syndrome.

 

My two cents...

 

Misti

[ShovelStrokeEd]

Being a strong proponent of the MYRP, I normally have my pegs weighted a bit when riding, even in a straight line. For any and all braking, I don't permit my body to rotate forward and put any force into the bars. Rather, I grip the tank with my knees and use my core muscles to control my upper body position. The idea being that, so long as my forearms are still loose, I won't be adding any steering force, or worse, crossed steering forces to the bars.

 

I have, during practice for extreme braking, engaged the ABS with my butt fully off the seat, knees gripping the tank as described above, and I am still here to type this. I can't imagine doing it in a full stand up on the pegs mode though. The only time I tend to do that is when seeking a little knee relief on the freeway and I'm pretty sure of my path before doing so. The riding position on my bikes is such that my torso is pretty much down and forward all the time anyway so, unless I let go of the bars, I can't stand up that high to begin with.

[Francois_Dumas]

Sounds to me that braking hard on the RT while standing up, you're gonna need a new set of teeth real soon..... I squeeze the tank when braking hard, can't see how to do that while standing. HOW hard you can brake before flying over I can't tell... you'd have to try it yoursefl I'm afraid

[Shaun]

Immediately began imagining rider reactions in MotoX. The question is a bit nebulous. Any specific answer depends on rider physiology/strengths, quality/appropriateness of apparel, and the bikes (including tires) reaction to loading dynamics (what constitutes control?). The interfaces between bike and rider typically occur at three locations; the grips, the seat and the pegs. Where these are located with respect to the riders situation and time variable CG are also key factors in determining the distribution of forces/reactions necessary to maintain equilibrium or control (consider your example with a R1200 GS vs. R1200 S).

 

In my particular case, with my particular bike, and a bit of a challenging road I try to float off the seat therefore the pegs are 100% weighted. Control placement and my CG are such that vertical forces are counteracted through the pegs, deceleration through knees/thighs against the tank and acceleration at the pegs and grips (in principle anyway).

 

If I were to gradually raise my CG (toward standing) under maximum braking, at some point I forsee that I would have insufficient strength/leverage to maintain control. However, on the same bike under identical circumstances another rider may reach that limit sooner or perhaps later.

[Joe Frickin' Friday]

Maybe the answer is that you just lose control and fly over your bars if you are even 1% weighted on your pegs.

 

Center of gravity (center of mass, really) has everything to do with where the mass is located in space, and nothing to do with how it's supported against the effects of gravity. You can lift your butt a thousandth of an inch off of the saddle (pegs 100% weighted), and although all of your weight is now borne through the footpegs, the location of your center of gravity has changed very little. In order to really screw up the situation, you can't just "weight the pegs;" you'd need to be very much standing up, which elevates your center of gravity and puts you in a position where your thighs and knees can't grip the fuel tank and bear the usual decelerative load. All you've got left in that scenario is your feet and your hands; your feet can exert a good decel load durign braking (courtesy of friction against the footpegs), but the net effect is to rotate your upper body forward, and if you're standing bolt-upright, your arms will be poorly positioned to counter this effect.

 

That said, In order to fly over the bars during such a braking event, a couple of things would have to happen:

 

-friction between your body and the bike would have to remain low, and

-braking would somehow have to be sustained even while you are parting company with the bike.

 

The reality is that neither of these conditions will be met. As your body is forced forward, you're going to snag on the tank, the handlebars, and the windscreen, creating an awful lot of friction to hold you back. At the same time, you're going to let go of the brake lever, ending the braking event. The net effect is that you may be flopped violently against the bike - you may even lose control - but you're not going to launch over the handlebars like a circus dude being shot out of a cannon.

[rondob4]

The net effect is that you may be flopped violently against the bike - you may even lose control - but you're not going to launch over the handlebars like a circus dude being shot out of a cannon.

 

I wonder what Honda's intention is with the Gold Wing air bag...to provide a pillow to stop against or a trampoline to boost you up and over the windshield?

[pmdave]

The body's inertia wants it to continue straight ahead at the same speed and direction. During a max energy stop, the body doesn't slam into the bike, rather, the decelerating bike slams back into the body. Even if the feet on the pegs had enough "traction" to do something, the effect would be to rotate the body around it's CoG. (think feet decelerating faster than the head)

 

To attempt to stay with the bike that's trying to slide back under you, you must brace yourself against the decelerating bike. Arms, knees, crotch all help. Legs don't help much unless your machine has significantly "feet forward" foot supports.

 

Where you support yourself on the bike while braking will have an effect. Pushing against handlebars that are mounted high (think risers or apehangers) resists the bike's deceleration at a level much higher than the bike's CoG, which would impart some additional "pitch" forces. But the primary forward pitch is from the mass of the bike and rider attempting to continue forward while the contact patches attempt to retard forward movement. (what we usually call "weight transfer")

 

Frankly, I suggest the dynamics are a moot point when it comes to making a maximum-energy stop. It happens so fast that there is no time to think, stand, sit, lean, etc. The controlling factor in how hard you are able to brake may be your ability to decelerate as quickly as the bike. If you can't stay with it, you'll probably ease off on the lever.

 

That's a real problem when riding two-up, since the passenger doesn't have much to hang onto, other than the rider's back slamming into the passenger.

 

pmdave