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Discussion Starter #1 (Edited)
From time to time, when freeway traffic is light enough that I'm certain there is and is going to be nobody coming off onto the same exit behind me, I practice maximum braking stops from 60+ MPH when exiting one of the freeways.

Nearly always, the initial 60-40 MPH speed reduction is accompanied by a strange, non-smooth motion. I'm not sure what it is. There is no sideways component to it. Sometimes I think there might be a tiny bit of fore/aft motion of the forks, which I sense through the handlebar. But that is hard to be sure of, what with much of my weight pushing forward on the grips at the same time. (And it's hard to distinguish a braking force variation from a tiny fore/aft motion.) I estimate its frequency at about 1.5 - 2 Hertz, (a little faster than once per second.)

My questions here are:

Is this normal for the V-Strom?
Or does it mean my bike is not setup right or has excess play?
Has anybody found a technique for making it not happen?
 

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FORUM GODFATHER.....R.I.P. PAT
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Practice from 20mph. It's safer and uses the exact same reflexes and movements.
 

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Practice from 20mph. It's safer and uses the exact same reflexes and movements.

No you want to practice panic stops at the speed you ride. You need to experience how hard you can brake and how long it takes to stop at speed. Also you need to overcome the fear of hard braking to scrub off speed, you aren't going to develop any of that at 20mph.
 

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Discussion Starter #5
braking practice

Practice from 20mph. It's safer and uses the exact same reflexes and movements.
I do plenty of hard stops at 20 MPH and 35-40 MPH, mostly as practice. When I do, the strange, 1.5-2 times/second, braking force pulsation does not occur. It seems to occur only at the higher speeds, above 40 MPH.

As for a stop from slower speed using the same reflexes and movements, I respectfully disagree. At higher speeds, I am responding to things happening on a freeway, which virtually never involves something getting into my path at low velocity relative to mine. Events take longer to develop, and reflex is less important than mental engagement and a sense of trajectories and where the open escape routes will be. At arterial speeds, the quick, full stop is much more critical, and the reflex to get to full braking quickly is crucial. Before encountering this pulsating effect I opened this thread with, I would have agreed about "the exact same movements". But those pulsations are quite dramatic at high speed only when I approach as hard a stop as I can routinely do smoothly at lower speeds. So I end up modulating the brake pressure to keep that strange effect from being alarmingly severe, (a different movement). At lower speeds, I practice hard braking at the force which engages the ABS sometimes, and sometimes at a force just below that (traction) threshold. At the higher speeds, I have not engaged the ABS but once when necessity demanded. As I approach that same force during my 60+ MPH practice stops, that shimmying is enough to make me want to ease up.

My concern is really a safety concern. I want to be able to confidently approach either the ABS threshold or the "stopee" limit, from freeway speeds should that suddenly be necessary. I have slowly increased braking force during these practice maneuvers to be sure that I can recognize when the back wheel starts to lift, under conditions where there is nothing I'm about to hit in front of me. That way, I think I have a better chance of executing a maximum stop when it really counts.
 

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Discussion Starter #6
Possibly brake rotors warped or bad bearings?

..Tom
Do warped brake rotors do something at higher speed only? It seems like a reasonable hypothesis, but I do not see the pulsating effect slow down in proportion to speed. It just disappears when I have scrubbed speed down to about 40 MPH.

I checked bearing play about 6,000 miles ago, when they were fine. I'll have to do it again.

Regards.
 

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I was re-reading your original post and thought about the frequency. If it was two times a second at 60 mph that couldn't be wheel speed related. 60mph is 90 feet per second... Two hertz would mean a wheel circumference or about 45 feet so what I was thinking can't be right unless it was some strange harmonic.

..Tom
 

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Since the shimmy has no sideways component, and it is at such a slow rate, all the usual suspects are out the window. -Especially if the bearings are good.

The only thing I can think of is that it is either fore/aft fork flex, as you suggested, which you may be able to test by lowering the front a bit (raising the forks in the triple tree). That would make the front end stiffer, but is odd, since I have not read of anyone complaining of the same symptoms.

Spring preload set way low, with super low fork oil viscosity? I think that is unlikely.

This is a puzzler, for sure, with undamaged forks and proper sag settings and proper fork oil. I am going to watch this thread.
 

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You have an ABS bike. In an emergency stop you just hold the brakes full on. I don't know what is the cause of your shimmy. There might be some flex of the upper fork tubes that no one else has reported. Or maybe something else, but we don't know what. Tire cupping and shimmy would be related to the tire rotational speed, not what you report. Brake disc judder (which is not warped brake discs) also would be related to rotational speed. Loose steering stem bearings probably would not shimmy, they'd just set in place. There is a possibility of one of the pressed brake disc buttons being tighter or looser than its mates, but this seems unlikely.

The semi-floating brake discs on a motorcycle are there to allow for both light weight and thermal expansion. These are the outer rotor attached to the inner section by the pressed buttons. The rotor should expand smoothly when it is warmed by the friction of the brake pads. If some buttons have loosened in service there might be a bit of unintended movement, but again, that should relate to the rotational speed.

Here's more about the myth of warped brake discs:
Tech Article: Warped Brake Discs
 

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Discussion Starter #11 (Edited)
update

This fast braking practice is something I've done mostly on a particular freeway exit near where I live. Today, I took the opportunity to practice on a different exit, one which has considerably smoother pavement. The initial 60-40 MPH slowdown was smooth as silk.

I think it must be an interaction of unsmooth pavement and the braking which accentuates the fore/aft motion. A normal stop produces nowhere as much fore/aft motion as I get when doing the hard stop. I had thought that the motion due to surface roughness would simply add to the simple, leaned-forward motion of stopping, but it looks like there may be a multiplicative effect.

After I've had time to explore this more thoroughly, I will report back. Having troubled folks here with this issue, they at least deserve whatever closure I can manage.

Thanks for the ideas.
 

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FORUM GODFATHER.....R.I.P. PAT
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Rough pavement can decrease traction as the suspension has difficulty keeping tire pressure on the road. That can even activate ABS as the tire exits bumps.
 

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Discussion Starter #13
the light comes on

Rough pavement can decrease traction as the suspension has difficulty keeping tire pressure on the road. That can even activate ABS as the tire exits bumps.
That seems like an excellent hypothesis. One thing about the rough pavement is that it is harder to feel the pulsing of the ABS activating through the foot brake pedal, and with the handlebar rumbling along, I might be missing that pulsing in the hand brake lever too. I will be attentive for this as I further explore the phenomenon.

(This next I mention only partly as a refrain of my earlier response to your idea that slow speed stops are effective practice.)

It seems obvious (now!) that there is going to be somewhat less stopping force available when forward speed combines with unlevel pavement to produce fluctuating force at the contact patches. This means that there is behavior to be learned and accommodated at the higher speed which is gone or much reduced at lower speeds. To me, (with a physical engineering background), it confirms the idea that tests need to include as much of the system being characterized as can be practically managed, under conditions covering all the intended operating region. It is things like this multiplicative traction loss effect which (partly) invalidate trying to extend knowledge of the low speed realm to predict what will happen outside that realm.
 

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FORUM GODFATHER.....R.I.P. PAT
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I understand the benefit of familiarity with high speed stops. What I mean about stopping hard from about 20mph is that establishes muscle memory so a hard stop becomes a reflex action. The MSF braking drills are done from about 20mph. Building a reflex takes hundreds to thousands of practice events. 20mph stops and 60mph stops develop the same reflexes. Practicing hard stops from high speeds is not necessary to build the proper reaction and would be unnecessarily dangerous to do hundreds or thousands of times. Once the reflex is developed, practice to learn the bike's threshold area is best done from about 30mph.

http://www.msgroup.org/Tip.aspx?Num=230&Set=
 

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Halfway through this I was going to ask about road surface issues but I see you already experimented and determined it is road surface. Keep us informed, I spend most of my riding miles on freeways so this is good data from my point of view.
 

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I have felt something very similar in my K2 ... my expectation is that it will go away when I replace the steering head bearings with taper roller bearings.... I think that the factory ball style stem bearings are the cause under high load conditions... but just my $0.02 worth ... I have been unsuccessful in creating a stoppee on this bike... but I am a big guy @ 6'4 and #290....even locking the rear is hard to do on this one... :)
 

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Greywolf is spot on with his recommendation to practice from lower speeds, such as 20 or 30 mph. He is also correct with the need for many many repetitions to master a skill. I spent 12 years as a MSF instructor, teaching both advanced and basic classes. It is amazing what you can learn. You can much more easily (and safely) master the finer points of proper technique at 20 or 30 mph in a parking lot. The principles of proper braking technique are the same from 30 as they are from 60. If the OP has not already, take a class. You dont know what you dont know. I do know that I have personally witnessed literally hundreds of students significantly reduce braking distances practicing at low speeds in a parking lot.

In a class (or simply in a parking lot) you can practice over and over again, actually being able objectively monitor the impact technique has on your braking distance rather than guessing. Off the cuff practice on the highway is at best a guess - you really will have no clue how much better or worse you are doing.

Engineering normally involves measurable facts, not guess work.
 

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Discussion Starter #18
quantifying braking, somehow

I'm just responding to some of Mike's points and implications.

[Worthy observations on the value of low speed braking practice]

I am not on the other side of any stupid debate about the wisdom of learning to brake well at low or medium speeds. Practice is a big part of that, for the reasons elaborated here, and has the additional benefit of providing visual knowledge of feasible stopping distances. (I distinguish "visual" knowledge from what a tape measure might say.)

You dont know what you dont know.
I lift this quote from its low speed braking context to help with my point that it is also valuable to have some inkling as to what happens with higher speed stops.

Off the cuff practice on the highway is at best a guess - you really will have no clue how much better or worse you are doing.

Engineering normally involves measurable facts, not guess work.
Here, I think you are off the mark. My freeway speed braking practice is not about making incremental improvements requiring a tape measure to quantify. I do it for these sufficient reasons:
1. To be sure I know what happens during a higher speed, hard stop. (We might say "to learn what I don't know.")
2. To gain a visual knowledge of what a 60 to 0 MPH stop requires in the way of distance, and a sense of how long it takes using the same "clock" I use to gauge following distances.
3. To become familiar with any control issues that arise and master them.
4. To ensure that I am not surprised by unexpected phenomena should I find myself suddenly having to dedicate my mind to avoiding a developing collision situation.

None of that is "guess work". You can perhaps scoff at my having not brought a tape measure to where I have done my freeway speed hard stop practice, but the fact is that it would do no good because I will not have a tape measurement when gauging the distances involved when faced with a sudden swerve/stop/jump choice.

I'm with Greywolf (and you I suppose) in suggesting that low speed braking practice is to be greatly favored, especially for novices. But I do not think it is wise to believe that is the only valuable speed realm for learning to brake effectively, except for riders who ride only at similarly low speeds.

Now, since education on engineering has come up: Engineering is about going beyond guesswork, with appropriate analysis and quantification. For some problems and objectives, that might involve a laser interferometer, (something I have used on a project for good reasons.) For other situations, a tape measure of unknown accuracy and stability might suffice. And for some, careful eyeballing is enough, and that need not be called "guess work".
 

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Greywolf is spot on with his recommendation to practice from lower speeds, such as 20 or 30 mph. He is also correct with the need for many many repetitions to master a skill. I spent 12 years as a MSF instructor, teaching both advanced and basic classes. It is amazing what you can learn. You can much more easily (and safely) master the finer points of proper technique at 20 or 30 mph in a parking lot. The principles of proper braking technique are the same from 30 as they are from 60. If the OP has not already, take a class. You dont know what you dont know. I do know that I have personally witnessed literally hundreds of students significantly reduce braking distances practicing at low speeds in a parking lot.

In a class (or simply in a parking lot) you can practice over and over again, actually being able objectively monitor the impact technique has on your braking distance rather than guessing. Off the cuff practice on the highway is at best a guess - you really will have no clue how much better or worse you are doing.

Engineering normally involves measurable facts, not guess work.

Sure you can practice at 20mph but there's not much to stopping from that speed. Developing the reflexes is vital to emergency situations I agree but a big part of emergency braking is overcoming the fear of clamping on the brakes at higher speeds.

It's another experience altogether to brake hard from 70 than 20.
 

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Stop from 20 a lot to build muscle memory and make the action a reflex so thinking is not required. Stop from 30 enough to become familiar with the sound and feel of threshold braking. Stop from 60 or 70 occasionally to prove to yourself you can do it and so you aren't surprised by anything if you need to do it for real. The faster you go, the fewer times you should do it. Making practice dangerous has a poor return on effort.
 
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