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60 MPH stops unsmooth, why?

5K views 30 replies 12 participants last post by  Trepidator 
#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?
 
#6 ·
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.
 
#3 ·
Practice from 20mph. It's safer and uses the exact same reflexes and movements.
 
#4 ·
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.
 
#7 ·
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
 
#8 · (Edited)
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.
 
#9 ·
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
 
#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.
 
#12 ·
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.
 
#13 ·
the light comes on


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.
 
#14 ·
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=
 
#16 ·
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... :)
 
#17 ·
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.
 
#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".
 
#20 ·
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.
 
#21 ·
Well said and absolutely correct. And while on subject, most who do practice emergency braking do so incorrectly. Additional common mistakes are:

Using engine braking instead of keeping the clutch lever in and downshifting through the gears to match the proper gear to deceleration speed

Not downshifting durring emergency braking

Focusing straight ahead while concentrating on technique instead of scanning the horizon for other dangers and escape routes

Never practicing accident avoidance techniques with or without combined braking.

Emergency braking practice can help save your life one day, but learning and practicing it correctly can dramatically increase the odds.
 
#22 ·
Not sure the value of downshifting during emergency braking. The goal is to scrub off speed and at most one other thing, to anticipate turning. Braking and turning are dangerous activities to do simultaneously. Downshifting can be done once the danger is passed.

You guys can ponder all you want on the best speed to practice at. But bikes do weird things at 60 that they may not do at 20. I get the muscle memory idea GW and other MSF instructors use. MSF trains in parking lots though for reasons including liability.
 
#23 ·
Being in the correct gear once speed is scrubbed can be necessary for avoidance maneuvers. Accident avoidance at times requires acceleration and gear selection can be imperative. All motors and advanced riding courses teach this.
 
#24 ·
Greywolf and T-dog's last posts pretty much nail it. I have seen hundreds of instances of the mistakes T-dog described at the start of the braking drills. By the end of a class, the vast majority of the students have put those mistakes behind them.

As to liability being reason for classes in parking lots - sure I suspect that is a consideration. So should your own safety. A spill of antifreeze on the public road you are practicing on could lead to some bad consequences - though you would likely learn how protective your riding gear is if you have not already learned the core techniques in a controlled environment.
 
#26 ·
Tom hit on my point well.

We are discussing practice not learning the core techniques. I have taken the MSF course. We as others practiced in big parking lots. I understand developing the muscle memory...I get it, I got it.

But, I live where there are no parking lots. I am blessed with nice empty straight 2 lanes with forgiving wide shoulders where I live in a sparsely populated county. So, I use the road. I also use higher speeds.

I can also understand the lower gear idea, but I am prioritizing a situation where I expect to be fixated on not hitting something, looking for a path around, and maximum braking. If I can even come close to my goal without my brain locking up....I will be working down through the gears.

I have hit one car and avoided another when maximum braking was needed. You may have also, I do not know. But, I experienced severe target fixation both times. The real thing is nothing like a planned stop. If I can just slow down before I collide I consider it a success.
 
#29 · (Edited)
I can also understand the lower gear idea, but I am prioritizing a situation where I expect to be fixated on not hitting something, looking for a path around, and maximum braking. If I can even come close to my goal without my brain locking up....I will be working down through the gears.

I have hit one car and avoided another when maximum braking was needed. You may have also, I do not know. But, I experienced severe target fixation both times. The real thing is nothing like a planned stop. If I can just slow down before I collide I consider it a success.
Ahh yes, Ive hit a few objects over the years due to target fixation, including a car and even a cow. I guess my point should have been that for those that practice and can properly execute emergency braking, the next step is the addition of downshifting durring the process.

Not to downplay MSF instruction at all, but they rely more on entry level fundamentals, even in their secondary classes. More advanced classes taught in accordance to Law Enforcement Motors standards, employ additional techniques to those fundamentals. Many think of MSF instruction as an end all to their formal education and rely solely on road experience for their continuing education rather than seeking more advanced accredited instruction

One of my buddies is an ex PD Motors instructor who currently coaches one of the top Western Motors cone competition competitors. One of the many things I've learned from him dragging me to practice with them on various competition courses over the years is the carryover of target fixation avoidance in slower maneuvering practice, to real life scenerios. While executing back to back excersizes in a full cone course, one of the key necessities is trying to locate an exit cone right after entering an excersize. Once an exit cone is located it's imperative to begin scanning for an entry cone to the next excersize, all the while avoiding any cone contact, repetitively.

Although seemingly elementary, repetitive scanning for entry and exit points at course speed, under pressure, with hundreds of orange "threats" does help with fixation in real word scenarios. Even though it's at a slow speed and everything else is stationary, it trains the eyes and mind to consistantly look for a way out, or in if that's the case. The same can apply to practicing other techniques at lower speeds such as braking. However practicing at higher speeds is certainly more exhilarating and seemingly more rewarding :yesnod:
 
#27 ·
update on smooth/rough roadway effect w/ fast braking

After several more hard stops from 60 and 70 MPH, (one on a freeway I had to myself for 1/3 mile behind), all on relatively smooth pavement, I can say confidently that there is no issue with how my 2013 DL-650A performs. I've done another few hard stops on the rougher exit I was mostly using for this, and find the phenomenon repeats as long as I commence the stop where the pavement is uneven. (It's an asphalted surface which has become a bit undulated and also degraded with age.) But on smooth pavement, I get uniformly smooth stops.

I'm not sure what hazard I am courting with these maneuvers. I sure as hell am looking for the rear end to come up or for the bike to start getting the least bit sideways, and am prepared to instantly release braking pressure. I have found that the ABS makes it difficult to even start getting the bike not aligned with the velocity (vector), even when braking as hard as the ABS will allow.

A few thoughts on down-shifting during a "panic" stop: Unless there is nothing to do but stop as hard as you can, there will be a time when most of one's speed is gone and "normal" riding can be contemplated, even if that is to weave through some openings. I find that doing 2 or 3 quick downshifts from 6th to 4th or 3rd gear after getting to 20-25 MPH takes so little time that I am not even tempted to start downshifting earlier when my full attention is on bleeding speed to avoid things completely in front of me. (I have had to do a few hard stops of necessity when riding urban Puget Sound area freeways.) If one of the instructors for the MSF courses I've taken is sneering at my technique (from heaven or some such), I'm willing to absorb that. Approaching hard objects at speeds of 40-70 MPH creates intense focus on what has to be done, and I am loathe to dilute that with things that can wait.
 
#28 ·
At least when I was an MSF instructor, we taught total focus on scrubbing off speed. The average rider won't brake as well if trying to downshift at the same time. If the situation allows downshifting, great. The main job though is to scrub off as much speed as possible before even thinking of anything else.
 
#30 · (Edited)
Yeah, LEOs get lots more training and need to ride at levels beyond the mere mortal due to pursuits. My dad was a motorMP officer in the army.

He was big on dirt bikes all along and started me very early on two wheels. He thought that dirt bikes were good to learn braking and steering since doing both at the same time is easier and more commonly needed in the dirt. You also are always scanning ahead for the rocks and "good" line on dirt bikes. I still ride them for the fun and the transfer of skills to my street bike.

I will not speculate on whether advanced training would help me or not. I do have my doubts but that's irrelevant and the courses are not offered reasonably close to me anyway. I do plan on throwing my dirt bike around though as long as I can.

As for target fixation, I will just wing it I guess. I was riding at 55mph when the car I hit pulled out on me. I anticipated it happening, it did, and I maximum braked down to around 30mph maybe, before swerving to the right and hitting her car at an angle, in the rear passenger door. The lady froze in my lane when I blew my horn. My Harley's crash bars did their thing and I luckily limped away...requiring minimal follow up medical care. The Harley required extensive medical care and her insurance company totaled it.

The second time the car kept going and I put it off road. The braking helped me be at a low enough speed that the off road excursion and follow up low side did me no harm. The car kept going and they saw what they did.

ATGATT and ride no faster than your angel, for they need to be there with you when it hits the fan.

P.S. - Louisville no longer uses motor officers except for parade duty. Too many got hurt.
They stick to wrecking cars now.

P.S.(2) - The bike in my Avatar, a 2002 RK Police was the one that went splat. I reincarnated it with a salvage title and rode it another couple years. Bought my Vee during the repair work which took me all summer. Miss that bike....a little.
 
#31 ·
more on unsmooth fast hard stops

I've been doing some more experimenting on the exit where I have had the unsmooth stops a maximum braking above 40 MPH.

On the same pavement, if I brake just below the pressure where the ABS cuts in, the stops are definitely smoother. I suspect there is an interaction, perhaps a bit chaotic, between where the pavement surface undulation causes more slip (due to the normal force reduction) and how the ABS reduces and reapplies brake pad force.

The (somewhat) controlled experiment I plan is to see if I can improve upon a max-control pressure, ABS-activating stop by using less control pressure so as to keep the ABS from activating. (I can start the stop at a fixed place and mark where it ends. This will not be precise, but if there is enough effect to matter, that should become apparent. I will see if I can use the control pulsing as feedback.)

I'll report back when I know more.
 
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