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The Spooky Slides


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There used to be a time when slides were predictable, like digging parts hard enough into the asphalt to level the wheels off the ground or whacking the throttle open at maximum lean. But 10 years ago, I began suffering from slides erratically and unexpectedly. Over the last decade, this has eaten into my confidence.

 

Example one: GSX600F Katana, fitted with Dunlop D204s (or was it 205s?), had great grip wet or dry on asphalt. But on worn tarmac, it was like riding on marbles. Getting slowed down, steering and cornering became precarious, dramatically different to what it was on other surfaces. Braking distance at least doubled.

 

Example 2: Same bike, but now with BT45 front and ME550 rear. At first, the rear would just slide out with an inch of chicken strip, scuff marks about 90 degrees to the rolling direction clearly visible. I cleaned the rubber and sanded it, but it didn't help. With time - and lots of slides that saw me play dirt tracker on dry asphalt - the tyres gripped better, but the final 1/4 inch stayed unused save for the marks left from the slides. A later fitted SuperVenom didn't slide.

 

Example 3: XT600 on Pirelli Scorpions would slide the front or the rear or both at very shallow leans at times, especially near interesections and on on-ramps. At other times, it would lean to the point of no chicken strips without a hint of slip. Then I fell off.

 

Example 4: VT500FT on ME330 front and ME77 rear. Behaves very similar to the XT600 in that I may have great grip around one bend and then sliding at much less lean around the next. Very limited grip in the wet, feels like skating, almost. Tyres have been little used, but are old. But I've ridden on old, hard tyres before. They delivered consitently poor grip and where hence predictable, unlike these items.

 

Example 5: CB400SF on D253s. Again, these unexpected slides at moderate leans, from both ends. Very soft suspension. After adding oil to the fork for more air spring plus fitting stiffer, but still supple, Hagon shock absorbers along with a Nankang sport touring tyre I've not had further slides.

 

So how do one deal with this? My old KZ650 on cheap rubber works fine, but the other day riding the VT I decided that the tyres would stick and just relaxed and rode it through an intersection. Only to have both tyres slide. The XT slid there as well. So all these slides - plus I've hit a lot of sand, mud and manure all over our roads lately - makes it really hard to ride even with a hint of briskness. I really need to work out why this happens, what cause them. Suggestions?

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Wow, you sure are having a lot of slides on the street! That's a tough one, so many variables that can come into play to cause slides, even before you start thinking about tyres.

 

Do you think that you've gradually been riding faster on the street? Or would you say that your speed has stayed fairly constant over all those years?

 

One observation I would put out there is that the quality and ability of tyres has improved quite a lot. So maybe you were more comfortable when you were riding on older rubber because you were able to find their limits? It can be a bit of a mental challenge to try and use a tyre and push it when you don't quite know where the tyres limit is.

 

How did you feel all those times when the tyres slid? Were you tense and gripping hard... were you thinking about whether or not the tyres would slide?

 

This may seem to be going a bit left field (and may not even apply to you), but stay with me... If you're worrying about sliding, I would say that you've just got to stop worrying. This is an entirely mental technique/issue. Learning riding skills and techniques that raise your skill level and allow you to be more confident in your ability will no doubt help with confidence. But for some people I think it still just comes down to a "mind over matter" type problem. It's just through sheer willpower that they're able to force themselves to stop worrying about things. The same applies for a person who is worried about crashing - I believe it becomes just like target fixation. You can't not think about something. An example: if I told you "do not think about pink elephants", I can probably guess fairly accurately what you just thought about. wink.gif If you apply that to riding - imagine someone who is constantly worrying about crashing while they're riding, thinking to themselves "don't crash, don't crash..." What's going to happen...? That's not to say that a person will immediately crash as soon as they think about it, but if that's what they're constantly thinking about there is a much higher chance that they will actually crash.

 

I will let some others add their thoughts now, so many things to consider in this subject.

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Thanks for chiming in.

 

I will say that I ride slower now, often significantly so and particularly the last two years. I have also been working hard on riding relaxed during these two seasons, something I've never done before. Still not perfect, but I'm at a level where I can will myself to relax mid-corner if the bike is reluctant to steer and I notice I'm a little tense. Earlier, I've been gripping the bars hard. Also, I used to brake late and deep - sometimes all the way to the exit! - and now I try to stay away from the brakes or at least brake early.

 

So in theory, I ride more correctly now. And on some bikes, like my old Kawasaki and also with the new suspension settings and different rear tyre my CB400, it seems to work. But I find my bikes are in general acting far more inconsistently now, for whatever reason.

 

You say tyres have progressed, yet I only ever had issues 25-30 years ago if the tyres were old and hard or of the touring type - and (apart from hitting slick spots) the lack of grip was consistent. But the trouble I have now is that around one bend I can lean my VT500 45 degrees (guesstimate, but tyres have scuff marks reaching all the way up on the sidewalls where they meet the thread) only for it to slide 4 inches sideways around the next corner at 30 degrees. And that's the real culprit here, that the slides happen at such shallow lean and so randomnly.

 

Sure, some of it can be in my head, but far from all. And I've tried not to worry as well and been met with some pretty spectacular (for me) slides that really do take a lot of the joy out of riding. Because there is no doubt that waiting for the tyres to slide makes me a worse rider.

 

Perhaps it is so easy that the tyres and/or geometry and/or suspension and/or my current way of riding doesn't match well. Maybe the hard braking followed by "point-and-shoot" heated the tyres more. Perhaps the heavily increased traffic leave more dirt on the road compared to earlier. I don't know. Wish I did, though!

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Are you, by any chance, riding on dual compound tires now, that have a different compound at the edges versus in the middle? Lots of tires are that way now, and it could make sense that you are feeling the grip change at different lean angles, which would not have been a factor years ago.

 

Also, on one particular dual compound tire that I used to use, there was a very soft aggressive compound at the edges, that was super grippy, but wore out quickly and got very slick once they were worn out. On those when I leaned the bike over and transitioned from the harder compound to the softer once, the tire would abruptly begin sliding. The tires were great until they wore out but I didn't like the unpredictability once they did start to go off, so I stopped using them.

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I doubt that's the cause for me, unless there is a transition zone with less grip? Some have been dual compound, but not all. Not to mention that as a slower and slower street rider I do not wear out the shoulders. Also, I can lean way over in one corner and get a slide with surprisingly little lean in the next.

 

It's the inconsistency that nags me. If a bad tyre slide at 35 degrees, well, just lean less. But when I can corner fine with 45 degrees of lean and then slide at 30 degrees for no apparent reason, it messes with me head. I'm sick of crashing.

 

This is a fall I performed last year. Although it happened near the maximum lean (for me on the bike) there hadn't been a hint of a slide all day over 160 miles, then it let go so suddenly I didn't get a chance to react at all. BTW, the same bike and tyres would every now and then slide at shallow leans, but much gentler.

 

Fall close to the end

 

 

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I tried watching the video but can't see anything well enough to have any thoughts about what is happening - I assume you are the rider in front, not the rider actually carrying the camera, and if so, on my screen the size/graininess of the image and the shadow make it really hard to see anything.

 

My thought about the dual compound tires came from your comment that you could lean the bike over a lot and get good grip, but at shallower lean angles suddenly slide - since you would be riding on the harder compound at shallow angles you might really GET less grip and thus get surprised by a slide.

 

But, there are a lot of other things it could be! First, some basic stuff - what tire pressures do you run? Have you set your suspension up? Are you tires and suspension in good condition? Did you notice anything about the surface of the road?

 

Do you ever use your rear brake in turns?

 

Take a specific (and typical) example of an unexpected slide - where in the turn did it occur, at the entry, the apex or the exit? What other details do you remember, were you entering faster or slower than normal, turning in a different place, driving harder or less, were you using the brakes, and any details of what you felt the bike DO, exactly, right before and during the fall. Maybe with the collective wisdom of the group we can help you diagnose the cause of these unpleasant slides!

 

Of course the best solution of all would be to get thee to a school so you can have a coach watch you all day long, that would probably get it solved in no time flat. :)

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Thank you for trying to help out, Hotfoot - and your final sentence is probably the one I should emphasize the most ;)

 

 

Yes, I were the rider in front. The crash happened as I began to gently accelerate out of the corner. There were lots of rubber left by thousands of cars that may have contributed to the sudden loss of grip.

 

The point about dual compound tyres is well taken, but cannot explain all cases. Could be for some, though.

 

I run standard street pressure; 36PSI front and 42PSI rear. Then it drops until I can be bothered to check again :D It can get as low as 26/30, but usually I re-inflate around 32/36. I cannot say I notice much difference and in grip or handling on most tyres, but some are very soft and will feel vague quickly. Other tyres are stiffer in construction and may feel harsh on standard settings.

 

Suspension back when was horrible when new and totally clapped out when I got my hands on them, yet it never seemed to affect grip at my level. My KZ650 runs on stock 35 year old suspension and doesn't have grip issues with its Heidenau front and Cheng Shin rear. But no doubt could - and should - the suspension have been better on my bikes. The CB400 is very soft in every way, the VT500 is quite firm but with a lack of rebound in the rear. Still better than the KZ650, which is stiffer still and whose rear dampers lost their damping ages ago :D

 

I always replace tyres before they are worn out, usually with 2mm left of thread. If my issues came with old and/or worn tyres, I would have a constant. But they also happen with new supposedly sticky tyres.

 

Road surface is for me the most likely culprit, but we must then be talking about "invisible" dust or that the stones in the asphalt become polished in a way that grip is reduced.

 

I sometimes use the rear brake entering the turn and I sometimes apply it to tighten my line, but I cannot relate my brake use to the slides.

 

The typical unexpected slide tend to take place around apex, usually at a constant or minutely decreasing pace, no brakes and no or maintaining throttle. It also tend to happen when I ride fairly gently, that is with little slowing for the corner. I turn in quite rapidly by street rider standards, but we are not talking violent, bar-bending inputs by any means. Up until the slide, the bike usually felt totally normal until - as a norm - the front or both tyres gently slide out anywhere from 1 to 4 inches. Grip is regained very smoothly more often than not. A few times, noteably on the GSX600, XT600 and VT500, only the rear have slid with the front sticking. This have also happened before I get on the throttle, that the rear goes.

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Wow, I do type too much :(

 

Went for a brisk ride today alone. Hell bent on believing in my tyres and my Ascot. It went well, I will say, and I may have stumbled upon a few discoveries, all of which will be very familiar to the coaches at the very least.

 

1. Even riding "the pace" leaving a sensible margin for the unexpected isn't always enough. as I learned when finding a full corner covered with dried mud. Did OK since I was well below "the pace" pace. Lucky.

 

2. Committing to a corner seems to assist grip and control.

 

3. Riding carefully over time makes me a lousier rider. Leading my son, who's learning, and watching him cornering in my mirrors haven't aided my ability to ride properly.

 

4. Relaxing in the bars still works, but

 

5- it can be difficult if I feel my pace is a little excited, which is why

 

6. I seem to ride better when I do one corner at a time and focus on relaxing before I begin the corner process and reset after each exit.

 

7. Some of the minor rear end slides I've felt may be the chassis flexing, allowing the wheels to follow different trajectories.

 

8. I went through a long sweeper today at the same speed (as far as I can tell) as I once did with my GSX600F. The Suzuki did at that point have a floaty feel from the front and the rear was sliding a little all the way through the corner. The VT was on rails and could have gone faster, but it was fast enough for comfort.

 

QUESTION: Going around a roundabout at medium lean, just as I started to open the throttle, the bike added quite a bit of lean. Like it would if the tyres let go. Only I don't think they did. What input could I have given to cause that?

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QUESTION: Going around a roundabout at medium lean, just as I started to open the throttle, the bike added quite a bit of lean. Like it would if the tyres let go. Only I don't think they did. What input could I have given to cause that?

 

Going to quote directly from Twist II here:

"If your throttle control is standard, the only things that will change the lean angle of the bike to any great degree are a slide/catch action or steering input."

 

This is from Chapter 13 and it is well worth reading the entire section.

 

Is there any chance that you pull on the bar slightly when you roll on the throttle? Are you hanging off a lot, and if so, when you hang off all the way AND try to roll on the throttle, does it create an akward angle that can cause an unintentional steering input? (If you can, try putting your bike on a stand, hang off, and simulate rolling the throttle all the way on, and see how comfortable it is for you, some riders's wrist get bound up in right hand turns, and some have trouble reaching the throttle when hanging off on left hand turns, either of which can create an accidental steering input.)

 

Totally agree with you on "riding carefully". Have you abalyzed WHAT specifically changes in your riding when you "try to be careful", and what the effect are?

 

And yes, looking in the mirrors while riding is difficult! We do that some, as coaches, and it can take a while to get used to it. It is very easy to make a steering error while doing it. For example, looking too long in the left-side mirror while in a right hand turn can make you run wide (and vice-versa), presumably some form of "we go where we look!". :)

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Thanks again, HF :)

 

No, not hanging off at all. And after I posted I tried to think if I'd inadvertedly pulled on the bar end as I gently applied throttle. I'm not sure, but it would be strange if I did since it's not common for me and I were pretty relaxed. However, it's an option. It's a rather dusty roundabout, however, so perhaps the tyres gave a little that I didn't detect? Not sure. I still have those two options.

 

Regarding careful riding; I have tried - a lot - to analyze what happens, but I have not come up with any solid answers.My current pet theory is that the main cause is lack of focus, becoming slack. So ever so often, one is caught a little off guard, with the bike being pointed slightly wrong or a corner being a little too sharp or something appear on the road that must be dodged. And unlike when you're on it, the tendency is to fire off some SRs that again lead to me tightening up and as such sending unwanted inputs to the chassis.

 

But I also think it has to do a bit with the machine I'm riding. For instance, when I had the old KZ400 twin, I could lean well over in a corner and still look around to take in the vistas. Riding slow or fast presented no problem. And I think I lot of that came down to how quickly and intuitively the bike reacted. And since the bike never spooked me, I could ride relaxed and happy. On bikes that have slid unexpectedly, I think I'm less able to relax fully and probably also probably subconsciously expecting the tyres to slide and setting off, if not SRs, at least unwanted tensions.

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Eirik,

 

I am not bringing an answer to your problem nor trying to question your piloting skills in any way, just following a logic thought: :rolleyes:

 

Your case is very interesting because you have had similar random results from several combinations of bikes, tires and road conditions.

 

Among other things, tire grip that resists sliding forces depends on the coefficient of friction and the force that is normal to the road surface.

Centrifugal forces that induce skids depend on the speed of the bike and radius of turn.

Lean angle relocates the bike to balance those forces and can be changed with steering inputs via counter-steering.

 

If all the above is true and grip fails randomly for the same speed and turn radius, three things may be happening (in a separated or combined way):

 

1) The coefficient of friction between rubber and pavement suddenly changes only for the point at which the skid happens (roughness, sand, liquids, etc.).

 

2) The normal force gets suddenly reduced (and poorly compensated by deformation of frame, suspension and tires) for the point at which the skid happens (front-rear re-distribution of weight via throttle or brake input, road irregularities).

 

3) Additional load is added to the centrifugal force for the point at which the skid happens (steering correction, braking, acceleration).

 

For #1 there is no much you can do on the street but slowing down in turns enough to create a safety margin.

 

For #2, a painfully slow throttle input may help, as well as avoiding braking on the turn and experimenting with reducing air pressure up to a safe value that does not cause over-heating of the tires.

 

For #3, steering with the inner hand mostly (avoiding fighting of both hands and multiple little corrections during the turn).

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Hm, I often steer two-handed, so I must look into that as well. Some of the slides no doubt must stem from lack of grip, but I'm pretty sure I have issues to sort as well. I'll keep trying to focus on what happens until I crack it. Thanks for the inputs!

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You are welcome !

 

Sometimes, not even one hand is necessary, as this video shows after 0:30 :)

 

http://www.youtube.c...player_embedded

 

One more thing:

Transferring weight from one tire to the other takes time, because the CG has inertia.

Hence, the normal force on a contact patch can only grow up to the optimum value at certain rate.

Sudden accelerations and decelerations can load the rubber transversely much faster than weight transfer can load it perpendicularly.

 

As stated by a friend:

"Realize that the tire will take a great load, but it won’t take a sudden load…and so you practice this smooth loading at every moment in/on every vehicle."

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The TOTW2 book talks about CSS students reporting spooky sliding behavior and a pace that were way below track records. Keith eventually discovered it was the cause of inconsistent throttle inputs (on-off-on again, etc). A tight grip on the bars (and all the tiny unintended steering inputs that brings with it) may have also been a factor, but I'm not sure about this second part.

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  • 4 weeks later...

I have now ridden both the Z650 and the Ascot quite bit in cool conditions and roads have also often been dirty, yet I haven't experienced a single slide. So it seems pretty certain that I have inflicted my bikes with unwanted inputs, although I'm still not quite sure what. Tensing up seems the most plausible explanation.

 

Thanks to all who gave their inputs cool.gif

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I have now ridden both the Z650 and the Ascot quite bit in cool conditions and roads have also often been dirty, yet I haven't experienced a single slide. So it seems pretty certain that I have inflicted my bikes with unwanted inputs, although I'm still not quite sure what. Tensing up seems the most plausible explanation.

 

Thanks to all who gave their inputs cool.gif

 

That's great that you've seen some improvement. Congrats.

 

I'd also recommend a GoPro focused on your controls in the lower half of the frame and the road in the upper half of the frame. That would give you better data than "here is what I think I'm doing." It would let you compare what something feels like to what it looks like, as well as producing something you could post here for video feedback.

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