A Lesson Learned - Chatter Under Braking

[YellowDuck]

So, just as a conversation starter, here's a story from my first season of track riding last year...maybe will help another relative noob with the same problem....

 

I was starting to go a bit faster, but ran into a consistent problem in the hardest braking zone, right at the end of the longest straight. I would get this fairly violent chatter through the bars under hard braking, and so would have to wait a long time for the bike to settle down before I could turn in. Completely sapped my confidence in the brakes and prevented me from making any progress at all.

 

Zip tie on the forks said I still had plenty of travel (at least an inch). Tried reducing rebound damping to prevent packing, adding preload (not sensible, given what the zip tie said), etc. Nothing worked. Asked the tire guy what he thought - he suggested reducing front tire pressues (when you have a hammer, everything looks like a nail...). No dice. Very depressed, can't fix it. My bike sucks, can't find the setup.

 

Since there were aftermarket cartridges in the forks and I knew that when I installed the cartridges they extended the forks a bit, I convinced myself that maybe they were internally limited, or maybe the oil height was too high. Phoned Traxxion Dynamics - they asked me if I was *sure* that it was front end chatter, and not the rear skipping. "Of course I'm sure - I feel it through the bars". No help there. That week I took the forks all apart, took lots of measurements - not internally limited mechanically for sure. Lowered the oil height a skitch. (1 skitch = 12 mm).

 

Next track day - exactly the same. Again very depressed. Decided to humour the guys at TD and try staying 100% off the rear brake, instead of dragging it a bit as was my habit.....

 

Problem solved. 100% totally, completely solved. Rode the rest of the day in complete bliss and dropped several seconds. It was the rear end hopping afterall. Who knew it could feel like that though the bars?

 

Lessons learned:

 

1. I am an idiot.

 

2. Stay off the rear brake under hard braking.

 

3. I can't always trust my own impressions to figure out what the bike is doing. Be open to possibilities, especially those that are easy to test, even if they seem unlikely.

 

4. When something isn't right, don't suspect the hardware first - it's probably me.

[Kevin Kane]

I was starting to go a bit faster, but ran into a consistent problem in the hardest braking zone, right at the end of the longest straight. I would get this fairly violent chatter through the bars under hard braking, and so would have to wait a long time for the bike to settle down before I could turn in. Completely sapped my confidence in the brakes and prevented me from making any progress at all.

Yellow Duck;

 

I had the exact same problem at the same point in my track riding experience and the same reaction to it. For me, I swapping out the heavier fork springs installed by the previous owner and that solved my problem completely. I continued to use the rear brake but the front fork chatter was gone. I also ride a Duc so I was surprised by how your solved your problem.

 

Rainman

[warregl]

...

 

Lessons learned:

 

1. I am an idiot.

 

2. Stay off the rear brake under hard braking.

 

3. I can't always trust my own impressions to figure out what the bike is doing. Be open to possibilities, especially those that are easy to test, even if they seem unlikely.

 

4. When something isn't right, don't suspect the hardware first - it's probably me.

...

 

 

I find I am repeatedly learning lesson 1, but I am open to it these days so it comes eaiser (and with less pain in the end). Many years ago I was having and "issue" with my bike (I honestly can't remember what it was) when I first heard the advice that I am sure we have all heard one time or another - "Your problem is with the nut that connects the handlebars to the saddle..."

 

But then again, that's why we are all here right?

 

Great post Duck (and thanks for the definition of a skitch - that one has bothered me for years).

[mblaster]

I find myself an expert in category 1 as well. Hopefully CSS will lower my status in that category!

[mugget]

Ahhh, yes... trying to get "the setup". Glad you ended up finding that it was an easy fix! I think it's always best to try and change something in our riding to see if that helps (you can do it straight away and it won't cost you $$$), but sometimes it really is a setup problem, like Rainman mentioned on his bike, or like after I got my suspension tuned and ended up with 40mm rear sag and 15mm front sag... (hhmmm... sounds more like I had my suspension de-tuned!)

 

It can be a bit tricky when something like your chatter starts to affect your riding, because the way I see it there's only two ways that you will be able to recognize the cause (or solution):

1. experience - through having the problem before and knowing how it was fixed

2. rider training - knowing how to correctly operate a motorcycle avoids all kinds of issues that can be magnified or cause by in-proper inputs.

To me that makes a fairly good argument for rider training, skip all the bad experiences and just get right to the fun!

[khp]

It can be a bit tricky when something like your chatter starts to affect your riding, because the way I see it there's only two ways that you will be able to recognize the cause (or solution):

1. experience - through having the problem before and knowing how it was fixed

2. rider training - knowing how to correctly operate a motorcycle avoids all kinds of issues that can be magnified or cause by in-proper inputs.

To me that makes a fairly good argument for rider training, skip all the bad experiences and just get right to the fun!

Agree on the two. Since rider training should be less painful that experience (and hopefully less costly over time), I prefer #2 option over #1.

 

That said, I have to say that I don't feel that my suspension on the racebike is a problem at all (the roadbike is a separate issue), but I'd love to learn more about suspension and tyre wear from a guy like Dave Moss. We don't have freelance guys like him at the trackdays I've attended in Europe. And flying Dave to Europe (or the bike to the US) would be ... a little expensive.