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What Causes This?


aslcbr600
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I am watching a video of an expert level CCS race and I am seeing a lot of vibration coming from the front end and then at 3:43 it looks like his front tire slid and then at 6:35 he gets that heavy vibration again and then he low sides. Is this due to an improper front suspension setup? I have never seen so much vibration from the front end like that!

 

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Suspension certainly could be a problem here - lack of rebound damping and springs/compression too stiff - but there are things the rider could have done to improve the situation. It appears that he is really asking a lot of the front tire; getting on the throttle sooner would shift some weight rearward, turning the bike quicker would have allowed him to carry less lean angle, and relaxed arms would make a big difference on the load on the front tire.

 

It seemed like the chatter was worst when he was leaned over, crossing a bumpy part of the track, and off the gas. It also appeared he went wide on his turn exits compared to the other bikes, which could be because of stiff arms and also made worse by lack of rebound damping.

 

My husband watched this with me and also suggested possibly low tire pressure, with the tire getting overheated making the problem progressively worse. (But the FIRST thing he noticed was that the guy is really "on his front tire a lot")

 

Here's a question : when he crashed, was he ON or OFF the gas? Could better throttle control have prevented that crash?

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He was off the gas when he crashed, I figured when I saw his front tire slide more then once their had to be something wrong mechanically or physically he was doing. Low tire pressure also crossed my mind but that was just a random guess not really anything I would have absolute confidence in saying was the issue.

 

I didn't think about being too tight on the bars, when I can't see the persons body positioning I just subconsciously assume that they have proper body positioning. He would have to have quite the death grip to give off that much chatter right? I know with more speed everything is amplified but that still seems like a lot....would you say it's more mechanical or rider error?

 

Better throttle control could have for sure made his race much smoother, it seemed like he waited until the very last second to get back to the gas. Also I noticed when he was going through the chicane he didn't neutralize the throttle he rolled off the throttle.

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god that wasn't pretty was it. Hotfoots covered a lot of what's going on above, definitely rebound damping needs improving a lot, but it could also be the camera is mounted somwhere which is exagerating the motion. Unquestionably when he crashed though, the chatter was worse and could be improved by technique.

 

Bullet

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So it was pretty much a mixture of both rider and mechanical errors. I am still learning to better understand suspension, would this mean he needed go down in rebound? Too much rebound would increase chatter I would presume?

 

 

It's hard to tell of what the rider was actually doing on the bike with bar input, but you can tell what he's doing with the gas, so as Hotfoot said, what did you hear?

 

With rebound, that looked to me like not enough rebound damping. The rebound damping controls the return of the compressed spring. if it's too much it keeps the forks/shock too deep in it's stroke, gradually winding down the bike lower and lower (at it's worst). With too little damping as we have here, you get the spring just ping back quickly and you can get chatter. it effectively can induce this resonance to the bike (though tyres can do this a bit too).

 

 

A spring in it's natural state as you'll probably be aware, will contract and expand and bounces either end of it's travel, gradually reducing the energy put into it. The dampers job is to control the rate of this action, you ideally want just enough to control the spring, but not too much. It can also be further confused by low and high speed damping, which many shocks have, (i.e. small little shocks or big ones).

 

 

That help?

 

 

 

Bullet

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So it was pretty much a mixture of both rider and mechanical errors. I am still learning to better understand suspension, would this mean he needed go down in rebound? Too much rebound would increase chatter I would presume?

 

 

It's hard to tell of what the rider was actually doing on the bike with bar input, but you can tell what he's doing with the gas, so as Hotfoot said, what did you hear?

 

With rebound, that looked to me like not enough rebound damping. The rebound damping controls the return of the compressed spring. if it's too much it keeps the forks/shock too deep in it's stroke, gradually winding down the bike lower and lower (at it's worst). With too little damping as we have here, you get the spring just ping back quickly and you can get chatter. it effectively can induce this resonance to the bike (though tyres can do this a bit too).

 

 

A spring in it's natural state as you'll probably be aware, will contract and expand and bounces either end of it's travel, gradually reducing the energy put into it. The dampers job is to control the rate of this action, you ideally want just enough to control the spring, but not too much. It can also be further confused by low and high speed damping, which many shocks have, (i.e. small little shocks or big ones).

 

 

That help?

 

 

 

Bullet

 

 

 

 

Ah gotcha! I was watching a youtube video of a race engineer for Triumph bikes in the UK and he was going over suspension stuff and the difference in the adjustments between high speed and low speed settings. I also have Keith Codes guide to understanding your suspension in Andy Ibbott's book just haven't gotten to that part yet.

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I didn't think about being too tight on the bars, when I can't see the persons body positioning I just subconsciously assume that they have proper body positioning. He would have to have quite the death grip to give off that much chatter right? I know with more speed everything is amplified but that still seems like a lot....would you say it's more mechanical or rider error?

 

 

Did you notice that the chatter got progressively worse as the race went on? And that the chatter was inconsistent, sometimes really bad and sometimes mild - even on the exact same parts of the track?

 

What "suspension component" is most likely to be the cause of inconsistency in the bike's handling? :)

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I didn't think about being too tight on the bars, when I can't see the persons body positioning I just subconsciously assume that they have proper body positioning. He would have to have quite the death grip to give off that much chatter right? I know with more speed everything is amplified but that still seems like a lot....would you say it's more mechanical or rider error?

 

 

Did you notice that the chatter got progressively worse as the race went on? And that the chatter was inconsistent, sometimes really bad and sometimes mild - even on the exact same parts of the track?

 

What "suspension component" is most likely to be the cause of inconsistency in the bike's handling? :)

 

 

 

In fact I did notice it wasn't consistent but I thought maybe it had something to do with variance in speed, track pavement or lean angle. I didn't notice they were different on the same parts of the track though so that part I did miss!

 

If were talking suspension only I would have to venture the rear shock because the rear tire is more likely to slide or slip causing the rear swingarm to raise. If by quotation you actually mean throttle control and proper manipulation of the throttle would be the most likely cause.

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I didn't think about being too tight on the bars, when I can't see the persons body positioning I just subconsciously assume that they have proper body positioning. He would have to have quite the death grip to give off that much chatter right? I know with more speed everything is amplified but that still seems like a lot....would you say it's more mechanical or rider error?

 

 

Did you notice that the chatter got progressively worse as the race went on? And that the chatter was inconsistent, sometimes really bad and sometimes mild - even on the exact same parts of the track?

 

What "suspension component" is most likely to be the cause of inconsistency in the bike's handling? :)

 

 

 

In fact I did notice it wasn't consistent but I thought maybe it had something to do with variance in speed, track pavement or lean angle. I didn't notice they were different on the same parts of the track though so that part I did miss!

 

If were talking suspension only I would have to venture the rear shock because the rear tire is more likely to slide or slip causing the rear swingarm to raise. If by quotation you actually mean throttle control and proper manipulation of the throttle would be the most likely cause.

 

 

The most likely cause of inconsistency in the bike's handling is something the rider is doing. Actual suspension parts don't change from lap to lap, but rider behavior can change at any moment! You can see the variations in throttle control on the video, as you mention above, and it is also highly likely that the rider gets progressively more fatigued throughout the race and begins to hang onto the bars to support himself, and/or as Eirik pointed out, stiffens up due to anxiety.

 

It is possible that the rider is pushing himself beyond his comfort zone and firing off SRs, causing a variety of errors - hanging on the brake too long, slow turn-in, late throttle action, etc., and all the scary feedback from the front end was probably creating some tension, too!

 

You asked how stiff arms can cause chatter: see Chapter 8 in Twist of the Wrist II for a detailed explanantion with good illustrations. In short, the handlebars need to move to absorb irregularities in the pavement; if the rider is stiff and prevents that movement, the tire can be forced to slide or skip across those bumps. Additionally those stiff arms will transmit that chattering and shaking to the rider and the rest of the bike, which can cause the GoPro to rattle around and screw up the video. :)

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I didn't think about being too tight on the bars, when I can't see the persons body positioning I just subconsciously assume that they have proper body positioning. He would have to have quite the death grip to give off that much chatter right? I know with more speed everything is amplified but that still seems like a lot....would you say it's more mechanical or rider error?

 

 

Did you notice that the chatter got progressively worse as the race went on? And that the chatter was inconsistent, sometimes really bad and sometimes mild - even on the exact same parts of the track?

 

What "suspension component" is most likely to be the cause of inconsistency in the bike's handling? :)

 

Im guessing the oil in the forks/shocks is getting overheated due to too much extra input...

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  • 2 weeks later...

You answer disguised as a question hits the nail on the head here. That is a very bumpy, fast section at Jennings, and one of the most important corners on the track. This turn (13), requires that you settle the bike early to set yourself up to get out of 14 and launch yourself down the front straight. Why does he feel the need to trailbrake here??? Turn 8 is another area where you see a lot of lowsides because it is slightly off camber and people rush up and carry large amounts of brake into the corner. Result; lowside... This is more of a rider issue than a setup issue.

 

Matt

Suspension certainly could be a problem here - lack of rebound damping and springs/compression too stiff - but there are things the rider could have done to improve the situation. It appears that he is really asking a lot of the front tire; getting on the throttle sooner would shift some weight rearward, turning the bike quicker would have allowed him to carry less lean angle, and relaxed arms would make a big difference on the load on the front tire.

 

It seemed like the chatter was worst when he was leaned over, crossing a bumpy part of the track, and off the gas. It also appeared he went wide on his turn exits compared to the other bikes, which could be because of stiff arms and also made worse by lack of rebound damping.

 

My husband watched this with me and also suggested possibly low tire pressure, with the tire getting overheated making the problem progressively worse. (But the FIRST thing he noticed was that the guy is really "on his front tire a lot")

 

Here's a question : when he crashed, was he ON or OFF the gas? Could better throttle control have prevented that crash?

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My thoughts on the video are that it is rider error.The camera might produce this vibration effect and not the suspension - tires.I think that he fell down because he had completely closed throttle at that point of the track.I never been at that track so I do not know how it feels but from the beginning of the video I was looking where the throttle will be closed to long.

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This is all rider. I'm one of the worst with suspension, as I have a 7 year old bike with stock suspension (fluid and all) that isn't set up properly, and I'm 220 lb. The first one looks/sounds like it happens as soon as he gets back on the throttle, so I'd venture to guess it's a rear slide. The second is probably a trail brake thing as he's just starting to drift out when he goes down, and unless you're braking, it's pretty hard to get the front to wash if you're just turning the bike, unless there's something on the track.

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