Buttonwillow, 13CW Riverside

[fortyonethirty]

I crashed during practice for the AFM round 2. I got knocked out for a couple minutes, so the whole thing is a bit fuzzy. I have some ideas on what happened, but I wouldn't mind a little BARF wisdom.

What do you guys think?


youtu.be//8d_fksc3Uaw

 

[stangmx13]

very hard to tell.

I wonder if u chattered the front end. for about 1sec before u actually crash, theres a fluttering noise and some extra shaking on the video. also, the black line that goes by looks to be rubber not a seam. its a broken line, implying the tire was bouncing. do u know what chatter feels like?

did u brake at all? if I get in really hot into that corner, I make sure to brake a little bit to load the front end and tighten my turning radius.

 

[Slow Goat]

Looks like the front tire left a skid mark as it was going down.

Hope you’re okay.

 

[afm199]

very hard to tell.

I wonder if u chattered the front end. for about 1sec before u actually crash, theres a fluttering noise and some extra shaking on the video. also, the black line that goes by looks to be rubber not a seam. its a broken line, implying the tire was bouncing. do u know what chatter feels like?

did u brake at all? if I get in really hot into that corner, I make sure to brake a little bit to load the front end and tighten my turning radius.

I'm with this. I just had the same front chatter yesterday at Sears Point, woke me right up.

 

[tzrider]

You were on the gas then closed the throttle about a second before crashing. From the available info, it's likely you overloaded the front.

It may be that simple, though could have been exacerbated by having had pressure on the bars. We can't tell about that from the video; only you might know whether or not that was a factor. Being off the throttle, it's more likely than not.

 

[viva_brasil]

what would cause the chatter in this case?

Isn't chatter usually caused by bottoming out the forks - so corner speed + closing throttle + potentially weight on the bars = bottom out and chatter?

 

[stangmx13]

Chances the OP bottomed the front end into Riverside are slim to none. And, bottoming out doesn’t necessarily cause chatter. Chatter is an uncontrolled oscillation where some disturbance creates a feedback loop that leads to all that. Well it can be that. It’s so complicated that it’s hard to nail down w specifics. Nearly anything with a bikes setup can be the cause and fix for chatter issues: springrate, tire pressure, ride height, etc.

 

[Smash Allen]

could a bad tire cause chatter?

 

[tzrider]

It could, though if this rider had several laps on the tire already without feeling chatter, that's probably not it, unless something physically failed.

 

[BabyRider]

it could have been the tire was starting to blister?

 

[tzrider]

Given that we can observe riding errors, let’s use Occam’s Razor.

 

[viva_brasil]

I understood "chatter" was the tire slipping slightly and re-gripping in fast succession (i.e., the fork is unable to absorb / control the forces on the tire, including a bottomed out fork or too much rebound potentially, etc.)?

Sounds like that's not right, so just trying to understand what it is... "Uncontrolled oscillation" of what?

Chances the OP bottomed the front end into Riverside are slim to none. And, bottoming out doesn’t necessarily cause chatter. Chatter is an uncontrolled oscillation where some disturbance creates a feedback loop that leads to all that. Well it can be that. It’s so complicated that it’s hard to nail down w specifics. Nearly anything with a bikes setup can be the cause and fix for chatter issues: springrate, tire pressure, ride height, etc.

 

[stangmx13]

Given that we can observe riding errors, let’s use Occam’s Razor.

What riding errors do u see?

Closing the throttle there is correct. If anything, it was closed too soon. Perhaps it was closed too fast.

 

[stangmx13]

I understood "chatter" was the tire slipping slightly and re-gripping in fast succession (i.e., the fork is unable to absorb / control the forces on the tire, including a bottomed out fork or too much rebound potentially, etc.)?

Sounds like that's not right, so just trying to understand what it is... "Uncontrolled oscillation" of what?

The forks moving up and down in very fast succession is the chatter part, is the uncontrolled oscillation. But of course u can have chatter at the rear too. Uncontrolled == unstable == does not decrease in magnitude over time. Oscillation == cyclic movement. A tire slipping and regripping could cause chatter, or chatter can cause that.

 

[Smash Allen]

i was pitted with ian in the garage

he was on bridgestones, we (not ian, he was loopy all day after that) were thinking at the time it was a bad front tire

if not the tire, i would be interested to find out the condition of the suspension / suspension fluid

it reminds me of a tank slapper, but going 'up and down' instead of 'side to side'

 

[tzrider]

What riding errors do u see?

Closing the throttle there is correct. If anything, it was closed too soon. Perhaps it was closed too fast.

Admittedly, it's been a number of years since I was at BW, but I'm not sure why a rider would be on the gas and then suddenly chop it there. To me, that's an error.

 

[stangmx13]

If your drive to Riverside is strong, u gotta slow down at some time to make it through that corner. A 600 can just roll off until you get near 1:51-52. A fast 1000 needs to brake for sure. A racer should of course be WOT through the kink before Riverside. To go really fast, u need to turn in a little while WOT too.

But ya, “suddenly” may always be a mistake cuz it asks for grip without creating the grip by loading the front smoothly. Good engine braking control can help mitigate that. Who knows if that was the cause.

 

[jaybocc2]

i was pitted with ian in the garage

he was on bridgestones, we (not ian, he was loopy all day after that) were thinking at the time it was a bad front tire

if not the tire, i would be interested to find out the condition of the suspension / suspension fluid

it reminds me of a tank slapper, but going 'up and down' instead of 'side to side'

A couple of my friends have switched between pirelli and 'stones and they frequently complain about chatter with the 'stones.

They don't really adjust their suspension for the stones, and i think they're a stiffer tire causing those issues for them. They have no chatter with the pirelli.

I have other friends going very fast with little issue on stones aswell though so i guess what i'm saying, has he always run stones or was it a recent change?

 

[fortyonethirty]

So, as far as I can tell, the main cause of this crash was my error in going in too fast.

I remember that day, this was the first day of a new AFM practice group, I had previously been in 4 and this day they combined 4 and 5. So when Andrew Lee went by me like I missed shift, I thought, "Crap, I'm so slow." I felt pressure, way more that I should have.

I had also made a fairly large adjustment in the front tire pressure, and it seemed to help a lot. So much so that I was really having fun pushing the front to it's new limit. Riverside being so long, it gives you a lot of time to sneak up on the limit, and I was enjoying the new feedback. The tires at this point were pretty worn, i was planning to get a new set later that day.

My forks at this point were about a year old from the last rebuild, and I could notice they were not as good as they had been previously.

But, this was not my first practice session, nor the first lap of the session. I knew the condition of my equipment. I think was just riding over my head, and out of my regular experience, this was only my fifth AFM race after all.

So, mid corner, I'm already near the limit of the front, but I know that near the exit it tightens up a bit and it gets bumpy, so I roll off to try to slow down a bit, and the front gave.

 

[stangmx13]

So, as far as I can tell, the main cause of this crash was my error in going in too fast.

I remember that day, this was the first day of a new AFM practice group, I had previously been in 4 and this day they combined 4 and 5. So when Andrew Lee went by me like I missed shift, I thought, "Crap, I'm so slow." I felt pressure, way more that I should have.

I had also made a fairly large adjustment in the front tire pressure, and it seemed to help a lot. So much so that I was really having fun pushing the front to it's new limit. Riverside being so long, it gives you a lot of time to sneak up on the limit, and I was enjoying the new feedback. The tires at this point were pretty worn, i was planning to get a new set later that day.

My forks at this point were about a year old from the last rebuild, and I could notice they were not as good as they had been previously.

But, this was not my first practice session, nor the first lap of the session. I knew the condition of my equipment. I think was just riding over my head, and out of my regular experience, this was only my fifth AFM race after all.

So, mid corner, I'm already near the limit of the front, but I know that near the exit it tightens up a bit and it gets bumpy, so I roll off to try to slow down a bit, and the front gave.

how can that be if Andrew Lee went in tons faster? extra speed might have been the immediate cause, but reducing it is not the solution since we are talking about racing. unless u are at lap-record pace, theres always room to go faster with the proper skills and equipment.

1yr on a set of forks won't make them perform noticeably different, esp if you have a set of aftermarket carts. they keep the oil really clean. and 1yr isnt enough time to make the oil break down or anything in a set of forks.

going up in front tire pressure can be a good way to reduce chatter. it also can help the bike turn better, esp when hard on the brakes. the drawback to this is that slow experts and novices might have a hard time getting the front tire hot enough w/ a higher pressure. but u didnt say u went up in pressure.

its possible that your front tire was too worn to hold that higher pace, but I doubt it. it goes without saying that someone could have gone faster on your front tire. how many sessions/days did it have on it?