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Old 05-11-2013, 08:17 AM   #91
atomicalex
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Quote:
Originally Posted by David R View Post
With slow maneuvers, I apply the rear brake and the bike is more stable and I have more control.

Is this trail braking too?
David, no, not really. The primary purpose of trailbraking is to scrub speed, which, during slow speed maneouvers is not an issue. You are using brake modulation to settle the suspension, though, and that is a great skill to keep up. The suspension settling that occurs during trailbraking is a side effect, not the primary purpose.
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Old 05-11-2013, 09:06 AM   #92
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Of course, but if you are on even a moderately sporty street tire, you have WAY WAY WAY more traction available than many give credit. I've had my 675 on its front tire only at about a 30* lean, hanging off the side and everything. I wasn't running slicks or even DOT race tires, they were just diablo rosso corsas, an aggressive street tire. Granted, that was on a track so that allows some extra due to better asphalt, but I came to the conclusion years ago that most sport touring tires are far far more than you need for the street, you have to be going so bloody fast to get near the limits of traction that its near suicidal.
Two questions, understanding I have never been on a track in my life.

Lee Parks book says braking at lean requires more cornering force from the tire than the added traction from the forward weight transfer adds. I guess that is because you are also requesting more braking force as well? I posed a question to Nick Ienatsch asking about the differences between wheelies and stoppies at lean angle and he replied that a stoppie at lean angle is absolutely possible, just not an efficient technique for cornering so you don't see racers doing it. Also he noted that usually the front tire cannot sustain as much lateral traction so while it's possible it is not to the level possible on the rear.

Second question, regarding limits. Is there an appreciable difference in the stress on the tires at different velocities if the acceleration is the same? Dragging knee while on the binders at 80mph is any different from doing it at 140? Given the same lean angle and same deceleration rate.
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Old 05-11-2013, 10:01 AM   #93
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Originally Posted by hooliken View Post
Maybe one of the "experts" can weigh because I am not sure.

But I do the same thing with the rear brake. Use the clutch and rear brake often to stabilize at parking lot speeds and stop signs.
"Professionals" call this "dragging the rear brake".
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Old 05-11-2013, 10:27 AM   #94
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"Professionals" call this "dragging the rear brake".
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Old 05-12-2013, 03:55 AM   #95
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Originally Posted by hooliken View Post
Agree with it all. But of course an argument could be made that if you need to trail brake on an unfamiliar road, then you are going to fast for conditions/skill level.

The grip level on even DS tires is truly amazing now. I cannot believe how some of the DOT DS tires I have run on the SE grip compared to years past.

I am not saying that I personally do not trail brake........but not sure that it is something beginners should be focusing on until they have some seat time.
I concur.
I will say that exceeding the available traction several times has taught me a lot. Not that anyone WANTS to bin it, but you learn lots from doing so.
Lucky for me, I did most of that on a motard, which are free to crash. No damage. Oh, and in leathers too.
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Old 05-12-2013, 06:48 AM   #96
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Quote:
Originally Posted by shaddix View Post
Two questions, understanding I have never been on a track in my life.

Lee Parks book says braking at lean requires more cornering force from the tire than the added traction from the forward weight transfer adds. I guess that is because you are also requesting more braking force as well? I posed a question to Nick Ienatsch asking about the differences between wheelies and stoppies at lean angle and he replied that a stoppie at lean angle is absolutely possible, just not an efficient technique for cornering so you don't see racers doing it. Also he noted that usually the front tire cannot sustain as much lateral traction so while it's possible it is not to the level possible on the rear.
There isn't close to as much traction on the front, there is a lot less area, you basically never want to pull the rear up when you have any real amount of lean, its not what you would call an idea situation, for the rear it doesn't really matter a lot of the time coming off apex on a hairpin you have next to no weight on the front wheel anyway. A lot of the time it happens in if you jump the throttle and the slides a little bit, it will almost always pick up the front when it catches.



Quote:
Originally Posted by shaddix View Post
Second question, regarding limits. Is there an appreciable difference in the stress on the tires at different velocities if the acceleration is the same? Dragging knee while on the binders at 80mph is any different from doing it at 140? Given the same lean angle and same deceleration rate.
I can't claim that I have ever had a knee down while still on the brakes at 140, I've slide the front from trailbraking at that speed, but that was kind of an emergency, I was chasing a buddy that was using a race line vice a "trackday" or qualifying line, as he put it "You may be faster in the turn one, but you aren't beating me too it." Basically I was busy staying on his rear and missed that he didn't start to brake until he was two markers deeper than I have ever attempted that corner, so getting it hauled down from 160 or so (the rev lights are on in 6th gear there) taught me a couple lessons, 1) that I can actually pull that off 2) that I NEVER want to do that again, I was nearly sideways to apex, with the front sliding and I got everything back in line with about 5mm left on the outside of the curbing.

Great if you are in AMA, NOT FUCKING FUN on a street bike.

I don't race for a reason, I'm not willing to ride with that level of commitment, at 80 if I'm on the brakes at all with knee level lean going something is fucked up, usually by the time you start feeling with your knee you are completely off of the brakes
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Old 05-12-2013, 07:34 AM   #97
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my musings on trail braking

I frequently see (or at least say) things differently than others so I'll give it a go on trail braking.

The key thing about trail braking is that it makes the entry into the corner less of a black and white corner entry point into a range that lets you adjust the exact point where you stop braking and start turning. I find that making these adjustments give me the flexibility I need to adapt do changing conditions on the street. On a track, you are always going into the same corners again and again. This lets you pick your braking and turning points with very fine specifics. On the street, I'd argue that it's even more important for riding aggressively on the street to allow the flexibility that trail braking gives.

There's another point that's not generally discussed. The amount of aggression or how close to the edge of the traction envelope seriously impacts whether trail braking is possible. If you are riding at the back of a group of several riders you may not be running at the edge of your envelope and you can trail brake. If your bike is capable of reaching much higher corner entry speed than it can carry through the turn then you will frequently be needing to scrub off a very large amount of speed before the turn. This is best done by braking when vertical. To me this means that sometimes you need to heavily break when vertical.

Putting these two together gives me the ideal solution. Do your heavy, hard braking with the bike vertical then finish by trail braking into the corner as it makes sense. Maybe this is exactly what's meant but the point doesn't seem to be made in a way that I got it.

I learned these same lessons many years back with my 1978 toyota corolla and my 1986 corvette. I decreased my autocross times (and scared my passengers) the most when I kept on the throttle as long as I could, did maximum braking right before the turn, and then rode through the turn at the very edge of traction.

When I took the MSF BRC ten years ago to get back into motorcycle riding I heard the don't brake in turn lessons and it didn't quite make sense. I was braking in the turn in every lesson. My Tiger lets me make line adjustments, brake, add or reduce throttle, change my weight, etc. without any negative consequences. This has led me to using that flexibility whenever it makes sense.

There is one other part of the discussion that I can corroborate. My Tiger has very soft suspension. It's better now that I worked on the suspension but it's still soft compared to most bikes. The control I have and the speed I can carry through corners is hugely impacted by how loaded the suspension is. If I brake maximally with front and rear brakes right before a corner exit point and enter the turn with the suspension fully weighted to the front then I have to deal with the transfer of the suspension back to normal while I'm in the first half of the turn. I found that it's waaay more stable if I brake maximally with both brakes before the turn then back off the front brake near the beginning of the turn and trail off the rear brake until closer to the apex of the turn. For my Tiger, trail braking makes it hugely more stable through the turns and I'd be crazy not to use it both on the street.
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Old 05-12-2013, 08:10 AM   #98
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The unorthodox front suspension on the R12 GS means less geometry change with braking so the benefits of trail braking are probably less, but I still do it. My goal is to be very smooth in throttle-brake transitions. I find it hard to modulate the throttle on a snatchy and lash-prone shaft drive while using the same right hand to feather the front brake. I am trying to practice the series of transitions that goes something like:

1. Off throttle & hard onto the front brake (rear is not much of a player here)
2. Lean in and decrease brake in proportion to lean all the way up to the apex.
3. Just past the apex, all braking is done and throttle roll-on begins
4. The more upright the bike, the more throttle can be applied.

#3 is where I have the roughest transition. Need work there.

The R1200 os not going to lift the front so I can whack it pretty hard as I
approach full upright.

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Old 05-12-2013, 09:57 AM   #99
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Quote:
Originally Posted by Tripped1 View Post

Of course, but if you are on even a moderately sporty street tire, you have WAY WAY WAY more traction available than many give credit. I've had my 675 on its front tire only at about a 30* lean, hanging off the side and everything. I wasn't running slicks or even DOT race tires, they were just diablo rosso corsas, an aggressive street tire. Granted, that was on a track so that allows some extra due to better asphalt, but I came to the conclusion years ago that most sport touring tires are far far more than you need for the street, you have to be going so bloody fast to get near the limits of traction that its near suicidal.
That one is a tough call on the street. If you were on a track chances are your tire temps were getting near 200*F depending on your pace. At that temp sport tires are pretty much a round ball of glue that adheres to the track. I'm sure you can lift the rear tire while leaned over at street tire temps but it wouldn't be 30*.
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Old 05-12-2013, 10:48 AM   #100
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Quote:
Originally Posted by pizzaman383 View Post
I frequently see (or at least say) things differently than others...

When I took the MSF BRC ten years ago to get back into motorcycle riding I heard the don't brake in turn lessons and it didn't quite make sense.
I think you are right on with most of the (crazy) trailbrakers around here so far.... It's a valuable tool in the kit, so keep it clean and ready for use.

I think most instructors are a little bit freaked out by people with motorsports experience. Our threshold of risk is just different.
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Old 05-13-2013, 09:46 AM   #101
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There isn't close to as much traction on the front, there is a lot less area, you basically never want to pull the rear up when you have any real amount of lean, its not what you would call an idea situation, for the rear it doesn't really matter a lot of the time coming off apex on a hairpin you have next to no weight on the front wheel anyway. A lot of the time it happens in if you jump the throttle and the slides a little bit, it will almost always pick up the front when it catches.





I can't claim that I have ever had a knee down while still on the brakes at 140, I've slide the front from trailbraking at that speed, but that was kind of an emergency, I was chasing a buddy that was using a race line vice a "trackday" or qualifying line, as he put it "You may be faster in the turn one, but you aren't beating me too it." Basically I was busy staying on his rear and missed that he didn't start to brake until he was two markers deeper than I have ever attempted that corner, so getting it hauled down from 160 or so (the rev lights are on in 6th gear there) taught me a couple lessons, 1) that I can actually pull that off 2) that I NEVER want to do that again, I was nearly sideways to apex, with the front sliding and I got everything back in line with about 5mm left on the outside of the curbing.

Great if you are in AMA, NOT FUCKING FUN on a street bike.

I don't race for a reason, I'm not willing to ride with that level of commitment, at 80 if I'm on the brakes at all with knee level lean going something is fucked up, usually by the time you start feeling with your knee you are completely off of the brakes
Thanks for the detailed response!

Reviewing Total Control Page 16 under the heading title "Cornering" it states this:

"As you close the throttle, the engine acts as a brake (this is called compression braking), slowing the rear wheel, which causes the motorcycle to pitch forward. The front wheel must also support a larger portion of the cornering load. Unfortunately, the increase in traction from the greater pressure is less than the additional cornering load put on the tire. This results in a net loss of traction, which can cause the front tire to wash out. Put another way, the front tire's appetite becomes bigger than the amount of pizza available"

I can understand if you are using the front brake to slow, therefore the front tire is now accelerating both laterally and longitudinally, so you may in fact go outside what the tire is capable of handling. I also understand how chopping the throttle would cause the front to wash because of how quickly the load is transferred. But I do not understand how just the fact that more weight is on the tire now means that it can no longer handle the cornering load.

As you stated, even at the apex of a corner, you don't need the front tire on the ground, and that's under throttle.
With nearly maximum lateral acceleration and enough throttle to pick the front up, the rear tire is all that is needed to handle the entire weight of the bike.
However, with no front brake whatsoever, and near maximum lateral acceleration, the front tire cannot handle the entire weight of the bike?

What this line of thought leads me to believe, is that as you add total weight to a bike, it becomes more likely to understeer than to oversteer. Only because more weight means less lateral acceleration, even at zero longitudinal acceleration. So if you have a bike heavy enough, you wouldn't be able to turn it at all. This seems unlikely to me, because I know an 800lb bike can lean to 45 degrees given the proper tires...
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Old 05-13-2013, 10:13 AM   #102
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Quote:
Originally Posted by shaddix View Post
Thanks for the detailed response!
"As you close the throttle, the engine acts as a brake (this is called compression braking), slowing the rear wheel, which causes the motorcycle to pitch forward.
That is a little dated, for the last decade most of super sports have been coming stock with slipper clutches or intake strategies that reduce compression braking. Even back in the bad old days of carbs and no slippers that was the reason that you blip-throttled your downshifts, trying to bring the bike to idle from speed as you are dumping four gears and unloading the rear with the brakes makes for LOT of chadder, this is why you blip the downshifts, and when you do it right you keep the rear in line and the drama to a minimum.

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Originally Posted by shaddix View Post
The front wheel must also support a larger portion of the cornering load. Unfortunately, the increase in traction from the greater pressure is less than the additional cornering load put on the tire. This results in a net loss of traction, which can cause the front tire to wash out. Put another way, the front tire's appetite becomes bigger than the amount of pizza available"
Something of an oversimplification, there are times you want to trail break, these are usually when there is an S turn or some reason to chop the apex and stay close to the inside curb.

In a snap turn you are on the throttle as soon as you release the brake ideally, with the throttle you balance the bike on the rear wheel essentially, its larger and has a bit more play.

The other place where you really ride the crap out of the front end is multi-compound corners, where you go hard lean>shallow lean>brekes (leaned) and back to hard lean...you really REALLY ride the crap out of the front end if you are doing something like that at speed, it was one of those where I managed to pull a 70mph endo.

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Originally Posted by shaddix View Post
I can understand if you are using the front brake to slow, therefore the front tire is now accelerating both laterally and longitudinally, so you may in fact go outside what the tire is capable of handling. I also understand how chopping the throttle would cause the front to wash because of how quickly the load is transferred. But I do not understand how just the fact that more weight is on the tire now means that it can no longer handle the cornering load.
Remember these are all vector sums, and the bike isn't straight up and down, so all of that weight is balanced on a 3-4 square inch patch, and its trying to go everyway but loose.

This is where "When in doubt, throttle out" comes from, the way you save the front when you are over doing it laterally, is to HIT THE GAS, that is as true on the road, as on the track, as in the dirt, you unload the front and it stops sliding.

Quote:
Originally Posted by shaddix View Post
As you stated, even at the apex of a corner, you don't need the front tire on the ground, and that's under throttle.
With nearly maximum lateral acceleration and enough throttle to pick the front up, the rear tire is all that is needed to handle the entire weight of the bike.
Not exactly, you aren't at max lateral if can add enough throttle to pick up the front tire not even close, the rear would slide out too, in fact its a LOT easier to slide the rear than it is the front.

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However, with no front brake whatsoever, and near maximum lateral acceleration, the front tire cannot handle the entire weight of the bike?
You don't want either tire alone trying to handle a 1G of lateral acceleration, that is a pretty sure recipie from having an agricultural experience. The bike is designed to function with both tires on the pavement, in fact super sports are biased heavily to the front so that the action of the throttle balances the suspension.

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What this line of thought leads me to believe, is that as you add total weight to a bike, it becomes more likely to understeer than to oversteer. Only because more weight means less lateral acceleration, even at zero longitudinal acceleration. So if you have a bike heavy enough, you wouldn't be able to turn it at all. This seems unlikely to me, because I know an 800lb bike can lean to 45 degrees given the proper tires...
You are over thinking it.

Remember max traction is generally considered to be in the 1G range using a G of acceleration as a basis means that its a sliding scale. One G acceleration on my 675 is still its 409lbs curb weight, just like one G on a Road King is something on the order of the 850lbs that you cited There is just no assurance that that 1G is moving in the same direction as the bike.. Remember static friction is F(s)=(mu)*mass*gravity, so the variance is the surface (grossly over simplified) the value of mu is the coefficient of friction.
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Old 05-13-2013, 11:38 AM   #103
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That is a little dated, for the last decade most of super sports have been coming stock with slipper clutches or intake strategies that reduce compression braking. Even back in the bad old days of carbs and no slippers that was the reason that you blip-throttled your downshifts, trying to bring the bike to idle from speed as you are dumping four gears and unloading the rear with the brakes makes for LOT of chadder, this is why you blip the downshifts, and when you do it right you keep the rear in line and the drama to a minimum.



Something of an oversimplification, there are times you want to trail break, these are usually when there is an S turn or some reason to chop the apex and stay close to the inside curb.

In a snap turn you are on the throttle as soon as you release the brake ideally, with the throttle you balance the bike on the rear wheel essentially, its larger and has a bit more play.

The other place where you really ride the crap out of the front end is multi-compound corners, where you go hard lean>shallow lean>brekes (leaned) and back to hard lean...you really REALLY ride the crap out of the front end if you are doing something like that at speed, it was one of those where I managed to pull a 70mph endo.



Remember these are all vector sums, and the bike isn't straight up and down, so all of that weight is balanced on a 3-4 square inch patch, and its trying to go everyway but loose.

This is where "When in doubt, throttle out" comes from, the way you save the front when you are over doing it laterally, is to HIT THE GAS, that is as true on the road, as on the track, as in the dirt, you unload the front and it stops sliding.



Not exactly, you aren't at max lateral if can add enough throttle to pick up the front tire not even close, the rear would slide out too, in fact its a LOT easier to slide the rear than it is the front.



You don't want either tire alone trying to handle a 1G of lateral acceleration, that is a pretty sure recipie from having an agricultural experience. The bike is designed to function with both tires on the pavement, in fact super sports are biased heavily to the front so that the action of the throttle balances the suspension.



You are over thinking it.

Remember max traction is generally considered to be in the 1G range using a G of acceleration as a basis means that its a sliding scale. One G acceleration on my 675 is still its 409lbs curb weight, just like one G on a Road King is something on the order of the 850lbs that you cited There is just no assurance that that 1G is moving in the same direction as the bike.. Remember static friction is F(s)=(mu)*mass*gravity, so the variance is the surface (grossly over simplified) the value of mu is the coefficient of friction.
A practical answer to a theoretical question.

Your statement about it being easier to slide the rear than the front was my assumption previously, and it makes sense since most bikes are designed to oversteer, that makes it a bit counter-intuitive when thinking about you can hold a greater lean angle with the front off the ground than the rear off the ground, but of course the design of the bike plays into the reasons for that as well.

The gist of my confusion stems from your last paragraph, as it seems to be at odds with Mr Park's statement that simply adding weight significantly decreases the cornering force possible. I find myself thinking that this is not what Mr. Parks is really intending to say. Maybe he is trying to say that if the tire is loaded suddenly, then it requires more cornering force than the tire can provide, as it takes a second for the contact patch to flatten out and the additional weight to add the additional traction, or maybe he is trying to say that the longitudinal acceleration when added to a large cornering load is more than the tire can provide. How it is written however, seems to preclude both of those alternate explanations… Still confused
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Old 05-13-2013, 12:34 PM   #104
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Shad--correct me if I'm wrong--but you seem to be implying that adding weight adds traction but weight adds mass. Traction is still fixed.

(and if it isn't...well it should be dammit!)
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Old 05-13-2013, 12:39 PM   #105
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Quote:
Originally Posted by shaddix View Post
A practical answer to a theoretical question.

Your statement about it being easier to slide the rear than the front was my assumption previously, and it makes sense since most bikes are designed to oversteer, that makes it a bit counter-intuitive when thinking about you can hold a greater lean angle with the front off the ground than the rear off the ground, but of course the design of the bike plays into the reasons for that as well.
Indeed, many things about riding motorcycles are counter-intuitive.


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Originally Posted by shaddix View Post
The gist of my confusion stems from your last paragraph, as it seems to be at odds with Mr Park's statement that simply adding weight significantly decreases the cornering force possible. I find myself thinking that this is not what Mr. Parks is really intending to say. Maybe he is trying to say that if the tire is loaded suddenly, then it requires more cornering force than the tire can provide, as it takes a second for the contact patch to flatten out and the additional weight to add the additional traction, or maybe he is trying to say that the longitudinal acceleration when added to a large cornering load is more than the tire can provide. How it is written however, seems to preclude both of those alternate explanations… Still confused
That is simple physics, if you have 1G of acceleration(in pounds/Newtons etc) for available traction, the lighter the vehicle overall the faster you are going when you reach that 1G lateral, or the faster you can make the transition.

So the statement is more or less correct in a practical fashion, a heavier vehicle can't turn as fast as a lighter one given the same acceleration. The wording leaves something to be desired.

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Shad--correct me if I'm wrong--but you seem to be implying that adding weight adds traction but weight adds mass. Traction is still fixed.

(and if it isn't...well it should be dammit!)
Weight adds friction, which is also independent of surface area. So says Coulomb, anyway (I know there are a pile of holes in those laws) which is likely why we use the term traction for vehicles and not friction.

Traction is finite and variable, the centripetal forces are easily measured.

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That one is a tough call on the street. If you were on a track chances are your tire temps were getting near 200*F depending on your pace. At that temp sport tires are pretty much a round ball of glue that adheres to the track. I'm sure you can lift the rear tire while leaned over at street tire temps but it wouldn't be 30*.
Not arguing there, its not something that I would want to try really. In fact I didn't mean to that time, I was lining up a guy to pass, and didn't know there was another rider coming around, so I lost my intended line AND my out at the same time to an incoming decreasing radius, it was get it slowed down WAY sooner than I intended to or be so far inside that I would have no chance of getting around the curve
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