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Tilford on Sagan
Last Post 09/13/2013 05:22 PM by Elle S.. 27 Replies.
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JS

Posts:61

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09/10/2013 10:13 PM
Posted By Elle S. on 09/10/2013 06:32 PM
  (Sagan is, despite his immense natural athletic prowess, not using natural ability here; he's using a learned skill.)

Nope, not even close. Your logic suggests that anybody can "learn" to do what he did and that is simply not true.
Oldfart

Posts:484

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09/10/2013 11:55 PM
Yeah not everyone can learn. But I did. Good point L about motorbikes being far heavier than the rider. That is certainly way different. I think leaning the bike more than the body allows the bike to just turn more quickly with less steering whereas a more upright bike needs more steering input to turn at the same radius. Sometimes on slick north shore roots and baby heads at slow speeds one does try and keep the bike more upright otherwise you go down. But that's different. I read somewhere that to turn a bike tighter mid turn, like to avoid something to push down on the inside grip. That leans the bike more and also moves your body to the outside. Some riders recommend for off road to lean the bike, not the body and push down on the outside grip straight down to push the tire into the ground. I'm not sure I agree with pushing down on the outside grip actually pushes the bike straight down but I do think it puts your body in a better position. Been thinking about this quite a bit this summer after reading some tips on off road turning. Thinking a bit more, you still have the same 156 pounds of bike and rider (in my case.on a good day) stuck the ground on the same contact patches trying to hold the same forces. Same traction requirement no? That's why the rider with the not so leaned over bike over steers and front wheel washes out.
durielk

Posts:41

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09/10/2013 11:57 PM
I think Sagan is great.
He can corner, what he did on the last turn was take the apex away from the lead rider on the outside. In racing you should protect the inside otherwise Sagan dives in, turns harder and is gone. Once the leader lost control of the inside (& the apex), he had to check up and change his line to way out wide. But that is racing! It is going to be hard to beat him, put it in the books for Sagan.
CarbonGecko

Posts:39

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09/11/2013 07:57 AM
L7 I think you need to explain yourself to the physics challenged like myself.

In my thinking Sagan's corner required MORE traction. He went around the corner faster in a shorter arc and generated more centrifugal force. (Centrifugal force isn't really an independent force, it is the inertia of bike and rider that wants to continue to go in a straight line). That inertia had to be compensated by his tires traction or the tires would have slid out.

It would seem to me that what Sagan is doing by leaning (angulating) the way he does is more effectively maintain traction. It allows him to maximize the diagonal vector that loads his tires more and generates more traction. That allows him to corner faster. Just like skiers angulate to maximize the effectiveness of their edge. Two skiers trying the same arc at the same speed; if one can cause their edge to grip but the other can't then one generates enough traction to make the turn, the other has insufficient traction and slides out.

The riders who lean further without angulating start to have less of a diagonal vector and more of a horizontal vector. That reduces their ability to load their tires, it decreases their traction, and they have to slow down or take a longer arc. Because they have less traction, they need to decrease their inertia or the amount of traction they are generating will be overcome and their tires will slide out.

I guess what I am asking is that if Sagan is cornering sharper, at higher speed, and generating more forces... how can he require less traction to make the turn?
Keith Richards

Posts:740

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09/11/2013 09:43 AM
Posted By jeff sanford on 09/10/2013 10:13 PM
Posted By Elle S. on 09/10/2013 06:32 PM
  (Sagan is, despite his immense natural athletic prowess, not using natural ability here; he's using a learned skill.)

Nope, not even close. Your logic suggests that anybody can "learn" to do what he did and that is simply not true.


I somewhat disagree. Anyone can be taught a technique, but not everyone will "get it". Can anyone learn the principals to the cornering technique that Sagan is using and become a better rider for it? No question the answer is yes.

Will they be able to do what he did in a race situation? No...well, a few might "get it" and be able to. But that leads back to what I said up thread, who is teaching cornering technique? The advice most people get is "hold your line".
----- It is his word versus ours. We like our word. We like where we stand and we like our credibility."--Lance Armstrong.
durielk

Posts:41

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09/11/2013 10:01 AM
What Sagan did was go around a corner more like a motocross rider, who is standing on his pegs which allows the bike to be controlled and angled separately from the rider. It allows greater bike lean & quicker changes in direction, and quicker adjustments to the turn, and the bike is riding more on the side of the tire.
Most riders typically go with the standard butt on the seat turn, where one leans mostly with the bike or leans the body a little more than the bike, like MotoGP racers. They do it to keep the tire patch bigger with the ground as the tires profile has a flatter appearance (on the side of the tire after a certain angle, there is very little patch on the ground) & they are anticipating hitting the throttle ASAP. But changes in the corner or direction are more difficult, they set up for a corner & they are locked in within a narrower arc of control.
If you go around a corner, the tires load up the same if the arc of the corner is the same, whether the tire is more vertical or horizontal, the loading is similar. The patch contact with the ground is dependant on the tire profile. Once the maximum load is reached, they all are going to slip or step out.
Orange Crush

Posts:1212

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09/11/2013 10:41 AM
Its like the kids' track and field coach said, anyone can learn a trick/skill but if they can be taught to "get it" at a young age (< 10 yrs give or take), they can operate several steps above those that get taught the skill at a later age. Sagan is one of those rare occasions where ability, interest and drive lined up at a very young age.

My friend's oldest kid at age 10 is showing some amazing bike handling and snowboarding athetism. I am sure that if he applied himself he could give Sagan a run for his money in terms of bike tricks by the time he reaches that age. But so far the stars do not align in that he's not really interested in competitive sport.
C2K_Rider

Posts:171

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09/11/2013 12:40 PM
Seems like he did what I do on descent curves - actively push the inside bar towards the outside of the turn. You can see he keeps his left arm straight and right is flexible as he dives to the left. When I do it, it feels like the bike is pulled into the curve without losing speed. Only a couple other riders in the front are doing that, the rest have both arms bent, which means they are just leaning. I just wonder about it because a descent curve has a definite radius and cant, while a flat street does not. The technique might be different.
jmdirt

Posts:708

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09/11/2013 08:56 PM
While I am far from a physics expert, when certain things like centripetal force and coefficient of friction are absent, the analysis is incomplete.

Food for thought: why does banking or a berm aid cornering speed?

Yes, you can "teach" people to corner like that but only about 2% will actually be able to do it.
ElleSeven

Posts:48

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09/12/2013 05:19 PM
jmdirt, I suppose we could get into the pure physics but I think we should probably do that off-line. It would involve some pretty extensive unit-vector calculus and whatnot, and I can't see a proper discussion coming off in less than fifteen pages, which wouldn't be tolerated as a forum entry!

Where does the 2% figure come from? When I was yakking with my "guru" this morning, he said that he'd never yet encountered anyone, no matter how ill-adept in a native sense, who couldn't learn to do this pretty well. By "pretty well" he would not mean, "as well as a pro who uses the technique." He would mean, "faster than what they did previously, and, more critically, way, way, way safer."

jmdirt

Posts:708

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09/12/2013 10:11 PM
When I said that only 2% will actually be able to do it like that, I was referring to doing it as well as a pro (we were talking about Sagan weren't we?). I was being generous with 2%.
longslowdistance

Posts:697

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09/13/2013 08:44 AM
As far as motorcycles go, the optimal is angle the bike under the rider off road ( slippery surface) but keep aligned on asphalt. At least that is what my teachers say.
ElleSeven

Posts:48

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09/13/2013 05:22 PM
Maybe the best way to address these questions is the old-fashioned empirical way: go out and try it. Change direction not by steering (in the conventional sense of aiming the handlebar towards the exit) but by pushing down and forward on the inside drop (exactly as CK describes). All the other elements -- the exaggerated bike lean and angulation, the COM shift, and so on -- sort of take care of themselves. Counter-steer/Angulation is so easy, the main danger is that you'll remove a hand from the bar to slap your head.
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