matt17
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Posts posted by matt17
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The time difference for a small increment in speed is independent of the initial speed.
Matt, I should mention that I made a typing error in my example above, having stated the dimensions for the second turn were the same as the first. They are not and are corrected in that post.
I followed your math, but don't see that it supports your quote above, as stated. Taken literally, we could simplify the example to remove the turn and say we're riding the same 1,000 feet of straight road. If we make a pair of passes, one at 50 and the other at 51 mph, the difference in the time it takes to cover the 1,000 feet is .27 seconds. If we make a pair of passes at 100 and 101 mph, the elapsed time difference is .07 seconds.
For your statement to be true, the distance covered must be proportionally larger. Your math allows for this, but the opening statement doesn't seem to.
That statement is only true in the context of the situation you presented, a constant radius turn at a defined speed and lat acceleration. These two values determine the radius and length of the turn. Of course, on a straight road the distance is the same for different speeds, thus the difference in elapsed time varies inversely to the speed.
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I ran some calculations to compare turns of different sizes, but with similar configurations. To pick a couple out of many examples, my turns are 90º and the line is constant radius. I decided that the limiting factor on how fast the rider can go is traction, rather than bravery, so I determined a target speed based on a known lateral acceleration value.
Assumption: The bike and surface will support about .8g lateral acceleration (± a bit)
Turn 1:
Radius = 150'Turn length for 90º at this radius = 235.6 feetLap 1 speed = 42.25 mphLap 1 lateral accel = .8gLap 1 elapsed time = 3.8 secondsLap 2 speed = 43.25 mph (1 mph increase)Lap 2 lateral accel = .84gLap 2 elapsed time = 3.71 secondsElapsed time difference = .09 secondsTurn 2:
Radius = 150'Turn length for 90º at this radius = 235.6 feetLap 1 speed = 84.5 mphLap 1 lateral accel = .8gLap 1 elapsed time = 7.6 secondsLap 2 speed = 85.5 mph (1 mph increase)Lap 2 lateral accel = .82gLap 2 elapsed time = 7.52 secondsElapsed time difference = .09 secondsThe above comparison shows the break even point in the turn length: For a fast turn that is twice as fast as a slow one, the fast turn must be 4 times longer than the slow turn before a 1 mph increase will result in the same elapsed time reduction in the turn.
The time difference for a small increment in speed is independent of the initial speed.
Let v = initial speed, A = max. lat acceleration, theta = turn angle (90deg in your example)
The radius for the given speed and lat acceleration is r = v^2 / A.
The length of the circ segment L = (pi) (theta / 180) r = (pi) (theta / 180) (v^2) / A
The time for the segment t = L / v = (pi) (theta / 180) (v) / A
Take the derivative, dt / dv = (pi) (theta / 180) / A
For a small change in speed dv, the change in time dt = (pi) (theta / 180) dv / A.
Example (Turn 1):
theta = 90 deg
A = 0.8g = 7.848 m/s^2
dv = 1 mi/h = 0.447 m/s
dt = (3.14159) (90 / 180 ) (0.447 m/s) / ( 7.848 m /s^2 ) = 0.0895 s
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How about anyone else - do you find yourself dodging a bullet with your training?
It happened for me while taking level 3... it had started to rain and I got distracted by that and a passing rider (first mistake) and misjudged the entry speed for a slow corner (second mistake) causing a scary feeling rear slide... which worked out OK and actually looked rather cool on video after. The only things I remember doing are keeping the throttle steady and relaxing my arms.
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What tires do CSS run on the s1000rr's?
I heard Will mention to another student last week that the school currently is using GPA's instead of Q2's because Dunlop apparently can't produce and distribute Q2's fast enough...
Interesting... Perhaps we'll get some real-world comparisons of the Q2 v. GP-A, e.g. wear rate, qualitative impressions from students, etc.
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What tires do CSS run on the s1000rr's?
Dunlop Q2s on the student bikes; Coach bikes, IIRC, race take-offs.
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Superbike School student (age: 75) review
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This is good advice regarding sighting laps; I would think some homework reviewing track maps, pictures or videos might help too. The track entry and exit is another thing to consider, to anticipate other riders entering and exiting. This is more troublesome at certain tracks where riders enter on higher speed sections.
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Thinking about the question of peg weighting when leaned over at speed, the best explanation of the effect on traction that I can come up with is the 'box' analogy I mentioned on the previous page. Hopefully this diagram will better explain my reasoning:
Thinking at extremes makes it easier for me to understand, so imagine that the rider in the above picture is right on the limit of traction. If you look at the angle of the outside peg to the tyre contact patch - it's basically straight on top of it. If I can use the 'box' analogy again - weighting the outside peg would be the equivalent of pushing down on the top of the box, which isn't very likely to make the box slide along the floor.
But if you look at the inside peg, any weight there will practically be pushing at the contact patch from the side. This would be the equivalent of pushing on the side of a box - it's going to slide along the floor.
Does that make sense? What do you think?
It's entirely possible that I have it completely wrong as well!
Is this a pic from your recent track day following CSS L1?
For simplicity let's assume the knee and elbow sliders are just hovering above the surface. As a consequence of Newton's Third Law, it is not possible for the rider to exert a net lateral force on the bike as there is no counter force. That is, nothing to press against. The rider's weight (vertical force of gravity, downward) is countered by an equal force of the bike pressing against the rider vertically (upward). There is a net torque which results from the offset of the point of application of the vertical forces.
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I'm a bit confused by your last sentence... do you agree that a motorcycle with a constant speed requires no steering input to maintain a path through a corner?
I agree with the technique of one steering input and then relax through the corner.
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OK, I'll take a shot at this; not sure I can manage plain English, though.
First, let's tackle weighting the pegs (either, or both) as opposed to sitting with all your weight on the seat. When you need to steer the bike, you have to lean it over, or rotate it about its roll axis. Putting weight on the pegs instead of on the seat puts your weight closer to the center of mass which makes it easier to steer the bike, because the bike rotates around the center of mass. (As Keith puts it in Twist II, "The center of mass is the part of the bike that moves the least, so getting your weight closer to it means you have to move that weight less distance"- see page 85 in Twist of the Wrist II.)If the bike and rider form a rigid body (rider is locked-on the bike) then the center of mass and inertial moment are independent of the attachment point. Now if the rider lays down on the tank instead of sitting upright this will get the rider's mass closer to the bike's center of mass.
Hypothetically, once the bike is leaned over, putting more weight on the inside peg would put the weight lower than putting it on the outside peg, and possibly that could help tighten your line - however you are talking about trying to overcome substantial gyroscopic forces, so unless you are going paralyzingly slow, I don't think it would make very much difference - certainly not enough to overcome the better BODY stability and anchor points we get from putting weight on the outside peg instead.
With the rider locked-on, the net forces on the bike are determined only by the rider's relative position w.r.t. the bike. A lateral displacement of the rider to the inside does have a a slight leaning effect, which is the equivelent of a streering torque of +1..4 Nm. Since most bikes have a small negative steering torque at typical lean angles and path curvatures, an optimal hang-off position will completely balance the steering torque, resulting in neutral steering.
Weighting the outside peg helps you get a very strong pivot point from which to initiate your counter-steering effort (which of course takes more effort if you are going fast), and this aspect is so important that I think it far outweighs any marginal benefit you could get from weighting the inside peg. I also think switching weight from one peg to the other mid-turn (to try to tighten your line) could cause instability in your body and thus possibly wiggle the bike, not desirable mid turn.
IMHO the only use of peg weighting is for pivot steering.
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I only use the rear brake at low (parking lot) speeds. I'm still perfecting the basic cornering skills, so rear brake is more a distraction at this point.
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Johnny Rod makes some great points.
Part of the fun of riding is finding the quickest way through a given turn, by making the best use of your own skills, the bike's capability, the characteristics of the particular corner AND how the corner ties into the track before and after it! So clearly it's not a one-size-fits-all answer. One thing I really liked in CodeRace was an exercise where we took various lines through a corner and they had a radar gun set up to show speed on a large display board - so we could see, at turn exit, the different exit speeds, and we could experiment with different lines to see which gave the best result. Very cool.
There is a rule in Twist of the Wrist, to choose the ideal line. Challenge to the group: see if you can find it and post it up here! Here's a hint, the sentence starts and ends as follows: "The line that... ________ ...is an ideal line." Who can fill in the blank?
... permits exact application of throttle control rule #1 ... (from memory, don't have my TOTW with me at the moment)
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Im currently riding on a restricted licence on a KTM Duke 125 and im now looking at getting a 33bhp bike to meet the limit im allowed (looking at the new Kawasaki 250r).I want to do the school but wanted to know if it would be worthwhile doing it on my own bike, as i wouldnt be able to hire one of the schools?Also does anyone know what insurance would cost me for the day?Thanks Billy
Consider the Honda CBR250R... £4100 with ABS. A girl at the office purchased one on my recommendation and she finally let me take it for a short ride. It feels like a really nimble CBR600RR, not cheap like the Kawa 250 IMHO. For street riding the ABS is very desirable. One downside is slightly less power (26bhp v. 33bhp).
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I think what Crash is asking is whether he risks crashing from intiating the change of direction, something he will not do under normal conditions ...
Your right, Eirik. I am afraid to change directions under ANY conditions. Pesky darned corners!
There are few things in this world that are 100%. There is always some risk of crashing.
Fear, uncertainty and doubt are often more harmful that the original concern though. These contribute to SRs. When riding, confidence is essential. The only way I've found to develop this confidence is by previous experience. Most riders, after a few track days or a school, experience the limits are much greater than they previously thought and become confident routinely turning (and braking and leaning, but not all at once!) at much higher levels. Then when encountering the need to turn suddenly to avoid a car e.g. it is a practiced skill - reaction - and doesn't trigger SRs as much, leaving attention for other things.
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One question is how does the PC5+SFM compare to the BMW HP race ECU and software?
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Classic or Infield?
First, let's tackle weighting the pegs (either, or both) as opposed to sitting with all your weight on the seat. When you need to steer the bike, you have to lean it over, or rotate it about its roll axis. Putting weight on the pegs instead of on the seat puts your weight closer to the center of mass which makes it easier to steer the bike, because the bike rotates around the center of mass. (As Keith puts it in Twist II, "The center of mass is the part of the bike that moves the least, so getting your weight closer to it means you have to move that weight less distance"- see page 85 in Twist of the Wrist II.)
Fast Turns Vs. Slow Turns - Where To Make Time?
in Cornering and Techniques
Posted
+1
We aren't considering that really high-speed turns may not be limited by lat acceleration, think e.g. of Turn 1 at Laguna Seca.