Joined Oct 2006
3K Posts | 34+
Tar Heel State
Joined Apr 2008
7K Posts | 3K+
Out of Nowhere
Joined Aug 2007
11K Posts | 3K+
Pomona NY
Joined May 2008
3K Posts | 79+
Southern Aridzona - Hell's doorstep.
Argh! I'm SO sick of people trying to say that the Toxic Midget is laboring under some terrible handicap.
When braking on clean, dry surface, a MotoGP bike is stoppie-limited. Too much brake will cause the bike to flip forward. Now, consider this image.
11414:COG.jpg]
Note that, when looking from the front contact patch, the line to the rider's (estimated) COG is higher than the line to the bike's estimated COG. Under these circumstances, LOWER rider weight produced LESS forward torque on the bike and rider as a whole. LIGHTER RIDERS HAVE A BRAKING ADVANTAGE! If the rider could lower his COG until his COG-to-front-wheel-line was lower than that of the bike, then increasing his weight would actually work to hold the bike down, relative to a riderless machine.
The same mechanism holds true for acceleration in the lower gears, when the bike is wheelie-limited. And once the driving torque has dropped to the point that the rider can use full throttle, simple power to weight ratio dictates that lighter is better. I don't buy the aero handicap either - remember when Haystack needed to have a barn-door fairing made for the Pedrocycle? The small Dani-sized fairing punches a much smaller hole in the air...
I do agree that Peddles suffers during steering transitions, when more weight and strength are a big help. There may also be situations where an accelerating bike is traction limited. In these rare cases, a heavier rider might also cause the bike to accelerate better
Attachments
Argh! I'm SO sick of people trying to say that the Toxic Midget is laboring under some terrible handicap.
When braking on clean, dry surface, a MotoGP bike is stoppie-limited. Too much brake will cause the bike to flip forward. Now, consider this image.
11414:COG.jpg]
Note that, when looking from the front contact patch, the line to the rider's (estimated) COG is higher than the line to the bike's estimated COG. Under these circumstances, LOWER rider weight produced LESS forward torque on the bike and rider as a whole. LIGHTER RIDERS HAVE A BRAKING ADVANTAGE! If the rider could lower his COG until his COG-to-front-wheel-line was lower than that of the bike, then increasing his weight would actually work to hold the bike down, relative to a riderless machine.
The same mechanism holds true for acceleration in the lower gears, when the bike is wheelie-limited. And once the driving torque has dropped to the point that the rider can use full throttle, simple power to weight ratio dictates that lighter is better. I don't buy the aero handicap either - remember when Haystack needed to have a barn-door fairing made for the Pedrocycle? The small Dani-sized fairing punches a much smaller hole in the air...
I do agree that Peddles suffers during steering transitions, when more weight and strength are a big help. There may also be situations where an accelerating bike is traction limited. In these rare cases, a heavier rider might also cause the bike to accelerate better
I agree, except i would have thought if there were an acceleration disadvantage due to the lack of rider weight over the rear wheel they would just run a lower pressure to compensate.
Joined Jun 2008
1K Posts | 365+
USA
Geo, fantastic post. Rog, agree (even though I don't understand the entire reason why).
"Toxic Midget"!
Well putting all the science ect aside. If you read the handbook for your bike or car it will say something like rear tyre pressure 32psi heavy load 42psi. So the heavier weight needs higher pressure because of weight compression and therefor tread foot print. Tread foot print meaning grip and traction.
Joined Jun 2007
10K Posts | 1K+
Norah Head
But you still can't avoid the fact that the horizontal vector of stopping force is higher for the fatties ............. its a can of worms really and a dilemma to the layman, but the mere fact that all decent riders are "slim" indicates that its the equation must be generally in favour of the lighter guy.
Argh! I'm SO sick of people trying to say that the Toxic Midget is laboring under some terrible handicap.
When braking on clean, dry surface, a MotoGP bike is stoppie-limited. Too much brake will cause the bike to flip forward. Now, consider this image.
11414:COG.jpg]
Note that, when looking from the front contact patch, the line to the rider's (estimated) COG is higher than the line to the bike's estimated COG. Under these circumstances, LOWER rider weight produced LESS forward torque on the bike and rider as a whole. LIGHTER RIDERS HAVE A BRAKING ADVANTAGE! If the rider could lower his COG until his COG-to-front-wheel-line was lower than that of the bike, then increasing his weight would actually work to hold the bike down, relative to a riderless machine.
The same mechanism holds true for acceleration in the lower gears, when the bike is wheelie-limited. And once the driving torque has dropped to the point that the rider can use full throttle, simple power to weight ratio dictates that lighter is better. I don't buy the aero handicap either - remember when Haystack needed to have a barn-door fairing made for the Pedrocycle? The small Dani-sized fairing punches a much smaller hole in the air...
I do agree that Peddles suffers during steering transitions, when more weight and strength are a big help. There may also be situations where an accelerating bike is traction limited. In these rare cases, a heavier rider might also cause the bike to accelerate better
I don't think your theory is correct for the following reasons
1. Stopping a bike or infact any road going vehicle happens due to 2 things
a. friction between brake pads and disk
b. friction between tyres and and road (if there is no friction, the wheels will lock up into a slide). In braking conditions, the weight of the bike comes to the front tyre and the friction generated will be dependent on the weight on front tyre (friction = coeffgrav force on wheel). So lower the weight, lower the friction and lesser braking!
2. I don't understand what is forward torque? there is no torque generated at braking as the force on the front wheel is applied at the dead centre and hence no torque.
Please correct if I am wrong somewhere
Cheers
Renjith
1. The rider COG will be around pelvic/hip region. So it doesn't change too much between shorter and taller riders
Joined May 2008
3K Posts | 79+
Southern Aridzona - Hell's doorstep.
Greetings, Renjith.
Point #1
Friction is not a problem! There is more friction (raw braking force) available than can be used.
Think of it this way.
11415
edrosa_Faceplant.jpg]
Point #2
The green arrows represent the two forces at work; bike (+rider) momentum, and the ground 'pushing' back at the tire's point of contact. Since the bike's center of gravity is above ground level, these two forces will produce a forward torque (red arrow) on the bike. Counteracting this is the weight (blue line) that also acts through the front contact patch to provide a rearward torque. When the forward torque becomes the stronger of the two, the rear wheel will lift off the ground and the bike will start to flip forward. The effect is identical to pushing the base of a tall glass of beer (or anything else that is free to move.) Push gently and the glass remains upright, push harder (higher acceleration) and the glass will topple over.
Since the rider is seated above the bike, his weight will add to the instability of the machine. More weight (or more height) = less stability = less maximum braking force before the bike flips. A lighter rider will produce a lower overall center of gravity, allowing higher braking forces to be applied through the front wheel withoutsmearing Perdrosa's smarmy, smirking face into the cold, hard pavement causing the bike to endo.
Point #1
Friction is not a problem! There is more friction (raw braking force) available than can be used.
Think of it this way.
11415
edrosa_Faceplant.jpg]Point #2
The green arrows represent the two forces at work; bike (+rider) momentum, and the ground 'pushing' back at the tire's point of contact. Since the bike's center of gravity is above ground level, these two forces will produce a forward torque (red arrow) on the bike. Counteracting this is the weight (blue line) that also acts through the front contact patch to provide a rearward torque. When the forward torque becomes the stronger of the two, the rear wheel will lift off the ground and the bike will start to flip forward. The effect is identical to pushing the base of a tall glass of beer (or anything else that is free to move.) Push gently and the glass remains upright, push harder (higher acceleration) and the glass will topple over.
Since the rider is seated above the bike, his weight will add to the instability of the machine. More weight (or more height) = less stability = less maximum braking force before the bike flips. A lighter rider will produce a lower overall center of gravity, allowing higher braking forces to be applied through the front wheel without
Attachments
Good theory g, could be applied with some opposite relativety to a particular incident in which pedders was practicing his start.....
Yeah! But, you are a female....................
True. But still.....!
chopperman' timestamp='1296340478' post='265039 said:
Without!
.
Greetings, Renjith.
Point #1
Friction is not a problem! There is more friction (raw braking force) available than can be used.
Think of it this way.
11415
Point #2
The green arrows represent the two forces at work; bike (+rider) momentum, and the ground 'pushing' back at the tire's point of contact. Since the bike's center of gravity is above ground level, these two forces will produce a forward torque (red arrow) on the bike. Counteracting this is the weight (blue line) that also acts through the front contact patch to provide a rearward torque. When the forward torque becomes the stronger of the two, the rear wheel will lift off the ground and the bike will start to flip forward. The effect is identical to pushing the base of a tall glass of beer (or anything else that is free to move.) Push gently and the glass remains upright, push harder (higher acceleration) and the glass will topple over.
Since the rider is seated above the bike, his weight will add to the instability of the machine. More weight (or more height) = less stability = less maximum braking force before the bike flips. A lighter rider will produce a lower overall center of gravity, allowing higher braking forces to be applied through the front wheel withoutsmearing Perdrosa's smarmy, smirking face into the cold, hard pavementcausing the bike to endo.
Since I don't own a sports bike, can someone provide the approximate front fork spring stiffness and normal spring travel under hard braking for a sports/race bike. I am trying out some amateur calculations on the discussion above and need these values.
Also, is it safe to assume a normal Motogp bike can be slowed down from 250-275 km/hr to 100 km/hr in 2.5 secs?
Thanks
Renjith
Think of it this way.
11415
If that blue line is bigger or more valuably, further back, the rider can brake harder. Rossi is the tallest guy on the grid, Dani is the shortest. One is particuarly good on the breaks, the other is particularly bad.
