Troy Bayliss to test Ducati GP9

<div class='quotetop'>QUOTE (clarkjw @ May 9 2009, 03:38 AM) <{POST_SNAPBACK}><div class='quotemain'>Grip increases at lean angle, but with no power going to the wheel, it has a stopping force. A guy like Casey is always done turning by apex, which is why he gets better corner drive than the other Ducatis. Nicky seems to correct post apex or not carry enough speed pre apex.

Lex, I think you're a bit off on the physics of braking at high speed. Using the rear at lean stands the bike up. Trail braking the FRONT pivots the bike's rear wheel. Example: In a tight right hand turn, trail braking the front end pushes the rear of the bike toward the left fork, allowing it to sweep.

I'll try to find a video, I think KTM has a good one.
Toward the end you'll see his hand on the brake navigating a left turn. This guy also counter steers alot too, but don't get those confused.
http://ktm.com/1190-RC8.100204.20.html

Grip decreases as a bike is leaned over because the contact patch gets smaller. Centripetal force increases because of the shape of the contact patch. I suppose GP tires could be so ridiculously advanced that they might have more grip as the contact patch shrinks, but as a general rule you have far less grip on most tires. I would be interested to see how multiple compound road tires perform. I don't know that it means much in reference to the GP world though, because multiple compound tires are much too hard in the center so they last 10,000 miles in regular riding conditions.

Trail braking doesn't pivot the rear around the front, that's just what it feels like. The rear actually stays on its normal line and the front pivots inward of off the rear. I know, it seems impossible, but it's not.

Go into your garage and clamp on the front brake on your bicycle. Try everything you can to pivot the rear around the front. Then stop, and clamp on the rear break. Pivot the front around the rear. It only works one way unless you slide the rear tire. The rear handles a majority of the turning g-forces once the bike is turned in because the front pivots off of it. As the front pivots off of the rear, the rear tire is rotated. The front is used to rotate the rear tire and get it onto the correcting heading.

Obviously, it's not an absolute rule because torsional flex in the chassis allows the rear to turn a little bit, but for the most part, the front pivots off of the rear.

I think you might be right about the rear brake though. You can't simultaneously square a corner and use the rear to keep the bike down. One of them is wrong.

The point being that all the functions of cornering must be done and each individual rider will tend to use some methods more than others to get the job done. Some methods work on one bike and not another. Some riding methods have to be used simply because, as in the present case, the carcass construction of the front tire will not allow for extreme maneuvers without collapsing or deforming. It is the core of the sport so of course it is interesting to understand especially for me since I'm not a racer and don't know first hand.

<div class='quotetop'>QUOTE (mylexicon @ May 9 2009, 08:39 PM) <{POST_SNAPBACK}><div class='quotemain'>Grip decreases as a bike is leaned over because the contact patch gets smaller. Centripetal
Sorry you're just plain wrong. Contact patch is quite small upright.
Trail braking doesn't pivot the rear around the front, that's just what it feels like. The rear actually stays on its normal line and the front pivots inward of off the rear. I know, it seems impossible, but it's not.
This makes no sense to me and I will personally attest that the rear doesn't hold its line. I've been down and felt it. I've run wide and felt it. I've nailed corners and felt it.

Go into your garage and clamp on the front brake on your bicycle. Try everything you can to pivot the rear around the front. Then stop, and clamp on the rear break. Pivot the front around the rear. It only works one way unless you slide the rear tire. The rear handles a majority of the turning g-forces once the bike is turned in because the front pivots off of it. As the front pivots off of the rear, the rear tire is rotated. The front is used to rotate the rear tire and get it onto the correcting heading.
This is not bicycling.
Obviously, it's not an absolute rule because torsional flex in the chassis allows the rear to turn a little bit, but for the most part, the front pivots off of the rear.

They engineer nearly all torsional flex out of GP bikes. This actually something Bayliss didn't like very much.
I'm not sure what you ride or how hard you've pushed it, but please take more track days. You're not safe out there

It may be partly misleading to speak of grip increasing or decreasing with the lean angle/speed. What increases or decreases with the lean angle/speed is the attrition forces of the tyre against the tarmac--grip (or the loss of it...) results from the combination of these attrition forces and the relative characteristics of the tarmac and tyre.

<div class='quotetop'>QUOTE (J4rn0 @ May 10 2009, 11:19 AM) <{POST_SNAPBACK}><div class='quotemain'>It may be partly misleading to speak of grip increasing or decreasing with the lean angle/speed. What increases or decreases with the lean angle/speed is the attrition forces of the tyre against the tarmac--grip (or the loss of it...) results from the combination of these attrition forces and the relative characteristics of the tarmac and tyre.
More contact patch is achieved at lean. This is fact, however you'd like to define it.

<div class='quotetop'>QUOTE (clarkjw @ May 10 2009, 12:47 PM) <{POST_SNAPBACK}><div class='quotemain'>More contact patch is achieved at lean. This is fact, however you'd like to define it.

It's not just a matter of wording but of substance--if we assume grip increases with the lean angle, then if that was correct no one would ever lose grip when leaning the bike more... The limit would be the physical geometry of the bike interfering with the ground. Unfortunately it's not like that

Conversely, if we had to assume grip decreases with the lean angle, then no one would ever be able to lean a bike at high speed. Everybody would crash.

So speaking of grip in that way is not correct. Sorry for both you and Mylexicon.

<div class='quotetop'>QUOTE (J4rn0 @ May 10 2009, 01:33 PM) <{POST_SNAPBACK}><div class='quotemain'>It's not just a matter of wording but of substance--if we assume grip increases with the lean angle, then if that was correct no one would ever lose grip when leaning the bike more... The limit would be the physical geometry of the bike interfering with the ground.
This is just stupid. You can lose grip at any time at any angle. THE CONSEQUENCES OF LOSING GRIP ARE DIFFERENT DEPENDING ON LEAN ANGLE. If you're tire skips when up, you'll stay up. If it's skips at full lean, you go down - even with 2x the grip.

Grip and contact patch are not independent. The contact patch is greater at a lean. When force is applied (inertial or torque), grip is created. Sometimes I wonder if you guys even ride sportbikes.

<div class='quotetop'>QUOTE (clarkjw @ May 10 2009, 03:47 AM) <{POST_SNAPBACK}><div class='quotemain'>More contact patch is achieved at lean. This is fact, however you'd like to define it.

No it's not. Contact patch size is dependent entirely upon the profile of the tires, construction of the tires, and even little things like air pressure. GP tire are very aggressively profiled and they have very hard carcasses so there is a possibility optimum contact patch could be a some lean angle other than zero.

I highly doubt though, that it would be an efficient use of the tires to design maximum contact patch at full lean, especially very little time is spent at full lean during the race.

<div class='quotetop'>QUOTE (mylexicon @ May 10 2009, 04:22 PM) <{POST_SNAPBACK}><div class='quotemain'>No it's not. Contact patch size is dependent entirely upon the profile of the tires, construction of the tires, and even little things like air pressure. GP tire are very aggressively profiled and they have very hard carcasses so there is a possibility optimum contact patch could be a some lean angle other than zero.

I highly doubt though, that it would be an efficient use of the tires to design maximum contact patch at full lean, especially very little time is spent at full lean during the race.
Agree, I'm mystified about the origin of Clark's misapprehensions here. A racing bike is very inefficient when it is leant over. Despite the classic lines which define the current 800cc formula, you will still see the bikes being lifted up as early as possible on the exit of the corner. This is to increase the contact patch and obtain maximum drive. It was most noticable in the 990 days, but was also a characteristic associated with the 500cc bikes. When Katoh moved up to Moto GP I remember he had real difficulties initially adapting to this form the 250 style. The 800's are more of a compromise, but watch Dani who is one of the chief exponents of technique, watch how quickly he picks it up out of the corner and gets it upright to get on the gas. You can see him tug the opposite bar and shift his weight on the seat and the pegs to achieve this.

Clarke, are you simply saying that there are greater forces of grip being exerted during cornering, or that the contact patch is greater?

The only reason I'm pushing so far with this is so we can have reasonable go at Nicky's problems and sensible discussions on racecraft.

The contact patch is greater. This is necessary for stability in turning. When a bike is upright torque forces are going in the direction the rider desires (forward). At apex, torque is perpendicular to desired direction. That's why the bike's get picked up. These are turns, not circles.

Since you don't believe me
http://books.google.com/books?id=akcdioKmR...lt&resnum=3

http://www.cornerspeedphoto.com/blog/2008/...compromise.html

Just because it makes logical sense in your head, doesn't make it true.

He're the Bridgestone profile
http://www.bridgestonemotorsport.com/Bridg...ogy/motogp.html

http://www.mynetmoto.com/motorradreifen_ne...sport_tyre.html

And do you think Avon is ahead of Bridgestone?
Avon's Hybrid Belt system, combined with other advanced construction features, creates an intelligent tyre with a contact patch that grows with increased lean angle and offers precise handling characteristics and consistent stability throughout the tyre's life.

<div class='quotetop'>QUOTE (mylexicon @ May 9 2009, 01:00 AM) <{POST_SNAPBACK}><div class='quotemain'>I also think Stoner uses much less countersteer at the apex. If you look closely he lets the front wheel pull itself into the turn (like he's letting it tuck). But on a rear-wheel biased bike, letting the front pull itself into the turns is what creates cornering load at the front and eliminates the vagueness.
I have no idea if Casey uses less or more countersteer (and you don't either - just your usual debating technique of stating conjecture as fact) but the camera pointed at his front wheel/contact patch/suspension got a lot of air time in Jerez and CS was definitely countersteering like a madman as his tyre squashed into an expanded contact patch at radical lean angles.

<div class='quotetop'>QUOTE (clarkjw @ May 10 2009, 06:43 PM) <{POST_SNAPBACK}><div class='quotemain'>Since you don't believe me
http://books.google.com/books?id=akcdioKmR...lt&resnum=3
Just because it makes logical sense in your head, doesn't make it true.

He're the Bridgestone profile
http://www.bridgestonemotorsport.com/Bridg...ogy/motogp.html
Excellent find.

Read the paragraph on P.16 concerning lean angle. As I said, less lean angle = more traction/drive. Shame you couldn't include Chapter 8. Nonetheless this is an excellent extract.

<div class='quotetop'>QUOTE (clarkjw @ May 10 2009, 10:43 AM) <{POST_SNAPBACK}><div class='quotemain'>The only reason I'm pushing so far with this is so we can have reasonable go at Nicky's problems and sensible discussions on racecraft.

The contact patch is greater. This is necessary for stability in turning. When a bike is upright torque forces are going in the direction the rider desires (forward). At apex, torque is perpendicular to desired direction. That's why the bike's get picked up. These are turns, not circles.

Since you don't believe me
http://books.google.com/books?id=akcdioKmR...lt&resnum=3

http://www.cornerspeedphoto.com/blog/2008/...compromise.html

Just because it makes logical sense in your head, doesn't make it true.

He're the Bridgestone profile
http://www.bridgestonemotorsport.com/Bridg...ogy/motogp.html

http://www.mynetmoto.com/motorradreifen_ne...sport_tyre.html

And do you think Avon is ahead of Bridgestone?
Avon's Hybrid Belt system, combined with other advanced construction features, creates an intelligent tyre with a contact patch that grows with increased lean angle and offers precise handling characteristics and consistent stability throughout the tyre's life.

The total control article doesn't discuss the effects of compression on the contact patch other than to say that it gets bigger. I'm quite convinced that heavy braking at modest lean creates a contact patch much bigger than the contact patch available at full lean.

Since this discussion is not about cornering in theory, I can't say that I find the contact patch section relevant.

However, I will say that the article has demonstrated beyond a shadow of a doubt that the profile of modern sports tires are designed to deliver more contact patch as the bike is leaned over.

Whether or not a tire leaned at 15 degrees under compression from a handful of brake has a smaller contact patch than the same tire at 65 degrees of lean remains to be seen. I suppose it would depend very highly on the profile, the carcass construction, the compound, and the air pressure.

<div class='quotetop'>QUOTE (clarkjw @ May 10 2009, 01:59 PM) <{POST_SNAPBACK}><div class='quotemain'>This is just stupid. You can lose grip at any time at any angle. THE CONSEQUENCES OF LOSING GRIP ARE DIFFERENT DEPENDING ON LEAN ANGLE. If you're tire skips when up, you'll stay up. If it's skips at full lean, you go down - even with 2x the grip.

Grip and contact patch are not independent. The contact patch is greater at a lean. When force is applied (inertial or torque), grip is created. Sometimes I wonder if you guys even ride sportbikes.

You call me stupid? I feel sorry for you
I ride bikes since I was 8 years old, I was born in Imola in a family of motorcycle mechanics and we have always prepared and raced our own bikes. I go to Mugello for fun every other sunday. Anyway, having racing experience I know only too well that it has not much to do with logical thinking, so it can't help you here. YOu just do not think logically.
Read what I have posted. I objected to your way of putting things as incorrect. You can only answer asking if I ride or not--are you 15 years old?

<div class='quotetop'>QUOTE (J4rn0 @ May 10 2009, 10:11 PM) <{POST_SNAPBACK}><div class='quotemain'>You call me stupid?
You can only answer asking if I ride or not--are you 15 years old?
I didn't call you stupid. That wasn't my only answer.

<div class='quotetop'>QUOTE (Arrabbiata1 @ May 10 2009, 06:20 PM) <{POST_SNAPBACK}><div class='quotemain'>Excellent find.

Read the paragraph on P.16 concerning lean angle. As I said, less lean angle = more traction/drive. Shame you couldn't include Chapter 8. Nonetheless this is an excellent extract.
Sure. The but the power to the ground is great when you have more rubber touching. That doesn't mean it's forward power.

Lex, I'd say contact patch, grip, etc has alot to do with cornering. In your first argument you said Grip decreases as a bike is leaned over because the contact patch gets smaller.
If the contact patch get's bigger, then what?

This discussion is interesting to me if mostly beyond my ken.

Even to a casual observer though stoner seems to ride at extremely radical lean angles, and in 2007 most of his dominant performances were reportedly on the hard compound bridgestone tyres, which he reputedly was the only rider able to use or even warm up to optimum operating temperature. Perhaps the multiple compound thing comes into it as well as lex says, with the tyre different at lean than upright as well.

<div class='quotetop'>QUOTE (michaelm @ May 11 2009, 12:03 AM) <{POST_SNAPBACK}><div class='quotemain'>Perhaps the multiple compound thing comes into it as well as lex says, and hence the tyre is different at lean than upright as well.
The tire's are much softer on the sides. They often use 4 or more compounds with varying softness.

Don't forget to factor in corner banking guys! .... its everso slightly of some import .... whilst you guys are saving the cornering world

Coupla things for you Clark ....

1. go back to basics .... look at the contact patch as "an about to shear stress plane" ........ its important to remember that that grip yield stress ( dependent of the frictional bond ) still follows the old equation Stress = Force/area ........ yes I know its a chicken and the egg thing because the less the area the greater the force per unit are ...... but when all is said and done .. we have to have sensible contact patches that account for road surface friction coeficcient changes ( eg. a patch of dust/oil/bug)


In short I think its best to leave the tyres to the guys who have the data on them .... ie. now its Bridgestone only for Mgp



P.S. I don't think you should go calling J4rno stupid .... I believe he is talking much sense .... for what thats worth here J4rno seems to be saying a lot more of the right things about contact patches thats for sure.

It will be sad if this thread degenerates into name calling. Some really good info is coming out here.