Troy Bayliss to test Ducati GP9

I was just thinking how pointless this entire conversation might be if my memory is working correctly. I was looking on Wikipedia at friction and coefficients of friction when I remembered something from highschool physics.

Aren't frictional forces independent of surface area and dependent upon mass or perpendicular force?

Or am I cracked?

I vaguely remember doing an experiment with a wood block testing it on different sides with varying surface areas only to find that the frictional forces were the same.

If I'm remembering correctly, the larger contact patch is important mainly for distributing frictional forces and minimizing wear. Contact patch actually has no effect on the grip levels at all, BUT a larger contact patch allows for the use of softer compounds b/c the forces are more evenly distributed so the top layer of soft rubber is able to sustain cornering.

A motorcycle loses the ability to turn primarily because the forces of cornering are increasingly less perpendicular (you need more centripetal force/friction to fight them). Softer compounds help compensate for the loss of perpendicular force.

Is grip more on the side of the tire? We can't know without compression data and data of the coefficient of friction. If the edges are softer, they have a higher coefficient of friction. However, when a bike is on its side it cannot utilize compression via the brake or the throttle.

Is the contact patch growing to the edge? A preponderance of the evidence points to "yes" but I'm still not satisfied without compression data. Very little time is spent with a relaxed right hand.

Edit: I found an MIT lecture on friction

Watch at 10 minutes

Link

<div class='quotetop'>QUOTE (mylexicon @ May 11 2009, 12:44 PM) <{POST_SNAPBACK}><div class='quotemain'>I was just thinking how pointless this entire conversation might be if my memory is working correctly. I was looking on Wikipedia at friction and coefficients of friction when I remembered something from highschool physics.

Aren't frictional forces independent of surface area and dependent upon mass or perpendicular force?

Or am I cracked?

Not cracked

its a wacko thing to get ones head around thats all.

They are dependent on the surface area, but ( the chicken and the egg bit ) ... the bigger the area the smaller becomes the force/area for any given mm^2 for example. Which kinda says the whole thing kinda evens out ( thats probably what you are remembering? from HS physics). I think the benefits of a larger contact area are more reliable surface for adhesion, and in extreme cases its opportune too keep the stress in the material down a bit ( eg. drag car tyres ..... spread the HP or you'll rip them to shreds )

Cornering is the high load time for Mgp tyres so I think they pretty much fit the usual "spread that load" bill. Only in Mgp they would be working not just at working in loads that don't shred them but also keep the temperature down to keep them in a good/reliable operating range of friction.

Yea, maximum frictional force is determined by Force X cF.

There are some wrinkles:
Running soft gooey tires allows the rubber to 'flow' into the micro-structure of the road. This affords more total horizontal resistance to sliding than pure cF calculations might suggest. There are also atomic and molecular interactions between the rubber and road that also add to the available adhesion. These secondary interactions will roughly scale with contact patch surface area. (I'm guessing, but it sounds right.)

HOWEVER none of the above guarantees grip! The limiting factor is the strength of the rubber. Where do you think skid marks come from? (No, I'm not talking about Pinky's underwear!) Skids represent rubber than has been overstressed and torn apart. This is why you need a big contact patch - to divide the horizontal load among more rubber molecules, so that each one is able to survive the load without tearing.

p.s. Many race tires are somewhat triangular in cross section. They are designed to apply the largest possible contact patch to the road when the tire is at maximum lean.

-Moo!

<div class='quotetop'>QUOTE (Geonerd @ May 11 2009, 07:24 AM) <{POST_SNAPBACK}><div class='quotemain'>-Moo!


Hehehehehe!
yeah will go with that!!!

I bet you've been waiting for this one Junkie?

Anyway, I just wanted to add that the 16"/16.5" rims are very much a part of this equation as well.
The rubber of today are accepting a remarkable amout of flex without deformation. As seen in close up pictures the rubber flex a lot under load. This enable the tire to maintain or even increase the contact patch size even when the bikes are leaning at the edge of the rolling surface.
Allthough the rims are 16.5" the radius of the top of the tire is the same. In other words they use higher profile tires both for better larger contact patch and/or to improve the suspension duties of the tires. At maximum lean angle the traditional suspension is much less efficient and the bike rely on tire/frame/swingarm/fork flex.

And regarding to the black marks, yes it's rubber being riped to pieces but there is a big change to this during the years. The tires has become much more predictable and (my speculation of course) insted of melting down as we still see with cars locking up tires resulting in dramatic loss in friction coeffcient, the rubber are teard off causing only a marginal loss of friction.

Just to add to this. In SS600 they are not allowed to use anyting but the 17" rims. As a substitute they stretch the formula by also there increase the profile. I don't think it says so on the tire, as I suspect it's not allowed, but try to fit a Dunlop Supersport tire under a tight fit Hugger and you end up like me, with a big hole in the hugger.

My understanding is that bayliss was always going to do this testing, whether for promotional reasons or otherwise; I think it was announced last year.

Perhaps more salient to ducati and nicky, according to crashnet juan martinez, apparently a fluent english speaker, is to take over as hayden's crew chief. Perhaps ducati corse follow the forum .

<div class='quotetop'>QUOTE (clarkjw @ May 11 2009, 01:12 AM) <{POST_SNAPBACK}><div class='quotemain'>The tire's are much softer on the sides. They often use 4 or more compounds with varying softness.
I ask in ignorance, but are the different compounds in the tyre thermally insulated from each other ie does using the soft edge part of the tyre warm up the whole tyre?

<div class='quotetop'>QUOTE (michaelm @ May 11 2009, 07:44 AM) <{POST_SNAPBACK}><div class='quotemain'>My understanding is that bayliss was always going to do this testing, whether for promotional reasons or otherwise; I think it was announced last year.

Perhaps more salient to ducati and nicky, according to crashnet juan martinez, apparently a fluent english speaker, is to take over as hayden's crew chief. Perhaps ducati corse follow the forum .
Interesting, didn't Sete really, really want Martinez as his crew chief going into the season? I remember there being a big stink when Ducati wanted to use their own people there.

<div class='quotetop'>QUOTE (michaelm @ May 11 2009, 12:55 PM) <{POST_SNAPBACK}><div class='quotemain'>I ask in ignorance, but are the different compounds in the tyre thermally insulated from each other ie does using the soft edge part of the tyre warm up the whole tyre?
I don't know, but probably not. There's a great article on crash.net with Colin Edwards and Michelin on weird things that they can do with rubber. I can tell you that I ride Pirelli diablo super corsas and the are not insulated based on the tire wear. The soft stays reasonably cool when it doesn't get friction.

<div class='quotetop'>QUOTE (Geonerd @ May 11 2009, 07:24 AM) <{POST_SNAPBACK}><div class='quotemain'>Yea, maximum frictional force is determined by Force X cF.

There are some wrinkles:
Running soft gooey tires allows the rubber to 'flow' into the micro-structure of the road. This affords more total horizontal resistance to sliding than pure cF calculations might suggest. There are also atomic and molecular interactions between the rubber and road that also add to the available adhesion. These secondary interactions will roughly scale with contact patch surface area. (I'm guessing, but it sounds right.)

HOWEVER none of the above guarantees grip! The limiting factor is the strength of the rubber. Where do you think skid marks come from? (No, I'm not talking about Pinky's underwear!) Skids represent rubber than has been overstressed and torn apart. This is why you need a big contact patch - to divide the horizontal load among more rubber molecules, so that each one is able to survive the load without tearing.

p.s. Many race tires are somewhat triangular in cross section. They are designed to apply the largest possible contact patch to the road when the tire is at maximum lean.

-Moo!
Reads like a tom post, total bollocks.

<div class='quotetop'>QUOTE (roger-m @ May 11 2009, 03:42 PM) <{POST_SNAPBACK}><div class='quotemain'>Reads like a tom post, total bollocks.

Ahhh rog dont worry about the 'experts' (I gave up on them!)
just go with the MOOOOOOOOOOOOOO!!!

<div class='quotetop'>QUOTE (Babelfish @ May 11 2009, 01:14 AM) <{POST_SNAPBACK}><div class='quotemain'>I bet you've been waiting for this one Junkie?

Well it’s comforting to know we have several engineers on this site to help us all understand the complexity of a MotoGP bike. Haha

Nah, but really, I'm very impressed with Ducati. They are now shuffling their staff, hiring one of the all time greatest racers to test their machines, and the team boss has stated that having only one competitive rider on a Ducati is unacceptable and this must change. So kudos to Ducati. What a stark difference between Honda and Ducati. Yeah, Hayden is so far doing much worse performance wise, but at least the team is trying to figure it out as to why. You can't ask more than that.

Perhaps some of you guys that understand the "physics" behind it all should write Suppo a letter.


(Don't take it serious, just ...... with you. Jokes don't seem to go over well these days).

<div class='quotetop'>QUOTE (Geonerd @ May 10 2009, 11:24 PM) <{POST_SNAPBACK}><div class='quotemain'>Yea, maximum frictional force is determined by Force X cF.

There are some wrinkles:
Running soft gooey tires allows the rubber to 'flow' into the micro-structure of the road. This affords more total horizontal resistance to sliding than pure cF calculations might suggest. There are also atomic and molecular interactions between the rubber and road that also add to the available adhesion. These secondary interactions will roughly scale with contact patch surface area. (I'm guessing, but it sounds right.)

HOWEVER none of the above guarantees grip! The limiting factor is the strength of the rubber. Where do you think skid marks come from? (No, I'm not talking about Pinky's underwear!) Skids represent rubber than has been overstressed and torn apart. This is why you need a big contact patch - to divide the horizontal load among more rubber molecules, so that each one is able to survive the load without tearing.

p.s. Many race tires are somewhat triangular in cross section. They are designed to apply the largest possible contact patch to the road when the tire is at maximum lean.

-Moo!

English please.

<div class='quotetop'>QUOTE (Jumkie @ May 11 2009, 10:47 AM) <{POST_SNAPBACK}><div class='quotemain'>English please.
Well, some of it might border on ........ or irrelevancy, but.

You get maximum friction force from how hard something's pushing down multiplied by how "rough" (close enough for now) it is. Surface area doesn't come into play here. This is the standard model taught in basic physics courses. Like everything taught in basic physics and chemistry classes, it's a useful lie in many ways.

The road's bumpy, and the rubber molds around the lil' bumps in the road, making it grip better. He also claims that the tires stick like glue to the road.

What happens when traction between rubber and road is lost isn't really the same sort of deal covered by the basics physics model. The rubber gets ripped the .... apart and left on the road. The tire doesn't just slide on the road, pieces of it get ripped off by the road. If you have a bigger contact patch, each bit of the tire has less load on it so is less able to get ripped apart.

Tires are sorta pointy with broad sides, so they put more rubber on the road when you need it most.

<div class='quotetop'>QUOTE (Jumkie @ May 11 2009, 08:47 AM) <{POST_SNAPBACK}><div class='quotemain'>English please.

You troublemakers are all alike - hiding in the back of the room, screwing off during class.
Let's see some effort, Jumkie! Try to keep up.

<div class='quotetop'>QUOTE (roger-m @ May 11 2009, 06:42 AM) <{POST_SNAPBACK}><div class='quotemain'>Reads like a tom post, total bollocks.



No it's not. I did some more research and I found that Guillaume Amontons developed the idea that surface area and friction are independent. However, some say that DaVinci started tribology hundreds of years before Amontons did his work.

Amontons theory applies mainly to solids. Elastic substances like rubber muddy the laws of friction somewhat. One of the easiest ways you can change the coefficient of friction of elastic substances is to change the surface tension (air pressure is the easiest way). Reducing the surface tension by reducing the air pressure can raise the coefficient of friction and make the tires more grippy without altering the compound.

So the amount of air you put in the tire can actually affect the frictional forces supplied by the tire. Like Geonerd was saying, the elasticity changes the road holding properties on micro/nano/atomic level as does altering the compound.

Also the idea that super skinny tires can deliver the same performance as large tires if both tires have the same compound is somewhat misleading and subject to limitations.

If you make the tire too small, the surface rubber can't survive the frictional forces or the heat during cornering and the tire moves into its kenetic friction coefficient which is lower than static friction. In some extreme instances the tires may appear to be incapable of gripping at all b/c the surface compounds are destroyed before than can do any significant work.

<div class='quotetop'>QUOTE (mylexicon @ May 11 2009, 07:09 PM) <{POST_SNAPBACK}><div class='quotemain'>

No it's not. I did some more research and I found that Guillaume Amontons developed the idea that surface area and friction are independent. However, some say that DaVinci started tribology hundreds of years before Amontons did his work.

Amontons theory applies mainly to solids. Elastic substances like rubber muddy the laws of friction somewhat. One of the easiest ways you can change the coefficient of friction of elastic substances is to change the surface tension (air pressure is the easiest way). Reducing the surface tension by reducing the air pressure can raise the coefficient of friction and make the tires more grippy without altering the compound.

So the amount of air you put in the tire can actually affect the frictional forces supplied by the tire. Like Geonerd was saying, the elasticity changes the road holding properties on micro/nano/atomic level as does altering the compound.

Also the idea that super skinny tires can deliver the same performance as large tires if both tires have the same compound is somewhat misleading and subject to limitations.

If you make the tire too small, the surface rubber can't survive the frictional forces or the heat during cornering and the tire moves into its kenetic friction coefficient which is lower than static friction. In some extreme instances the tires may appear to be incapable of gripping at all b/c the surface compounds are destroyed before than can do any significant work.
im sure all the riders bare that in mind mid corner as we do when watching the race. We all know over or under inflated tyre pressures affect it performance. Some of you lot love to blow your own trumpet geez.

<div class='quotetop'>QUOTE (Geonerd @ May 11 2009, 10:34 AM) <{POST_SNAPBACK}><div class='quotemain'>You troublemakers are all alike - hiding in the back of the room, screwing off during class.
Let's see some effort, Jumkie! Try to keep up.




Just having a go brotha. Hey, don't go taking over Curvy's job of picture-posting now.

<div class='quotetop'>QUOTE (roger-m @ May 11 2009, 11:22 AM) <{POST_SNAPBACK}><div class='quotemain'>im sure all the riders bare that in mind mid corner as we do when watching the race. We all know over or under inflated tyre pressures affect it performance. Some of you lot love to blow your own trumpet geez.

Yeah, but it's contrary to the laws of friction as put forth by Guillaume Amontons mainly because he was writing about inelastic solids.

Obviously, anyone can see that the two contradict and it could be lead people to believe that the laws of friction have been misstated b/c they are contrary to common observations.

I was also trying to point out that reducing tire pressure doesn't increase grip by increasing the contact patch (in most applications), it changes grip because it alters the tire's coefficient of friction. The chemical composition hasn't changed so a majority of the frictional increase results from the adhesion with the pavement on a micro level like Geonerd was saying.

<div class='quotetop'>QUOTE (Jumkie @ May 11 2009, 07:34 PM) <{POST_SNAPBACK}><div class='quotemain'>

Just having a go brotha. Hey, don't go taking over Curvy's job of picture-posting now.

I have a buddy who wears those in his ears.