My car tire impressions- for real

[upside22]

I suspect that the issue here is a little more complicated than has been presented. The normal force at any point on the surface of a tire is going to be inversely related to the total weight of the bike and the contact area. Thus the bigger the contact area the lower the normal force at any point in the contact area. This is why they use big tracks to hold up an M1A1 tank instead of round wheels - bigger surface area results in less normal force at any specific contact point.

The force being applied to the tire also gets spread out over the same contact area. It doesn't matter if this is torque applied by the engine or centripetal force from going around a corner.

Where this gets complicated is that the total action between a tire and the surface is going to be a statistical relation integrated over the entire contact patch, i.e. at any instant of time one point on the contact patch may have the friction force exceeded while another point does not. I suspect what a rigorous statistical analysis would show is that the larger the contact patch the higher the total torque has to be to exceed the total friction force.

If this was *NOT* the case then it would make more sense to run racing bicycle tires on our motorcycles in order to reduce rolling friction since the same friction force would be available to hold the motorcycle to the road regardless of the size of the contact patch.

[Kawhead]

Originally Posted by 1badbagger

All I know is....this discussion is way over my head. I was a music major.

You godda watch some a these guys bagger. Do you think for a second A. Einstein or Stephen Hawking, two gents who teach people who teach people about physics, would get on a motorbike and haul ass through the Tail of the Dragon? Would they commute to work in major metropolitan areas amongst cage drivers texting, sexting, and sellfoneing. Would they ride one at night through rural areas when furry woodland creatures are most active and like to play in the rode ??? Would they even consider putting a car tire on a bike when you only have 2 of 5 treads contacting pavement in a turn ???

<marquee>I THINK NOT!!! :(" title="" border="0"/> :(" title="" border="0"/> :(" title="" border="0"/> </marquee>

[blaneb]

Originally Posted by waterman

Actually Todd, the coefficient of friction is a constant. It is a fraction of the amount of energy (force) required to move a mass. As you increase mass, the nominal force to move that mass increases but only by the proportion of the coefficient of friction. Now we could also get into talking about kinetic friction and static friction coefficients.

Trust me Todd. I taught physics for a year in college.

So, an 800 lb. bike will have the same traction on the Moon as on Earth. Same mass, right. Come on, please!

A dragster might have 1000 lbs. of normai force (not nominal force) on the tires at launch, but will have 5000 lbs. of normal force at speed due to the downforce of the rear wing. Same mass, stopped or at speed. Dramatically different normal force on the tires. Mass has no direct correlation to the normal force.

[hammer]

Nope, Einstein is dead and Hawking would need a very specially designed bike or a bigger motor on his wheelchair.

Physics is a big part of the design of every car and bike tire out there. Physics played a big role in getting us to the moon too. Maybe the astronauts did not spend too much time going deep into it but I am pretty sure they appreciated those who did.

Would you get in a small capsule under whatever tons of highly explosive tanks and........? Well, maybe I would if I could.

[Sin City Stan]

Originally Posted by hammer

.

Would you get in a small capsule under whatever tons of highly explosive tanks and........?

In a second!!

[blaneb]

Originally Posted by upside22

I suspect that the issue here is a little more complicated than has been presented. The normal force at any point on the surface of a tire is going to be inversely related to the total weight of the bike and the contact area. Thus the bigger the contact area the lower the normal force at any point in the contact area. This is why they use big tracks to hold up an M1A1 tank instead of round wheels - bigger surface area results in less normal force at any specific contact point.

The force being applied to the tire also gets spread out over the same contact area. It doesn't matter if this is torque applied by the engine or centripetal force from going around a corner.

Where this gets complicated is that the total action between a tire and the surface is going to be a statistical relation integrated over the entire contact patch, i.e. at any instant of time one point on the contact patch may have the friction force exceeded while another point does not. I suspect what a rigorous statistical analysis would show is that the larger the contact patch the higher the total torque has to be to exceed the total friction force.

If this was *NOT* the case then it would make more sense to run racing bicycle tires on our motorcycles in order to reduce rolling friction since the same friction force would be available to hold the motorcycle to the road regardless of the size of the contact patch.

Not correct. The normal force of the tank will be the weight of the tank, period. That weight is the same weather it is on tracks or on wheels. What is different is the pressure applied to each square inch of contact area. A track will spread the normal force over a much larger apparent area of contact than wheels can. So, once again, the normal force applied to a material (in this case a track or wheel) remains the same (in this case the weight of the tank) regardless of the size of the apparent areas of contact.

If you want to insist that the apparent area of contact has a direct correlation with the force of friction then you are arguing against over three hundred years of understanding on the subject. The minute you produce one scintilla of evidence that overturns the findings of Da Vinci, Amontons or Coulomb in regards to the nature of static friction, I will be the first to submit you work to the Nobel committee for your prize in Physics. No one ever has in over three hundred years, but who knows, you might be the one!

I'll wait for your evidence, good luck with the committee.

[blowndodge]

I've always understood the "Theory" the angle of the dangle and the square of the hair, divided by the heat of the meat = the cube of the tube..

That's why I run a car tire!!

[waterman]

Originally Posted by blaneb

So, an 800 lb. bike will have the same traction on the Moon as on Earth. Same mass, right. Come on, please!

A dragster might have 1000 lbs. of normai force (not nominal force) on the tires at launch, but will have 5000 lbs. of normal force at speed due to the downforce of the rear wing. Same mass, stopped or at speed. Dramatically different normal force on the tires. Mass has no direct correlation to the normal force.

Ok, I am talking about the gravity on earth. Haven't seen a nomad on the moon yet or has Dan been there yet. If you want to bring that up, how about Jupiter, Mars or heck a black hole!

Nominal force is the downward force against the surface. When you start talking about wings and the downward thrust that those apply we are looking at engineering and physics. Those are designed to take the force of the wind (again it is a mass and convert it to a downward force). However, without those included you are talking about mass, especially when you are at slow speeds. If you really want to start talking about it then we need to discuss center of gravity and how that changes with the kinetic force when braking. As you brake hard the weight distribution is more forward than at a constant speed. There is more weight distribution on the front wheels as compared to the rear.

[blowndodge]

OOPS! I forgot the "gloom of the moon" in my equation!!!!

[ringadingh]

WoW! You guys have convinced me that I need a wing on my Nomad.

[Todd]

I did say "in the gravity I live in"......I wasn't aware we needed to address it on other planets...

although I guess we can debate whether Pluto should really be considered a planet?? or maybe just a moon, or for BD, just a disney character. ::) ::)

[blaneb]

Originally Posted by waterman

[quote author=blaneb board=general thread=17345 post=267756 time=1273865479]

So, an 800 lb. bike will have the same traction on the Moon as on Earth. Same mass, right. Come on, please!

A dragster might have 1000 lbs. of normai force (not nominal force) on the tires at launch, but will have 5000 lbs. of normal force at speed due to the downforce of the rear wing. Same mass, stopped or at speed. Dramatically different normal force on the tires. Mass has no direct correlation to the normal force.

So, you feel the laws of physics are different on the Moon than they are on Earth. Are you saying the same bike has a different mass on the Moon than on Earth, of course they're the same, it has the same mass anywhere in the universe. But as any 5th grade science student understands, mass and force are completely different concepts. A hydraulic press that weighs 50 lb. can apply 20,000 lbs. of force, but it will never have more than 50 lbs. of mass.

And again, when talking about the force of friction, it's called the NORMAL force, NOT the nominal force. The "nominal" force is meaningless unless you think the force is whatever you say it is, and then I guess that would be a "nominal" force. But the normal force has an actual value, and really has little to do with just mass.

Also, the normal force is the upward force the road applies the apparent contact patch of a tire, not the downward force of the tire on the road.

Nothing else you said really make any sense in relation to a discussion of the Coulomb\Amontons model of friction, which clearly states that the force of friction is the result of the nature of the material involve and is directly proportionate to the normal force and is independent of the apparent area of contact.

I again welcome you to demonstrate where the apparent area of contact has any relationship to the force of friction.

[hammer]

http://i853.photobucket.com/albums/a...ghtjoker_2.jpg

[Todd]

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[dantama]

Yikes, see what happens when you go against the force and say that car tires don't stop you faster :-/ ???

I'm going to go back and change my findings to say this:

Wow, holy sh*t! When you hit the brakes with the car tire on you really have to brace yourself, it stops so much faster it'll almost pitch you over the bars. And when you measure it, it stops way shorter!

OK plaid shirt guys, get back to work :)