Physics talk

[mossy1200]

Im not the brightest guy in the world but idd like a big fat sticky contact patch telling me I have grip. Biscuit tyres and hp dont do alot for me other than skids.

[bogan]

What causes adhesion?

Chemicals, fuck knows which ones, there's probably at least three of them in there. I just scraped through with 7th form chem so its beyond my field of expertise.

Going to need a better source than another forum OAB, seriously I could just cite myself on another forum and say "Oh look, I agree with myself!"

He wasn't quoting it for scientific fact, just cos they explained it well. Are you really struggling with the concept of adhesion, or are you just being deliberately obtuse now? If its the later, I would say an 'I must be right' ego is one of the biggest impairments to learning, and at your stage you should have a lot to learn, and nothing to get in the way.

[Drew]

Im not the brightest guy in the world but idd like a big fat sticky contact patch telling me I have grip. Biscuit tyres and hp dont do alot for me other than skids.

Interesting, have you considered the front contact patch on a large bike, and the load distribution between it and the rear whilst tipping into a turn?

[Akzle]

the answer is π.

funnily. it's also the question.

[Dave-]

He wasn't quoting it for scientific fact, just cos they explained it well. Are you really struggling with the concept of adhesion, or are you just being deliberately obtuse now? If its the later, I would say an 'I must be right' ego is one of the biggest impairments to learning, and at your stage you should have a lot to learn, and nothing to get in the way.

No, I'm usually wrong, but then I go and find out and I become right, you just happened to catch me on something I was once wrong about.

Judging by your wee personal user title you can probably tell me something about ARQ protocols?

[mossy1200]

Interesting, have you considered the front contact patch on a large bike, and the load distribution between it and the rear whilst tipping into a turn?

you seen the fizzer after testing front end contact footprint stickness. It unloaded the content of my wallet and made my wife cry.

[Ocean1]

Chemicals, fuck knows which ones, there's probably at least three of them in there. I just scraped through with 7th form chem so its beyond my field of expertise.

Partly correct.

This part:

fuck knows

At least, as of a year or so ago nobody knows.

A few shrewd suspicions, to be sure. But that's it.

[scracha]

He wasn't quoting it for scientific fact, just cos they explained it well. Are you really struggling with the concept of adhesion, or are you just being deliberately obtuse now? If its the later, I would say an 'I must be right' ego is one of the biggest impairments to learning, and at your stage you should have a lot to learn, and nothing to get in the way.

I can't lurk anymore. You're obviously struggling with the fact he's educated and quoting scientific fact.
Friction is 100% independent from the area of contact.

The coefficient of friction is dynamic, partly due to the way a wide tyre deforms and changes temperature.

[onearmedbandit]

Going to need a better source than another forum OAB, seriously I could just cite myself on another forum and say "Oh look, I agree with myself!"

See this quote Dave

He wasn't quoting it for scientific fact, just cos they explained it well. Are you really struggling with the concept of adhesion, or are you just being deliberately obtuse now? If its the later, I would say an 'I must be right' ego is one of the biggest impairments to learning, and at your stage you should have a lot to learn, and nothing to get in the way.

If a wider surface area doesn't provide more 'grip', then can you explain to me why I've experienced otherwise? I realise the 'friction' doesn't change. But explain why a car with the same weight, same power, will lose 'grip' earlier on asphalt with narrower tyres? That's my experience in the real world.

[mossy1200]

Im thinking that if the brains are designing abs,traction control and launch control etc on bikes I might be better off with an older bike.

Rider feedback sounds safer than someone get his/her math wrong.

[Kickaha]

That's my experience in the real world.

The real world dosn't count if a forumla in a book somewhere says different

[onearmedbandit]

If a wider surface area doesn't provide more 'grip', then can you explain to me why I've experienced otherwise? I realise the 'friction' doesn't change. But explain why a car with the same weight, same power, will lose 'grip' earlier on asphalt with narrower tyres? That's my experience in the real world.

I may have found the answer to my question. Ok does this work for you then Dave?

So do wider tyres give better grip?

If the contact patch remains the same size and the coefficient of friction and frictional force remain the same, then surely there is no difference in performance between narrow and wide tyres? Well there is but it has a lot to do with heat transfer. With a narrow tyre, the contact patch takes up more of the circumference of the tyre so for any given rotation, the sidewall has to compress more to get the contact patch on to the road. Deforming the tyre creates heat. With a longer contact patch and more sidewall deformation, the tyre spends proportionately less time cooling off than a wider tyre which has a shorter contact patch and less sidewall deformation. Why does this matter? Well because the narrower tyre has less capacity for cooling off, it needs to be made of a harder rubber compound in order to better resist heating in the first place. The harder compound has less mechanical keying and a lower coefficient of friction. The wider tyres are typically made of softer compounds with greater mechanical keying and a higher coefficient of friction. And voila - wider tyres = better grip. But not for the reasons we all thought.

http://www.carbibles.com/tyre_bible_pg3.html

[Spuds1234]

This also explains it pretty well (the wider tyre thing). Perhaps a bit more simply.

Mehcanisms of Tire grip.

Friction
Mechanical Keying
Adhesion

As they are madr from deformable rubber, tires dont exactly follow basic friction theory. So to just say that F=mu*r is strictly wrong. Although it basically does floow this during the elastic range.

Tires only give grip when they are at the correct temperature. this is the most important thing you can remember about tires .


Now on to business.

Tires are the most important part of the suspension, either they are designed to fit it, or the suspension is designed around the tire.

People who say wider tires make more grip because ;''there is more rubber on the road' are wrong. They are both wrong that it makes mroe grip and that there is more rubber on the road.

When you make a tire wider, you alter the contact patch to be wider , but it reduces in length. So depending on sidewall stiffness, a wider tire can actually give less rubber on the road.

The main reason for tires being the size they are is actually heat management. Wider, low sidewall tires will cool better than narrow tall tires. If you can;'t get a tire up to temperatie it will give no grip, if you get it too high you will cook the rubber and ruin the set of tires.

Back to contact patch, you can safely assume that contact patch stays roughly the same area with wide or narrow tires (as long as the load stsys the same). Narroe will have longer contact patches and wide tires will have shorter.



The reason why F1 tires are wide is primarily so that they dont cook (remember they arent just wide, they are fairly high sidewalled), but they ten dto have wider contact patches because they will give better grip going round corners.

A wide tire will generate more lateral force per slip angle making cornering better. F1 cars DO NOT have wide tires for linear acceleration.


Conversely (Mike im goin to have to disagree with you here) drag racers acutally use the tires not becuase of the width, but the tallness. As we know a wider contact patch gives better cornering performance, a narrow but long contact patch is what you want for linear acceleration.

so strangely, drag racers will actually be better with narrow tires. So why do they use wide tires? (remember the most important gip aspect of tires) Temperature! They want as longer contact patch as they can get, but need the width for cooling. (eith 4000+ horsepower you do kind of build temp rather well)

But if you look at the contact patch shape between say, an F1 car or drag racer. (both are considered to use wide tires). The F1 patch will be wider and shorter for good cornering, the drag patch will be longer and narrower (relatively) for good linear acceleration.


So to sum up: Wider tires are not always better. They dont always give better traction. It depends on the car, the situation, the conditions.

Eg. Rally cars use wider tires when on tarmac rallys, and use (surprisingly) very thin tires on ice rallys.
F1 cars used to use narrow tires until aero began to be used in the 60's.
Drag racers acutally want tall tires, width is there to stop the tire being destroyed.

I found it here http://www.physicsforums.com/showthread.php?t=330790

[jonbuoy]

Centrifugal force doesn't exist, so I'm not sure what you're on about there.

But even if your tyre expands by 2% it's pressed on to the road by some mass which is going to be greater than the 2% increase, or so I think, and my very quick calcs would suggest.

I'm actually putting together the idea of the smart-bike which would take your velocity primarily from GPS and/or accelerometer it's only a matter of time before the bike becomes "smart"



GPS reads in 3 dimensions from at least 4 satellites in geosynchronous orbit (which means they don't move relative to the earth) so even when you're going up or down hill you get the magnitude of velocity.

Are you sure? GPS Speed Over Ground is exactly that. It doesnt use altitude for the calculation.

[bogan]

No, I'm usually wrong, but then I go and find out and I become right, you just happened to catch me on something I was once wrong about.

Judging by your wee personal user title you can probably tell me something about ARQ protocols?

But this same point keeps coming up, what you find out about being textbook right, only gets you to almost being real world right. Thats when you have to listen to people with real world experience, and fit their observations into your model rather than just posting simplist equations.

No, even googled the acronym, still don't care.

Partly correct.

This part:

At least, as of a year or so ago nobody knows.

A few shrewd suspicions, to be sure. But that's it.

Huh, thats kinda cool they haven't quite figured it out yet.

I can't lurk anymore. You're obviously struggling with the fact he's educated and quoting scientific fact.
Friction is 100% independent from the area of contact.

The coefficient of friction is dynamic, partly due to the way a wide tyre deforms and changes temperature.

I don't think I ever said friction was dependant on contact area, just that grip was; grip = friction + adhesion