[Sheel]

Treads help in channeling out water. I think this is where tread is necessary, at least on road.

[vikram_d]

Originally Posted by SS-Traveller

Bald tyres don't pick up nails and don't get punctured.

There might be a very small amount of truth to this statement seeing how tyres harden with age. Also since the softer rubber bits are completely worn out, the harder layers beneath may be more resistant to punctures.

[drpullockaran]

Guys, guys, and girls if there are any here. Please get out your physics class 12 books and read up on factors that affect coefficient of friction and friction as such. You will be darned surprised as to what you had read up in the classrooms; physics is physics. Tire width has nothing to do with grip of a tire in the dry and in the wet the cycle tire will any day perform better than a wider tire. A cycle tire and a tire as wide as a monster truck will provide you with the same grip during braking if fitted on the same vehicle with the same compound. This statement may be laughable but do pester Google uncle before dismissing it out right. For starters here is a link.
http://www.waltersforensic.com/artic...n/vol1-no8.htm

[Aroy]

Originally Posted by smartcat

Just curious!

Taking the same logic forward, as road tyres' tread wears out over 50,000 kms+, does the grip levels increase on our normal roads when its not raining? If no, why?

I see millions of taxis, buses and trucks with bald tyres and they seem to manage the grip/braking part fairly well - most of the time.

Grip of a tyre is dependent on the area of the rubber in contact with the road
. A tyre with no tread pattern will have more area in contact
. A tyre at lower pressure will have more contact area
. A softer compound will have more coefficient of friction compared to a harder compound, but will wear out much faster.

A tyre which has gone bald
. will expose its cords, which can lead to their damage and tyre failure
. will have gone hard due to age and not grip as well as a new tyre
. will skid on wet, stony and sandy surfaces

So on the whole as far a better grip and breaking is concerned a "Tread less" as opposed to bald tyre will be better on a dry flat surface as in a race track, but a disaster in the varied conditions faced by us on the road.

[drpullockaran]

Originally Posted by Aroy

Grip of a tyre is dependent on the area of the rubber in contact with the road.

Correct if I am wrong but the area of the contact patch has nothing to do with the grip of the tire. It might sound ridiculous but please do look up our dusty trusty 12th class text books before refuting this. The only thing that affects friction is the force between the two surfaces and the chemical composition of the two surfaces in contact. If more grip was available based on area of cotact patch then formula 1 cars would have huge tires on the front axle similar to the ones on the rear. Wide tires are there in the rear only to last longer with softer compounds. The wide tires we use if made of harder compound and that which can carry heavier loads will only result is less grip and not the other way around. As long as there is tread the total square mm contact patch will be less than the same tire gone bald. Each tire is made for optimum weight and load carrying capacity. Varying away from the ideal weight will reduce grip especially lateral G's.

[thoma]

Hmm..makes me think of how a locomotive brakes with so little area of contact. I am tending to guess that it is the downward force that matters more than the area there.

[ramzsys]

This has been discussed a few years back.

http://www.team-bhp.com/forum/modifi...tml#post373935

[YaeJay]

NO! There is more to a Tyre than the tread or lack of it. Softer the compound more grippy it is. And the compromise is on the life of the Tyre. And there are so many other factors that go into a tyre. A bald road Tyre is not an F1 Tyre. I would would say its not a tyre at all. From my limited experience.

[honeybee]

Imagine this: A typicall race tyre used on an F1 car may not even last the entire distance of the race, while a road tyre is expected to last about 40,000 kms. So the road tyre is about 1000 times harder than the race tyre.

Also if you study the cornering speeds, the corners which we should ideally take at around 40-50kmph are easily taken at nearly 3 times the speeds by the F1 cars, and if we were to attempt some of their hairpin bends, we would be slowing down to a crawl. So the grip levels of the tyres too are many times more.

These are observations of a layman. You could debate further on the compounds and other more technical matters, but these two observations should help you understand racing slicks which are brand new out of the factory and bald road tyres worn out from years of use (or abuse) are worlds apart.

[vikram_d]

For 12th standard text books, things have been over simplified. They don't look at variables like tire flex, tread flex, heat, slip angle, tire deflection, etc. All of these variables make the contact patch important. Oh and F1 tyre sizes are governed by regulations. Remember the six wheeled car F1 car? If I remember correctly it was a Williams car.

[amit_purohit20]

Originally Posted by drpullockaran

Guys, guys, and girls if there are any here. Please get out your physics class 12 books and read up on factors......missing it out right. For starters here is a link.
http://www.waltersforensic.com/artic...n/vol1-no8.htm

Originally Posted by drpullockaran

Correct if I ...... capacity. Varying away from the ideal weight will reduce grip especially lateral G's.

Originally Posted by ramzsys

This has been discussed a few years back.

http://www.team-bhp.com/forum/modifi...tml#post373935

Originally Posted by vikram_d

For 12th standard text books, things have been over simplified. They don't look at variables like tire flex, tread flex, heat, slip angle, tire deflection, etc. All of these variables make the contact patch important. Oh and F1 tyre sizes are governed by regulations. Remember the six wheeled car F1 car? If I remember correctly it was a Williams car.

I work in a Tractor company and this same question in a different format haunts many people and many dont really have the answer for it - Why are the 2WD tractors Rear tyre bigger?
1) A contact patch between a tyre and a road is oval in nature. It can be increased by a) Increase the tyre width or b) Increase the diameter of the tyre.

As per Ideal static friction law area doesnot play a role in determining the Frictional force generated.
Frictional Force (F)= Coefficient of Friction (Mu) X Weight of the body(W)
so neither the Frictional force nor the Coefficient of Friction is dependent on Area then why do we really need a bigger contact patch (area)?
Well the above law is for ideal bodies which do not deform and also with no surface imperfections. But in real conditions both the tyre and the road deform and have external surface imperfections.The above law has no meaning if we simply skip the surface finish of the two bodies in contact in real world terms.
For bodies which deform the "Law of asperities" holds true. In simple terms Law of asperities states that surfaces of any body is made up of minute imperfections in the shape of a Hacksaw tooth (called as asperities). Imagine a Hacksaw which corresponds to the Tyre and oppositely faced and in contact with another hacksaw tooth corresponding to the road surface.So the tooth of the tyre rubber gets in the cavity of the road and vice versa. Due to movement these tooth try to shear or break out each other thus creating frictional force.(In this case it is obvious that the asperities on the rubber tyre side would be more easy to break/shear and so tyre wears out faster than the road.)
So more the number of asperities to break more the Frictional force. For a bigger area of contact or contact patch the number of asperities will be more thus creating more frictional force. So in real world a bigger contact patch ie. a big fat tyre will always give more better grip and braking as compared to a thinner tyre.
Consider the asperities in the micro concept, for very very large asperities such as a pothole the mechanics would change drastically.

One more point not to miss is that there exists a force of cohesion between the rubber tyre and the tarmac. A soft compound rubber tyre will have more force of cohesion with the tarmac thus also helping to increase the grip/traction. Its like the softer rubber will more properly fill all the minute cavities in the road in turn meaning more closely packed asperities to shear and rub against each other, otherwise as per the above discussion given the same contact patch a steel wheel should also have the same grip as a rubber tyre! Remember that when locomotive steel wheels start slipping on the rails, fine sand is used to create friction between the two.
Coefficient of friction depends upon the nature of materials in contact.

So again ideally a bald tyre should be more gripper than a tyre with treads. I also feel that treads hardly play a role in dry grip between tyre and good flat road conditions.
But practically it might not be so because:
a) The bald tyre might not have worn evenly causing uneven contact between tyre and road leading to reduced contact patch.
b) The rubber compound becomes harder and harder over the use of the tyre life period.
c) The rubber compound used below the tread depth might be more harder than the external rubber in contact when the tyre was new.

Tyre tread provides help in draining water outside the contact patch as soon as possible and its role is significant in non-ideal road conditions. For eg a Knobby tyre on a motor cross bike or a tractor tyre with lugs.

Other than these many other factors affect grip:
1) Non tarmac conditions.
2) The softer the compound of the rubber the higher the grip.
3) Slip angles.
4) Hard and soft suspension setup.
5) Nature of Tyre deformation during cornering and braking.
6) Weight transfer of the vehicle during braking and cornering.
7) Shape of the tyre when inflated for eg. some bike rear tyres have a more round shape profile for better cornering and higher lean angles but then they provide less support in straight line braking.
8) Less pressure in the tyre means more bigger contact patch so again increasing grip but leading to large scale tyre deformation which can also be detrimental sometimes.

One could also go through my comment on selecting a motorcyle tyre:
http://www.team-bhp.com/forum/motorb...ml#post2853071

[speedmiester]

In a simple word "No". You cannot even comprehend the difference in design and compound of racing and road tyres.

This reminds me of a time when I asked my friend to change his tyres immediately in his Omni which had completely worn out cross ply tyres. His response was on similar lines. "Dude, dont you watch formula 1. Bald tyres are best for grip."
Needless to say that was the last time I ever came close to him and his car.

[drpullockaran]

http://www.tribology-abc.com/abc/history.htm

This is liable to get more confusing. Have a read though.

[vikram_d]

Originally Posted by drpullockaran

http://www.tribology-abc.com/abc/history.htm

This is liable to get more confusing. Have a read though.

Nice article, but it does not talk about heat. Coefficient of friction increases with heat. That is the reason racing slicks are pre-heated to the optimum operating temperature.

[AlphaKilo]

Originally Posted by amit_purohit20

I work in a Tractor company and this same question in a different format haunts many people and many dont really ...

So essential I understood only thing from your post:

"The worse the road condition, the best one's chance of braking" - Hurray! Any politician will be happy to hear my conclusion.

One serious question to you: Why do the rear tyres of tractors have such huge treads? Why are they outwards like spikes rather than inwards like in other road vehicles? (it would be really hard to drive the tractor on smooth tarmac (well if you can find one such road anywhere in India))

a. Because they are mostly used in slush environment where grip needs to be ploughed

b. some other technical reason behind it

c. Just for fun dude!creativity!!looks cool