[YaeJay]

But they do have a lot of rolling resistance and if you got them baldies up front (Nuts!) the steering does feel heavy. But that does not equate to grip. I never have baldies I change way much ahead. But have driven cars with baldies for a few kms. I think this confusion might originate from that.

[amit_purohit20]

Originally Posted by AlphaKilo

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

Tractor rear tyres are big and have huge treads because:
1) Bigger diameter tyres means more ground clearance.
2) A tractor has to pull a plough which is as high as 21 inches deep inside the soil, so you can understand how high the pulling force is required. Its not similar to towing a vehicle on plain road. The forces involved are very high and severe in nature.
3) The deep treads sink deep in soil and then when the tyre rotates its like the treads push a chunk of soil back thus creating traction. The difference between on-road tyres and tractor tyres is smilar to two rotating pulleys in contact with each other and two gears in positive contact with each other respectively.
Some more tractor tyre facts:
a) Indian tractor tyres are filled with 70% water to ballast them additional weight.
b) Additional ballast weights are also added to increase the tractor weight.
c) 15% Wheel slip during farming is considered a normal practice. Thus tractor tyres dont last long inspite of being made up of hard rubber.

I really did not understand your question regarding inward and outward spikes and neither I am any tractor tyre expert to answer your exact query.Sorry for that, all I know is that there are lot of complex soil mechanics taken into consideration for deciding the same.

Also as per the link attached above thanks for reminding me that its the amontons law of asperities.

To confuse more:
Torque (T)= Force (F) X Radius (R) where R is radius of tyre transferring power and T is the torque at the axle.
Considering torque at the axle remaining the same which one would be better a scooter or a motorcycle to climb a hill-road and why?
For a scooter the force F will be more because of less tyre radius so a scooter should ideally be better to climb a hill. But practically its the motorcycle right! (This question was asked to me in my Final engineering Viva )

Consolidating the above literature:
Actual Friction (leading to traction) is dependent to less or more on:
1) Nature of materials in contact.
2) Area of contact patch.
3) Adhesion of two materials.
4) Surface finish of bodies to a certain extent.
It seems Friction has its own ways of being dependent of many things but at the same time remain independent of many parameters at least in theory!

[subratasenn]

Originally Posted by AlphaKilo

2. Harder the compound, better the chances are to survive a Foreign object damage(FOD) hence, make a tyre hard (may be possibly out of iron , i know i know you all would be wanting to kill me now! hey come on, we won't have any more punctures) and make them "mogambo ishtyle" hurray! Super grip! Isn't that what our trucks and taxi's doing? Desi ishtyle and technology!

Well, yes. Bullock carts and hand-pulled rickshaws in Kolkata run on this principle. Wooden wheel, covered with steel plate, over which is placed a hard rubber cover. Trucks and taxis can go for this kind of wheels.

[Aroy]

Big lugs on tyres, especially tractor and off road tyres are more for gripping in mud and slush than for gripping on a flat surface. If you go through catalogs of off-road tyres, then you will see that the tyres for "hard rock" areas have more area while those for mud have more logs (less area).

For better traction on flat surface, lower pressure is used to increase the contact patch. The grip of a tyre is the force that can be exerted on it to move the vehicle forward. Similarly a larger contact patch increases the breaking on a flat hard surface.

[Maverift]

To answer your first question:

Given all other conditions are same (and dry), a tyre with more more contact surface on road will be grippier.

This is not to say that old bald tyres are gripper than fresher treaded tyres. More like the tyres would be grippier if the grooves in treads were completely filled with the same soft compound which grips the road.

In my opinion:

• Slick Tyres used in F1 is Mr. India style
• Bald Tyres used in some taxis is Mogambo style
• Grooved Treaded Tyres is Apache Indian style

Grip Wise on a smooth and dry tarmac it is Mr.India > Apache Indian > Mogambo.

In changing conditions better bet would be Apache Indian > Mr.India > Mogambo

Whatever it is, Mogambo is most unsafe and best avoided.

[bijuiser]

Originally Posted by Maverift

Given all other conditions are same (and dry), a tyre with more more contact surface on road will be grippier.

In other words- with Slick\Bald tyres and a little change in condition (just a little sand/gravel/pebble/water) may result in minimum or no road surface contact.

[n.devdath]

Originally Posted by Maverift

• Slick Tyres used in F1 is Mr. India style
• Bald Tyres used in some taxis is Mogambo style
• Grooved Treaded Tyres is Apache Indian style

Grip Wise on a smooth and dry tarmac it is Mr.India > Apache Indian > Mogambo.

In changing conditions better bet would be Apache Indian > Mr.India > Mogambo

Whatever it is, Mogambo is most unsafe and best avoided.

This answer says it all and very correctly.

[amit_purohit20]

Originally Posted by amit_purohit20

To confuse more:
Torque (T)= Force (F) X Radius (R) where R is radius of tyre transferring power and T is the torque at the axle.
Considering torque at the axle remaining the same which one would be better a scooter or a motorcycle to climb a hill-road and why?
For a scooter the force F will be more because of less tyre radius so a scooter should ideally be better to climb a hill. But practically its the motorcycle right! (This question was asked to me in my Final engineering Viva )

Well answer to the above question lies in two aspects:
A) How much tangential force the tyre can apply to the ground and
B) How much return force (traction availability) the ground can apply to the tyre.

For point "A" it is completely dependent on the equation T=FXR so that means a scooter tyre will have more tangential force than a motorcycle tyre for the above case.
But, practically a motorcycle tyre will have more contact patch due to the larger tyre radius thus having more traction available ie. point "B" which depends on:
a) Vertical weight on the tyre contact patch.
b) Contact patch area.
c) Nature of ground-tarmac,mud etc.
d) Tyre characteristics (includes tyre compound,type, etc etc).
So the traction available for a motorcycle tyre will be more.

Force applied through tyre to the ground (Fa earlier F)
and say Force reaction by ground (Fg).
If Fa=Fg the vehicle will move forward.
If Fa>Fg the tyre will start slipping.
So a higher Fa (as in the case of a scooter tyre) is of no use if the contact patch cannot provide sufficient Fg.

One more point in consideration, I have never observed a bald tyre fully flat like a racing slick tyre so no question of comparing the two at least on available contact area wise.
For a dual sport motorcycle tyre (conditions match indian roads) the best way I think is to have a hard compound in the central patch region and soft compound on the tyre edges for good cornering grip.

[vivekgm]

Worn out tyres that are bald don't compare to slicks at all and are downright dangerous to yourself and to the general public.

Bald tyres don't have any meaningful rubber left or the rubber that is left is too thin and very close to exposing the carcass of the tyre to provide any meaningful grip. They overheat very quickly at speed or under emergency braking, weakening the already worn tyre even more and can cause dangerous blowouts at any time.

The best tyre for tarmac (ONLY DRY TARMAC) is one that provides the maximum contact patch with the road. Hence slicks on racing cars. But they don't work at all on differing surfaces that normal road cars run on - hit a patch of water on slicks at speed and you have an express ticket to heaven. These racing tyres generally use softer rubber compounds than road car tyres and last just a 100 or 200 km before they have to be discarded. Also, unlike worn tyres, they have a thick layer of usable rubber which provides the grip.

I hope this answers your question. Cheers

Originally Posted by smartcat

Just curious!

F1/Nascar car tyres are as bald as Mogambo's head, and are called as "Racing Slicks". The idea behind using these tyres is that contact patch is more than grooved tyres, and hence the tyres are grippier when the track is dry.

Racing Slicks:
Attachment 1048522

Wet Tyres:
Attachment 1048524

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.