[Phil №❶]

I know this is a dumb question, because we see examples of the answer all the time at racetracks but.

If each wheel has a specific load or weight applied to it, how does increasing the contact surface area increase grip. Why doesn't the stiletto effect counteract this.

[Surferdude]

A pretty good question Phil. And not an easy one to answer. Might take a discussion, rather than quoting some definitive formula.
Assuming I understand what you mkean by the stilleto effect, lets expand on that a bit.
The downward force applied through a stillto heel is just that. Downward force /pressure.
A tyre's grip comes from a combination of things. The equalisation of weight throughout the footprint.  The shape of tread blocks (both loaded and unloaded - and in transition). The compound of the rubber. And probably others which will occur to me later.
Let's imagine someting the size of a stiletto heel and using a good glue, stick it to a given surface. Now, take something a little larger than the size of your hand with fingers outstretched, and using the same sort of glue, stick it to the same type of surface.

Now, which one do you reckon you would be able to work loose first?

[Just Rick]

surferdude,I'm far from a scientist,my simplistic look at it is what you have already said(I think),the greater the surface area the greater the grip,especially with a downforce applied

[Phil №❶]

Yes but, would you rather be trodden on by the toe of a stiletto shoe, or the heel. Same downward force but completely different effect. Even though I know you are correct, it must have something to do with co-efficient of grip.

[Doggie 1]

Yes but, would you rather be trodden on by the toe of a stiletto shoe, or the heel. Same downward force but completely different effect. Even though I know you are correct, it must have something to do with co-efficient of grip.

I'm more used to phone books, actually.

[Phil №❶]

Can't say I've ever been trodden on, by a phone book.   

[Just Rick]

Yes but, would you rather be trodden on by the toe of a stiletto shoe, or the heel. Same downward force but completely different effect. Even though I know you are correct, it must have something to do with co-efficient of grip.

Phil
Ah! but using this scenario,I know which I would prefer,but I know which one would be easier to get out of.
I would prefer to be trodden on by the toe of the siletto shoe has the load is spread over a larger area hence less pain,but alas if I had someone step on my foot with the pointy heel it would be easier to pull my foot from underneath it. as the contact area would be so much smaller and easier to break the point of contact.

Dave
Phone books REALLY,your no longer in the force,your not allowed to use phone books these days  although effective at not leaving bruising,highly illegal these days    (And Yes I'm Joking)

[Phil №❶]

But if it's spread over a larger area then the pressure must be substantially less at any particular point, therefore, the chance of slipping must be easier to achieve, yes / no ?

[Surferdude]

Yes but, would you rather be trodden on by the toe of a stiletto shoe, or the heel. Same downward force but completely different effect. Even though I know you are correct, it must have something to do with co-efficient of grip.

A tyre's grip comes from a combination of things. The equalisation of weight throughout the footprint.  The shape of tread blocks (both loaded and unloaded - and in transition).
Exactly! 

[Just Rick]

But if it's spread over a larger area then the pressure must be substantially less at any particular point, therefore, the chance of slipping must be easier to achieve, yes / no ?

Phil
I'm just a simple bloke  your now just flumexing me with lodgic  I know lodgically what you are saying sounds correct  but in reality it is not what happens  Suferdude Hhheeeeeeeeellllllllllppppppppp Pleaseeeee 

[Surferdude]

But if it's spread over a larger area then the pressure must be substantially less at any particular point, therefore, the chance of slipping must be easier to achieve, yes / no ?

Phil
I'm just a simple bloke  your now just flumexing me with lodgic  I know lodgically what you are saying sounds correct  but in reality it is not what happens  Suferdude Hhheeeeeeeeellllllllllppppppppp Pleaseeeee 

He's answered it himself with the co-efficient of grip comment.
One of the most important functions of a tyre is to maintain as large and as evenly spread a contact with the road as possible. The rubber over the whole area of the contact is working to keep the car from sliding sideways, or locking up and sliding forward under brakes.
The tyre is helped in this by the car's suspension. Graham Scudamore-Smith from Fulcrum Suspensions explained to me years ago that the whole purpose of having wheel alignment settings correct was to ensure that the tyre had the maximum possible contact with the road at any given moment. The sidewall of the tyre "gives" in such a way as to facilitate this also. In addition, the tread contact helps to keep the tyre sidewall in the shape it's supposed to be. So all the components are working together and complementing one another. If the only contact you have with the road is a stiletto heel sized patch, any distortion will dramatically affect all those factors and a sudden loss of grip is gonna happen.

[The Gonz]

 
Grip is entirely about contact area. Another factor that interferes with achieving maximum contact area is water. Race cars are good examples of always reaching for maximum grip and the water problem is visibly tackled not by reducing tyre width but by going from slicks (yes, maximum grip) in the dry to appropriately grooved tread to help pump the water away quickly enough to sustain sufficient grip, even in the absence of that ideal slick contact. Obviously, slicks in the wet will bring about aquaplaning as they tend to capture the water rather than expel it.

[Phil №❶]

Some very intelligent people in this forum, (don't keep it locked inside chaps), thanks everyone, well done. 

[AlanHo]

In theory, and ignoring the effect of tyre tread block displacement, the lateral force on the contact surface of a tyre is not significantly effected by the contact patch area. The need to increase the contact patch area is driven by other factors.

Racing car tyres do not behave in the same way as the road going tyres we all use. The rubber compound of a race tyre becomes "sticky" at high temperature to produce a very high coefficient of friction. Cornering. acceleration and braking forces produce a shearing force on the tyre surface.  This rubber is relatively weak in shear and a racing car has extra wide wheels to produce a large contact patch in order to spread the shearing force over a large area of rubber.  Pirelli have recently proposed that the F1 tyres for 2014 need to be wider to increase the contact patch area because the new 1.6 turbo engines will develop higher torque than the current engines and apply shearing forces on the tyre tread not sustainable by the present tyres.

The grooves in the wet weather tyre reduce the contact patch area and thus increase the surface pressure between the road and tyre helping the tyre to cut through the water layer and displace it to maintain grip. A slick tyre would not penetrate the water boundary layer and produce no grip.


I will now get back in my box..............................

[eye30]

I run slicks on my push bike.

Grip great in dry,  hopeless in wet.

Now i know why.