Tire contact patch shape Length vs width

[g-force_addict]

First, How do you change its shape?
I assume for a wider tire contact patch gets wider, and for a larger tire (diameter) its contact patch gets longer.
Am I right? Of course tire inflation matters...

Its a wide and short contact patch better suited to acceleration and braking, and a long and slender contact patch better for cornering?
For simplicity let's assume both the long and slender and the short and wide contact patches surface area is the same.

[Jersey Tom]

Why would you want to focus on the footprint shape, rather than focusing on the tire performance as a whole?

[Nando]

For simplicity let's assume both the long and slender and the short and wide contact patches surface area is the same.

My ignorant mind tells me you will end up with the same results because the contact patch essentially has the same area.

[g-force_addict]

For simplicity let's assume both the long and slender and the short and wide contact patches surface area is the same.

My ignorant mind tells me you will end up with the same results because the contact patch essentially has the same area.

I beg to differ.
I guess it's better to have the contact patch spread its area among a line perpendicular to the desired force.
For example for acceleration and braking its better to have a short and wide patch while for cornering a long and narrow one.

I guess this is specially important when recovering from a skid.
For example ice skates offer little resistance to forward motion while offering considerable resistance to sideways movement. Of course ice skates blade area remains the same yet it offers more resistance in one axis.

[gato azul]

.
I guess it's better to have the contact patch spread its area among a line perpendicular to the desired force.
For example for acceleration and braking its better to have a short and wide patch while for cornering a long and narrow one.

Not so sure about this, maybe your ice skating analogy, while good to explain your line of thought, is not a good comparison in this context.
Have a look at a kart (shifter go kart to have 4 wheel braking) and compare it's max. braking performance vs. max. cornering performance (G-G diagram) compared to a more "conventional" car, let's say a Formula Ford.
Then take a look at the tyre dimensions and the effect it has on foot print length vs. width.

[thisisatest]

if the skate's blade was made of sandpaper, it would make more sense, but even then, youre dealing with a hard object digging into the surface as opposed to the other way around.

[Cam]

Some equations and information in here. Talks about a formula that is capable of describing the characteristics of side force, brake force and self aligning torque, through a joint study between Volvo and a University.

Bit over my head, hopefully it helps you.

http://www.theoryinpracticeengineering. ... ejka87.pdf

[Richard]

For simplicity let's assume both the long and slender and the short and wide contact patches surface area is the same.

My ignorant mind tells me you will end up with the same results because the contact patch essentially has the same area.

A short and wide patch could only be created by a low profile wide tyre at high pressure. A long narrow patch would need a tall narrow tyre at low pressure. Surely they would have markedly difernt performance?

[Greg Locock]

I'd suggest building a brush type model of the contact patch and investigating the effect of the orientation of the cp on the grip.

Failing that a perusal of longitudinal and lateral flattrac data might reveal some interesting insight.

[PlatinumZealot]

Some equations and information in here. Talks about a formula that is capable of describing the characteristics of side force, brake force and self aligning torque, through a joint study between Volvo and a University.

Bit over my head, hopefully it helps you.

http://www.theoryinpracticeengineering. ... ejka87.pdf

Give us a summary in a few sentences please.

[olefud]

For simplicity let's assume both the long and slender and the short and wide contact patches surface area is the same.

My ignorant mind tells me you will end up with the same results because the contact patch essentially has the same area.

I beg to differ.
I guess it's better to have the contact patch spread its area among a line perpendicular to the desired force.
For example for acceleration and braking its better to have a short and wide patch while for cornering a long and narrow one.

I guess this is specially important when recovering from a skid.
For example ice skates offer little resistance to forward motion while offering considerable resistance to sideways movement. Of course ice skates blade area remains the same yet it offers more resistance in one axis.

I always thought the opposite. By lengthening the contact patch in the direction of the desired thrust the patch is better mutually reinforced against distortion. Rather like (but different) you would want a beam to have its major dimension in the direction of the major load.

Don’t ask for a cite on this thought.

[Cam]

Found this Texas University experiment which might help. It's about truck tyres, but the info should give some assistance.

To determine the gross contact area for a number of statically loaded truck tyres using a variety of tire inflation pressure and axle load combinations. Results looking at contact area and contact pressure distributions. Using an inked tyre with an imaging system to read the print.

Might give you some further information that could scope out to different widths and circumference (length & width).

http://library.ctr.utexas.edu/pdf2/386-1.pdf

[Jersey Tom]

It's an interesting - albeit academic (ie not particularly practical for a race engineer) topic. You can try to think of it in a situation where you take all carcass deflection out of the picture and you're just looking at localized slip in a "rigid" footprint... but carcass control on footprint is just too much a part of reality to ignore. So let's say you went from Tire A to Tire B, which has a larger outer diameter, resulting in less longitudinal curvature of the mold shape and a different trend of footprint length versus load. In doing so you've also changed the structure of the thing. And really, who cares what the static footprint is doing if you're really interested in limit traction and the whole thing is distorted?

In any event, with a Coulomb friction model it should make zero difference what your footprint dimensions are if your area and global "mu" isn't changing. If slip velocity is a factor and you have post-saturation fall off... I'd think intuitively you'd want the spread of localized slip velocities to be as small as possible.

Or if you really want to waste your time going deeper down this rabbit hole, think about some other very real challenges - how about pressure distribution? Very flat versus higher in the center? What if the footprint is rounder rather than squarer? All things which make this sort of thing best left in the hands of the tire companies, as it's just going to be convoluted for the end user engineers IMO. To use a phrase from one of my competitors... sometimes you just have to put the boogeyman back in the closet and focus on other things.

As an aside it's also quite easy to get very misleading results (or interpretation of those results) from flat track data, should you be fortunate enough to have it.

[delacf]

Wider tires are better cornering. Both tires begin to slide at the same distance (roughly) from the center of the tread (if the pressures, diameter,... are the same), but a tread is wider than the other. Grip area is higher in the wider tire.

By increasing the length of the footprint perhaps can not achieve increase grip. Perhaps we may only increase the area of ​​the sliding region.
¡¡¡ We increase the area where the vertical force is high !!!