wider tires = more traction?

[LIONS*LEADER]

i made the title a simple question that would hopefully attract the attention of those wanting to shoot down the statement off the bat, as well as those who are more knowledgable.

to start off with, from reading alot about it over the last few hours, i have found that basicly nobody knows what the best ratio of tire width to car weight is. even the companies making the tires. they just have to make educated guesses with the information they have and then strap the tires onto the car they made it for and see if they improved on thier previous model.

this would be due to the vast amount of variables that affect the tires when driven. such as the temperature change. the weight shifting of tires during turning, acceleration and braking. just to name a few i came across.


but i suppose the main question that needs to be answered is (and i dont mean the psi you fill your tires with)

Where do we find the pressure range for optimal gripping performance for specific tires?

both the minimum and maximum pressure are important

you would want to know what the minimum was so that you you could set up your suspension and tire width such that in any cornering condition no tire would ever be below that minimum.

you would want to know the maximum since exceeding the max would cause the temperature to rise signifigantly changing the performance of the tires and how fast they would wear. on top of which im sure there is a point of diminishing returns.



i suppose the next question would be,
Where do we find the adhesive limit expressed in "G's" or any other usable measurement, of both tires alone, as well as tires installed on preconfigured cars?(like sports cars such as corvettes and porches) since once installed on cars the adhesive limit signifigantly drops. (most likely due to having reached the point of diminishing returns in terms of weight/ tire width)


and lastly

Are there any programs out there where you can take a virtual car that you can upgrade and tweak the stuff on it? on 2 levels, a realistic level where you make modifications that improve horsepower/weight and all the little settings, or a less realistic level where you set the horsepower weight, tire width suspension settings and whatnot , reguardless of the specific model of car's limitations in that area. (like a car that wouldnt be able to handle 20inch 365/55 tires)


i know the videogame forza for xbox has an extensive list of settings you can tweak on every car

anyway, hope everyone learns something from trying to answer my questions.

[CapriRacer]

I debated with myself whether to give you a long detailed answer, or to shorten the post considerably and allow you ask additional questions if there are points that need to be discussed in more detail. So here goes:

"Where do we find the pressure range for optimal gripping performance for specific tires?"

You seemed to have focused in on width, but a tire also has aspect ratio and rim dameter, and with those three dimensions you can determine the maximum load carrying capacity. Please note that there is some variability in load capacity for a given set of "dimensions", but all similarly sized tires are pretty close, and for practical purposes the same.

Put another way, larger dimensional tires have more load capacity than small ones. Using Load Index is a good way to compare a tire's load capacity.

Load capacity is important because it is a gauge on how much deflection a tire will have at a given load - and therefore, how large the footprint will be.

The rim width also has an effect on the shape of the footprint. A narrow rim will tend to "arch" the tread, and the "flatness" of the tread is, of course, dependent on the inflation pressure.

So already there are too many variables to make a specific pressure recommendation, and we haven't even discussed how the footprint interacts with the texture of the pavement and how inflation pressure affects that.

"Where do we find the adhesive limit expressed in "G's" or any other usable measurement, of both tires alone, as well as tires installed on preconfigured cars?"

The problem is that camber has a profound affect on cornering capability, so if you want the info for the tire itself, you need to specifiy what camber you want as well as all the variables listed above.

Needless to say, every suspension has a different camber curve, so if you want the info for a specific vehicle, ...well.... that limits the possiblilities a bit, but there are still too many variables.

However, vehicle engineers use something called "Carpet Plots" to assist in understanding how a specific tire reacts to cornering. These are run on what is know as a "Force and Moment" machine and the plots are extremely complex and have evolved from a series of graphs (pre-computer era) to a collection of data points which is what a digital computers needs - which is how vehicle engineers analyze vehicle dynamics nowadays. Vehicle tests are used to verify the validity of the computer model.

"Are there any programs out there where you can take a virtual car that you can upgrade and tweak the stuff on it?"

Yes, and there are some simple programs to help analyze suspensions, but these are fairly crude.

However, detailed programs to analyze what affect a tire has on vehicle dynamics are WAY. WAY beyond the capability of a home PC. You need incredible computing power - which is this type of stuff is done by research floks connected with vehicle manufacturers.

"I know the videogame forza for xbox has an extensive list of settings you can tweak on every car.

Yes, but this is done from a macro point of view - increase the cornering power, increase the oversteer, etc. It is mimicing what happens, but the game designer is not constrained by reality and a lot of what is programmed into the game doesn't translate into the real world.


OK, so what is one to do?

First, if you have a given vehicle that you want to maximize the cornering capability, a Pyrometer is an excellent tool for generating information. Not to mention a precise pressure gauge, and a stop watch.

Second, because the answers you seek depend on the type of conditions you are operating under - road racing, circle track, autocross, rallycross, etc. - a good source of info are the folks who are currently participating. They've "been there, done that."

And last, a lot of setting up a vehicle is more about optimizing what the driver experiences rather than optimizing the grip of the tire. Speed means nothing without control.

Hope this helps.

[LIONS*LEADER]

thanks for your efforts.
when you said

"The problem is that camber has a profound affect on cornering capability, so if you want the info for the tire itself, you need to specifiy what camber you want as well as all the variables listed above."

where would i go to input all these variables, in order to find the information?

which still leaves the variable of weight on the tires, which for the moment is my main concern. how much weight should my car put on each tire in order to have the optimum gripping performance? is it the less the better? which would imply the wider tires the better?

im not asking for a answer to fit all tires, heck giving me an answer for just one tire would be sufficient.

im just trying to find out what the relationship is between weight per square inch of contact area, and the ability to corner with all other variables being equal, including the weight of the car.

is it false to say that the more contact area you have on a car's tires the better it will corner, with all the other variables being equal.

as well as the lighter a car is with all other variables being equal the better it will corner.


once i find out this information i can move on to understanding other specific variables and how to improve a cars performance through them.

but one step at a time.

[CapriRacer]

"where would i go to input all these variables, in order to find the information?"

Into a Force and Moment machine. Needless to say, this is not something the average guy has access to.

But to cut to the chase: Lighter vehicle weight is always better. Wider tires is always better (Remember we are keeping everything else the same.)

"is it false to say that the more contact area you have on a car's tires the better it will corner, with all the other variables being equal."

Unfortunately, it's impossible to keep all other variables equal. Yes, more contact area is better for cornering, but what usually doesn't stay equal is the aspect ratio and the rim width.

And you have to be careful that you don't lapse into thinking that a lower inflation pressure would be better because it increases the contact area. The problem is that the footprint may develop areas of extremely low contact pressure - and that would hurt the overall grip.

[LIONS*LEADER]

awesome thanks for the answers, that simplifies things.

what would you think would be the next variable to investigate? the camber?

[CapriRacer]

First, I think you ought to read Fred Puhn's book "How to make your car handle" (I hope I have both the author and the title right.) This book does a great job of the basics in trying to make a vehicle perform.

The second book I'd recommend is by Paul Van Valkenberg "Race Car Engineering and Mechanics"

(OK I checked on both books as I couldn't remember how to spell Paul's last name.)

Read these with the idea that you want to understand "The Big Picture" and not to answer a specific question.

[Knap]

If looking in general at handling balance in the case of tyres, the cof drops off as you increase the weight on the wheel and you can tune a car's handling by adjusting the anti-roll bar.

The bigger the contact patch the more grip you can get. In a drag race, dropping the tyre pressure increases the contact patch area and increases grip.

When you look at lateral grip other factors start to matter. The tyre develops side force because of the slip angle between the tyre and the road. This slip angle means the tread is being pulled sideways by the road surface. At the front of the contact patch the deflection is relatively small. As you move back along the contact patch the deflection increases steadily. At some point, the sideways forces in the tyre exceed the friction between the tread and the road and the tread starts to slip relative to the road. When the tread is slipping like this it produces less grip on the road. As the slip angle increases the sideways deflection builds up quicker so the front of the contact patch works harder. But more and more of the back of the contact patch is sliding and losing grip. At some point you reach a maximum point where more slip angle means less side force because you are losing more grip at the rear of the contact patch that you are gaining at the front.

The longer the contact patch is, the more gradually break away occurs. If you shorten the contact patch, the break away occurs more abruptly but you get more absolute grip at the peak as there is less variation in sideways distortion between the front and back of the contact patch, more of the contact patch reaches maximum grip and starts to slide at the same point.

When you fit wider tyres the contact patch wider and shorter for the same tyre pressure. This means you get a more abrupt breakaway but more grip right on the limit.

If this logic is correct then increasing pressure in the tyre further improves grip, since more pressure = less contact patch area = shorter contact patch = better grip?
However more rubber on the road does help grip due to the hysteresis properties of rubber. As rubber expands to fill a depression in the road, it takes some time to do so. When a tyre is sliding (and due to the slip angle, the rear most portion of the contact patch slides at even low cornering forces), this means that the upward rise of the depression to which the tyre is moving has more rubber acting on it that does the upwards rise on the other side. This allows a pressure differential in the lateral plane, providing frictional resistance over and above that offered by simple friction. As the tyre vertical load increases, the rubber is forced more fully, and more quickly into the depressions, overcoming the hysteresis and reacting on both sides of the upward rise from the depression more evenly – giving less pressure differential and less grip.
Low tyre pressure is better for grip from deformation and hysteresis.
Tuning the pressure is about balancing the contact patch length (which is better as pressure goes up), and the contact patch pressure (which is better as tyre pressure goes down). Even though the optimum grip may be achieved at low pressures higher slip (because the hysteresis element is significant),low pressure increases tyre deflection, which increases heat (less even radius over longer contact patch). It therefore appears that the best way to increase grip is a wide tyre as this gives a shorter contact patch for the same inflation pressure.

However tuning the handling balance using tyre pressures, appears to be a combination of trying to match front and rear slip angles, ultimate grip at the limit, and effect of heat which may effect inflation pressure and tyre compound?