A quick note on traction

[sanioll]

You have to assume that wider/bigger tires that you are putting have the same rubber material as the origional tire.

So, since your car weights so much with you in it. Say 3000 lbs.

3000lbs = 1359 kg= Fn=normal force

Imagine that we suddenly had no gravity pulling us down. So no pressure between the tires and road. That means you would have no friction whatsoever.

That being said Friction is dependent on pressure between two objects. In this case, automobile's weight is exerting downforce on the road. That downforce is called the Normal Force. It is actually your weight.(3000lbs on earth)

Since you put wider tires it should give you more traction right?

No, it will not.

Tire 1 has a contact area of 1 square inch. Pressure = force/area

since your weight is 1359kg, you are exerting 1359 Newtons of downforce on that 1 square inch. So your Friction = Coefficient of friction * 1359 N

After putting wider tire, which has 2 square inches area, now you are exerting 1359 newtons of downforce on 2 square inches. Which means every square inch gets (1359N/2) half the downforce. But since you've got 2 square inches it adds up to origional amount of friction.

In summary, if you put tires the width of bicycle tire on your car(assuming the same rubber material as before), then you will have the same amount of traction. But they will wear out quickly. Why? Becuase per square inch it sees much more downforce, thus much more stress. So it works harder per square inch, and it wear down quicker.

Having said all that, if you would like to increase traction for your automobile, then you have to change the rubber material, not contact area of the tire. More contact area simply will give you more tire/thread life.

When you change rubber material, from hard to soft, you are actually modifing the coefficient of friction(see image, above formula). On a regular automobile with stock tires, coefficient of friction is about 0.7 on a dry pavement. Putting Z rated tires will change coefficient of friction from 0.7 probably to 0.85-0.9. And that is a drastic improvement.

Having 265mm wide Z rated tires vs having 205mm wide Z rated tires WILL NOT GIVE YOU MORE TRACTION!! IT WILL GIVE YOU MORE TIRE LIFE! 29.3% more thread life to be exact.

Do not spend extra hard earned dollars on that shiny alloy wheel so that you may fit a wider tire!

thats all.
Modified by sanioll at 3:34 PM 11/25/2005

[zippitta]

I actually had to do a report on that in my physics class when I was in 11th grade. Be careful, I didnt think I was going to make it out of my class alive after I proved that...lol

Indirectly though a wider tire will increase traction. Soft compound tires are required to be wider in order for the side-wall to support the weight of the car.

[TrueSlide]

Note noted

[sanioll]

Soft compound tires are required to be wider in order for the side-wall to support the weight of the car.

I don't get it, plz explain. Side walls, don't have anything to do on how wide your tires are. They have to have shorter side walls now to lower the flex.

So you have to increase the diameter of the wheel, and decrease height of the rubber towards the center.

Ex: 205 60HR 15 <-- H rated. But when we switch to high performance it is a good idea to lower the side wall to 205/45ZR17. (assuming the matching wheels) since the rubber is softer now, you will need better side support.

Correct me if I am not understanding you properly.

[MinisterofDOOM]

Excellent post.I've been trying to convince a friend of mine that wider tires are WORSE for winter. He argues that more surface area means more contact and therefore more traction. I've tried to explain the corellation between spreading weight across area, and it goes right over his head---probably because I am doing a bad job describing it. Now I've got this nifty thread.

I wish stuff like this was in the manual of your car, just like tips on other basic safety items. A lot of people would be properly informed.

This is one of the reasons I have yet to purchase a set of 18x7.5" wheels for my car that would be shod in 225/40VR18 rubber: my 205/65HR15s are excellent in snow and rain.Ice is another matter altogether.

[zippitta]

Lets see if I can manage to make since with words....if the tire is too narrow for how soft the composition is, the tire will roll off of the rim due to the side wall not giving enough support. If you widen the tire while retaining the same side wall height, you will decrease the aspect ratio allowing the sidewall to support the weight.

I guess you could also do this by just reducing sidewall height but you can only do that so much and then you would be riding on the rim.

It makes since in my head atleast...lol

[sanioll]

Lets see if I can manage to make since with words....if the tire is too narrow for how soft the composition is, the tire will roll off of the rim due to the side wall not giving enough support. If you widen the tire while retaining the same side wall height, you will decrease the aspect ratio allowing the sidewall to support the weight.

I guess you could also do this by just reducing sidewall height but you can only do that so much and then you would be riding on the rim.

It makes since in my head atleast...lol

well, how about you do both of us a favour, and assume that there is no side wall. Assume that tire is put on a 20" wheel, and if you run outta rubber, you will be scraping the alloy wheel.

So no side wall, just a rubber thread and a wheel. Under that assumption, friction/traction doesn't depend on contact area if the pressure is kept constant. (like your weight is always constant on earth)

=====================================================

Having a side wall will give you just a bit more static traction. Well actually make you feel like you have a bit more static friction.

The flex of the side wall will act as a spring and absorb Force Shock extremes and will keep it under the static Friction's threshold. (Meaning, if you suddendly steer left, that side wall will absorb that sudden force and will apply it at a slower pace to the tire's bottom.)
Modified by sanioll at 1:44 PM 11/25/2005

[naed240sx]

Wider tires have the same contact patch area as thinner tires, as long as all other variables are equall. You are also overlooking many factors that affect how well a tire grips.

[zippitta]

You miss undestood what I was saying. I wasnt saying that the sidewall itself was what was giving the tire the traction. I was saying that in oreder to have an extremely soft compound tire, then you would need a stronger sidewall to support it. I was saying that wider tires are almost always made out of a softer compound. Mainly due to the afct that wider tires are usually made for increased performance.

So do me a favor and reread my posts.

[Magnes]

You have to assume that wider/bigger tires that you are putting have the same rubber material as the origional tire....On a regular automobile with stock tires, coefficient of friction is about 0.7 on a dry pavement. Putting Z rated tires will change coefficient of friction from 0.7 probably to 0.85-0.9. And that is a drastic improvement....Do not spend extra hard earned dollars on that shiny alloy wheel so that you may fit a wider tire!...thats all.

That's all... wrong!

1- Even if we assume that two different tire sizes use the same rubber compound, wider tires can still improve grip. Their construction, operating pressure and temperature, as well as increased track width can influence grip levels, not to mention that increased siping can improve wet traction.2- A tire's speed rating gives no indication of it's coefficient of friction.3- You don't have to, I recomment that others do if they are looking to improve grip.

[naed240sx]

I agree completely.

[navysnail]

while increasing the tire width may not directly increase traction, it can increase traction indirectly. it also reduces the tire's tendancy to follow groves in the pavement (all per chet's faq iirc)

zerothread?id=81404

[zippitta]

That's all... wrong!

1- Even if we assume that two different tire sizes use the same rubber compound, wider tires can still improve grip. Their construction, operating pressure and temperature, as well as increased track width can influence grip levels, not to mention that increased siping can improve wet traction.2- A tire's speed rating gives no indication of it's coefficient of friction.3- You don't have to, I recomment that others do if they are looking to improve grip.

while increasing the tire width may not directly increase traction, it can increase traction indirectly. it also reduces the tire's tendancy to follow groves in the pavement (all per chet's faq iirc)

zerothread?id=81404

You have to remember that this is all in theory. Of course there are going to be things like road imperfections. If roads were completely flat then there would be no difference in the narrow and wide tires. But since we dont have perfect roads, wider tires increase the probability of keeping contact with the ground.

It was all ready stated that narrow tires heat up faster and wear quiker than wider tires.

[Q45tech]

Traction is the intermolecular forces binding the compound to the road. Weight per square inch of tread. Depending on compound and road material there is just one optimum interface temperature [usually ~~ 180F].Traction goes up as interface temp goes up until the cliff temperature then in falls rapidly! Wear goes up as temp goes up. High wear=high traction.Wider tires have more surface area which allows more radiant cooling faster as the tire rotates.

Unfortunately, street tires with tread grooves and sypes are noy ideal for traction -- the void ratio is too high to allow for cooling and water on road.

[sanioll]

I was saying that wider tires are almost always made out of a softer compound. Mainly due to the afct that wider tires are usually made for increased performance. So do me a favor and reread my posts.

I read your post one more time, but some stuff don't make sense.(nothing personal)

1) Wider tires are not made for increased performance. If you put softer tires, the same size as before, they are going to wear out quicker. So you will be getting 6 months tire life out of them, intead of 12. And no one likes to change the tires, or pit that often during the racing appilcations.

When you make the rubber softer, you have to add more rubber to compensate the wear rate, in order to get adequately same amount of life out of your tires.

In order to increase the tire life you can:a) Make the tire thicker on the bottom, more rubber, more thread. But that will create thermal issues. As the heat will build up on longer travels and highway speeds. You are risking the meldown of the tire. This is the reason why slick tires in racing situations are made of thinner thread, to avoid heat buildup.

b) You make them wider, wider means less downforce per squire centimeter, so less wear per centimeter squire. Also thermal buildup is not an issue, since you have more area to dissipate the heat.

You miss undestood what I was saying. I wasnt saying that the sidewall itself was what was giving the tire the traction.

That has nothing to do with the point of this thread. This thread talks about the non-dependency of friction on the contact area. Why did you bring it up in the first place??(no need to answer)

I am not even going to spend time to answer Magnes and navysnail, since they don't have correct knowledge in this topic. Bunch of teenagers.

Oh and also, this thread doesn't discuss thread design, grooves for water channeling. That is another topic, which I don't think I should bring up.(so much hatred already )

=====================================================

Here is another thing to make you guys hate me harder:

Having less mass/weight will not improve your braking distance. As in less distance. No it will not!!

Also, in creasing the weight of your car during the winter(IE putting weights on the rear for rear wheel drive automobiles) is a good idea. It will not improve your braking, but it will improve traction on your DRIVE WHEELS.


Modified by sanioll at 2:25 PM 11/29/2005

[JimmyMethod]

I've been thinking about this for a long time...

The math makes perfect sense.However, why do slicks give you better times in the 1/4?

[naed240sx]

Really soft rubber compound, large footprint, and more ground contact than a grooved tire.

[sanioll]

I've been thinking about this for a long time...

The math makes perfect sense.However, why do slicks give you better times in the 1/4?

They don't give you more traction with their larger footprint, it is all about the rubber compound.

They are too soft, thus made with more rubber to compensate fast rubber lost.

[JimmyMethod]

Then why do people have they're drag cars with wheels that are 2 and a half feet wide? They add a TON of weight to be useless.

[naed240sx]

Then why do people have they're drag cars with wheels that are 2 and a half feet wide? They add a TON of weight to be useless.

Exactly.

Sainoll: More footprint is beneficial. Period

[sanioll]

Then why do people have they're drag cars with wheels that are 2 and a half feet wide? They add a TON of weight to be useless.

Exactly.

Sainoll: More footprint is beneficial. Period

Nope.

As long as it has an area that will not penetrate the ground under the given downforce, it doesn't matter.(like have a needle intead of tire, which will penetrate the ground.)

check with your physics professor, then come back to me.

[naed240sx]

Ok so why do drag racers use huge wide tires as jimmy mentioned? They have way more mass than skinny tires(which are lighter, and would thus produce better acceleration, assuming equal grip). Why? Because they produce MORE grip. Your math is correct, but it overlooks a large number of factors, and is thus applied wrong. Essentially what you are saying is that if the made two types of tires that fit a drag car, one that was an inch wide, and one that was 20, they would have equall grip, as long as the same tread compound was used. WRONG.

Nope.

As long as it has an area that will not penetrate the ground under the given downforce, it doesn't matter.(like have a needle intead of tire, which will penetrate the ground.)

Tires do in fact have area that that react in a similar was as this. The ground is not perfectly smooth, it has raised portions, and pits(all of these are very small of course, but ocurr on any surface, be it asphalt or cement). The surface of a tire bends to fill in, and mold over such imperfections. So, in a sense, the tire is penetrating the ground, and you have proved yourself wrong.

[zippitta]

Do your homework before you start spouting off.......

[nissanconvert]

wow, a lot of 1 dimensional physics mis-applied in this post.Although i agree with most of what was said nobody mentioned a thing about rolling and sliding friction which are equaly if not more important the the vertical 1-dimensional friction and the reasons wider tires are used.Sure the weight of the car is spread out more on the wider tire, but the cars power is being applied horizontally to the road surface. When you have much power you need more area to keep the tire from slipping too much. This is a dynamical wheel problem not to be confused with the static box problem from high school physics. Its not so simple as one would hope. As far as water and snow, thats a whole different type of problem altogeather-hydrodynamics. In such a case tread pattern and smaller footprint matter more because the tire friction coefficients change with conditions.

[Magnes]

Thanks nissanconvert, I knew there was more to the theory, I just wasn't sure what that was.I beg to differ regarding wider tires on wet roads. From what I've read the tire manufacturers tend to take the increased dry-weather performance envelope of wider tires and use it to improve the tire package as a whole(wet grip, tire wear, dry grip...).

[Fenvy]

nice thread, I'd like to see more of this

[Fenvy]

another thing I'd like to address is that despite sanioll's theroy, those who had same brand/model of tire in different size probably felt a difference when change is made.

I had 205/55/15 and 225/50/15 both yoko es100, driven for at least 5000 miles on both. The wider one is without a doubt have a noticeable better traction at 100mph+

[AmoebAssassin]

Lots of the amateur analysis in this thread is dubious at best, and neglects a myriad of intricacies that professional tire manufacturers consider with every tire they produce.

Drag racers use massively wide tires with tall sidewalls for this reason: drag race tires are designed to be relatively under-inflated.

How many of you have watched a top-fuel dragster launch in slow motion? As torque is initially applied to the drive wheels, the sidewalls deform and the tire squats down upon itself. This deformation's net effect is that of elongating the contact patch of the tire in a longitudinal sense (the contact patch gets longer in a direction parallel to the motion of the dragster). Since the tire's contact patch is elongated longitudinally under accelleration due to it's underinflation, it is logical that a wider tire will have a greater area gain than a narrow tire. Since coefficients of friction are directly related to surface area that the friction acts on, then a wider tire that produces a greater gain in contact patch will thereby have a greater coefficient of friction and therfore will produce a greater accelerative force on the chassis.



Note how longitudinally wide the contact patch is due to the deforming sidewall that you can see on the front side of the tire.

That said, track and road cars benefit from wider tires not only due to the fact that wider tires are often produced with softer compounds, but also because that when you press a tire into the ground, the rubber will deform and match the shape of the ashphalt it is being pressed into, on a microscopic level. This has the same effect as holding two gears, one fixed in it's rotation and then applying torque to the other one. The teeth of the gears act like the mechanical mesh of the tire into the asphalt, and prevent the tire from breaking loose from the ground under accel, braking, and cornering. A wider tire will provides more surface area (although not a linear increase with tire width) for this action to occur upon.

Additionally, wider tires are more suited to increasing traction with large levels of downforce, for the same reason as the dragster example: as the aero downforce acts upon the tire, the contact patch of the tire widens and elongates. A wider tire will provide more area under elongation and thus more traction under downforce conditions. This is why Formula 1 cars have such wide tires at the cost of weight (also, the titanium flexure joints that connect the inboard sections of F1 A-arms to the chassis are so stiff that in effect, the tire spring rate becomes the effective spring rate of the vehicle. A larger tire is more suited to dealing with such stresses imparted upon it).

Also, wider tires have longer tread life due to lower tire loads per unit area of tire (wider tire for the same force being applied) as compared to a narrower tire.

[UK-SRi]

The first analysis in this thread made a common mistake of assuming that the friction is fully linear, in a real tyre/road situation this is not true.

The coefficient of friction can actually be over 1 due the the deformations mentioned in later posts.

http://www.autozine.org/techni...3.htm

This shows the non-linearity of friction and weight on tyre. Increasing the width fractionally widens the track which makes a small difference to the weight transfer.

Mike

[InsanityInc]

You also forgot that tires have adhesive properties, which has nothing to do with weight. This is why your tires will wear down even if you never lose traction. Having more rubber on the road is better for that reason as well, because more rubber = more adhesion, regardless of pressure.

EDIT: Oh, and you forgot heat dissipation as well. Thinner tires obviously heat up WAY faster and don't dissipate heat very well, which is bad.