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Wider tire giving better traction debate!

by slim617
Tags: debate, giving, tire, traction, wider
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slim617
#1
Aug14-09, 11:19 PM
P: 2
so ive joined this forum to discuss this topic. IN class ive learned that wider tires does not give better traction and it is the same traction similar to a more narrow tire. now i have friends telling me that i am wrong bringing up that F1s do not use narrow tires because of traction. if someone can please clarify this to every instance that they can. if you would an could rebutal any of this please do. and tell me if i am wrong. thank you

http://i19.photobucket.com/albums/b195/slim617/Book.jpg

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here is the tibit from my book.
response from friend
Mark Giannini
Traction and friction are two (slightly) different concepts. Not only that but using car tires in a physics book is stupid (and something I've never actually seen before) simply because their coefficient can exceed 1, which changes everything. On top of that the standard equation does not account for deformation of the tire (which can be accounted ... Read Morefor through rolling resistance). Further more, even though the contact patch is the same regardless of tire size (generally) AT REST, the shape that it takes under dynamic load is better distributed by a slightly wider tire giving better traction. While a wider tire does gain some heat benefit from a greater surface area it's only a small part of it.

Never trust your physics book for real world situations. Life doesn't involve frictionless surfaces and weightless ropes.
about an hour ago Delete

Mark Giannini
Also your argument of "it's for heat distribution" is stupid. If I am able to achieve a better coefficient of traction by keeping temperatures down through using a larger tire then I've still achieved more traction by using a larger tire.


Ed Yuen
simple home experiment:

1) drag a piece of scotch tape across a table using slight pressure.
2) using the same pressure, use a thinner piece of tape.
... Read More
let me know if theres a difference in friction.
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rcgldr
#2
Aug15-09, 12:20 AM
HW Helper
P: 7,135
This wiki article explains tire load sensitivity:

http://en.wikipedia.org/wiki/Tire_load_sensitivity

In the case of tires, although traction increases with load, it increases less than linearly, and coefficient of friction decreases with load. A larger contact area reduces the load per unit area, resulting in more grip. There is a point of diminishing returns, such as weight and aerodynamic drag. It's also true that a larger tire dissapates heat and with a lighter load involved, it wears less. Another reason for a larger contact area is to compensate for debris or track imperfections interfering with the tire and pavement contact.

Note that load sensitivity is commonly used to adjust the understeer or oversteer of car. When a car turns, the downforce on the outside tires is increased and the downforce on the inside tires is decreased. The body of a car also rolls a bit, and the supension can be used to unequally distribute the load between the front and rear tires. If the front end is relatively stiffer, then more of the downforce is exerted on the outside front tire, and the relative grip is reduced because of tire load sensitivy. A stiffer front end causes the front end to lose some grip in turns, resulting in understeer. A relatively stiffer rear ends results in oversteer. Street cars are generally setup with understeer, while race cars are setup with a small amount of oversteer.

For a variety of reasons, such as deformations, molecular bonding type reactions as well as surface roughness, real world friction isn't the simple thing described in physics books. From the wiki article on friction:

in general the relationship between normal force and frictional force is not exactly linear (and so the frictional force is not entirely independent of the contact area of the surfaces) :

http://en.wikipedia.org/wiki/Friction
Ranger Mike
#3
Aug16-09, 06:35 AM
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Thanks to Jeff Reid for the excellent post...I am currently in Key Laro so don't have access to my data base..but in racing ...it is all about tires..tires..TIRES. The more tire foot print you can use effectively, the faster you will go straightline...this is why drag racers drop a full second or more off their elapsed time (ET) by bolting on a set of drag slicks..ET drops because you are transmitting the same amount of " acceleration " to the pavement more effectively..its the same car, same horsepower...wider tires... The more tire contach patch you can maintain without losing grip, the better you can enter and exit the turn.

Don't get hung up on the tire footprint vs static load per wheel... its ok to calculate this when looking at SNOW...( a combat tank can traverse snow better than a GI walking with 90 pounds of combat toys..good mind drill but thats as far as it goes...

xxChrisxx
#4
Aug16-09, 08:55 AM
P: 2,048
Wider tire giving better traction debate!

Mehcanisms of Tire grip.

Friction
Mechanical Keying
Adhesion

As they are madr from deformable rubber, tires dont exactly follow basic friction theory. So to just say that F=mu*r is strictly wrong. Although it basically does floow this during the elastic range.

Tires only give grip when they are at the correct temperature. this is the most important thing you can remember about tires .


Now on to business.

Tires are the most important part of the suspension, either they are designed to fit it, or the suspension is designed around the tire.

People who say wider tires make more grip because ;''there is more rubber on the road' are wrong. They are both wrong that it makes mroe grip and that there is more rubber on the road.

When you make a tire wider, you alter the contact patch to be wider , but it reduces in length. So depending on sidewall stiffness, a wider tire can actually give less rubber on the road.

The main reason for tires being the size they are is actually heat management. Wider, low sidewall tires will cool better than narrow tall tires. If you can;'t get a tire up to temperatie it will give no grip, if you get it too high you will cook the rubber and ruin the set of tires.

Back to contact patch, you can safely assume that contact patch stays roughly the same area with wide or narrow tires (as long as the load stsys the same). Narroe will have longer contact patches and wide tires will have shorter.



The reason why F1 tires are wide is primarily so that they dont cook (remember they arent just wide, they are fairly high sidewalled), but they ten dto have wider contact patches because they will give better grip going round corners.

A wide tire will generate more lateral force per slip angle making cornering better. F1 cars DO NOT have wide tires for linear acceleration.


Conversely (Mike im goin to have to disagree with you here) drag racers acutally use the tires not becuase of the width, but the tallness. As we know a wider contact patch gives better cornering performance, a narrow but long contact patch is what you want for linear acceleration.

so strangely, drag racers will actually be better with narrow tires. So why do they use wide tires? (remember the most important gip aspect of tires) Temperature! They want as longer contact patch as they can get, but need the width for cooling. (eith 4000+ horsepower you do kind of build temp rather well)

But if you look at the contact patch shape between say, an F1 car or drag racer. (both are considered to use wide tires). The F1 patch will be wider and shorter for good cornering, the drag patch will be longer and narrower (relatively) for good linear acceleration.


So to sum up: Wider tires are not always better. They dont always give better traction. It depends on the car, the situation, the conditions.

Eg. Rally cars use wider tires when on tarmac rallys, and use (surprisingly) very thin tires on ice rallys.
F1 cars used to use narrow tires until aero began to be used in the 60's.
Drag racers acutally want tall tires, width is there to stop the tire being destroyed.

TEMPERATURE!!!!!! rawr.

As example I can think of is formula student cars, they used to use 8inch tires but couldnt get them up to temperature. They switched to 6.5inch and got more grip because they can get them up to temp.


hoyl beep thats the longest post i've ever done. I should do a tl;dr summary.
Ranger Mike
#5
Aug16-09, 09:32 AM
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and an excellent psot is is, Chris..
i whole heartedly agree on the drag slicks..i did not want to cloudy up thinhs and bring in deformation..anyone who has been at the Christmas Tree ( starting line) at the 1/4 mile drag strip would see the slicks " growing" as the RPMs rev. like the y get very TALL going thru the traps (end of the 1/4 mile4) .and...they are running so low a tire pressure that they have to use sheet metal screws in each wheel rim drilled into t h e tire bead to keep the slicks from spinning...but your addition into the height or addinonal " rollout" length is absolutely spot on...

shorter wider tires offer better management of scrub radius and this goes back to Center of Gravity and Roll Center location...a lot of other factors regarding suspension but you ca nread up on this in the Mechanical Engineering Forumn
also the wider shorter tire will have less moment of inertia and spin up quicker than the taller narrower tire...any time you can reeduce rotating weight by one pound, its like taking ten pounds of the car weight..as far as the car thinks when accelerating..some other points but will dig up my old links in a bit..
rcgldr
#6
Aug16-09, 10:01 AM
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Quote Quote by xxChrisxx View Post
When you make a tire wider, you alter the contact patch to be wider , but it reduces in length.
Unless the pressure is reduced to increase the overall contact area.
xxChrisxx
#7
Aug16-09, 10:23 AM
P: 2,048
That is true, you can increase the width but decrease the pressure to compensate. So as long as the tires dont become too snappy, and you can keep the heat under control this would be a perfect wxample of when wider tires are good.

However if you kept increasing the width and decreasgin the pressure to compensate for the contact patch, you can shift the heat to the outside of the tire causing massive local heating and destroy the tires. Having low pressures will also majorly screw you in wet conditions. :)

It's all about balance, sometime wide tires are good others not so much. It's just a pet peeve that people think that wider always = better.
rcgldr
#8
Aug16-09, 06:44 PM
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Quote Quote by xxChrisxx View Post
However if you kept increasing the width and decreasgin the pressure to compensate for the contact patch, you can shift the heat to the outside of the tire causing massive local heating and destroy the tires.
Part of the reason that F1 cars run relatively large amounts of camber, especially on the front tires. As you mention there's an optimal size, too wide and you end up past the point of diminishing returns.
slim617
#9
Aug25-09, 02:48 PM
P: 2
soo wat is the verdict of this? do wider tires give better traction?
xxChrisxx
#10
Aug25-09, 02:50 PM
P: 2,048
Sometimes but not always.

Going wider will not always give better traction.


If you want an all sweeping statemnt that is roughly true. Wider contact patch sacrifices linear traction for lateral, narrow tyres sacrifices lateral for longditudinal traction. And the most important thing about tyres is not contact patch area but that they are correct working temperature.
turbo
#11
Aug25-09, 03:14 PM
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My friend was a the national champ in his class (bracket-racer) a couple of times. I watched him progress over the years, and by far the biggest improvement in his times came when he switched from moderate slicks to very wide slicks and started running very low tire pressures to increase the size of the contact patch. He was running perhaps 4 psi in those rear tires, and his car was putting so much power to the wheels that he had to drill the flanges of the rims and insert screws into the beads of the tires to keep from spinning the rims out of the tires.

BTW, he had to go to a really heavy-duty rear-end in order to cope with the extra strain. When he dumped the clutch, that 340 Duster would pull a 2-foot+ wheelstand on the line.
xxChrisxx
#12
Aug25-09, 03:17 PM
P: 2,048
Turbo that means nothing though, as when you change the width of the tyres you arent just changin gthe width. You are changing the effective rates of the wheel, etc. In effect you are making a very extensive change to the suspension (as the tyre is the most important part of it).


Someones experience of putting on wider tyres is not proof that wider tyres = better. Its also not definative that it was acutally the width that made them go better.

You will also find that as people have got into the mentality that WIDE = GOOD, tyre companies have been savvy and strted making their uber wide tyres out of a softer compound. In many cases its the compound change that does the job, not the width. The fact he's runnign at stupidly low pressures (I suspect to build heat) had got to give wear rate problems round the shoulder. And im not surprised he had to screw the tyres on to stop them collapsing at 4psi.

EDIT: Drag racing is a funny business though, beause Like I said above for linear acceleration narrower longer contact patches are acutally better. It's just practical reasons they have to be mega wide.
turbo
#13
Aug25-09, 03:23 PM
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Wider may not always be better in real-life situations, but the drag track is a harsh mistress, and these guys succeed or fail on hundredths of a second. There are no funny-cars or competitive dragsters running narrow tires, unless they are show-cars powered by rockets or jet engines.
xxChrisxx
#14
Aug25-09, 03:28 PM
P: 2,048
Quote Quote by turbo-1 View Post
Wider may not always be better in real-life situations, but the drag track is a harsh mistress, and these guys succeed or fail on hundredths of a second. There are no funny-cars or competitive dragsters running narrow tires, unless they are show-cars powered by rockets or jet engines.
I made an edit specifically regarding drag racing.

The point is though the mentaility that wider always = better is wrong. There is an optimum limit even on drag racers.

Tbh though drag racing has never done it for me, yes its impressive that top fuel make 4000+ HP and go a zillion miles an hour. But racing for me = open wheel or sports car.

I tried to get into touring cars but I dunno they just dont do anything for me.


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