Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Its been a while

Does anyone else here remember when "physics" teachers, in drag racings infancy in the late 50s early 60s, said that
the fastest possible speed a piston powered
dragster could EVER physically achieve in the quarter mile from a standing start was like 140mph?

I've read that a few times over the years. It
always made me chuckle. The first time I remember reading it, pro-stock cars were almost into 200mph territory. Top fuel dragsters were aproaching the 300mph mark.
Now the record is what, over 325 I think.

Another big point you are missing is that drag slicks give at the sidewall to lessen the shock of translating rotational force into forward motion.

Just look at any drag race for proof. No misguided "advanced physics" needed... :rolleyes:

I'd stop while you are way behind...

Besides the fact that the original post asked about mounting slicks that were not necessarily wider, here is an explanation as to why wider tires offer more traction (even though the physics that TheContourGuy mentioned is correct...)

Let's look at the history of drag racing.

The first "slicks" were truck tires that had the grooved tread shaved off. They used these for a number of reasons. Two of the reasons were: one, the taller tires added gearing to final drive ratio and; two, they were wider and spread the load over a large area to gain traction.

"Huh?" you say, "How did number two work?" .

Well, let's look at the road surface. It's not perfectly smooth like the laboratory table, as a mater of fact, it's rather rough and porous. A thin tire will spin and the road surface will fill with rubber from the melting tire, when the pores are full of hot melted rubber, the surface tension (i.e., friction) is reduced and grip is lost. However, if you spread that over a larger area (i.e., reduce the surface tension per square inch by spreading the pressure), it takes longer to fill and the surface tension is maintained longer. The longer you can maintain the surface tension, the faster you'll launch.

Theories are for perfect worlds... not practicality.

I knew this would happen....it is a difficult concept to grasp. Surface area does not change your friction! Do what I said with the box....it proves it perfectly on a non-perfectly smooth surface!

The reason that dragsters use the big tires is:

-stickier rubber compound
-sidewalls that wrinkle under low pressure
-last much longer
-heavier for more traction

The width of the tire is irrelevant. Look at the tires when they hit the gas....the contact area becomes much smaller as the tire's diameter increases by almost 25%. The wider tire does help when you are in a turn, as lateral grip is an enitrely different thing. Friction is dependent on WEIGHT DUE TO GRAVITY. If what you all claim is true, then why get cross-drilled brake rotors? or gas slotted? That would actually give you worse braking due to less surface area(yes, I know they are to allow rotors to cool faster and to channel hot gases away). Cross-drilled/gas-slotted 12" rotors will stop no slower than a normal 12" rotor.

This theory works in our everyday lives, not under ideal conditions.

Guy, you have to stop revelling in what you read in a book and think about what you are typing. At least I am not disputing the physics that you are regurgitating. Just think logically - if narrow tires worked for a dragster, then everybody would use them. Two of your reasons (stickier, soft sidewall) can all be applied to a narrow tire so they are mute. Also, if cross-drilled rotors were no better than non-drilled rotors, then there are some really stupid racers out there (in the real world). You show some understanding when you mention that cross-drilled cool faster - that is one of the varaiables that are at work...

In the 'box' case, this is correct.

[/qb]

VERY GOOD, which helps them do what? Get more grip. Same thing on any other car.



False.



Bah. That'd be one sorry a$$ marketing gimmick. Look what you typed earlier in this post. Contradiction is bliss. Almost ANY car will get a faster ET w/ wider slicks, guaranteed.



Tell that to a friend of mine's that got a 60' time of 2.2 w/ street tires, and 1.8 w/ slicks.

Your overall concept is correct re: box, but that does not apply to regular cars.

As somebody stated, put a set of 185/60-16 tires on the rear end of a Viper, and see what you get.

John

Look up the term 'slip angle' re wide tires to find out the correst definition...

Here is a BRIEF description about what tires do at drag races, such as top fuel.

1. Car with cold rear tires does a rolling burnout way past the traps.
2. Rubber gets laid down on the track for about 10-15 yards.
3. Tires get warm in the process.
4. A wide patch of sticky hot rubber contacting another surface of sticky rubber causes a very high mount of friction. This friction helps to transfer the power to the ground causing the vehicle to move forward.

Dan, back to the "box theory". I do understand about weight distribution and how the larger contact patch will still have the same weight (lbs/square in.) but, that's not the goal of drag racing tires. We are talking about the physical properties of the rubber. A wider tire will give more friction to the tire relative to the ground.

You have to look at a few different variables when finding the right drag tire/wheel combo.

1. "Stickiness" of the rubber compound.
2. Amount of power going to be tranferred through the wheels.
3. Downforce applied to the wheels at launch (vehicle weight, distribution, and suspension are factored in)
4. Diameter of the tire and of the rim (see Terry's Slip Angle)
5. Road surface (composition, temperature, slope, etc.)
6. Tire pressure and temperature

This could get into a REALLY large, and probably heated, discussion.

One thing to think about when discussing tires and "grippiness".

There are two different states of the tire for observing friction: When it is slipping, and when it is not slipping.

From "Ask a Scientist"

Index Key: PHY002
Author: beaver
Subject: Wide tires
Text: If friction is surface area independent, then why do dragsters
have wide tires?

Response #: 1 of 2
Author: A. Smith
Text: The force of friction that the tires experience is independent of
the tire size, certainly. However, what a dragster does not want is for the
tires to slip - so the tires are spinning and the car is going nowhere. What
determines when the tires will start to slip is the point at which static
friction gives way to sliding friction. That force must of course increase
with the area of the tires, and so the bigger the tires, the bigger the force
you can use before you start slipping, and so the faster your dragster can
accelerate.

Response #: 2 of 2
Author: Eric Peterson
Text: Wide tires for drag racing tires also come in a variety of
hardnesses or durometer ratings. The softer the tire, the more initial
traction is provided. If you will notice, too, one of the biggest reasons for
these wide tires has nothing to do with traction: When the car is sitting at
the line, the diameter of the tire is relatively small. When the tires are
spinning, the tires are constructed in such a way to allow the centrifugal
force to expand the diameter of the tire. This has the same desirable effect
of changing the final drive gear ratio to allow for higher speeds. Racers
very carefully size tires to allow for the optimum change in diameter over a
given rotational speed of the wheel. This allows the racer to take advantage
of the very narrow torque curve of their engines without changing gears too
many times. This reason is more so taken into consideration than the
width/friction reason.

And from www.topfueltour.com

The rear tires of a Top Fuel-dragster are approximately 18 inches wide and close to 118 inches (three meters) peripheral. The tires are of slicks-type, having no tread and without the carrying cord regular radial tires have. Instead the side of the tire is soft to make it possible for it to twist in the starting moment.

The height of the tire increases by the centrifugal force and that decreases the surface area and the rolling resistance at the same time that it increases the top speed by changing the gear ratio. The pressure in the slicks is fairly low and the tire is squeezed to the rim by a ring, a so-called beadlock, to prevent it from revolving on the rim.

I'm not professing to be a physicist here ;), but in our drag racing example isn't there a force acting upon the tire which exceeds the impact of mere gravity?

Obviously everything is relative to gravity to some degree, but aren't there additional factors to consider in a dragster tire situation than a box of books situation?