17" vs 18" with racing in mind. . . (narrow vs wide tires)
02-19-04, 01:04 PM
#101
Lives on the Forum
I need to be more like, Mark. Just sit back let someone else do all the work LOL 
Originally posted by ArcWelder
Nope, not digging your grave. I too had to remove myself from the debate for mental health reasons. Actually the debate has caused me to do some thinking, and that's probably not a bad thing. I do, however, still hold to my initial belief brought up on page 1.
Mark
Nope, not digging your grave. I too had to remove myself from the debate for mental health reasons. Actually the debate has caused me to do some thinking, and that's probably not a bad thing. I do, however, still hold to my initial belief brought up on page 1.
Mark
02-19-04, 01:14 PM
#102
Lives on the Forum
Inside Racing Technology by Paul Haney; page 65.
Quoted from Sam Garrett; racecar designer and graduate mechanical engineer. Helped design the Kudzu Camel light cars as well as Dallaras.
"When I was a student at Georgia Tech, a physics professor asked our class why we were preoccupied with putting wider tires on our street cars. We told him we wanted to 'put more rubber on the road'. He tried to tell us that friction force is independent of contact area.
In most cases he's right. Friction force (Ff) depends on a coefficient of friction (Cf) which is characteristic of the materials involved and the vertical force (Fv) pressing the materials together: Ff=Cf x Fv. Area does not appear in the equation. In the real world, however, this only applies to materials with a 'hard' surface. To understand why that is, you have to look at what happnes on a microscopic level.
All materials no matter how smooth or flat they appear to our unaided eyes, have small surface imperfections as shown in the sketches. To simplify the sketch we show points on one side only, but really both blocks have irregular surfaces. When two solid objects touch they have an 'apparent' contact area which is the surface you can see and measure, but they also have a true, microscopic contact area which may be quite different. But for hard solids, the true contact area remains constant regardless of the apparent contact area. Here's why.
When two hard surfaces come in contact, they meet at many sharp points or peaks like you see in the sketch. If you apply a force the presses them together, the material actually yeilds and the peaks flatten out, increasing the actual area of contact. If we increase the size of the parts in order to increase the the apparent contact area, we lower the force at each peak because there are more peaks to take the same overall load. With less load on each peak the points flatten out less, and the actual area of contact is less per peak so, overall, the true contact area is about the same as before we made the parts bigger. That's why hard materials don't show an increase in friction forces with an increase in contact area.
Rubber is different. Rubber is an elastic solid which 'gives' at a very low stress level. There is no fixed yield point and the deformation is elastic-rubber deforms and recovers. It deforms at low stress levels, and conforms to the microscopic imperfections of a surface with which it comes in contact. You can see the sketch that more contact area means more imperfections to conform to. With rubber you get more friction force when you increase contact area"
___________End of article____________
This my friends explains why a lightweight and well handling but low horsepower car like a Formula Ford has no need for much wider tires at the rear compared to the front: it doesn't have enough horsepower to need the extra grip at the rear wheels. On the other hand, something like a Formula 1 car that is also lightweight and well handling but with very high horsepower needs much extra tire width at the rear in order to be able to actually use all the power it has. With narrower rear tires the car would automatically be handicapped as far as putting the power down. You'll find that unless rules limited, cars with big horsepower always have wider treads on the driven wheels compared to the undriven wheels. This allows the car to actually use the power because the wider wheels offers more grip! Shape of the contact patch be damned! It don't matter!
All you need to get more grip is to bring more rubber into contact with the road. It's that simple.
Quoted from Sam Garrett; racecar designer and graduate mechanical engineer. Helped design the Kudzu Camel light cars as well as Dallaras.
"When I was a student at Georgia Tech, a physics professor asked our class why we were preoccupied with putting wider tires on our street cars. We told him we wanted to 'put more rubber on the road'. He tried to tell us that friction force is independent of contact area.
In most cases he's right. Friction force (Ff) depends on a coefficient of friction (Cf) which is characteristic of the materials involved and the vertical force (Fv) pressing the materials together: Ff=Cf x Fv. Area does not appear in the equation. In the real world, however, this only applies to materials with a 'hard' surface. To understand why that is, you have to look at what happnes on a microscopic level.
All materials no matter how smooth or flat they appear to our unaided eyes, have small surface imperfections as shown in the sketches. To simplify the sketch we show points on one side only, but really both blocks have irregular surfaces. When two solid objects touch they have an 'apparent' contact area which is the surface you can see and measure, but they also have a true, microscopic contact area which may be quite different. But for hard solids, the true contact area remains constant regardless of the apparent contact area. Here's why.
When two hard surfaces come in contact, they meet at many sharp points or peaks like you see in the sketch. If you apply a force the presses them together, the material actually yeilds and the peaks flatten out, increasing the actual area of contact. If we increase the size of the parts in order to increase the the apparent contact area, we lower the force at each peak because there are more peaks to take the same overall load. With less load on each peak the points flatten out less, and the actual area of contact is less per peak so, overall, the true contact area is about the same as before we made the parts bigger. That's why hard materials don't show an increase in friction forces with an increase in contact area.
Rubber is different. Rubber is an elastic solid which 'gives' at a very low stress level. There is no fixed yield point and the deformation is elastic-rubber deforms and recovers. It deforms at low stress levels, and conforms to the microscopic imperfections of a surface with which it comes in contact. You can see the sketch that more contact area means more imperfections to conform to. With rubber you get more friction force when you increase contact area"
___________End of article____________
This my friends explains why a lightweight and well handling but low horsepower car like a Formula Ford has no need for much wider tires at the rear compared to the front: it doesn't have enough horsepower to need the extra grip at the rear wheels. On the other hand, something like a Formula 1 car that is also lightweight and well handling but with very high horsepower needs much extra tire width at the rear in order to be able to actually use all the power it has. With narrower rear tires the car would automatically be handicapped as far as putting the power down. You'll find that unless rules limited, cars with big horsepower always have wider treads on the driven wheels compared to the undriven wheels. This allows the car to actually use the power because the wider wheels offers more grip! Shape of the contact patch be damned! It don't matter!
All you need to get more grip is to bring more rubber into contact with the road. It's that simple.
02-19-04, 02:49 PM
#103
Lives on the Forum
Huh? You went from looking at the microscopic level of rubber molecules giving and stretching to peaks and valleys in the asphalt, and extrapolated that example to a full blown F1 car? F1 cars need bigger rear tires cuz they corner with more g-loads than a FF? Ok, resuming Arc Welder-mode
Originally posted by DamonB
This my friends explains why a lightweight and well handling but low horsepower car like a Formula Ford has no need for much wider tires at the rear compared to the front: it doesn't have enough horsepower to need the extra grip at the rear wheels. On the other hand, something like a Formula 1 car that is also lightweight and well handling but with very high horsepower needs much extra tire width at the rear in order to be able to actually use all the power it has. With narrower rear tires the car would automatically be handicapped as far as putting the power down. You'll find that unless rules limited, cars with big horsepower always have wider treads on the driven wheels compared to the undriven wheels. This allows the car to actually use the power because the wider wheels offers more grip! Shape of the contact patch be damned! It don't matter!
All you need to get more grip is to bring more rubber into contact with the road. It's that simple.
This my friends explains why a lightweight and well handling but low horsepower car like a Formula Ford has no need for much wider tires at the rear compared to the front: it doesn't have enough horsepower to need the extra grip at the rear wheels. On the other hand, something like a Formula 1 car that is also lightweight and well handling but with very high horsepower needs much extra tire width at the rear in order to be able to actually use all the power it has. With narrower rear tires the car would automatically be handicapped as far as putting the power down. You'll find that unless rules limited, cars with big horsepower always have wider treads on the driven wheels compared to the undriven wheels. This allows the car to actually use the power because the wider wheels offers more grip! Shape of the contact patch be damned! It don't matter!
All you need to get more grip is to bring more rubber into contact with the road. It's that simple.
Last edited by SleepR1; 02-19-04 at 03:00 PM.
02-19-04, 03:54 PM
#104
Lives on the Forum
Originally posted by SleepR1
F1 cars need bigger rear tires cuz they corner with more g-loads than a FF
F1 cars need bigger rear tires cuz they corner with more g-loads than a FF
Motorcycles have skinny rear tires compared to cars, even though some bikes make more power than a small car! The motorcycle with its single skinny rear tire and small contact patch can out accelerate the car without spinning its tire because the motorcycle is much lighter; it doesn't need as much contact patch as the car in order to give the same performance in grip.
Whomever has convinced you of otherwise sells some really expensive snake oil
Don't buy anymore from him 
02-19-04, 09:30 PM
#105
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"Tire aspect ratio plays a significant role."
This falls in with my theory of the narrower tire able to exert less of it's longitudinal advantage due to a compression limit in the direction nearly perpendicular to the road. Upon reaching this limit the pressure increases greatly, overexerting the tire and it goes from cF(s) to cf(d).
The only way it would be able to dynamically form the contact patch to the longtudinally oriented one would be if the sidewall was not so stiff in the vertical direction and if the wheel were also made of rubber.
Does anyone else get what I was trying to say?
This falls in with my theory of the narrower tire able to exert less of it's longitudinal advantage due to a compression limit in the direction nearly perpendicular to the road. Upon reaching this limit the pressure increases greatly, overexerting the tire and it goes from cF(s) to cf(d).
The only way it would be able to dynamically form the contact patch to the longtudinally oriented one would be if the sidewall was not so stiff in the vertical direction and if the wheel were also made of rubber.
Does anyone else get what I was trying to say?
02-19-04, 10:11 PM
#109
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http://isb.ri.ccf.org/biomch-l/archi...-12/00016.html
http://isb.ri.ccf.org/biomch-l/archi...-12/00019.html
http://isb.ri.ccf.org/biomch-l/archi...-12/00027.html
Date: Fri, 2 Dec 1994 11:48:13 -40962758
Reply-To: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Sender: Biomechanics and Movement Science listserver
<BIOMCH-L@HEARN.BITNET>
From: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Subject: Friction
Colleagues;
During my class discussion today on friction, that is, the
force needed to overcome friction is proportional to the
normal force and the coefficient of friction--and not the
surface area--a student asked why then do performance cars
have wider tires? I muttered something about stability
and center of mass and base of support. Does anyone have
any other explanations, such as softer tires (higher
coefficient of friction) need more surface area to decrease
wear and improve tire stability? As usual, will post
responses.
Jeff Ives, PhD
Dept. Exercise Science
Campbell University
Buies Creek, NC 27506 USA
jives@camel.campbell.edu
Date: Fri, 2 Dec 1994 13:53:45 -0400
Reply-To: davis@bme.ri.ccf.org
Sender: Biomechanics and Movement Science listserver
<BIOMCH-L@HEARN.BITNET>
From: Brian Davis <davis@BME.RI.CCF.ORG>
Subject: Racing Cars and skidding
Dear Readers
I asked one of my colleagues who is a "bit of a car racing fanatic" why
performance cars have wider tires, and his reply is appended below. He
can be contacted at vesely@bme.ri.ccf.org for more info!
Regards, Brian Davis
--------------------------------------------------------------------
I agree that the frictional force is proportional to load, and that
the higher the contact pressure, the greater the frictional force.
However, tires are "a weird animal" that don't always follow the
laws of physics.
For rubber tires, the coefficient of friction decreases with contact
forces. The net effect is that past a certain load, the frictional
force needed to overcome inertia of a cornering automobile cannot
keep up with the centrifugal force. This means that the heavier the
car, the worse it corners on the same size tires. This makes sense
from experience, but not necessarily from physics. Again, the reason
behind it is that the coefficient of friction of tires drops with
increasing load.
This means that if you want to corner harder, you need more surface
area to decrease the contact pressure, and hence get wider tires.
Now, here's a twist. What about antiroll bars? Anti roll bars
prevent the car flow leaning out of the corner, and generally improve
handling. But they way they work is that they transfer weight from
the inside wheel to the outside. This means that a car with antiroll
bars has a higher proportion of the load on the outside tires. This
should mean that these tires should corner _worse_ according to the
principle just described. Well, they, do, but the loss of total
frinctional force is greately offset by the increase in frictional
force that can be generated because the tire is now perpendicular to
the road because the car isn't leaning.
Here's another twist. Why do cars that race on the ice remove the
antiroll bars, and often remove the shock absorbers as well? This is
so that they can corner better! Yes, but this goes against what I
just said above. It does, but it supports what I said right at the
beginning. Increasing the load _decreases_ cornering force. It
turns out that on ice, rule #1 is more important than rule #2.
This is why using rubber tires as an example of friction is such a
bad idea....
ivan
------ Forwarded message ends here ------
Date: Sun, 4 Dec 1994 10:34:18 -40962758
Reply-To: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Sender: Biomechanics and Movement Science listserver
<BIOMCH-L@HEARN.BITNET>
From: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Subject: Friction: responses
Colleagues;
Recently I posted the following query:
During my class discussion today on friction, that is, the
force needed to overcome friction is proportional to the
normal force and the coefficient of friction--and not the
surface area--a student asked why then do performance cars
have wider tires? I muttered something about stability
and center of mass and base of support. Does anyone have
any other explanations, such as softer tires (higher
coefficient of friction) need more surface area to decrease
wear and improve tire stability?
Instead of posting the individual responses, I will summarize
them and add my own findings. In general, most of the
responses were speculative, and centered on factors such as the
nature of the tire-road surface interface, heat dissipation,
tire deformation and elasticity, stability, and a myriad of
other environmental and engineering constraints. The 'best'
answer suggested that the tire problem did not fall under
the standard Coulomb (dry) friction parameters, thus using
tires as an example was comparing apples to oranges.
Indeed, further digging supports the latter statement.
According to Engineering Mechanics: Vol. 1, Statics (2nd ed),
JL Meriam and LG Kraige, Wiley and Sons: New York, 1986, the
coefficient of ROLLING RESISTANCE, while analogous to the
coefficient of static or kinetic friction, is really an
entirely different beast. It would be most difficult to
describe fully without a free body diagram, but is a function
of many factors, including, but not limited to: road and tire
deformation and the resultant pressure over the area of contact,
elastic and plastic properties of the mating materials, wheel
radius, speed of travel, and roughness of the surfaces. Meriam
and Kraige state, "... depends on many factors which are difficult
to quantify, so that a comprehensive theory of rolling resistance
is not available."
Moral of the story? There are two: 1) Theory is just that, and
2) Stick to wood blocks on inclined planes.
Thanks to all who wrote.
Jeff Ives, Ph.D.
Dept. of Exercise Science
Campbell University
Buies Creek, NC 27506
jives@camel.campbell.edu
Date: Mon, 5 Dec 1994 12:18:16 -40962758
Reply-To: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Sender: Biomechanics and Movement Science listserver
<BIOMCH-L@HEARN.BITNET>
From: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Subject: Friction: addendum
n
From Jeff Ives:
Colleagues:
Straight from the expert (Jim Sprague) comes this addition to the
tire/friction question posted and responded to earlier:
1. Lateral force generated by a race tire IS proportional to contact area
(among other things). When race tires get up to operating temperature
(200-300 F), the soft compounds become sticky and actually adhere to the
track surface, as evidenced by the gravel which sticks to the tires when
they go off course, or cross non-asphalt areas when being pushed back to
the garage.
2. Increasing tire width allows tires to be operated at a lower
inflation pressure for a given load. This is desirable (to a point) in
race tires as lower pressure allows the footprint to better adapt to the
irregular terrain, and gets the tire up to operating temperature sooner.
The lousy rolling resistance is seldom a problem for high powered cars on
road courses. Inflation pressures range from 8 psi for drag tires to 55
psi for heavy stock cars on oval courses with most road course type
for heavy stock cars on oval courses with most road course type
racing using about 18 to 25 psi.
3. Increasing tire width increases contact patch size which reduces
temperature and unit pressure and therefore slows tire wear... a
desireable trait in a sport where tires frequently have a life span of 45
minutes, or in the extreme case of top-fuel drag cars, 30 seconds.
4. Your argument of "base of support, stability and C. of M. "
unfortunately will need to be retracted as it doesn't really hold water.
Most racing classes have either a track width or a tire width restriction
or both, therefore if the only desired goal of the tire were to increase
effective track width, it could be achieved by using bicycle tires
cantilevered out to the most outward allowable position. Clearly this is
not the case except in some arcane racing classes like formula V (which
are relatively slow and underpowered cars anyhow).
Summary: Automobile tires in general and Racing tires in particular are
exceedingly poor examples of "classical" friction. Friction coefficients
for race tires range from approximately 0.9 to 2.2 and are dependent on a
large number of parameters. First order effects on mu (friction
coefficient) are typically
Slip Angle
Slip Ratio (longitudinal counterpart to slip angle)
Camber Angle
Road Condition (wet, icy, dirty, fresh, rubbered in...)
Road Surface Type
Operating Temperature
Inflation Pressure
Normal Load (mu decreases at high loads)
Tire Condition (wear, number of heat cycles...)
Additionally, lateral force is dependent on longitudinal force, this is
often referred to the traction ellipse concept.
These are mostly practical observations obtained from tire mechanics
research and coursework, and from working in the industry. A bona-fide
tribologist could give you a better explanation of the actual
micro-structure friction mechanisms.
Happy cornering!
.................Jim Sprague
Biomechanic and former Race Tire Engineer
U of Michigan biomechanics laboratory
sprague@engin.umich.edu or 71601.2752@compuserve.com
http://isb.ri.ccf.org/biomch-l/archi...-12/00016.html
http://isb.ri.ccf.org/biomch-l/archi...-12/00019.html
http://isb.ri.ccf.org/biomch-l/archi...-12/00027.html
Date: Fri, 2 Dec 1994 11:48:13 -40962758
Reply-To: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Sender: Biomechanics and Movement Science listserver
<BIOMCH-L@HEARN.BITNET>
From: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Subject: Friction
Colleagues;
During my class discussion today on friction, that is, the
force needed to overcome friction is proportional to the
normal force and the coefficient of friction--and not the
surface area--a student asked why then do performance cars
have wider tires? I muttered something about stability
and center of mass and base of support. Does anyone have
any other explanations, such as softer tires (higher
coefficient of friction) need more surface area to decrease
wear and improve tire stability? As usual, will post
responses.
Jeff Ives, PhD
Dept. Exercise Science
Campbell University
Buies Creek, NC 27506 USA
jives@camel.campbell.edu
Date: Fri, 2 Dec 1994 13:53:45 -0400
Reply-To: davis@bme.ri.ccf.org
Sender: Biomechanics and Movement Science listserver
<BIOMCH-L@HEARN.BITNET>
From: Brian Davis <davis@BME.RI.CCF.ORG>
Subject: Racing Cars and skidding
Dear Readers
I asked one of my colleagues who is a "bit of a car racing fanatic" why
performance cars have wider tires, and his reply is appended below. He
can be contacted at vesely@bme.ri.ccf.org for more info!
Regards, Brian Davis
--------------------------------------------------------------------
I agree that the frictional force is proportional to load, and that
the higher the contact pressure, the greater the frictional force.
However, tires are "a weird animal" that don't always follow the
laws of physics.
For rubber tires, the coefficient of friction decreases with contact
forces. The net effect is that past a certain load, the frictional
force needed to overcome inertia of a cornering automobile cannot
keep up with the centrifugal force. This means that the heavier the
car, the worse it corners on the same size tires. This makes sense
from experience, but not necessarily from physics. Again, the reason
behind it is that the coefficient of friction of tires drops with
increasing load.
This means that if you want to corner harder, you need more surface
area to decrease the contact pressure, and hence get wider tires.
Now, here's a twist. What about antiroll bars? Anti roll bars
prevent the car flow leaning out of the corner, and generally improve
handling. But they way they work is that they transfer weight from
the inside wheel to the outside. This means that a car with antiroll
bars has a higher proportion of the load on the outside tires. This
should mean that these tires should corner _worse_ according to the
principle just described. Well, they, do, but the loss of total
frinctional force is greately offset by the increase in frictional
force that can be generated because the tire is now perpendicular to
the road because the car isn't leaning.
Here's another twist. Why do cars that race on the ice remove the
antiroll bars, and often remove the shock absorbers as well? This is
so that they can corner better! Yes, but this goes against what I
just said above. It does, but it supports what I said right at the
beginning. Increasing the load _decreases_ cornering force. It
turns out that on ice, rule #1 is more important than rule #2.
This is why using rubber tires as an example of friction is such a
bad idea....
ivan
------ Forwarded message ends here ------
Date: Sun, 4 Dec 1994 10:34:18 -40962758
Reply-To: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Sender: Biomechanics and Movement Science listserver
<BIOMCH-L@HEARN.BITNET>
From: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Subject: Friction: responses
Colleagues;
Recently I posted the following query:
During my class discussion today on friction, that is, the
force needed to overcome friction is proportional to the
normal force and the coefficient of friction--and not the
surface area--a student asked why then do performance cars
have wider tires? I muttered something about stability
and center of mass and base of support. Does anyone have
any other explanations, such as softer tires (higher
coefficient of friction) need more surface area to decrease
wear and improve tire stability?
Instead of posting the individual responses, I will summarize
them and add my own findings. In general, most of the
responses were speculative, and centered on factors such as the
nature of the tire-road surface interface, heat dissipation,
tire deformation and elasticity, stability, and a myriad of
other environmental and engineering constraints. The 'best'
answer suggested that the tire problem did not fall under
the standard Coulomb (dry) friction parameters, thus using
tires as an example was comparing apples to oranges.
Indeed, further digging supports the latter statement.
According to Engineering Mechanics: Vol. 1, Statics (2nd ed),
JL Meriam and LG Kraige, Wiley and Sons: New York, 1986, the
coefficient of ROLLING RESISTANCE, while analogous to the
coefficient of static or kinetic friction, is really an
entirely different beast. It would be most difficult to
describe fully without a free body diagram, but is a function
of many factors, including, but not limited to: road and tire
deformation and the resultant pressure over the area of contact,
elastic and plastic properties of the mating materials, wheel
radius, speed of travel, and roughness of the surfaces. Meriam
and Kraige state, "... depends on many factors which are difficult
to quantify, so that a comprehensive theory of rolling resistance
is not available."
Moral of the story? There are two: 1) Theory is just that, and
2) Stick to wood blocks on inclined planes.
Thanks to all who wrote.
Jeff Ives, Ph.D.
Dept. of Exercise Science
Campbell University
Buies Creek, NC 27506
jives@camel.campbell.edu
Date: Mon, 5 Dec 1994 12:18:16 -40962758
Reply-To: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Sender: Biomechanics and Movement Science listserver
<BIOMCH-L@HEARN.BITNET>
From: Jeff Ives <jives@CAMEL.CAMPBELL.EDU>
Subject: Friction: addendum
n
From Jeff Ives:
Colleagues:
Straight from the expert (Jim Sprague) comes this addition to the
tire/friction question posted and responded to earlier:
1. Lateral force generated by a race tire IS proportional to contact area
(among other things). When race tires get up to operating temperature
(200-300 F), the soft compounds become sticky and actually adhere to the
track surface, as evidenced by the gravel which sticks to the tires when
they go off course, or cross non-asphalt areas when being pushed back to
the garage.
2. Increasing tire width allows tires to be operated at a lower
inflation pressure for a given load. This is desirable (to a point) in
race tires as lower pressure allows the footprint to better adapt to the
irregular terrain, and gets the tire up to operating temperature sooner.
The lousy rolling resistance is seldom a problem for high powered cars on
road courses. Inflation pressures range from 8 psi for drag tires to 55
psi for heavy stock cars on oval courses with most road course type
for heavy stock cars on oval courses with most road course type
racing using about 18 to 25 psi.
3. Increasing tire width increases contact patch size which reduces
temperature and unit pressure and therefore slows tire wear... a
desireable trait in a sport where tires frequently have a life span of 45
minutes, or in the extreme case of top-fuel drag cars, 30 seconds.
4. Your argument of "base of support, stability and C. of M. "
unfortunately will need to be retracted as it doesn't really hold water.
Most racing classes have either a track width or a tire width restriction
or both, therefore if the only desired goal of the tire were to increase
effective track width, it could be achieved by using bicycle tires
cantilevered out to the most outward allowable position. Clearly this is
not the case except in some arcane racing classes like formula V (which
are relatively slow and underpowered cars anyhow).
Summary: Automobile tires in general and Racing tires in particular are
exceedingly poor examples of "classical" friction. Friction coefficients
for race tires range from approximately 0.9 to 2.2 and are dependent on a
large number of parameters. First order effects on mu (friction
coefficient) are typically
Slip Angle
Slip Ratio (longitudinal counterpart to slip angle)
Camber Angle
Road Condition (wet, icy, dirty, fresh, rubbered in...)
Road Surface Type
Operating Temperature
Inflation Pressure
Normal Load (mu decreases at high loads)
Tire Condition (wear, number of heat cycles...)
Additionally, lateral force is dependent on longitudinal force, this is
often referred to the traction ellipse concept.
These are mostly practical observations obtained from tire mechanics
research and coursework, and from working in the industry. A bona-fide
tribologist could give you a better explanation of the actual
micro-structure friction mechanisms.
Happy cornering!
.................Jim Sprague
Biomechanic and former Race Tire Engineer
U of Michigan biomechanics laboratory
sprague@engin.umich.edu or 71601.2752@compuserve.com
02-19-04, 10:14 PM
#110
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Well there you go..
c(f) goes down as load goes up (da ****? damn rubber), hence more surface area needed.
Let's just say we all win and call it a night!
c(f) goes down as load goes up (da ****? damn rubber), hence more surface area needed.
Let's just say we all win and call it a night!
02-20-04, 05:22 AM
#112
Lives on the Forum
Like I said before. This stuff is complicated.
I must clarify one of the physicists in Clayne's post regarding sway bars. Sway bars resist weight transfer to the outside tires. The point of sway bars is to have the inside tires do some of the gripping during cornering.
If physicists and a tire engineer cannot agree on why race cars use wider tires, then there's no hope for a bunch of Rx7 enthusiasts in making an irrefutable argument one way or the other. So no one wins.
One thing's for sure--this thread ain't about who's got the best blow-off valve LOL
I must clarify one of the physicists in Clayne's post regarding sway bars. Sway bars resist weight transfer to the outside tires. The point of sway bars is to have the inside tires do some of the gripping during cornering.
If physicists and a tire engineer cannot agree on why race cars use wider tires, then there's no hope for a bunch of Rx7 enthusiasts in making an irrefutable argument one way or the other. So no one wins.
One thing's for sure--this thread ain't about who's got the best blow-off valve LOL
02-20-04, 05:24 AM
#113
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You start this whole damn controversy, and this is all you have to add to the fray?
Originally posted by PVerdieck
Hey, what rims are those?
Hey, what rims are those?
Last edited by SleepR1; 02-20-04 at 05:31 AM.
02-20-04, 05:35 AM
#114
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Originally posted by clayne
Well there you go..
c(f) goes down as load goes up (da ****? damn rubber), hence more surface area needed.
Well there you go..
c(f) goes down as load goes up (da ****? damn rubber), hence more surface area needed.
02-20-04, 05:38 AM
#116
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Originally posted by clayne
Does anyone else get what I was trying to say?
Does anyone else get what I was trying to say?
02-20-04, 05:44 AM
#117
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Originally posted by clayne
Damon, I don't think so! You're not getting off that easy.
Damon, I don't think so! You're not getting off that easy.
Be quiet. I'm gloating
I still can't believe some of the answers when I asked why dragsters have wide rear tires or why powerful racecars have wide rear tires. That's why I kept saying to forget the "science" and use your common sense. Everyone KNOWS wide tires give more grip, they just talked themselves out of it.
02-20-04, 05:46 AM
#118
Lives on the Forum
Re: 17" vs 18" with racing in mind. . .
We have over 112 posts, nearly 1000 views, and I'm not sure we've shed any light on your question.
In an effort to get this thread back on topic, here's a response related to your question.
The Type RZ wheel is 8.5 x 17 in back with 255/40-17, and 8 x 17 with 235/45-17 up front. Wheel offsets are 50-mm. Tires are Bridgestone Potenza S-07s (Japan market only).
In my experience, 9 x 17, 45-mm with 255/40-17 tires all around works very well for your intended purpose. It's a proven fitment.
We veterans apologize for hi-jacking your thread, and making it a debate on whether wider tires are better for drag racing LOL
Hey DamonB, I don't think anyone's declared you the winner...
(ducking and running LOL )
In an effort to get this thread back on topic, here's a response related to your question.
The Type RZ wheel is 8.5 x 17 in back with 255/40-17, and 8 x 17 with 235/45-17 up front. Wheel offsets are 50-mm. Tires are Bridgestone Potenza S-07s (Japan market only).
In my experience, 9 x 17, 45-mm with 255/40-17 tires all around works very well for your intended purpose. It's a proven fitment.
We veterans apologize for hi-jacking your thread, and making it a debate on whether wider tires are better for drag racing LOL
Hey DamonB, I don't think anyone's declared you the winner...
(ducking and running LOL
)
Originally posted by Splinemodel
The RZ has 17x8.5's if I am correct. my intent was to go with that size unless there's some combination that yields far better results. Most of the wheel threads here are along the lines of "let me see pictures." I'm more curious about handling and performance. let me know if you can shed any light on the topic. Thanks.
The RZ has 17x8.5's if I am correct. my intent was to go with that size unless there's some combination that yields far better results. Most of the wheel threads here are along the lines of "let me see pictures." I'm more curious about handling and performance. let me know if you can shed any light on the topic. Thanks.
Last edited by SleepR1; 02-20-04 at 05:49 AM.
02-20-04, 05:57 AM
#119
Lives on the Forum
Re: Re: 17" vs 18" with racing in mind. . .
Originally posted by SleepR1
Hey DamonB, I don't think anyone's declared you the winner...
(ducking and running LOL )
Hey DamonB, I don't think anyone's declared you the winner...
(ducking and running LOL
)
02-20-04, 07:34 AM
#120
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Re: Re: Re: 17" vs 18" with racing in mind. . .
Originally posted by DamonB
I don't want to be the "winner" I just want to know that somewhere after all this amount of typing I have done that someone gets it
I don't want to be the "winner" I just want to know that somewhere after all this amount of typing I have done that someone gets it
Mark
02-20-04, 07:55 AM
#121
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Originally posted by clayne
3. Increasing tire width increases contact patch size which reduces
temperature and unit pressure and therefore slows tire wear... a
desireable trait in a sport where tires frequently have a life span of 45
minutes, or in the extreme case of top-fuel drag cars, 30 seconds.
3. Increasing tire width increases contact patch size which reduces
temperature and unit pressure and therefore slows tire wear... a
desireable trait in a sport where tires frequently have a life span of 45
minutes, or in the extreme case of top-fuel drag cars, 30 seconds.
-Don (done beating this dead horse)
02-20-04, 08:34 AM
#122
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Originally posted by redrotorR1
I have been biting my lip on this thread for a while now. So there it is ... from the horse's mouth. Y'all convinced now?
-Don (done beating this dead horse)
I have been biting my lip on this thread for a while now. So there it is ... from the horse's mouth. Y'all convinced now?
-Don (done beating this dead horse)
02-20-04, 09:18 AM
#124
Somebody running 285/30/18 rears on SSR or other similar-to-stock weight wheels with the same brand of tire as they have mounted on their stock wheels go out and mount just one stock rear wheel, and go stand on it and tell me on which side of the road they ended up in the ditch.
02-20-04, 11:44 AM
#125
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We have TORSEN LSD
So this won't work...
Originally posted by ptrhahn
Somebody running 285/30/18 rears on SSR or other similar-to-stock weight wheels with the same brand of tire as they have mounted on their stock wheels go out and mount just one stock rear wheel, and go stand on it and tell me on which side of the road they ended up in the ditch.
Somebody running 285/30/18 rears on SSR or other similar-to-stock weight wheels with the same brand of tire as they have mounted on their stock wheels go out and mount just one stock rear wheel, and go stand on it and tell me on which side of the road they ended up in the ditch.