tires don't mean anything! What is your take on the quote?
- Thread starter ///M SPEED
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The guy is oversimplifying things and leaning on basic science to support his claim. The reality is that there are MANY complex, interactive factors at play and they cannot be simplified! A skid is extremely complex and dynamic.
Actually, there are two more types of coefficients of friction: molecular and deformation. Think about those words and it should be clear that they come into play also. His statement about how to calculate the coefficient is VERY MUCH a generalization that ignores many factors.
I agree with most of the previous comments, but consider this:
Tire quality/composition WILL make a difference EVEN IN A SKID. Consider how different rubber compounds will heat, shred, peel, flex, etc. in a skid, and therefore the COEFFICENT OF FRICTION WILL BE AFFECTED. Also consider that the sidewall design of two different tires will react differently in a skid and therefore affect the skid. This is the molecular coefficient and deformation coeffiecient at work, and this is where tire compound and design DO make a difference.
He even implies that he has used DIFFERENT cars to simulate skids. A major factor in friction calculations is WEIGHT. The coefficient by itself is a factor and has no units. It is only meaningful when applied to a calculation involving WEIGHT. If the WEIGHT varies the RESULT varies.
And what about dirt, grease, residue on the roadway? This affects the coefficient of friction.
Actually, it's unfortunate & scary that apparently the courts use him as an expert witness. He isn't. Not even close.
Actually, there are two more types of coefficients of friction: molecular and deformation. Think about those words and it should be clear that they come into play also. His statement about how to calculate the coefficient is VERY MUCH a generalization that ignores many factors.
I agree with most of the previous comments, but consider this:
Tire quality/composition WILL make a difference EVEN IN A SKID. Consider how different rubber compounds will heat, shred, peel, flex, etc. in a skid, and therefore the COEFFICENT OF FRICTION WILL BE AFFECTED. Also consider that the sidewall design of two different tires will react differently in a skid and therefore affect the skid. This is the molecular coefficient and deformation coeffiecient at work, and this is where tire compound and design DO make a difference.
He even implies that he has used DIFFERENT cars to simulate skids. A major factor in friction calculations is WEIGHT. The coefficient by itself is a factor and has no units. It is only meaningful when applied to a calculation involving WEIGHT. If the WEIGHT varies the RESULT varies.
And what about dirt, grease, residue on the roadway? This affects the coefficient of friction.
Actually, it's unfortunate & scary that apparently the courts use him as an expert witness. He isn't. Not even close.
![[hihi]](/images/smilies/icon_smile_hihi.gif "Hi Hi [hihi]"){kind=icon}
there was one thing said by dutch at the beginning. Winter tires actually do not "really suck" during summer. I have seen tests from the german automobil club ADAC. they had two identical cars, VW Golf if i am not mistaken. One with summers one with winters. the tests they did were braking straight line, braking in curve, lane change at high speed and acceleration straight line.
the test was performed in spring, so not exactly summer but definetly not winter conditions. some 20°C and sun.
result was, that the winter tire was only little weaker than the summer tire. his performance in all those categories was almost equal, speaking about 3-5% here. sure, this performeance has a price, life time. the wear and tear were highly increased as the rubber could not deal with the warmth that well. most obviously.
the reason why people tend to say that winter tires are way worse may be, that the summer tires are low profile and wider. that gives the car a whole new feeling. the balloon like winter tires are not as sporty and agil. the feeling is different but the performance is not as bad as the feeling.
as for this thread....yeah right....the world doesn´t need tires any more, the road will hold you on your rims, too, anyway.
the test was performed in spring, so not exactly summer but definetly not winter conditions. some 20°C and sun.
result was, that the winter tire was only little weaker than the summer tire. his performance in all those categories was almost equal, speaking about 3-5% here. sure, this performeance has a price, life time. the wear and tear were highly increased as the rubber could not deal with the warmth that well. most obviously.
the reason why people tend to say that winter tires are way worse may be, that the summer tires are low profile and wider. that gives the car a whole new feeling. the balloon like winter tires are not as sporty and agil. the feeling is different but the performance is not as bad as the feeling.
as for this thread....yeah right....the world doesn´t need tires any more, the road will hold you on your rims, too, anyway.
This dead horse needs more beating, cause I still don't understand. If this is true, then a 3 foot wide drag racing slick would not be needed on a dragster, he might as well use a 1 foot wide slick.
If I have 3 foot wide tires on my car and you have 1 foot wide tires on yours, same car, smooth slicks, same road, same test, am I to believe our stopping distances are the same if we lock up our brakes?
There are a lot of different discussions going on in this thread, so maybe I am taking this out of context, cause I haven't read the whole thread in detail.
If I have 3 foot wide tires on my car and you have 1 foot wide tires on yours, same car, smooth slicks, same road, same test, am I to believe our stopping distances are the same if we lock up our brakes?
There are a lot of different discussions going on in this thread, so maybe I am taking this out of context, cause I haven't read the whole thread in detail.
![[:p]](/images/smilies/tongue.png "Stick Out Tongue [:p]")
So no matter what the tire material or surface area, all tires have the same friction when skidding? I don't even think this is true at the molecular level WRT material interaction. Different rubber molecules are gonna interact differently with a given road molecule, skidding or not.
Point me to the dead horse.
Point me to the dead horse.
http://www.waltersforensic.com/articles/accident_reconstruction/vol1-no8.htm
I bolded what I think are key points that indicate tire design and composition do affect a skid.
The Skid-To-Stop Velocity Formula
The simple form of the skid-to-stop velocity formula requires known values for the coefficient of friction and the length of the skid marks. The pre-skidding velocity is given by:
V= / 255 m S
where:
V is velocity (km/h)
m is the friction coefficient
S is skidmark length (metres)
Coefficient of Friction
The coefficient of friction, (denoted by the greek symbol ("m ") is a rating of the grip or "traction" between a road surface and a tire. The value of the coefficient of friction is a fraction, which must be between zero and one. The lower the value of the coefficient of friction of the roadway, the more slippery the roadway will be. For example, an icy surface may have a coefficient of friction in the range of 0.1, while a clean, dry asphalt surface may have a coefficient of friction of approximately 0.7.
Factors Affecting The Coefficient of Friction
The main factors affecting the friction coefficient are road surface texture and condition and tire composition.
Condition of the roadway refers to the presence of snow, ice, sand and other lubricants. The presence of any of these will make the surface more slippery, which reduces the coefficient of friction.
Texture of the road surface refers to the natural roughness of the asphalt. A relatively new asphalt roadway has a "sharper" surface with a high coefficient of friction. An older well-travelled asphalt roadway has a smoother, slicker surface with a lower coefficient of friction.
Tire composition and wear surprisingly plays a lesser role in determining the coefficient. It appears as though road surface texture and condition are the more important factors. Tests show that on a clean, dry surface, bald, worn out tires actually will skid to a stop more quickly than newer, treaded tires. However, on a wet roadway, treaded tires are preferred.
Temperature has a small but generally negligible effect on the coefficient of friction; as temperature increases, the friction coefficient reduces minimally.
I bolded what I think are key points that indicate tire design and composition do affect a skid.
The Skid-To-Stop Velocity Formula
The simple form of the skid-to-stop velocity formula requires known values for the coefficient of friction and the length of the skid marks. The pre-skidding velocity is given by:
V= / 255 m S
where:
V is velocity (km/h)
m is the friction coefficient
S is skidmark length (metres)
Coefficient of Friction
The coefficient of friction, (denoted by the greek symbol ("m ") is a rating of the grip or "traction" between a road surface and a tire. The value of the coefficient of friction is a fraction, which must be between zero and one. The lower the value of the coefficient of friction of the roadway, the more slippery the roadway will be. For example, an icy surface may have a coefficient of friction in the range of 0.1, while a clean, dry asphalt surface may have a coefficient of friction of approximately 0.7.
Factors Affecting The Coefficient of Friction
The main factors affecting the friction coefficient are road surface texture and condition and tire composition.
Condition of the roadway refers to the presence of snow, ice, sand and other lubricants. The presence of any of these will make the surface more slippery, which reduces the coefficient of friction.
Texture of the road surface refers to the natural roughness of the asphalt. A relatively new asphalt roadway has a "sharper" surface with a high coefficient of friction. An older well-travelled asphalt roadway has a smoother, slicker surface with a lower coefficient of friction.
Tire composition and wear surprisingly plays a lesser role in determining the coefficient. It appears as though road surface texture and condition are the more important factors. Tests show that on a clean, dry surface, bald, worn out tires actually will skid to a stop more quickly than newer, treaded tires. However, on a wet roadway, treaded tires are preferred.
Temperature has a small but generally negligible effect on the coefficient of friction; as temperature increases, the friction coefficient reduces minimally.
