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Hi, so from what I remember from physics, the friction coefficient between two surfaces is constant.
The maximum lateral force applied on a tire before it slips is limited by the Force of Friction witch is calculated by
Force of Friction = (coefficient of friction) x (downward force applied on a tire)
I forgot how would you express the Force of Friction in terms of the area of contact patch to find the Maximum Force of Friction? Of course I am talking about static friction, before a tire begins to slip....
Last edited by hard drive : 06-27-2008 at 04:44 AM.
The interaction between a tire and pavement involves more than friction. If it was a pure friction issue, one could never go above 1g in acceleration force. We all know that drag cars do much better than 1g (go back to physics and calculate 1/4 mile in 5 sec.). Also, performance cars on performance tires exceed 1g in cornering force.
Theoretically, friction is independant of contact area. We know that is not true because tire contact patch size is important. There is some interference between the tire and the pavement that doesn't follow the laws of friction.
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"If everything seems under control, you're just not going fast enough." - Mario Andretti
Correct me if I'm wrong, but isn't normal force a huge factor in drag cars? When the car accelerates hard, the mass of the vehicles shifts to the back and tranfers to the ground. The normal force counters this and offsets it, creating more force to contribute to the overall lateral motion of the car. This happens because the normal force has a lateral component. This normal force aids in forming a dynamic situation as opposed to a static situation, thereby causing the car to haul a$$. Just a theory. prolly not entirely correct though.
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1992 Nissan Sentra SE-R (keepin' her completely stock for a while-well almost. hehe)
Thanks for the replies, I think my memory is coming back to me... So , the abstract physics says that the Force of Friction is independent of the contact patch, right? Therefore in theory the difference in traction between 195 and 215 slick tires would be almost negligible? While the difference in mass between these tires will defiantly have some negative aspect on car's acceleration, mpg, brake life, transmission life, etc etc etc... Physics says "wider is not always better." Just something to think about.
Why do you think old school sport cars designed by great physicists were running 155-185mm tires? Do you think the wide tires are just marketing gimmicks?
Last edited by hard drive : 06-27-2008 at 05:04 AM.
Old cars ran on narrow tires because that was the technology at the time. Tire design has improved in many ways, including materials and shape. It took the development of radial tires to allow a wider footprint. It took stiffer sidewalls to keep the contact patch on the road as the tires got wider. Take a look at the current SCCA production classes where the old school cars like MG's and Spridgets run. They have the fattest tires on them that they can get.
Although physics in theory says the size of the patch does not matter, in reality, there is a significant difference. That is the difference betweeen science and applied engineering.
Ok, I think tire engineers create more elastic rubber compounds to increase friction coefficient but application of these compounds requires greater tire width in order to dissipate heat during extreme racing conditions.
But for daily driving cars narrower tires are more resistant to hydroplaning. So if I go with 195/50/15 tires, would it be the optimal choice for wet and dry traction?
i took all the physics I could stand... and I can tell you - you should spend more time testing the limits of your car rather than calculating them. Have fun and don't worry about it
I'm not trying to be disrespectful though, its always good to apply what you study to what you like, or do.
What is the purpose tire's tread? If you think about it, 205 tire with thread will have the same about of rubber in contact with asphalt as 155mm slick tire. Does thread contribute anything to grip on a dry road, or just serves a purpose of water drainage and ventilation?
