认识抓翻

吼吼……
论坛再度回到友好和谐热烈讨论的氛围中了。
:em01:

回复 anordinaryman 的帖子

Actually I do not really understand "necessary but not sufficient condition".
To my understanding of this sentence "A rollover situation can only occur if there is enough friction between the tires and road to create sufficient centripetal force" from the article, is that, if the friction between the tires and road is not enough to create sufficient centripetal force, a rollover will not occur.
Therefore, if your car runs with a set of tires with less traction travelling at the same corner, at the same speed, the tendency of rollover will be reduced. However, the car will be more reluctant to make the corner, which is what so called "understeer".   

回复 nankey 的帖子

其实玩过M03的都有这个经验，就是不能用太“咬”的胎。

ray9394 发表于 11-5-31 16:43
回复 anordinaryman 的帖子

Actually I do not really understand "necessary but not sufficient conditi ...

When it is a necessary but not sufficient condition, it means if the outcome or specific event actually occurs, the condition must exist.  But the other way round, if the condition exists, the specific event may not necessary occur then it is not a sufficient condition.  Being a man is a necessary but not sufficient condition for a father, just an example.   As a matter of fact, the fiction between the tire and the road is for generating the speed (v) in producing the centripetal force and the fiction is not itself the speed.  While it is true that maximium speed is 'limited' by (in proportion to) fiction available, it is not a function to fiction in place, meaning that your can have a lot of fiction but still operating at a lower speed.  

In your example,  you can think the other way round.  If you run a car with a set of tires with very little traction and travel at a corner without rolling over, would it do so if your run again with a set of much higher traction tire at the same corner with the same speed?  Definitely not!  Does it answer your question?

我还没到这个地步！抓翻！！！

If you need to accelarate the car to a certain speed, the accelaration force must equal to friction (ideal condition).
If a car moving around the corner, the centripetal force must equal to the frictional force. Otherwise, the car can not move around the corner and it will go straight instead.
This centripetal force will generate an uplift force (a force component) which will destabilize the vechicle and it may rollover due to this uplift.
Therefore, I do not see why the frictional force (traction) is not related to rollover.

I have a different answer to your question, I think the answer should be yes. If you do not roll your car with a set of tires with lesser traction, you can run your car with a set of tire with better traction, and you can actually travelling the corner with even higher speed. That's why, the F-1 car has a set of fresher tires can attack the car in front with worn tires. However, if the car with a set of tires with lesser traction and already in the speed limit of rollover (it can just make the corner with a certain speed without rolling), the car with a set of higher traction tires can also make it with the same speed, but not over this speed, and my answer is yes again.

Also, if you are driving a car and you feel that it will rollover at one corner, you will drive slower than the critical speed for this corner. If you have a car that you know it will just go understeer in one corner, you actually can attack this corner. Why? Because you can do nothing if the car start to roll, but you can control understeer by releasing the throttle. If you ask the Tamiya M03 racer or even drive the M03, you will know more.  

ray9394 发表于 11-5-31 17:04
回复 nankey 的帖子

其实玩过M03的都有这个经验，就是不能用太“咬”的胎。

也玩过M03，当时发觉避免翻车最有效的方法还是在避震机内放垫片（从一个外国网站内看到的方法），这个经验后来从物理解释上才知道是透过减少droop来降低车身过弯时的重心高度。

Regarding to your provided equation, I believe that there is an assumption, which is, the frictional force is always equal to the centripetal force.

回复 anordinaryman 的帖子

是的。降低中心是有帮助的。没有异议。

回复 ray9394 的帖子

If you need to accelarate the car to a certain speed, the accelaration force must equal to friction (ideal condition). If a car moving around the corner, the centripetal force must equal to the frictional force. Otherwise, the car can not move around the corner and it will go straight instead.  This centripetal force will generate an uplift force (a force component) which will destabilize the vechicle and it may rollover due to this uplift. Therefore, I do not see why the frictional force (traction) is not related to rollover. I have a different answer to your question, I think the answer should be yes. If you do not roll your car with a set of tires with lesser traction, you can run your car with a set of tire with better traction, and you can actually travelling the corner with even higher speed. That's why, the F-1 car has a set of fresher tires can attack the car in front with worn tires. However, if the car with a set of tires with lesser traction and already in the speed limit of rollover (it can just make the corner with a certain speed without rolling), the car with a set of higher traction tires can also make it with the same speed, but not over this speed, and my answer is yes again. Also, if you are driving a car and you feel that it will rollover at one corner, you will drive slower than the critical speed for this corner. If you have a car that you know it will just go understeer in one corner, you actually can attack this corner. Why? Because you can do nothing if the car start to roll, but you can control understeer by releasing the throttle. If you ask the Tamiya M03 racer or even drive the M03, you will know more.
If A equals B in terms of magnitude and B causes event E to occur, can we conclude that A also causes event E to occur?  Of course not.  Centripetal force is the actual force that causes rollover to occur, not the fictional force. If you pass the corner with a higher speed and result in a rollover, it merely points to the conclusion that speed is a determining factor in a rollover event. If you agree that "if the car with a set of tires with lesser traction and already in the speed limit of rollover (it can just make the corner with a certain speed without rolling), the car with a set of higher traction tires can also make it with the same speed", you are actually confirming the proposition that higher traction (fiction) is not a determining factor (sufficient condition) for rollover to occur, aren't you? Understeer and rollover are two different concepts and are not mutually exclusive.  An understeering car simply means more traction is at the back instead of in the front (the other way round it will oversteer), but does not preclude it from the possibility of rolling over, the chance of which is ultimately determined by the speed. By the way, controlling (or 'rescuing' to be more appropriate)  understeering by releasing the throttle is effective for front wheel drive car but for rear wheel drive car, it can easily end up in oversteering or even totally out of control.
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