After all the talk about sensors. drive shaft speed. temperature, condition of tires, make of vehicle, Mph, Mpg, tach reading, A/C on or off, Windows open or closed, If one drive wheel is stopped the other one has to run 2 times the speedometer reading.
to the same mountainbike
obviously i did it with an engine. At that moment i didn’t realize that the speed of wheel will be double of what speedometer reads.
Although that “event” rised other question for me: imagine how fast planet gears must be spinning at this speed. I wonder is it safe to do so. I know, there is virtually no load, but even inertions forces alone i assume would be significant. Any thoughts?
Depending on what size tire it is, it’ll probably be rolling about 850 revolutions per mile.
174 mph would then be 850x174=147,900 revolutions per hour.
Divide that by 60 and you get 2,465 rpm at the wheel.
It’s crankin’, but without a load I doubt that it would hurt the gears. Without knowing the speed rating on the tire, it’s impossible to know what it would do. Tires are rated from below 100 mph maximum safe speed to over 150 maximum safe speed and there’s and even higher rating now. If they’re specialty tires, who knows. The custom made tires on a Bugatti Veyron have run at 268 mph under load. Many race cars routinely run at 200 mph under EXTREME load. Airplane tires go from zero to the landing speed of the plane in milliseconds and under…what’s higher than extreme…load.
Tire speed ratings are for sustained speeds, and they contain what’s called by designers an “error budget”. They’ll actually go faster than they rate them for without catastrophocally failing. Typically an error budget for a critical safety item will be as high as 50%, but there’s no guarantees.
"I am not an Vibe expert, but I find this hard to believe! " You don’t need to be a Vibe expert. It is true!!!
As an aside to the topic…the discussion of the speed rating of a tire intrigues me.
I read it here that this is the speed at which a tire cannot be counted on to withstand the centripetal force of spinning that fast. I always thought it had a lot more to do with a tire being unable to dissipate enough heat above that speed (and thus losing structural integrity due to heating up).
So, I know that any number of stresses could be building on a tire as speeds increase–the most limiting of which determines the speed rating. That said, is the “overheat” or the “centripetal force” explanation more realistic/common?
I do not know everything!! (most of you don’t believe anything I say) However, I would suspect the centrifical force has more to do with the speed rating.
Meanjoe,
Heat, while an issue, is a minor player compared to the centripetal forces with regard to tires at speed. The higher the speed rating of the tire, the more cap plies are used.
Example: V and higher speed rated tires typically use 2 spiral wound nylon cap plies. H speed rated tires typically use 1 and T and lower speed rated tires typically don’t use any. You will find exceptions to this, but that’s what’s typical.
I Will Add That CapriRacer Is Professionally Involved With Tires (A Tire Engineer For A Major Tire Manufacturer For Over 30 Years) And I’m Sure His Information Is Based On Facts, Rather Than Guesses Or Opinions.
CSA
Is the term "centripetal forces" correct? Surely a man with CapriRacer's credentials would not be wrong?I always get mixed up with regard to the use of centrifugal and centripetal. I know they are opposing directions so I supposed it doesn’t matter which term you use as then it is just a matter of whether the value is positive or negative.
Centrifugal force is outward, centripetal force is inward.
It just depends on the direction your referencing.
Well, it would probably be outward force on a tire rotating at 100 mph or better!!
According to my college text, centrifugal force is a fictious force. it does not exist in an inertial reference frame, and its usage should be avoid.
Centripetal vs centrifugal force can be understood as follows. If you spin a ball on a string around your head, it ‘feels’ like the ball is pulling outward on the string and your hand is resisting that pull. This is what is called centrifugal force. From a Newtonian physics point of view, an object will travel in a straight line at constant speed until some external force acts on it to change its direction or speed. Therefore, the ball wants to travel in a straight line. In order to cause it to travel in a circle, you must apply a constant force on it directed toward the center of the circle i.e. toward your hand. This force is called centripetal force. So it’s not that the ball is pulling outward on the string and your hand is resisting that pull, it’s that your hand via the string is pulling inward on the ball in order to continuously change its direction and the ball is resisting your attempt to change its direction! While simple in principle, this is a difficult concept for many people to grasp.
Here’s another fact sure to cause angst among the more sensitive readers. What is the speed of the point on a tire where it touches the ground? It may be hard to fathom but unless the tire is skidding on the ground, the speed where it touches the ground is zero! The top of the tire is actually traveling at twice the forward speed of the vehicle! Noodle that one for a while!
Excellent description of centripedal force.
The speed of the tire where it touches the ground is zero only in relation to its contact point on the ground. In relation to the car, it’s going backwards…at the same speed at which the top of the tire is going forwards, twice the vehicle speed. Speed is entirely relative.