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If the car's acceleration is higher when the wheel's angular acceleration is higher(tangential acceleration=alpha x radius). Why are higher gears not used to accomplish the acceleration of the car instead of lower gears?

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  • $\begingroup$ Low gear provides more available torque so accelerates better so long as you can still spin the wheels faster than the speed you are currently spinning at. Is that what you're asking? You might want to try and clean up your question. I find the detailed description rather incomprehensible. But from what I can interpret, the line "no longer remain constant" seems to follow from nothing. $\endgroup$
    – DKNguyen
    May 19, 2022 at 20:11
  • $\begingroup$ basically I tried so hard to clarify my question in simplest way . editing it further will lead me to a long essay. $\endgroup$ May 19, 2022 at 20:12

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The Rotational Inertia of individual gears doesn't matter.

You are way overestimating the effect of rotating gears on overall acceleration. The mass of gears is inconsequential compared to the weight of the vehicle (and the rest of the rotating mass. So a larger diameter first gear does have a slightly larger rotational inertia. But gear ratios overpower this small effect and renders it inconsequential.

In the end, acceleration is related to both the rotational and non-rotational mass. The small change in rotational inertia between first and second physical gears is immaterial.

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It is down to power against drag ie rolling & aerodynamic. After about 40mph, the aerodynamic drag is larger and increases with the square of the speed.

Basically the vehicle has to push more and more air out of the way the faster it goes. Once the power equals the sum of the drag, acceleration will be zero.

And it won't matter if you have 4, 14 or 40 gears or an automatic or cvt.

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  • $\begingroup$ Thank you for your answer > But that did not answer my question . I actually know this information , but I am asking about something else if you carefully read my question. $\endgroup$ May 19, 2022 at 19:35
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    $\begingroup$ @JesseFlynn won't the wheels be in contact withe the ground so any wheel acceleration is linked to vehicle acceleration? And you asked for "good reasons"... $\endgroup$
    – Solar Mike
    May 19, 2022 at 19:37
  • $\begingroup$ YES INDEED . I've just bold the keywords in my question . I'm talking about wheel ANGULAR acceleration not the vehicle's acceleration which is measured in m/s . $\endgroup$ May 19, 2022 at 19:40
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Every engine will start to choke when demand torque from the transmission, or better said from the tires, gets close to the engine's output torque at that state, RPM, breathing, engine capacity to shed the heat, and many other factors.

All engines need a burst of torque to accelerate their angular speed and that torque comes from the gap between available and demand torque.

A good driver or a good automatic transmission will keep the demand torque under available torque to let the engine breathe and rev up and deliver the best performance till the RPM nears the maximum engine's design RPM and available torque is so much more than the demand torque that will allow up-shifting for speed without choking.

And then and only then what you mean to say (if I understand correctly) is applied, higher gears are engaged or even overdrive.

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You are mixed UP. The angular acceleration of the wheel does not effect the entire car's acceleration. What will, is the force applied to the ground from the tires.

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  • $\begingroup$ That was my point. $\endgroup$ May 19, 2022 at 20:33

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