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Do more gears affect the top speed/acceleration of the car in any way? I know the gears won't increase hp since more gears would increase RPM but would decrease torque.

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    $\begingroup$ As Ben Goldacre says, "I Think You'll Find It's a Bit More Complicated Than That " $\endgroup$ Sep 3, 2021 at 13:16
  • $\begingroup$ Top speed is simple: power from engine = to power needed to move atmosphere out of the way and friction losses. Once that is equal then speed stays constant. $\endgroup$
    – Solar Mike
    Sep 3, 2021 at 13:18
  • $\begingroup$ Yes. In automobiles, the top speed of the first gear is much slower than the fourth or fifth gear. However, you have to think about how to get to the top speed without getting through the lower speed gears, and why. $\endgroup$
    – r13
    Sep 3, 2021 at 14:11
  • $\begingroup$ @r13 Easy: just put it in highest gear and ride that clutch really REALLY gently :-) $\endgroup$ Sep 7, 2021 at 11:51

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Yes and no. It requires power to reach a speed ; gears do not add power. The proper gears permit to engine to get to the maximum power which will produce the maximum velocity for the engine power and vehicle. As a boy I had several differentials for my Olds (cheap at the junk yard) , ratios ranging from 3.42 to 4.30. It took less than an hour to change one. The 3.90 ratio gave the highest speed in top gear. The engine did not have enough power to reach maximum speed with the 3.67, and the engine RPM would would reach maximum RPM before the possible top speed with the 4.30.

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there is a lot of relevant discussion in this question.

However, the answer is yes, in a manual shift car (automatic gearboxes are a different matter) the gears and the gear ratios affect the top speed.

If the gears get too long - although theoretically allows for a higher top speed- have the adverse effect. The reason is that the torque and therefore the force that accelerates the car, becomes smaller. As a result the car is never able (unless its downhill, or the wind is blowing favourably) to reach the top speed.

On the other hand the top speed is affected if the gears are too short. Although the car can accelerate faster, it is not able to reach as high a top speed as a slightly longer gear ratio.

So its a compromise, and there is always a sweet spot.

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  • $\begingroup$ Can you explain that distinction about automatic gearboxes? Slippage aside, they have an effective ratio in their highest speed setting too. $\endgroup$ Sep 7, 2021 at 11:52
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    $\begingroup$ @CarlWitthoft - whenever I say automatic gearboxes to my mind pulley based CVTs spring to mind (not planetary systems) - (my bad). In that -limited context - I would argue that due to the "infinite" range of gear ratios (pulley based CVTs), there are not limited in the same way as a fixed ratio gearbox. So you can't really short them too much, or make them long too much. I'd love to hear if that makes sense to you. $\endgroup$
    – NMech
    Sep 7, 2021 at 12:10
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    $\begingroup$ that's cool. Tho' even w/ a CVT, there's a max physically achievable ratio and so on. $\endgroup$ Sep 7, 2021 at 14:46
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All engines are designed to deliver enough torque to comfortably provide start-up power and a designated range of optimal speed.

The gears and all the other variables in the drive train such as the differential, engine power curve, wheels, and tires, are synchronized and tuned to be most effective in that performance envelope.

Sedan cars designed for 4-5 members of family passengers are geared to deliver a comfortable ride with adequate acceleration in mid-range speeds, if one tries to demand racing performance the gearbox and drive train are going to be stressed.

But the same engine with one or two passengers and a body with a lower sports profile can have a transmission with higher ratio gears and comfortably go faster.

Edit

you can test your own car simulating adding gears by installin larger size rings and tires.

If you usally drive an empty car at sea level and the engine can aspire comfortably it may benefit your ultimate speed.

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