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The things and calculation on gear ratios

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So, typically you all know gear ratios and how it affect the speed at given RPM at certain gear with respective ratio, as well as the maximum speed you can achieve on certain gear.

Add in along with the sizes of tyre, and the weight in though might affect the results, but we going to talk on stock settings.

So before we begin, every gear has own ratios (obviously), and no matter how many gear you have, you will have one Final Ratio which always will be the culprit that people complain they can’t reach the top speed as desired. A shorter (higher number) gear ratio is more powerful, that it can climb up the revs fast and thus faster acceleration, but on the other hand give up the maximum speed achievable in that gear; while on the other hand a long gear ratio is less powerful that it can’t climb up the revs as fast as a shorter ratio, but will be able to achieve higher speed on that gear.

Therefore it is why our transmission has multiple speeds aka gears that represents into gear ratio. Imagine that there is this vehicle, with only one gear… If the factory decided to put the gear ratio at 2.5 : 1, the vehicle can accelerate quite fast and can climb up a slope easily, but the maximum speed at the max RPM, lets say for example only 55KM/H. On the other hand, if the gear ratio is at exactly 1 : 1, the vehicle accelerate very slowly from standstill, and it can’t quite climb up a slope from standstill unless given a full throttle, but it can achieve a max speed at 160KM/H at maximum RPM. Note that all the figures given are examples, without taking in the tyre size and maximum RPM into play.

Below is the calculation of a stock Civic FD2 (K20Z2/6800RPM/5AT) and Civic Type R FD2R (K20A/8300RPM/6MT).

FD2(215/45/17) FD2R(225/40/18)
Gear Gear Ratio Max Speed @ Max RPM (KM/H) Gear Ratio Max Speed @ Max RPM (KM/H)
1st 2.651 71 3.266 60
2nd 1.516 120 2.130 95
3rd 1.081 167 1.517 134
4th 0.772 231 1.147 176
5th 0.566 310 0.921 219
6th 0.738 267
Final Ratio 4.562 5.062

To be continued…
3:23 AM

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