How come we can’t just add X amount of gears to a transmission and have one of the most efficient cars ever?

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How come we can’t just add X amount of gears to a transmission and have one of the most efficient cars ever?

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21 Answers

Anonymous 0 Comments

Space and weight for traditional gears. For the most part, CVT transmissions kind of accomplish this with belts and pulleys, and are pretty efficient. The reliability of many of them is the concern, though

Anonymous 0 Comments

CVT is most efficient but cars with CVT are only slightly more than 10 speeds with gas engines. The gas engine is the problem. Its only 30% efficient. In the future we will have more efficient cars.

Anonymous 0 Comments

We kinda did. Early cars had 3 speeds, and now we have 10. We also have CVTs with infinite ratios. At the end of the day it won’t help much. Adding more gears would make it possible to go faster while maintaining low engine rpm but at some point air will make it too difficult to reach those speeds with such low engine output. You could design those gears to be used at lower speeds to keep the engine in its efficiency zone but then your gearbox would need to constantly shift gears. Even 10 is too much really and it’s often annoying to drive. And even with infinite ratios CVTs are only slightly more efficient so there’s not much to be gained anyway.

Anonymous 0 Comments

Gears take up space, they’re made of heavy metal, and the more you add the bigger, heavier, and more complicated the transmission gets.

This is why smaller vehicles these days often use continuously variable transmissions (CVT). Instead of gears, the use two cones and a belt that rides up or down to adjust the ratio without using gears. The CVT can adjust the ratio anywhere between it’s minimum and maximum, as if were a geared transmission with infinite gears.

Anonymous 0 Comments

CVT can only handle so much power before slipping. If CVT could handle power we would have seen them in F1 ages ago.

Anonymous 0 Comments

Going from a 3 to 4 speed made a big difference. Going from 4 to 5 was a small improvement. Eah time you add a gear the percentage of improvement gets small. A 20speed in only slightly better than a 10speed with a lot more cost and complexity. My guess is manuals will probably stay in the 5-7speed range and autos/DCTs will max out in the 10-12 range.

Anonymous 0 Comments

Every additional set of gears is another source of drag. The friction of the gears will lower the efficiency of the transmission.

Also, if you only have x amount of space for the transmission in the car, more gears means each gear ratio will be thinner. Thinner gears means weaker gears. Say you have 1e inches in the transmission. A 3 speed can have gears 4 inches wide. A 4 speed, 3 inch wide gears. A 6 speed, 2 inch wide gears. An 8 speed, 1.5 inches wide. ALL that engine power has to go through that little surface.

Then there’s cost. The more gears, the more parts and the more engineering, the more wear, the more stuff can go wrong, and the more time to put it together. It just gets more expensive.

Last, it’s benefit. Realistically, your car is not going over 80 for very long. With a 5 speed, you’re still only dropping about 500 rpm between shifts, and cruising at 65 at around 2500 to 3000 rpm. Extra gears are ot going to get you that much. Even in sports cars, 6th gear is a cruising gear, not a top speed gear. It’s put in so the car is just above idle at highway speeds, so the car gets better fuel efficiency numbers.

Anonymous 0 Comments

We can add more gears, but it’s diminishing returns. We need space for all those gears, then we need an increasingly complicated transmission to manage the gears. That’s weight and expense. Of course, as others mentioned, we already have CVT transmissions that do effectively have infinite gears.

Then there’s the driving experience. Trying to get a standard transmission to select the optimum gear out of a massive selection means lots of shifting everytime the smallest thing changes, such as the grade of the road, or a gust of wind. CVTs can at least adjust with out you noticing.

But, wait a minute… If we already have infinite ranges in transmissions why are cars equipped with them already the most efficient ever?

Well that’s because the biggest factors in efficiency have nothing to do with transmissions. The best internal combustion engines are still throwing away ~60% of the available energy as heat. So simply getting rid of the internal combustion engine in favour of an electric one nearly triples the efficient use of energy. But that’s not even the biggest way to improve efficiency. That comes down to aerodynamics, especially as you go faster and faster.

Anonymous 0 Comments

You can, and modern cars have a lot of gears, but that adds cost and complexity and can be annoying to drive because it’s constantly shifting gears. There’s continuously-variable transmissions too, which use belts and funky pulley wheels to smoothly change between ratios, but people broadly gave up on those for cars (they had reliability issues putting down that much power), though they are popular in scooters and small motorcycles.

Anonymous 0 Comments

This is what we did for automatic transmissions. For regular ones, having a lot of gears get tedious.