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


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

In: 95

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

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.

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.

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.

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

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.

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.

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.

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.

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

Variable speed transmissions are basically a gear cone that slides up and down based on speed


They did make one car..but the inventor misteriously disappeared, his patent missing and family went silent.

Big corporation don’t want u to have one efficient car…that will last years..decades…they want u to buy one every year …

Gears don’t increase the power of the car. To drive at a given speed you need a given power, the engine has to provide that power no matter what gear you are in. In fact, with a transmission it has to provide a bit more power because of friction in the transmission.

Combustion engines are inefficient when they run very slow (few, slow combustion cycles) and when they run very fast (large losses from all the moving parts). They have a range where their efficiency is the best. Gears are used to keep the engine closer to that range for a large range of car speeds. With something like 5 gears you are already close to the maximum across the whole relevant speed range. Going to 10 gears is a very small improvement, going to 20 would be an even smaller improvement.

Its common for trucks or busses to have 10-12 gears, some even 18 gears. But thats because they have to pull tens of tons, with relatively small engines. For example a 20t iveco truck has a measly ~ 300 hp engine, with a 9 manual or 12 semi auto gearbox.

You need more power to be able to drive a higher gear. An example is my bike. I fitted a new final drive with a longer ratio because my old one grenaded itself. Now for a given speed I have a lower RPM in fifth gear but the ratio is too tall for my bike’s engine to overcome and I have a higher top speed in fourth.

So now I HAVE to fit a big bore kit to get more power.

That’s exactly how it is. Modern cars have automatic transmissions with more than regular 5 or 6 gears as common for manual transmission. The thing is it’s applied to automatic ones because it’d be horrible to manually switch 8-9 gears. But semi-truck (or whatever it’s called in English) drivers have way more, I believe up to 18 or something.

Btw, combustion engine cars are inefficient because of their engines which are inefficient by design. Diesel could theoretically be ~55-60% efficient, gasoline engine is even worse ~40%. That’s why electric engine with efficiency up to 99% is hella better option.

That’s exactly what we did! In 1950 Chevy came out with the first automatic transmission, the power glide! It had 2 gears and that was it, low and high. It wasn’t very efficient but it was ground breaking as a car could finally shift itself.

Then in 1969 Chevy came out with the Turbo 350 transmission. It had 3 gears closing the gap between low and high. It made the cars more fuel efficient and improved performance. In fact Turbo 350’s and Turbo 400’s (a beefier version of the 350) are still used for drag racing. They are the best transmissions for holding BIG power when upgrades. A fully upgraded Turbo 400 can handle 4,000+ horsepower. Crazy for something designed in 1969.

After that we get the 700r4. It was still an old school transmission but they added a 4th gear. This is an overdrive gear which is great for fuel mileage. It’s not designed for you to accelerate in, just drop the RPMS for better mileage. So once you hit 70mph and stopped accelerating and began to cruise, it would shift into 4th to get better mileage. This transmission gave way to the 4L60E & the 4L80E. The 4L60E is a 4 speed like the 700r4 except it’s electronically controlled. The 4L80E is just a beefier 4L60E like the turbo 400 is a beefier turbo 350.

In the ever increasing battle for better mileage in 2005 Chevy came out with the 6L80E. This is similar to the 4L80E but it has 6 gears instead of 4. Then in 2017 GM stepped it up again and made the 10L80E. A 10 speed transmission designed for high end sports cars.

Now it’s important to note WHY having more gears increases efficiency and why adding more gears isn’t always the right answer. The more gears you add, you suffer from diminishing returns in the area of efficiency. It also makes the transmissions significantly more expensive and complex. To be truthful the 10 speed is probably the most gears they will ever do and even then it’s a bit of a gimmick.

Ignoring the engine on the planet is going to have a spot in the RPM range where it is operating at its highest level of efficiency. It’s going to be fairly narrow just a few hundred RPMS.

So to get more efficient cars we want to keep them in that range while accelerating and cruising. By adding more gears you can maximize the amount of time you spend in that RPM range. If you have a 3 speed your range of RPMS range while accelerating may be from 1,500 to 3,500 RPMS. That’s a 2,000 RPM range, much larger than the efficiency range of the engine. If you have a 10 speed you may be able to keep the RPM range between 2,000 and 2,500 RPMS, a 500 RPM difference and definitely keeping you in the engines efficiency range. As you add more gears that range gets smaller and smaller. It doesn’t really improve efficiency because it’s still sitting in the efficiency range of the engine either way.

To get more efficiency you have to look at other ways. Things like better aerodynamics, less weight, and less friction.

In short because there is a point of diminishing return. Also the law of conservation of energy plays a factor here i.e more gears means more friction, heat, wear etc.

More gears more weight plus cost. CVT’s on the other hand can be more efficient but can only handle a relative low amount of power. For automatics we’re still trying to find the perfect amount of gears. We’ve found that for manual 6 seems to be the best for efficiency and power.