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Comment by ciconia | Hacker News Reader

> now automatic transmissions are so much more efficient than manual transmissions * for ordinary people *.

Efficient in what way? I find it highly unlikely an automatic would have better fuel economy than a manual.

They weren't for about 100 years, but automatics are now mostly better than manuals in terms of performance and economy. Unfortunately, some the the things that make them "better" like 8 gears makes the driving feel worse, with constant shifting. The other big gain is in improved torque conversion.

https://interestingengineering.com/transportation/how-automa...

Automatics traditionally had a single clutch and a viscous coupling to convert smooth the torque between gear shifts. Switching gears was slow and the transmission as a whole was less fuel efficient.

Modern automatic gearboxes have dual clutches and two separate sets of gears for even and odd numbers. You alternate between them as you shift up and down. Shifting is faster and smoother.

(The system isn’t perfect. If you switch to manual selection of gears the transmission computer sometimes guessing wrong — while you’re in 3rd and accelerating it’ll get 4th ready for on the even-numbers clutch, so if you suddenly brake and shift down there is a longer delay while the transmission shifts to 2nd instead.)

Here’s Audi’s marketing material on their version: https://m.youtube.com/watch?v=l_as29ym51M

That’s not quite how traditional autos worked, they also have sets of clutches and bands, controlled by a complex hydraulic system. Modern automatics are electronically actuated and are basically killing the need for DCTs, with VW Group and Hyundai (and some exotic makers) being the lone holdouts in the U.S. market.

Honda used what was essentially a manual gearbox with automatic controls for years, that's why a 2000 civic got decent mileage

DCTs are still best for that sweet-sweet 0-60 time. The max stall RPMs on a stock torque converted transmission is probably 2300rpms at the most, while Porsche PDK can launch at redline and modulate torque delivery precisely.

I don't know of a car with a torque converted that can hit sixty in under 3.0 seconds, but the Corvette and 911 can both do so with RWD due to the bonkers launches these cars manage.

The BMW M5 has a ZF 8HP and pulls off sub 3s 0-60s in CS trim. The new xDrive M3 comes close. I’m sure there are others. The key obviously is to have a torque converter stall speed that’s in powerband.

Yeah, you're right. I realize that I eluded to it in the subsequent statement, but didn't outright say it, but I meant to say,

> I don't know of a RWD car with a torque converted that can hit sixty in under 3.0 seconds on street tires,

It's insane what the C8 can do with RWD on street tires. Being able to launch at full HP without destroying the rear tires is amazing. DCTs have near EV levels of torque management capabilities.

So with the C8 and 911 they can’t be characterized as merely RWD for straight line acceleration purposes because of weight distribution. One of the biggest issues with launching is that by the time weight transfer happens tires are already spinning, so to get a good launch you want a softer suspension which would ruin the car’s performance at corner exit. Being mid or rear engined helps there because you’re starting with 55-60% of the mass over the rear wheels which is closer to AWD than RWD for launch traction.

I find it highly unlikely an automatic would have better fuel economy than a manual.

I saw a study from, I think it was Volvo, that basically concluded that while trained drivers focusing on driving efficiently could get better fuel economy out of a manual, 'normal' people driving normally got better fuel efficiency out of an automatic. And this was a good 10 years ago, so automatics have only gotten better.

Training on manual cars also improved last 10 years. Don't know about other countries but here fuel economy is a mandatory part of training. Recent manual cars provide indicators on when to switch. You can combine that signal and training for better fuel economy. TBH, I don't know how that compares with automatic.

At one point I had two manual and two automatic Citroën XMs, with identical 2.0 litre fuel-injected engines. On average driving, all four got 32mpg.

Bear in mind this was a relatively primitive late-80s Zf 4HP18 gearbox, with a lockup clutch in 3rd and 4th, giving similar ratios to 4th and 5th with the manual box. If anything the manual box let the engine rev a couple of hundred RPM higher in 5th, but the auto box would drop briefly out of lockup on moderate acceleration in top allowing the engine to reach a bit higher speed.

>Efficient in what way?

Mostly that the OEM's engineers can choose to tune it to upshift or resist downshifting in situations where the average consumer with a manual would just wind it out.

> I find it highly unlikely an automatic would have better fuel economy than a manual.

This was true 15 years ago.

Why do you think it unlikely an automatic can match or exceed a manual in fuel economy? Computers can better fit the torque needs to the most efficient RPM than most humans will, it's not a hard problem to solve.

Traditionally (and this is from the very olden days) manuals had an extra gear over automatics, which is why they'd have better fuel economy. Also less drivetrain loss. Nowadays the reverse is true, automatics consistently have more gears to play with, and automatic clutch packs are fantastically fast & good.

Now an efficient automatic is more complicated to design & manufactur, but that's where economies of scale and advancements in engineering tools and manufacturing come into play

In large SUV with powerful engine, modern automatic transmission like ZF 8speed surely have better fuel economy than scenario adequate manual transmission.

power transmission. With 7 and 8-speed clutched automatics, there is no longer the same transmission loss as with older torque converter models.

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